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Research Article

Genotype by Planting Date Effects on Cowpea in Humid Fringes, Southeast Nigeria

Godson Emeka Nwofia,*, Chinenye Rozzy Onyekwere, Emmanuel Ukaobasi Mbah
Plant Breeding and Biotechnology 2018;6(2):95-108.
Published online: June 1, 2018

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*Corresponding author: Godson Emeka Nwofia, enwofia@yahoo.co.uk, Tel: +234-803-562-7889
• Received: December 19, 2017   • Revised: February 22, 2018   • Accepted: March 13, 2018

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  • A two-year factorial arranged field experiment in randomized complete block design with three replications was carried out in 2014 and 2015 at Michael Okpara University of Agriculture Teaching and Research Farm, Umudike (latitude 05° 29′N; longitude 07° 33′E; altitude 122 m above sea level), Nigeria. The objectives were to assess growth and yield response of twenty newly released cowpea genotypes to different planting dates (July, August and September). Plant height, number of leaves/plant, number of branches/plant, shoot biomass, total dry matter, number of nodules/plant, weight of pod, number of seeds/pod, seed weight/pod and grain yield varied amongst the genotypes and across the different planting dates in both years. The association between grain yield and other variables analysed across both years was significant and positive except 100-seed weight and the phenological characters of the plant. Path coefficients analysis across two years indicated that seed weight/pod followed by number of branches/plant and number of seeds/pod had positive direct effect on grain yield of cowpea in contrast to characters that exhibited negative but direct effect on yield. The other traits had relatively negligible to low indirect effects that were positive through other component traits. The grain yield sequence of interaction between genotype and date of planting was in this order: IT06K-141 planted in July > IT11K-61-82 planted in September > IT99K-573-1-1 planted in August. IT06K-141 genotype was considered to be better endowed genetically while the mean across both years indicated August as appropriate planting date to ensure high and sustainable grain yield.
  • Key words: Vigna unguiculata genotype, Planting date, Inter-relationship, Path analysis, Grain yield
The field crop cowpea (Vigna unguiculata (L.) Walpers), is an annual herbaceous legume of the family Fabaceae. It is characterized by its great morphological and ecological diversity that makes it proficient as a good cover crop and soil fertility enhancer (Udealor 2002; Harrison et al. 2006; Oyewale and Bamaiyi 2013). It is widely grown in the tropics and sub-tropics where it has strong adaptation across a wide range of agro-farming systems. The varieties of cowpea come in a number of forms depending on the morphology of the plant such as prostrate, semi-erect, erect or climbing, derived from the stem structure while the pods could be coiled, round, crescent or linear (Pasquet 1999). According to Fageria et al. (1997) and Fatokun et al. (2012), most cowpea cultivars are indeterminate in nature, producing flowers and seed over a long period although some are determinate and produce flowers and seed within a season. Studies by Ogbonnaya et al. (2003), Awe (2008) and Agbogidi (2012) identified cowpea as one of the most economically important legume crops adapted to the savannah agro-ecologies, where it matures as grain under residual moisture and serves as a major contributor to the overall protein intake of most families in Sub-Sahara Africa. The seed contains about 24% protein, 63.6% carbohydrate, 1.9% fat, 6.3% fiber, 0.00074% thiamine, 0.00042% riboflavin and 0.00281% niacin (Davis et al. 1991). Studies have shown that Nigeria and Niger Republic account for 87% of the world’s cowpea production (Ortiz 1998; FAO 2003; Adaji et al. 2007).
A number of studies on cowpea breeding and genetic improvement programs pay attention on high yielding genotypes, time to maturity, photoperiod sensitivity, seed quality and the plant’s resistance to insect pests and diseases that exhibit negative agronomic effect on it (Coulibaly et al. 2002; Nwofia et al. 2006; Timko et al. 2007). However, there are limited information on a number of recently released cowpea genotypes from International Institute of Tropical Agriculture (IITA)–cowpea program, which are characterized by early or medium maturing ability with consumer-preferred traits such as large seeds, good seed coat texture, colour and taste (IITA, http://www.iita.org/).
Agronomic methods such as planting dates could be particularly important in low input farming systems, especially in the humid tropics (Bock and Jeger 1999) because the use of appropriate planting dates is not only essential for proper seed germination and emergence but also ensures that the crop is exposed to environmental conditions that are conducive for its optimum growth and development such that phonological phases of the crop matches with appropriate environmental factors (Azari and Khajepour 2003; Shegro et al. 2010). Furthermore, Ekesi et al. (1996) and Asante et al. (2001) in their studies reported that improved cultivars and alteration of planting dates such as planting in mid-June and mid-July as against planting in late July and early August in the humid tropics effectively reduced the menace of insect pest damage on cowpea pods and invariably increased grain yield. However, Lal (2009) and Hartman et al. (2011) submitted that optimum planting dates for different crops varies depending on crop cultivar and the agro-ecology of the area, though current climatic alterations in cropping seasons leading to wide fluctuations in quality and quantity of crop yields (Akande et al. 2012). More so, according to Wallace et al. (1991), the growth and development of legumes is highly dependent on genetic composition and environmental factors (moisture, soil fertility, mean air and soil temperature, photoperiodic day length among others), which enables the crop to optimize the use of natural resources and the variations of these factors depend on date of planting of the crop.
Therefore, appropriate time of planting and its interaction with genotype were evaluated among twenty newly released cowpea genotypes in Umudike, Nigeria to determine growth and yield performance of the cowpea genotypes under different planting dates as well as the inter-relationships between yield and associated traits in cowpea.
Experimental site
Field experiments were conducted during 2014 and 2015 growing seasons at Michael Okpara University of Agriculture Teaching and Research Farm Umudike (latitude 05°29′N; longitude 07°33′E; altitude 122 m above sea level) in the humid fringes of south eastern Nigeria. The area is characterised by a bimodal rainfall pattern with total rainfall of about 2,177 mm per annum. The wet season which commences in April is usually interrupted by a short August break followed by a short rainy period from September to October then the dry season commences from early November to March of the following year. Details of the weather conditions of the experimental site during the two cropping seasons (Table 1) indicated that though 2014 recorded less rainfall days, the amount of rainfall, sunshine hours and relative humidity was more compared with 2015 cropping season. The predominant vegetation of the site before it was used for the study was typical rainforest shrubs and grasses (NEST 1991).
Pre-planting composite soil samples were collected from each of the experimental plots using soil auger at a depth of 0–20 cm and a sub-sample collected and analyzed for soil texture, total nitrogen (N), phosphorus (P), potassium (K), organic carbon (OC), organic matter (OM), and pH according to standard soil science laboratory procedures at the Soil Science Laboratory, National Root Crops Research Institute, Umudike, Nigeria. The results showed the soil had 0.146 and 0.182% N, 35.20 and 67.80 mg/kg P, 0.065 and 0.079 cmol/kg K, 1.69 and 0.504% OC, 2.91 and 0.8% OM as well as pH 4.65 and pH 5.20 in water in 2014 and 2015 cropping seasons, respectively. The texture of the soil was sandy loam and classified as ultisol (Paleulstult) (US Soil Classification).
Cowpea genotypes, planting dates and experimental design
Twenty (20) cowpea genotypes of two maturity groups: early maturing (IT07K-299-6, IT10K-832-3, IT11K-61-82, IT97K-568-18, IT10K-843, IT10K-837-1, IT04K-227-4, IT10K-836-4, ITI0K-836-2, IT08K-125-107, IT96D-610, IT10K-866-1, IT07K-243-1-2) and late maturing (IT04K-332-1, IT89KD-288, IT06K-141, IT08K-126-19, IT07K-297-13, IT10K-837-1, IT99K-573-1-1). IFE BPC–LOCAL (CHECK) sourced from IITA were also used in the study. The experiment was a 20 × 3 factorial arranged in complete block design with three replications.
The plot size was 2 m × 3 m (6 m2) and the plants were planted at the spacing of 25 cm × 100 cm intra- and inter-row, which gave a plant population of 80,000 plants/ha at two seeds per stand. The plots were over-sown and thinned to the desired plant population at V2 (Fehr and Caviness 1977). Cowpea genotypes were planted at three different planting dates: early July (2nd July), early August (5th August) and Early September (9th September) in both cropping years (2014 and 2015).
Cultural practices
The field was cleared, ploughed, harrowed and levelled with a tractor before it was marked into experimental units. Weeding was done manually at 3 and 6 weeks after planting (WAP) to achieve a clean farm. The insecticide Cypermethrin was sprayed at two weeks interval after the second weeding using a knapsack sprayer at the concentration of 150 mL per 15 L of water for insect control.
Measurements
Growth data such as plant height, number of leaves/plant and number of branches/plant, shoot biomass, total dry matter and number of nodules/plant were taken on six sampled plants at 9 WAP. The number of nodules/plant was taken from three border plants from each plot carefully uprooted and the roots washed. The nodules were carefully removed and counted.
The weight of a dried pod, number of seeds/pod and seed weight/pod were collected from the six tagged and sampled plants as well as 100-seed weight/plot and grain yield (kg/ha) from the net plot at harvest.
Some phenological attributes such as number of days to flowering, which was obtained by counting the number of days from date of planting to date of first flower opening; number of days to pod filling as the number of days from pod setting to ripening; and number of days to maturity, which was counted as number of days from date of planting to date of pod ripening were also collected.
Statistical procedures
The data collected were subjected to analyses of variance using the GenStat Discovery edition 3 (https://www.vsni.co.uk/software/Genstat/) to estimate planting date and genotypemain effects as well as their interactions on the crop characters measured while mean separation was performed with F-tests (LSD) at P ≤ 0.05 according to Obi (2002). Pearson correlation coefficients of soybean grain yield to other plant attributes to examine the inter-relationships among the traits was calculated using the PROC CORR of SAS (SAS Institute, 2002) and the significance tested by referring to the standard table (Snedecor and Cochran 1980) with n - 2 degrees of freedom where n is the total number of observations. Path coefficients analysis was done to determine the direct and indirect effects of each trait to yield according to the procedure of Dewey and Lu (1959). Grain yield of cowpea (kg/ha) was considered as the dependent variable while the other traits were considered as independent variables.
Analysis of variance (Table 2) indicated that except plant height and number of leaves/plant in both years, number of branches/plant and number of nodules/plant in 2014, as well as grain yield in 2015, planting date significantly (P < 0.05) influenced all the variables evaluated (number of branches/plant, shoot biomass, total dry matter, number of nodules/plant, pod weight, number of seeds/pod, seed weight, and grain yield of cowpea).
Genotypes significantly affected all the variables assessed in the twenty cowpea genotypes both in 2014 and 2015 except shoot biomass in both years and total dry matter in 2014. The interaction between planting date and cowpea genotypes indicated non-significant (P > 0.05) variations amongst the growth and yield variables assessed in the test crop except plant height in 2015 and cowpea grain yield in both years.
Cowpea genotypes planted in early September (2015) gave the highest number of branches/plant, which was higher by 17.9 and 22.1% compared to July and August cowpea planting, respectively (Table 3). Among the cowpea genotypes tested, the number of leaves/plant ranged from 27.74 to 78.80 in 2014 and 25.40 to 63.90 in 2015. The number of branches/plant ranged from 3.17 to 4.37 and 2.71 to 4.52 in 2014 and 2015 cropping seasons, respectively. The highest number of leaves/plant and number of branches/plant were recorded under IT89KD-288 and IT06K-141 cowpea genotypes, respectively in both years.
The interaction between planting date and cowpea genotype (Table 4) indicated that IT99K-573-1-1 planted in August had taller plants compared with the genotypes planted at the same date and other planting dates, while the shortest plants were recorded when IT10K-837-1 genotype was planted in July.
The mean across the two years indicated that shoot biomass, total dry matter/plant and number of nodules/plant increased as the planting dates were adjusted from July, August and then to September (Table 5). Shoot biomass increased by 71.5 and 41.1%, total dry matter/plant by 65.8 and 19.0%, and number of nodules/plant by 21.3 and by 10.4%, respectively relative to July and August planting dates of the cowpea genotypes. The variables, shoot biomass, total dry matter/plant and number of nodules/plant increased by 71.5, 65.8 and 21.3%, respectively in July relative to 41.1, 19.0 and 10.4%, respectively in August. Among the cowpea genotypes across both cropping season highest total dry matter/plant and number of nodules/plant were recorded under IT06K-141 while IT10K-832-3 and IT10K837-1 recorded the lowest total dry matter/plant and number of nodules/plant, respectively.
Averaged across two cropping seasons, cowpea genotype planted in August gave the highest pod weight, number of seeds/pod and seed weight/pod compared with the other planting dates (Table 6). Among the cowpea genotypes, IT99K-523-1-1 gave the highest pod weight and seed weight/pod while the control (IFE BPC–LOCAL) had the lowest. Averaged across 2014 and 2015, the mean number of seeds/pod ranged from 8.89 to 14.84 with IT11K-61-82 exhibiting the highest seed number/pod.
The interaction between planting date and cowpea genotype (Table 7) indicated that IT11K-61-82 planted in September gave the highest grain yield while IT89KD-288 planted in July had the lowest yield in 2014. However, the trend was not the same in 2015, which showed IT06K-141 cowpea genotype planted in July as the highest yielder and IT99K-573-1-1 planted in September as the lowest compared with the other interaction treatments.
The correlation analysis across the two years between all the pairs of variables (Table 8) indicated that grain yield had positive and significant (P ≤ 0.05) correlation with seed weight/plant, number of seeds/plant, pod weight/plant and number of branches/plant but had negative and significant (P ≤ 0.05) relationship with phenological variables such as number of days to flowering, number of days to pod filling and number of days to maturity. However, days to maturity exhibited high and significant correlation with number of days to flowering and number of days to maturity with positive correlation coefficients (r) of 0.82 and 0.27, respectively but showed non-significant (P ≥ 0.05) relationship with the other variables. Pod weight/plant exhibited highly significant and positive association with 100-seed weight, seed weight/plant and number of seeds/pod. However, the association between 100-seed weight and grain yield was non-significant (P ≥ 0.05) due to individual small sizes of the sampled seeds from the grain yields. All the other variables evaluated exhibited different degrees of associations amongst themselves.
Path coefficients analysis of eight agronomic traits (100-seed weight, seed weight/plant, number of seeds/pod, pod weight/plant, number of days to flowering, number of days to pod filling, number of days to maturity and number of branches/plant) with grain yield were examined (Table 9). The direct effect of seed weight/plant was positive and of greater magnitude than the direct effect of 100-seed weight, number of seeds/plant and number of branches/plant while pod weight/plant, number of days to flowering, number of days to pod filling and number of days to maturity exhibited direct but negative effect on grain yield. Indirect effects of seed weight/pod via 100-seed weight, number of seeds/pod, days to flowering and number of days to maturity was positive, an indication that the trait is desirable and demands prime attention during crop improvement programs. The nature of the effects of the path coefficients analysis as represented in the diagram (Fig. 1) showed that the double arrowed lines indicated the inter-relationships among the agronomic traits as measured by the correlation coefficients while the single arrowed lines indicated the direct effects on grain yield as measured by the path coefficients. The letter R represents the residual factor that influenced grain yield of cowpea.
In the two cropping seasons, planting date and cowpea genotypes exhibited different degrees of variation among the crop characters evaluated. Similar studies by Akande et al. (2012) on planting date effect on cowpea seed yield and quality indicated that accurate time of sowing a crop in any particular environment is an important agronomic requirement for high yield. Planting date had effect on plant height, number of leaves/plant and number of branches/plant, which contrasted with its effect on number of branches/plant in 2015 cropping season. Cowpea genotypeshad significant effect on all the three variables due to strong inherited genetic properties that influenced their performance. These findings are in consonance with previous studies by Okpara and Oshilim (2001), Idahosa et al. (2010), Agbogidi and Egbo (2012), Nwofia et al. (2015) and Ezeaku et al. (2015) in which they stressed the importance of gene make-up as a key determinant that influences not only the morphological growth of cowpea under different environments but also its grain yield. Furthermore, Ezeaku et al. (2015) reported significant difference in growth attributes of cowpea across different sowing dates in the humid fridges of south eastern Nigeria. However, their observation indicated that early planting resulted in higher vegetative growth performance of the crop which was at variance with the results of this study.
Except number of nodules/plant in 2014, planting date influenced shoot biomass and total dry matter in both years as well as number of nodules/plant in 2015 while genotypes exhibited significant effect on the three growth variables evaluated. The findings obtained corroborated similar results by Nangju (1999), Adaji et al. (2007), Awe (2008), Dugje et al. (2009) and Nwofia et al. (2015) in their various studies on cowpea at different locations in which they reportedsignificant difference in vegetative growth attributes of cowpea genotypes across different sowing dates with August planting in the humid rainforest agro-zone of Nigeria recording enhanced performance in their growth characters. The variations observed among the genotypes may be attributed to genetic difference inherit in them, which responded differently to the crop’s micro-climate and environmental exposure.
The main factors (planting date and cowpea genotype) exhibited significant influence on pod weight, number of seeds/pod, seed weight/pod and grain yield contrary to their interactions except grain yield of cowpea in both years. Similarly, studies by Girish et al. (2006) on genetic variability in cowpea, Kelechukwu et al. (2007) on the effect of aluminium on some cowpea varieties in Alfisol, Ali et al. (2009) on performance of dual purpose dry season cowpea in the Fadama, as well as Ichi et al. (2013) on growth and yield response of selected cowpea varieties to irrigation interval and sowing date corroborated with our findings that inherent transferable parental trait differences of the tested genotypes influenced not only the growth performance of the test crop but also the grain yield and yield components, hence their response to different planting dates varied.
There was a strong and positive correlation between grain yield and seed weight/pod, grain yield and number of seeds/pod, grain yield and pod weight as well as grain yield and number of branches/plant which corroborated assertions by Ogunbodebe (1989), Nakawuka and Adiapala (1991) as well as Umar et al. (2010) in which they stressed that relationship studies among quantitative traits of crops is important for assessing the feasibility of joint selection of two or more traits. Therefore, these positive characters should be prioritized as prime traits during breeding and selection for forage and grain yield in cowpea. Furthermore, the associations agreed with several correlation reports made on other food legumes by other researchers such as Ene-Obong and Okoye (1992) on African yam bean (Sphenostylis stenocarpa), Ofori (1996) on Bambara groundnut (Vigna subterranean), Adebisi et al. (2001) on soybean, Achakzai et al. (2002) on non-inoculated and inoculated soybean crop, as well as Gihafoor et al. (2003) on the inter-relationship between SDS-page markers and agronomic characters in chick pea (Cicer arietinum).
Path coefficients analysis on eight agronomic traits was used to untangle cause and effects relationship that was confounded by correlation coefficients (Nwofia et al. 2013) indicated the importance of seed weight/pod, 100-seed weight, number of seeds/pod and number of branches/plant that exhibited positive, direct effect on grain yield of cowpea. The results corroborated similar works by Ombakho and Tyagi (1987) on yield and yield components of cowpea in East Africa, Udensi et al. (2012) on cowpea grown under lowland humid conditions, Yadav et al. (2001) on urd bean (Vigna mungo), and Shrivastava et al. (2001) on soybean (Glycine max) in which they submitted that grain yield is a complex polygenic trait that is normally influenced by many genes and factors working in synergy, hence, its improvement is the main target in legume breeding, selection and crop improvement under different environments due to variations that are often prevalent.
In conclusion, planting date influenced cowpea growth and yield. The findings indicated August as the most appropriate planting time for cowpea in the humid fridges of south eastern Nigeria due to progressive changes in the photoperiodic exposure of the legume to shorter days and longer night periods as well as less cloudiness due to seasonal variations from the cloudy rainy season to less cloudy dry season, which coincides with the phenological (flowering, podding, seed setting and maturity) period of the crop. The significant planting date by genotype interaction observed in grain yield indicated that IT11K-61-82 planted in September and IT06K-141 planted July was the highest yielding genotypes. However, IT96D-610 and IT06K-141 genotypes irrespective of planting date gave the highest grain yield while on the average across the two years; cowpea planted in August gave higher grain yield relative to the other planting dates.
Genotype had strong influence over most of the characters considered in the study especially IT06K-141, which consistently had the best performance in growth and yield. The other genotypes (IT11K-61-82 and IT96D-610) performed better relative to the other genotypes, hence exhibited good adaptation to the soil and climatic conditions of the humid agro-ecosystem. Growers can be encouraged to use them on-farm in the form of adaptive research trial prior to recommendation after out-station evaluation. Also, the information obtained from the plant characters would create a good platform for breeding of high yielding and stable cowpea genotypes for farmers in the agro-eco-farming systems in the humid fridges of south eastern Nigeria.
Fig. 1
Nature of casual system of variables for the path coefficients analysis in cowpea genotypes. Residual factor (R), unilateral pathway (P), values of correlation coefficients (r12 - r78) as obtained from mutual associations between variables of cowpea genotypes. Double arrowed lines (←→) denote mutual associations as measured by correlation coefficients. Single arrowed lines (←) denote direct influence and measured by the path coefficients analysis.
pbb-06-095f1.jpg
Table 1
Cumulative rainfall days, rainfall amount, sunshine hours and mean air temperature, every two months during the growing period of the crops in sole and intercrop for 2014 and 2015 cropping seasons and the mean of 10 years of agro-meteorological data of the experimental site (Umudike, Nigeria).
Table 1
Month 2014 2015
Cumulative Mean air temp. Relative humidity 1500 hours Cumulative Mean air temp. Relative humidity 1500 hours
Rainfall Sunshine Rainfall Sunshine
Days Amount (mm) (Hours) (°C) (%) Days Amount (mm) (Hours) (°C) (%)
May–June 28 531.0 10.7 30.5 71.5 36 593.0 4.4 33.5 69.5
July–August 34 559.1 5.9 30.5 78.5 29 495.4 5.2 29.6 80.5
September–October 34 570.4 7.0 31.0 75 29 656.2 6.4 29 76.0
November–December 11 147.4 9.1 32.7 56.5 33 49.7 12.2 33 47.0
Total 107 1807.9 32.7 - - 127 1794.3 28.2 - -
Mean monthly 13.4 225.99 4.09 31.2 70.4 15.9 224.29 3.5 31.3 68.25

Source: Agro-meteorological unit, National Root Crops Research Institute, Umudike, Nigeria.

Table 2
Analysis of variance showing significance (F pr.) of the main and interaction effects of planting date (PD) and cowpea genotype (G) on the ten response measurements examined.
Table 2
Source of variance Response variables
Plant height (cm) No. leaves/plant No. Branches/plant Shoot biomass (g) Total dry matter/plant (g) Number of nodules/plant Pod weight (g) Number of seeds/pod Seed weight/pod (g) Grain yield (kg/ha)
2014
 Planting date (PD) 0.163ns 0.181ns 0.192ns 0.002** 0.081* 0.186ns 0.051* 0.062* 0.095* 0.045*
 Genotype (G) < 0.001*** < 0.001*** 0.087* 0.363ns 0.753ns < 0.001*** < 0.001*** < 0.001*** < 0.001*** < 0.001***
 PD × G 0.242ns 0.229ns 0.165ns 0.968ns 0.893ns 0.474ns 0.165ns 0.254ns 0.192ns 0.01**
2015
 Planting date (PD) 0.242ns 0.183ns < 0.001*** 0.061* 0.074* 0.004** 0.077* 0.068* 0.002** 0.195ns
 Genotype (G) < 0.001*** < 0.001*** < 0.001*** 0.319ns 0.061* 0.777ns < 0.001*** < 0.001*** < 0.001*** < 0.001***
 PD × G 0.090* 0.176ns 0.159ns 0.864ns 0.323ns 0.175ns 0.408ns 0.262ns 0.192ns 0.063*

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 3
Effect of planting date and cowpea genotype on plant height, number of leaves/plant and number branches/plant in 2014 and 2015.
Table 3
Treatment Plant height (cm) No. leaves/plant No. branches/plant Plant height (cm) No. leaves/plant No. branches/plant
2014 2015
Planting date (PD)
 July 47.40 35.85 3.80 100.30 41.20 3.34
 Aug 74.80 46.61 3.50 107.60 41.30 3.17
 Sept 47.00 40.13 3.81 99.00 52.30 4.07
 Mean 56.40 40.86 3.70 102.30 44.93 3.53
 LSD(0.05) ns ns ns ns ns 0.3285**
Genotype (G)
 IT07K-299-6 44.30 34.23 3.17 78.70 33.30 2.78
 IT10K-843 77.30 48.42 3.55 138.20 46.00 3.22
 IT11K-61-82 72.00 37.36 3.30 136.70 35.30 2.74
 IT10K-837-1 28.30 31.16 3.96 59.70 33.00 3.07
 IT10K-832-3 45.70 46.31 3.78 120.20 50.50 3.89
 IT10K-836-4 32.30 30.83 3.70 83.60 43.00 3.33
 IT08K-125-107 66.50 46.00 3.63 97.30 32.80 2.71
 IT04K-227-4 22.80 32.88 3.63 44.20 31.40 3.55
 IT10K-866-1 42.10 34.32 3.56 93.30 40.40 3.22
 IT10K-836-2 33.40 27.74 3.78 56.70 38.90 4.00
 IT07K-243-1-2 90.70 39.10 4.18 101.50 43.40 4.19
 IFE BPC 91.70 49.75 3.37 151.20 67.70 3.59
 IT89KD-288 86.00 78.80 4.22 136.70 63.90 4.00
 IT08K-126-19 57.60 38.48 3.56 117.60 54.30 3.81
 IT04K-332-1 41.00 42.58 3.52 108.60 58.60 3.85
 IT96D-610 27.60 29.48 3.33 34.60 25.40 3.00
 IT07K-297-13 73.20 42.82 4.11 129.10 57.90 3.78
 IT97K-568-18 73.30 44.10 4.00 94.10 43.40 3.89
 IT06K-141 27.00 45.59 4.37 68.10 51.10 4.52
 IT99K-573-1-1 94.70 37.30 3.31 195.50 48.50 3.37
 Mean 56.40 40.86 3.70 47.11 44.93 3.53
 LSD(0.05) 25.06*** 10.482*** 0.7178* 25.00*** 14.17*** 0.7828***
PD × G ns ns ns 50.32* ns ns

Data analyzed with Least Squares Means and means separated with LSD.

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 4
Interaction of planting date and cowpea genotype on plant height (cm) in 2015.
Table 4
Genotype × Planting date
July August September Mean
IT07K-299-6 87.10 75.30 73.90 78.70
IT10K-843 124.80 126.70 163.10 138.20
IT11K-61-82 140.20 142.00 128.00 136.70
IT10K-837-1 19.70 96.80 62.70 59.70
IT10K-832-3 143.80 143.90 72.90 120.20
IT10K-836-4 94.50 84.10 72.10 83.60
IT08K-125-107 97.50 128.80 65.50 97.30
IT04K-227-4 46.70 54.50 31.40 44.20
IT10K-866-1 121.70 79.70 78.40 93.30
IT10K-836-2 54.50 60.30 55.30 56.70
IT07K-243-1-2 78.60 116.90 109.10 101.50
IFE BPC 150.10 175.30 128.10 151.20
IT89KD-288 137.60 129.60 143.00 136.70
IT08K-126-19 112.20 101.20 139.40 117.60
IT04K-332-1 105.40 103.10 117.40 108.60
IT96D-610 37.90 36.90 28.90 34.60
IT07K-297-13 123.20 130.10 134.00 129.10
IT97K-568-18 107.70 83.10 91.60 94.10
IT06K-141 57.00 71.20 76.10 68.10
IT99K-573-1-1 165.40 212.00 209.20 195.50
Mean 100.30 107.60 99.00
LSD(0.05) 50.32*

Data in interaction analyzed with Least Squares Means and means separated with LSD (P < 0.05).

Table 5
Effect of planting date and cowpea genotype on shoot biomass, total dry matter/plant and number of nodules/plant in 2014 and 2015.
Table 5
Treatment Shoot biomass (g) Total dry matter/plant (g) Number of nodules/plant
2014 2015 Mean 2014 2015 Mean 2014 2015 Mean
Planting date (PD)
 July 38.30 29.50 33.90 4.83 3.14 3.99 16.07 4.69 10.38
 August 69.10 71.00 70.05 9.41 9.46 9.44 15.88 7.76 11.82
 September 117.90 119.80 118.85 12.16 11.14 11.65 22.91 3.47 13.19
 Mean 75.10 73.43 8.8 7.91 18.29 5.31
 LSD(0.05) 31.80** 53.01* 3.702* 5.264* ns 1.860**
Genotype (G)
 IT07K-299-6 64.20 58.40 61.30 8.95 6.58 7.77 14.83 6.94 10.89
 IT10K-843 70.00 66.60 68.30 7.59 8.73 8.16 13.61 5.87 9.74
 IT11K-61-82 69.90 99.60 84.75 8.53 11.41 9.97 24.89 5.28 15.09
 IT10K-837-1 69.80 77.60 73.70 8.18 9.17 8.68 10.89 5.88 8.39
 IT10K-832-3 70.00 54.40 62.20 7.72 4.77 6.25 14.33 4.02 9.18
 IT10K-836-4 62.50 54.80 58.65 7.95 6.09 7.02 21.89 4.67 13.28
 IT08K-125-107 58.80 68.70 63.75 8.67 8.04 8.36 13.23 4.98 9.11
 IT04K-227-4 61.30 72.30 66.80 8.45 8.17 8.31 16.06 4.89 10.48
 IT10K-866-1 95.00 70.50 82.75 9.03 6.77 7.90 20.17 4.94 12.56
 IT10K-836-2 86.80 73.40 80.10 9.41 8.68 9.05 23.56 3.51 13.54
 IT07K-243-1-2 60.00 69.80 64.90 7.93 8.21 8.07 14.61 3.78 9.20
 IFE BPC 65.60 68.00 66.80 8.09 7.90 8.00 20.50 6.25 13.38
 IT89KD-288 67.70 53.10 60.40 7.61 7.28 7.45 20.28 6.78 13.53
 IT08K-126-19 69.80 86.20 78.00 10.13 10.66 10.40 15.89 4.17 10.03
 IT04K-332-1 78.80 80.90 79.85 8.29 8.08 8.19 19.50 6.61 13.06
 IT96D-610 74.20 79.10 76.65 9.48 6.98 8.23 20.00 4.67 12.34
 IT07K-297-13 98.40 83.10 90.75 9.05 7.65 8.35 12.61 6.28 9.45
 IT97K-568-18 86.70 43.40 65.05 10.18 4.98 7.58 22.22 5.36 13.79
 IT06K-141 120.70 89.90 105.30 11.07 11.03 11.05 35.53 4.91 20.22
 IT99K-573-1-1 71.80 119.20 95.50 9.67 7.07 8.37 11.11 6.33 8.72
 Mean 75.1 73.43 8.8 7.91 18.29 5.31
 LSD(0.05) ns ns ns 3.472* 8.122*** ns
PD × G ns ns ns ns ns ns

Data analyzed with Least Squares Means and means separated with LSD.

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 6
Effect of planting date and cowpea genotype on pod weight, number of seeds/pod and seed weight/pod in 2014 and 2015.
Table 6
Treatments Pod weight (g) Number of seeds/pod Seed weight/pod (g)
2014 2015 Mean 2014 2015 Mean 2014 2015 Mean
Planting date (PD)
 July 1.92 2.22 2.07 9.97 11.39 10.68 1.56 1.84 1.70
 August 2.24 2.37 2.31 11.22 12.16 11.69 1.85 1.95 1.90
 September 2.10 2.12 2.11 11.19 11.16 11.17 1.76 1.65 1.71
 Mean 2.087 2.234 10.79 11.569 1.72 1.813
 LSD(0.05) 0.2301* 0.1829* 0.7203* 0.6764* 0.1581* 0.1315**
Genotype (G)
 IT07K-299-6 2.17 2.38 2.27 11.04 12.41 11.73 1.75 1.88 1.81
 IT10K-843 2.10 2.25 2.18 12.04 12.09 12.07 1.71 1.75 1.73
 IT11K-61-82 2.28 2.64 2.46 14.20 15.47 14.84 1.94 2.16 2.05
 IT10K-837-1 2.27 2.27 2.27 9.91 10.66 10.29 1.95 1.89 1.92
 IT10K-832-3 2.02 2.18 2.10 11.84 12.53 12.19 1.72 1.78 1.75
 IT10K-836-4 1.96 2.06 2.01 9.66 10.32 9.99 1.63 1.72 1.68
 IT08K-125-107 2.39 2.40 2.40 12.18 12.11 12.15 1.96 2.00 1.98
 IT04K-227-4 2.05 2.27 2.16 11.63 12.71 12.17 1.68 1.86 1.77
 IT10K-866-1 1.78 2.17 1.97 11.58 12.68 12.13 1.51 1.73 1.62
 IT10K-836-2 2.10 2.36 2.23 9.69 11.06 10.37 1.70 1.88 1.79
 IT07K-243-1-2 2.10 2.37 2.23 10.37 11.33 10.85 1.73 1.92 1.82
 IFE BPC 1.64 1.71 1.67 9.98 11.01 10.49 1.39 1.44 1.41
 IT89KD-288 2.13 2.06 2.10 10.82 10.82 10.82 1.78 1.68 1.73
 IT08K-126-19 2.36 2.28 2.32 11.62 11.35 11.48 1.92 1.78 1.85
 IT04K-332-1 1.96 2.02 1.99 10.99 11.17 11.08 1.65 1.61 1.63
 IT96D-610 1.74 1.89 1.81 9.39 10.88 10.14 1.38 1.52 1.45
 IT07K-297-13 2.15 2.31 2.23 9.29 11.07 10.18 1.70 2.01 1.85
 IT97K-568-18 1.84 1.96 1.90 10.23 10.96 10.59 1.56 1.54 1.55
 IT06K-141 2.19 2.32 2.26 8.44 9.34 8.89 1.79 1.87 1.83
 IT99K-573-1-1 2.51 2.78 2.65 10.86 11.40 11.13 2.06 2.23 2.15
 Mean 2.087 2.23 10.79 11.57 1.72 1.81
 LSD(0.05) 0.2289*** 0.2255*** 0.9907*** 1.0689*** 0.1725*** 0.2117***
PD × G ns ns ns ns ns ns

Data analyzed with Least Squares Means and means separated with LSD.

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 7
Interaction of planting date and cowpea genotype on grain yield (kg/ha) in 2014 and 2015.
Table 7
Treatments 2014 2015
Planting date (PD) Planting date (PD)
Genotype (G) × July Aug. Sept. Mean × July Aug. Sept. Mean
 IT07K-299-6 265 1028 533 608 680 596 441 572
 IT10K-843 513 1150 838 833 438 350 337 375
 IT11K-61-82 779 909 1307 998 1264 1011 728 1001
 IT10K-837-1 629 637 900 722 407 421 437 422
 IT10K-832-3 495 1074 648 739 460 618 722 600
 IT10K-836-4 422 745 605 591 276 202 364 281
 IT08K-125-107 566 976 751 764 835 729 476 680
 IT04K-227-4 368 706 974 681 453 299 591 448
 IT10K-866-1 452 839 373 555 609 436 534 526
 IT10K-836-2 371 1117 598 695 654 249 482 462
 IT07K-243-1-2 507 1176 765 816 914 555 606 692
 IFE BPC 581 914 679 725 477 676 217 457
 IT89KD-288 125 368 150 214 459 475 407 447
 IT08K-126-19 521 999 671 731 618 463 555 545
 IT04K-332-1 570 1200 955 909 966 420 442 609
 IT96D-610 675 1511 935 1040 412 632 688 577
 IT07K-297-13 404 670 678 584 441 331 447 406
 IT97K-568-18 508 587 928 674 601 649 571 607
 IT06K-141 497 1290 963 917 1326 1033 699 1019
 IT99K-573-1-1 373 1273 672 773 725 644 193 520
 Mean 481 958 746 728 651 539 497 562
LSD(0.05) Planting date 334.70* ns
LSD(0.05) Genotype 207.00*** 209.2***
LSD(0.05) PD × G 434.20** 378.5*

Data analyzed with Least Squares Means and means separated with LSD.

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 8
Averaged over two cropping years linear correlation matrix between agronomic attributes and grain yield of cowpea.
Table 8
100 seed weight (g) Seed weight/pod (g) No. seeds/pod Pod weight (g) Days to flowering Days to Pod filling Days to maturity No. branches/plant Grain yield (kg/ha)
100 seed weight (g) 1.00 0.441** −0.331** 0.445** 0.023ns 0.138** 0.093ns 0.118* 0.019ns
Seed weight/pod (g) 1.00 0.549** 0.911** 0.021ns −0.036ns 0.022ns −0.074ns 0.135*
No. seeds/pod 1.00 0.547** 0.004ns −0.189** −0.063ns −0.148** 0.132*
Pod weight (g) 1.00 0.032ns −0.019ns 0.049ns −0.038ns 0.128*
Days to flowering 1.00 −0.121* 0.822** −0.162** −0.302**
Days to pod filling 1.00 0.270** 0.117* −0.131*
Days to maturity 1.00 −0.138** −0.332**
No. branches/plant 1.00 0.168**
Grain yield (kg/ha) 1.00

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 9
Path coefficients analysis of eight variables of cowpea averaged over two cropping years showing direct (diagonal) and indirect (off-diagonal) effects through the specific paths of plant traits on grain yield (kg/ha) of cowpea genotypes.
Table 9
Plant traits 100 seed weight (g) Seed weight/pod (g) No. seeds/pod Pod weight (g) Days to flowering Days to Pod filling Days to maturity No. branches/plant Grain yield (kg/ha) Correlation coefficients (r2)
100 seed weight (g) 0.054 0.148 −0.029 −0.114 −0.004 −0.019 −0.012 0.011 0.019ns
Seed weight/pod (g) 0.024 0.336 0.048 −0.233 −0.004 0.005 −0.003 −0.007 0.135*
No. seeds/pod −0.018 0.185 0.088 −0.139 −0.001 0.026 0.008 −0.013 0.132*
Pod weight (g) 0.024 0.306 0.048 −0.255 −0.006 0.003 −0.006 −0.003 0.128*
Days to flowering 0.001 0.007 0.000 −0.008 −0.195 0.017 −0.105 −0.014 −0.302**
Days to pod filling 0.007 −0.012 −0.017 0.005 0.024 −0.137 −0.035 0.010 −0.131*
Days to maturity 0.005 0.007 −0.006 −0.012 −0.160 −0.037 −0.128 −0.012 −0.332**
No. branches/plant 0.007 −0.025 −0.013 0.010 0.032 −0.016 0.018 0.089 0.168**
Residual 0.7987

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

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Genotype by Planting Date Effects on Cowpea in Humid Fringes, Southeast Nigeria
Plant Breed. Biotech.. 2018;6(2):95-108.   Published online June 1, 2018
DOI: https://doi.org/10.9787/PBB.2018.6.2.95
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Genotype by Planting Date Effects on Cowpea in Humid Fringes, Southeast Nigeria
Plant Breed. Biotech.. 2018;6(2):95-108.   Published online June 1, 2018
DOI: https://doi.org/10.9787/PBB.2018.6.2.95
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Genotype by Planting Date Effects on Cowpea in Humid Fringes, Southeast Nigeria
Image
Fig. 1 Nature of casual system of variables for the path coefficients analysis in cowpea genotypes. Residual factor (R), unilateral pathway (P), values of correlation coefficients (r12 - r78) as obtained from mutual associations between variables of cowpea genotypes. Double arrowed lines (←→) denote mutual associations as measured by correlation coefficients. Single arrowed lines (←) denote direct influence and measured by the path coefficients analysis.

Fig. 1

Genotype by Planting Date Effects on Cowpea in Humid Fringes, Southeast Nigeria

Cumulative rainfall days, rainfall amount, sunshine hours and mean air temperature, every two months during the growing period of the crops in sole and intercrop for 2014 and 2015 cropping seasons and the mean of 10 years of agro-meteorological data of the experimental site (Umudike, Nigeria).

Month 2014 2015
Cumulative Mean air temp. Relative humidity 1500 hours Cumulative Mean air temp. Relative humidity 1500 hours
Rainfall Sunshine Rainfall Sunshine
Days Amount (mm) (Hours) (°C) (%) Days Amount (mm) (Hours) (°C) (%)
May–June 28 531.0 10.7 30.5 71.5 36 593.0 4.4 33.5 69.5
July–August 34 559.1 5.9 30.5 78.5 29 495.4 5.2 29.6 80.5
September–October 34 570.4 7.0 31.0 75 29 656.2 6.4 29 76.0
November–December 11 147.4 9.1 32.7 56.5 33 49.7 12.2 33 47.0
Total 107 1807.9 32.7 - - 127 1794.3 28.2 - -
Mean monthly 13.4 225.99 4.09 31.2 70.4 15.9 224.29 3.5 31.3 68.25

Source: Agro-meteorological unit, National Root Crops Research Institute, Umudike, Nigeria.

Analysis of variance showing significance (F pr.) of the main and interaction effects of planting date (PD) and cowpea genotype (G) on the ten response measurements examined.

Source of variance Response variables
Plant height (cm) No. leaves/plant No. Branches/plant Shoot biomass (g) Total dry matter/plant (g) Number of nodules/plant Pod weight (g) Number of seeds/pod Seed weight/pod (g) Grain yield (kg/ha)
2014
 Planting date (PD) 0.163ns 0.181ns 0.192ns 0.002** 0.081* 0.186ns 0.051* 0.062* 0.095* 0.045*
 Genotype (G) < 0.001*** < 0.001*** 0.087* 0.363ns 0.753ns < 0.001*** < 0.001*** < 0.001*** < 0.001*** < 0.001***
 PD × G 0.242ns 0.229ns 0.165ns 0.968ns 0.893ns 0.474ns 0.165ns 0.254ns 0.192ns 0.01**
2015
 Planting date (PD) 0.242ns 0.183ns < 0.001*** 0.061* 0.074* 0.004** 0.077* 0.068* 0.002** 0.195ns
 Genotype (G) < 0.001*** < 0.001*** < 0.001*** 0.319ns 0.061* 0.777ns < 0.001*** < 0.001*** < 0.001*** < 0.001***
 PD × G 0.090* 0.176ns 0.159ns 0.864ns 0.323ns 0.175ns 0.408ns 0.262ns 0.192ns 0.063*

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Effect of planting date and cowpea genotype on plant height, number of leaves/plant and number branches/plant in 2014 and 2015.

Treatment Plant height (cm) No. leaves/plant No. branches/plant Plant height (cm) No. leaves/plant No. branches/plant
2014 2015
Planting date (PD)
 July 47.40 35.85 3.80 100.30 41.20 3.34
 Aug 74.80 46.61 3.50 107.60 41.30 3.17
 Sept 47.00 40.13 3.81 99.00 52.30 4.07
 Mean 56.40 40.86 3.70 102.30 44.93 3.53
 LSD(0.05) ns ns ns ns ns 0.3285**
Genotype (G)
 IT07K-299-6 44.30 34.23 3.17 78.70 33.30 2.78
 IT10K-843 77.30 48.42 3.55 138.20 46.00 3.22
 IT11K-61-82 72.00 37.36 3.30 136.70 35.30 2.74
 IT10K-837-1 28.30 31.16 3.96 59.70 33.00 3.07
 IT10K-832-3 45.70 46.31 3.78 120.20 50.50 3.89
 IT10K-836-4 32.30 30.83 3.70 83.60 43.00 3.33
 IT08K-125-107 66.50 46.00 3.63 97.30 32.80 2.71
 IT04K-227-4 22.80 32.88 3.63 44.20 31.40 3.55
 IT10K-866-1 42.10 34.32 3.56 93.30 40.40 3.22
 IT10K-836-2 33.40 27.74 3.78 56.70 38.90 4.00
 IT07K-243-1-2 90.70 39.10 4.18 101.50 43.40 4.19
 IFE BPC 91.70 49.75 3.37 151.20 67.70 3.59
 IT89KD-288 86.00 78.80 4.22 136.70 63.90 4.00
 IT08K-126-19 57.60 38.48 3.56 117.60 54.30 3.81
 IT04K-332-1 41.00 42.58 3.52 108.60 58.60 3.85
 IT96D-610 27.60 29.48 3.33 34.60 25.40 3.00
 IT07K-297-13 73.20 42.82 4.11 129.10 57.90 3.78
 IT97K-568-18 73.30 44.10 4.00 94.10 43.40 3.89
 IT06K-141 27.00 45.59 4.37 68.10 51.10 4.52
 IT99K-573-1-1 94.70 37.30 3.31 195.50 48.50 3.37
 Mean 56.40 40.86 3.70 47.11 44.93 3.53
 LSD(0.05) 25.06*** 10.482*** 0.7178* 25.00*** 14.17*** 0.7828***
PD × G ns ns ns 50.32* ns ns

Data analyzed with Least Squares Means and means separated with LSD.

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Interaction of planting date and cowpea genotype on plant height (cm) in 2015.

Genotype × Planting date
July August September Mean
IT07K-299-6 87.10 75.30 73.90 78.70
IT10K-843 124.80 126.70 163.10 138.20
IT11K-61-82 140.20 142.00 128.00 136.70
IT10K-837-1 19.70 96.80 62.70 59.70
IT10K-832-3 143.80 143.90 72.90 120.20
IT10K-836-4 94.50 84.10 72.10 83.60
IT08K-125-107 97.50 128.80 65.50 97.30
IT04K-227-4 46.70 54.50 31.40 44.20
IT10K-866-1 121.70 79.70 78.40 93.30
IT10K-836-2 54.50 60.30 55.30 56.70
IT07K-243-1-2 78.60 116.90 109.10 101.50
IFE BPC 150.10 175.30 128.10 151.20
IT89KD-288 137.60 129.60 143.00 136.70
IT08K-126-19 112.20 101.20 139.40 117.60
IT04K-332-1 105.40 103.10 117.40 108.60
IT96D-610 37.90 36.90 28.90 34.60
IT07K-297-13 123.20 130.10 134.00 129.10
IT97K-568-18 107.70 83.10 91.60 94.10
IT06K-141 57.00 71.20 76.10 68.10
IT99K-573-1-1 165.40 212.00 209.20 195.50
Mean 100.30 107.60 99.00
LSD(0.05) 50.32*

Data in interaction analyzed with Least Squares Means and means separated with LSD (P < 0.05).

Effect of planting date and cowpea genotype on shoot biomass, total dry matter/plant and number of nodules/plant in 2014 and 2015.

Treatment Shoot biomass (g) Total dry matter/plant (g) Number of nodules/plant
2014 2015 Mean 2014 2015 Mean 2014 2015 Mean
Planting date (PD)
 July 38.30 29.50 33.90 4.83 3.14 3.99 16.07 4.69 10.38
 August 69.10 71.00 70.05 9.41 9.46 9.44 15.88 7.76 11.82
 September 117.90 119.80 118.85 12.16 11.14 11.65 22.91 3.47 13.19
 Mean 75.10 73.43 8.8 7.91 18.29 5.31
 LSD(0.05) 31.80** 53.01* 3.702* 5.264* ns 1.860**
Genotype (G)
 IT07K-299-6 64.20 58.40 61.30 8.95 6.58 7.77 14.83 6.94 10.89
 IT10K-843 70.00 66.60 68.30 7.59 8.73 8.16 13.61 5.87 9.74
 IT11K-61-82 69.90 99.60 84.75 8.53 11.41 9.97 24.89 5.28 15.09
 IT10K-837-1 69.80 77.60 73.70 8.18 9.17 8.68 10.89 5.88 8.39
 IT10K-832-3 70.00 54.40 62.20 7.72 4.77 6.25 14.33 4.02 9.18
 IT10K-836-4 62.50 54.80 58.65 7.95 6.09 7.02 21.89 4.67 13.28
 IT08K-125-107 58.80 68.70 63.75 8.67 8.04 8.36 13.23 4.98 9.11
 IT04K-227-4 61.30 72.30 66.80 8.45 8.17 8.31 16.06 4.89 10.48
 IT10K-866-1 95.00 70.50 82.75 9.03 6.77 7.90 20.17 4.94 12.56
 IT10K-836-2 86.80 73.40 80.10 9.41 8.68 9.05 23.56 3.51 13.54
 IT07K-243-1-2 60.00 69.80 64.90 7.93 8.21 8.07 14.61 3.78 9.20
 IFE BPC 65.60 68.00 66.80 8.09 7.90 8.00 20.50 6.25 13.38
 IT89KD-288 67.70 53.10 60.40 7.61 7.28 7.45 20.28 6.78 13.53
 IT08K-126-19 69.80 86.20 78.00 10.13 10.66 10.40 15.89 4.17 10.03
 IT04K-332-1 78.80 80.90 79.85 8.29 8.08 8.19 19.50 6.61 13.06
 IT96D-610 74.20 79.10 76.65 9.48 6.98 8.23 20.00 4.67 12.34
 IT07K-297-13 98.40 83.10 90.75 9.05 7.65 8.35 12.61 6.28 9.45
 IT97K-568-18 86.70 43.40 65.05 10.18 4.98 7.58 22.22 5.36 13.79
 IT06K-141 120.70 89.90 105.30 11.07 11.03 11.05 35.53 4.91 20.22
 IT99K-573-1-1 71.80 119.20 95.50 9.67 7.07 8.37 11.11 6.33 8.72
 Mean 75.1 73.43 8.8 7.91 18.29 5.31
 LSD(0.05) ns ns ns 3.472* 8.122*** ns
PD × G ns ns ns ns ns ns

Data analyzed with Least Squares Means and means separated with LSD.

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Effect of planting date and cowpea genotype on pod weight, number of seeds/pod and seed weight/pod in 2014 and 2015.

Treatments Pod weight (g) Number of seeds/pod Seed weight/pod (g)
2014 2015 Mean 2014 2015 Mean 2014 2015 Mean
Planting date (PD)
 July 1.92 2.22 2.07 9.97 11.39 10.68 1.56 1.84 1.70
 August 2.24 2.37 2.31 11.22 12.16 11.69 1.85 1.95 1.90
 September 2.10 2.12 2.11 11.19 11.16 11.17 1.76 1.65 1.71
 Mean 2.087 2.234 10.79 11.569 1.72 1.813
 LSD(0.05) 0.2301* 0.1829* 0.7203* 0.6764* 0.1581* 0.1315**
Genotype (G)
 IT07K-299-6 2.17 2.38 2.27 11.04 12.41 11.73 1.75 1.88 1.81
 IT10K-843 2.10 2.25 2.18 12.04 12.09 12.07 1.71 1.75 1.73
 IT11K-61-82 2.28 2.64 2.46 14.20 15.47 14.84 1.94 2.16 2.05
 IT10K-837-1 2.27 2.27 2.27 9.91 10.66 10.29 1.95 1.89 1.92
 IT10K-832-3 2.02 2.18 2.10 11.84 12.53 12.19 1.72 1.78 1.75
 IT10K-836-4 1.96 2.06 2.01 9.66 10.32 9.99 1.63 1.72 1.68
 IT08K-125-107 2.39 2.40 2.40 12.18 12.11 12.15 1.96 2.00 1.98
 IT04K-227-4 2.05 2.27 2.16 11.63 12.71 12.17 1.68 1.86 1.77
 IT10K-866-1 1.78 2.17 1.97 11.58 12.68 12.13 1.51 1.73 1.62
 IT10K-836-2 2.10 2.36 2.23 9.69 11.06 10.37 1.70 1.88 1.79
 IT07K-243-1-2 2.10 2.37 2.23 10.37 11.33 10.85 1.73 1.92 1.82
 IFE BPC 1.64 1.71 1.67 9.98 11.01 10.49 1.39 1.44 1.41
 IT89KD-288 2.13 2.06 2.10 10.82 10.82 10.82 1.78 1.68 1.73
 IT08K-126-19 2.36 2.28 2.32 11.62 11.35 11.48 1.92 1.78 1.85
 IT04K-332-1 1.96 2.02 1.99 10.99 11.17 11.08 1.65 1.61 1.63
 IT96D-610 1.74 1.89 1.81 9.39 10.88 10.14 1.38 1.52 1.45
 IT07K-297-13 2.15 2.31 2.23 9.29 11.07 10.18 1.70 2.01 1.85
 IT97K-568-18 1.84 1.96 1.90 10.23 10.96 10.59 1.56 1.54 1.55
 IT06K-141 2.19 2.32 2.26 8.44 9.34 8.89 1.79 1.87 1.83
 IT99K-573-1-1 2.51 2.78 2.65 10.86 11.40 11.13 2.06 2.23 2.15
 Mean 2.087 2.23 10.79 11.57 1.72 1.81
 LSD(0.05) 0.2289*** 0.2255*** 0.9907*** 1.0689*** 0.1725*** 0.2117***
PD × G ns ns ns ns ns ns

Data analyzed with Least Squares Means and means separated with LSD.

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Interaction of planting date and cowpea genotype on grain yield (kg/ha) in 2014 and 2015.

Treatments 2014 2015
Planting date (PD) Planting date (PD)
Genotype (G) × July Aug. Sept. Mean × July Aug. Sept. Mean
 IT07K-299-6 265 1028 533 608 680 596 441 572
 IT10K-843 513 1150 838 833 438 350 337 375
 IT11K-61-82 779 909 1307 998 1264 1011 728 1001
 IT10K-837-1 629 637 900 722 407 421 437 422
 IT10K-832-3 495 1074 648 739 460 618 722 600
 IT10K-836-4 422 745 605 591 276 202 364 281
 IT08K-125-107 566 976 751 764 835 729 476 680
 IT04K-227-4 368 706 974 681 453 299 591 448
 IT10K-866-1 452 839 373 555 609 436 534 526
 IT10K-836-2 371 1117 598 695 654 249 482 462
 IT07K-243-1-2 507 1176 765 816 914 555 606 692
 IFE BPC 581 914 679 725 477 676 217 457
 IT89KD-288 125 368 150 214 459 475 407 447
 IT08K-126-19 521 999 671 731 618 463 555 545
 IT04K-332-1 570 1200 955 909 966 420 442 609
 IT96D-610 675 1511 935 1040 412 632 688 577
 IT07K-297-13 404 670 678 584 441 331 447 406
 IT97K-568-18 508 587 928 674 601 649 571 607
 IT06K-141 497 1290 963 917 1326 1033 699 1019
 IT99K-573-1-1 373 1273 672 773 725 644 193 520
 Mean 481 958 746 728 651 539 497 562
LSD(0.05) Planting date 334.70* ns
LSD(0.05) Genotype 207.00*** 209.2***
LSD(0.05) PD × G 434.20** 378.5*

Data analyzed with Least Squares Means and means separated with LSD.

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Averaged over two cropping years linear correlation matrix between agronomic attributes and grain yield of cowpea.

100 seed weight (g) Seed weight/pod (g) No. seeds/pod Pod weight (g) Days to flowering Days to Pod filling Days to maturity No. branches/plant Grain yield (kg/ha)
100 seed weight (g) 1.00 0.441** −0.331** 0.445** 0.023ns 0.138** 0.093ns 0.118* 0.019ns
Seed weight/pod (g) 1.00 0.549** 0.911** 0.021ns −0.036ns 0.022ns −0.074ns 0.135*
No. seeds/pod 1.00 0.547** 0.004ns −0.189** −0.063ns −0.148** 0.132*
Pod weight (g) 1.00 0.032ns −0.019ns 0.049ns −0.038ns 0.128*
Days to flowering 1.00 −0.121* 0.822** −0.162** −0.302**
Days to pod filling 1.00 0.270** 0.117* −0.131*
Days to maturity 1.00 −0.138** −0.332**
No. branches/plant 1.00 0.168**
Grain yield (kg/ha) 1.00

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Path coefficients analysis of eight variables of cowpea averaged over two cropping years showing direct (diagonal) and indirect (off-diagonal) effects through the specific paths of plant traits on grain yield (kg/ha) of cowpea genotypes.

Plant traits 100 seed weight (g) Seed weight/pod (g) No. seeds/pod Pod weight (g) Days to flowering Days to Pod filling Days to maturity No. branches/plant Grain yield (kg/ha) Correlation coefficients (r2)
100 seed weight (g) 0.054 0.148 −0.029 −0.114 −0.004 −0.019 −0.012 0.011 0.019ns
Seed weight/pod (g) 0.024 0.336 0.048 −0.233 −0.004 0.005 −0.003 −0.007 0.135*
No. seeds/pod −0.018 0.185 0.088 −0.139 −0.001 0.026 0.008 −0.013 0.132*
Pod weight (g) 0.024 0.306 0.048 −0.255 −0.006 0.003 −0.006 −0.003 0.128*
Days to flowering 0.001 0.007 0.000 −0.008 −0.195 0.017 −0.105 −0.014 −0.302**
Days to pod filling 0.007 −0.012 −0.017 0.005 0.024 −0.137 −0.035 0.010 −0.131*
Days to maturity 0.005 0.007 −0.006 −0.012 −0.160 −0.037 −0.128 −0.012 −0.332**
No. branches/plant 0.007 −0.025 −0.013 0.010 0.032 −0.016 0.018 0.089 0.168**
Residual 0.7987

ns, *, ** and ***stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 1 Cumulative rainfall days, rainfall amount, sunshine hours and mean air temperature, every two months during the growing period of the crops in sole and intercrop for 2014 and 2015 cropping seasons and the mean of 10 years of agro-meteorological data of the experimental site (Umudike, Nigeria).

Source: Agro-meteorological unit, National Root Crops Research Institute, Umudike, Nigeria.

Table 2 Analysis of variance showing significance (F pr.) of the main and interaction effects of planting date (PD) and cowpea genotype (G) on the ten response measurements examined.

stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 3 Effect of planting date and cowpea genotype on plant height, number of leaves/plant and number branches/plant in 2014 and 2015.

Data analyzed with Least Squares Means and means separated with LSD.

stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 4 Interaction of planting date and cowpea genotype on plant height (cm) in 2015.

Data in interaction analyzed with Least Squares Means and means separated with LSD (P < 0.05).

Table 5 Effect of planting date and cowpea genotype on shoot biomass, total dry matter/plant and number of nodules/plant in 2014 and 2015.

Data analyzed with Least Squares Means and means separated with LSD.

stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 6 Effect of planting date and cowpea genotype on pod weight, number of seeds/pod and seed weight/pod in 2014 and 2015.

Data analyzed with Least Squares Means and means separated with LSD.

stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 7 Interaction of planting date and cowpea genotype on grain yield (kg/ha) in 2014 and 2015.

Data analyzed with Least Squares Means and means separated with LSD.

stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 8 Averaged over two cropping years linear correlation matrix between agronomic attributes and grain yield of cowpea.

stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

Table 9 Path coefficients analysis of eight variables of cowpea averaged over two cropping years showing direct (diagonal) and indirect (off-diagonal) effects through the specific paths of plant traits on grain yield (kg/ha) of cowpea genotypes.

stand for not significant at the 0.05 probability level, significant at the 0.05, 0.01 and 0.001 probability level, respectively.

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