Abstract
Indian spinach (Basella spp. L.) is an underutilized and underexploited indigenous leafy vegetable which has high nutritional and medicinal value and extensively used in the sub-continent. Landrace germplasm is endowed with rich genetic variability for various yield and quality traits. A total of six accessions collected through an exploration during 2010 were pre-bred by selfing during the October–January cropping season in 2011. These landraces were evaluated in a randomized block design with four replications in June–September, 2012 at Vegetable Research Station, Dr. Y. S. R. Horticultural University, Rajendranagar to assess the genetic diversity, variability, heritability and genetic advance for yield and its components in the material. Multivariate analysis following Ward’s minimum variance-method revealed distinct clustering pattern. Analysis of variance revealed highly significant differences among all genotypes for all the studied traits indicating considerable variability among ecotypes for most of the measured parameters. There was significant variability for genetic potential of all genotypes for different traits under study. The highest variability at genotypic level was observed for stalk yield (73.95%) followed by leaf-stalk ratio (46.70%) and weight of tender shoot (41.25%). Low to high estimates of broad sense heritability were found in different traits. High estimates of heritability (>60%) coupled with high genetic advance as percent of mean (>20%) for petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index revealed that most likely the heritability is due to additive gene effects and selection may be effective.
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Key words: Genetic advance, Genetic diversity, Genetic variability, Heritability, Indian spinach, Landraces, Quality, Yield
INTRODUCTION
Indian spinach (
Basella alba L., 2n=48;
Basella rubra L., 2n=44) is one of the rapidly growing tropical leafy vegetables, also noted by regional names in different regions in Asia
viz., Ceylon spinach, Malabar spinach, saan choy (Chinese), mong toi (Vietnamese), alugbati (Philippines), pui saag (Bengali), remayong (Malay) belongs to the family Basellaceae and order caryophyllales. It is native to tropical Asia, probably originating from India or Indonesia. The distribution of
Basella extends from the tropical and subtropical regions mostly America, Africa, Madagascar and south India to New Guinea. It is grown in almost all parts of India, tropical Asia and Africa. It is gaining popularity in some of the tropical and temperate climates of Asia, America, Australia and Europe. Although the plant is a perennial climber (
Roshan et al. 2012), it is cultivated as an annual leafy vegetable. It is an important and reliable source of income for marginal and small farmers and tribal folks in southern states of India. It is widely adapted to a variety of soils and climates. It thrives well in tropical and subtropical climates (
Grubben 1997). Being a warm season crop, it is extremely heat tolerant (
Grubben and Denton 2004) and frost tender. It can thrive under conditions of moderate soil fertility and can grow in highly acid soils, but is quite responsive to nitrogen fertilizer. It is a minor leafy vegetable and since it is generally grouped together with other greens. The plant is found to be versatile in properties (
Saroj et al. 2012). It can be used as leafy vegetable, ornamental, dye and medicine. Tender shoots with succulent stem along with thick, semi-succulent and mucilaginous leaves are used as leafy vegetable. It is appreciated for its organoleptic characteristics (
Lucas 1988) and makes a tasty addition to salads, dips and meals. The leaves are also used for making soups (
Lucas 1988). It has high economic, nutritional and medicinal values. This crop is a valuable income source for marginal and small farmers near the principal urban centers. It plays a vital role in food and nutritional security particularly during the dry periods (
Maundu et al. 1999). It is rich in food value, supplying minerals, vitamins, proteins, carbohydrates and dietary fibre (
Adeboye 1996). It is found to be a good source of calcium, iron, vitamin A, vitamin B9 and Vitamin C (
Lucas 1988;
Okigbo 1990;
Palada and Chang 2003;
Grubben and Denton 2004;
Prance and Nesbitt 2005).
Basella alba has been used from a long time back for the treatment of many diseases like dysentery, diarrhea, anemia and cancer (
Roshan et al. 2012). The Ayurvedic treatment in India used
B. alba leaves and stems for anticancer such as melanoma, leukemia and oral cancer (
Premalatha and Rajgopal 2005). In India, it has been used for antipruritis and burn (
Saikia et al. 2006), and has been used in Bangladesh for acne and freckle treatment (
Akhter et al. 2008). Stems and leaves are used as mild laxative, diuretic and antipyretic (
Chou 1997). Roots and leaves have been used for the removal of after birth and stomach pains and for increasing milk production (
Pascaline et al. 2010). A decoction of the leaves is a good laxative for pregnant women and children (
Kirtikar and Basu 1975). The boiled leaves along with sorghum flour are an effective antiulcer agent (
Dixit and Goyal 2011). The roots are used in the treatment of diarrhea, the cooked leaves and stems are used as laxatives (
Larkcom 1991;
Phillips and Rix 1995). The juice of leaves has been prescribed against constipation especially for children and pregnant women (
Duke and Ayensu 1985). The flowers are used as an antidote to poisons and also as diuretic and febrifuge (
Duke and Ayensu 1985).
Basella in the process of domestication and cultivation over many centuries adapted to various eco-geographical zones in India and thus the landraces accumulated significant amount of variability. Several landraces of
Basella are under commercial cultivation in south India catering to the requirements of local markets. Heterogeneity in production and quality of crop is mainly due to lack of adequate efforts towards characterization and evaluation of sizeable germplasm and identification of elite accessions. Germplasm is the reservoir of genetic diversity. Germplasm collections play a key role for genetic improvement of any crop. Characterization and evaluation data of germplasm will increase utilization of germplasm so that people can make better use of biodiversity (
Bioversity International 2007). Genetic improvement of crops for quantitative traits requires reliable estimates of genetic diversity, genetic variability, heritability and genetic advancement in respect to the breeding material that is presently at hand in order to plan an efficient breeding program (
Dudley and Moll 1969;
Ulloa et al. 2007;
Chand et al. 2008). An accurate estimation of genetic diversity can be invaluable in the selection of diverse parental combinations to generate segregating progenies with maximum genetic variability and introgressing desirable traits from diverse or wild germplasm into the available cultivars to broaden the genetic base (
Ulloa et al. 2007). Genetic variability for agronomic traits is the key component of breeding programmes for broadening the gene pool of crops. In view of the above, collection, characterization and evaluation of germplasm facilitate estimation and better utilization of available diversity (
Dudley and Moll 1969;
Bioversity International 2007;
Ulloa et al. 2007;
Chand et al. 2008).
Until recently, research was concentrated mainly on major leafy vegetable species and very little attention has been given to minor but indigenous leafy vegetable species.
Basella is an indigenous minor leafy vegetable crop of increasing value but underutilized and underexploited. Despite its multiple virtues,
Basella crop is not included in the priority leafy vegetables for research in India. Until recently no or little attention was paid to its genetic improvement. From the survey of literature, it is evident that genetic studies in
Basella is limited, this trend is associated with little preference for this crop among researchers in the world, often termed ‘orphan crop’. Genetic studies in
Basella revealed that phenotypic coefficient of variation was higher than genotypic coefficient of variation for all the traits studied, indicating environmental influence on expression of these characters (
Varalakshmi and Devaraju 2010). Moderate heritability along with high genetic advance was recorded for leaf weight and total plant weight, indicating the presence of additive gene effects. Higher plant weight was found to be significantly and positively associated with branch number, leaf number, leaf weight and stem weight. Thus, for yield improvement in
Basella, emphasis may be laid on indirect selection through leaf characters like leaf number, leaf length and leaf weight. Hence, selection can be employed for improvement of these characters in
Basella (
Varalakshmi and Devaraju 2010).
The objectives of the study were to estimate the amount of genetic variability available in the Indian spinach accessions and to estimate heritability and genetic advance among agronomic traits for selection.
MATERIALS AND METHODS
Exploration survey and germplasm collection
A survey was conducted by the National Bureau of Plant Genetic Resources Regional Station, Hyderabad in collaboration with Vegetable Research Station, Dr. Y.S.R. Horticultural University, Rajendranagar during 2010. Following random sampling strategy, six landraces of
Basella were collected from two districts of Andhra Pradesh and one of Orissa from different locations (
Table 1). DIVA-GIS version 7.5.0, free downloadable software (
Hijmans et al. 2012) was used to map the collection sites of
Basella germplasm from Andhra Pradesh and Orissa (
Fig. 1).
Basella being a short day plant which requires less than 13 hours to induce flowering, was grown during rabi (October–January) season in 2011 at the Experimental Farm, Vegetable Research Station, Rajendranagar for maintenance and initial seed increase. Each of the six landraces collected were raised in triple-row plots of 3.0×1.8 m with inter-row spacing of 0.60 m and intra-row spacing of 0.30 m maintaining a population of 30 plants per genotype. Basella although autogamous, the flowering shoots were bagged with muslin cloth to prevent natural outcrossing. The fully ripe selfed fruits were harvested and dried.
Experimental material, design and crop management
A total of six landraces of
Basella (RNIS-1 to RNIS-6) thus collected and pre-bred were utilized for the present study (
Table 1). These six landraces were evaluated in a randomized block design with four replications at the Experimental Farm (latitude 17.19°N and longitude 79.23°E, and altitude 542.6 m) of the Vegetable Research Station, Rajendranagar under irrigated conditions during
kharif (June–September) 2012. Since long days of ≥13 hours precludes flowering in
Basella, landraces were evaluated for leafy vegetable production during long days of
kharif (June–September) for yield and quality traits. Each block consisted of 18 rows with 3 rows per genotype. Each genotype was raised in a triple row plot of 3.0 m length and 1.8 m width. In each replication, a plant population of 10 plants per row and 30 plants per plot and genotype was maintained. Two seeds per hill were dibbled with an intra-row spacing of 0.30 m and an inter-row spacing of 0.60 m. Thereafter, hills were thinned to one plant at two weeks after sowing. Recommended package of practices was followed to raise a successful crop. All agronomic practices were maintained for a whole duration of the experiment. Regular plant protection measures were carried out to safeguard the crop from pests and diseases.
The plants of Basella are subjected to periodical harvesting following shoot pickings at regular intervals as practiced by farmers. All the landraces were harvested simultaneously with first shoot picking at 45 days after sowing and subsequent harvests at 30 days interval over a period of 3 months. Observations on the agro-economic characters like leaf length (cm), leaf width (cm), leaf weight (g), petiole length (cm), length of tender shoot (cm) and internodal length (cm) were recorded from the random sample of 10 tender shoots selected from ten randomly selected competitive plants, while the observations on other characters like leaf yield (g/shoot), stalk yield (g/shoot), total biomass (g/plant), leaf-stalk ratio and harvest index were recorded on whole plot basis in each entry in each replication. Young tender shoots consisting of 10 intact leaves were harvested by clipping the stem with sharp knife. At first harvest in each treatment and replication, ten tender shoots with 10 leaves from the growing tip were utilized to record the biometric data on leaf lamina length (cm), leaf lamina width (cm), leaf weight (g), petiole length (cm), length of tender shoots (cm), internodal length (cm), weight of tender shoots, leaf yield/shoot (g) and stalk yield/shoot (g). These sampled tender shoots were stripped off leaves to facilitate recording of data on separated stalks and leaves. Leaf length (cm) was determined by measuring all 10 leaves stripped off from the individual shoots from the leaf base to the tip with a measuring scale. Leaf width (cm) was determined by measuring all 10 leaves stripped off from the individual shoots at the widest point of the leaf blade with a measuring scale. Average leaf weight (g) was determined by weighing all 10 leaves stripped off from the individual shoots in a digital analytical balance (±0.001 g). Length of tender shoot consisting of 10 leaves from the growing tip was measured in centimeters with a measuring scale. Length of tender shoot (cm) was divided with the number of nodes on the tender shoot to get internodal length (cm). Weight of 10 leaves stripped off from the tender shoots was measured in a digital analytical balance (±0.001 g) to arrive at leaf yield per shoot (g). Weight of 10 tender shoots excluding leaves was measured in a digital analytical balance (±0.001 g) to arrive at stalk yield per shoot (g). Data from each harvest were combined at the end of the growing season to estimate the total shoot yield per plot and total shoot yield per plant. Harvest index was taken as the ratio of leaf weight to total above-ground weight. The landraces were also characterized for 10 qualitative traits like growth habit, stem colour, stem shape, leaf colour, leaf margin, leaf margin colour, leaf apex, petiole colour and flower colour on single plant basis.
Statistical analysis of data
The data thus recorded were subjected to analysis of variance (
Steel and Torrie 1980). The mean performance of each individual genotype was employed in the statistical analysis and to estimate major genetic components using SAS Enterprise Guide Version 4.2 (
SAS Institute Inc 2009). The genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) were computed by adopting the method of
Burton and de Vane (1953) and
Burton (1952). The phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV) values were classified as low (<10.00%), moderate (10.00–20.00%) and high (>20.00%) as suggested by
Sivasubramanian and Menon (1973). Heritability in the broad sense was derived based on the formula given by
Allard (1960) and
Burton and de Vane (1953). The heritability values were classified as low (<30.00%), moderate (30.00–60.00%) and high (>60.00%) as suggested by
Johnson et al. (1955). The estimates of genetic advance (GA) at 5% selection intensity (2.06) and genetic advance as percent of mean were obtained using procedure given by
Allard (1960). The estimates of genetic advance and genetic advance as percent of mean were classified as low (<10.00%), moderate (10.00–20.00%) and high (>20.00%) as suggested by
Johnson et al. (1955). Hierarchical clustering (
Fig. 3) was carried out following Ward’s minimum variance method (
Ward 1963).
RESULTS
Characterization of landraces
Germplasm characterization was centered primarily on two major species,
Basella alba L. and
Basella rubra L. Of the six landraces under study, RNIS-1 RNIS-2 RNIS-3 RNIS-5 and RNIS-6 with green leaf margin colour were recognized as
Basella alba L., while RNIS-4 with red leaf margin colour was recognized as
Basella rubra L. Germplasm characterization was centered secondarily on qualitative traits. Six landraces of Indian spinach characterized in this study showed a broad variation for most of the qualitative traits under study (
Table 2). The variation in growth habit, stem colour, stem shape, leaf colour, leaf shape, leaf margin colour, petiole colour and flower colour, were easily recognizable with visual appraisal in the material (
Fig. 2). The comparative view of plants, tender shoots and leaves of six landraces is depicted in
Fig. 2. Plants of six landraces displayed great diversity in their growth habit (twining/twining but initially bushy/procumbent). Of the six landraces, the landraces RNIS-1 and RNIS-4 had twining growth habit. The landraces RNIS-2 and RNIS-3 had twining but initially bushy growth habit. The landraces RNIS-5 and RNIS-6 had procumbent growth habit. Stem was red coloured in RNIS-1, RNIS-4 and RNIS-5 and green coloured in RNIS-2, RNIS-3 and RNIS-6. Stems were round (RNIS-1, RNIS-2 and RNIS-3) to angular (RNIS-4, RNIS-5 and RNIS-6) in shape. Leaves were light green (RNIS-2, RNIS-3 and RNIS-6) to dark green (RNIS-1, RNIS-4 and RNIS-5) in colour. Leaves were oval (RNIS-4 and RNIS-5) to ovate ((RNIS-1, RNIS-2, RNIS-3 and RNIS-6) in shape. There was no variation in leaf margin (entire) and leaf apex (acuminate) among landraces. Leaf margin was green in almost all accessions except RNIS-4 (red). Petioles are green in almost all accessions except RNIS-4 (red). Flowers are light pink (RNIS-2 and RNIS-6) to pink (RNIS-1, RNIS-3, RNIS-4 and RNIS-5) in colour. There exists no relationship between the stem colour of the accessions and the leaf colour as well as the petiole colour (
Fig. 2).
Analysis of variance
From the analysis of variance (
Table 3), it is evident that highly significant differences among six landraces were observed for majority of the characters under study except leaf length, length of tender shoot, leaf yield and total biomass. No significant differences were observed within replications for almost all traits except harvest index.
Mean performance
The ranges of mean values revealed sufficient variation for all the traits under study (
Table 4). Wide range of variation was observed in most of the quantitative characters. In the materials used in this study, maximum range of variability (
Table 4) was observed for total biomass (473.33 to 814.67 g/plant) followed by weight of tender shoot (10.47 to 25.71 g) and stalk yield (2.77 to 14.04 g/shoot). Of the six landraces, there was considerable variation in shoot and leaf characters, which determine external quality of tender shoots of
Basella. Leaf size in terms of lamina length was minimum in RNIS-3 (4.16 cm) and maximum in RNIS-5 (6.37 cm) and in terms of lamina width was minimum in RNIS-3 (2.91 cm) and maximum in RNIS-6 (4.54 cm). RNIS-2 and RNIS-4 had highest harvest index (0.73). RNIS-4 had highest leaf-stalk ratio (2.77) followed by RNIS-2 (2.62).
Genetic diversity analysis
Following Ward’s minimum variance method, 6 landraces of
Basella were grouped into two clusters as evident from the dendrogram (
Fig. 3). Cluster I was the largest with 5 genotypes, while cluster II was the smallest with only one genotype. Cluster I was subdivided into two sub clusters namely sub cluster IA with three genotypes and sub cluster IB with two genotypes. All of the four genotypes from Andhra Pradesh state were grouped in one cluster, but one out of two genotypes from Orissa state was grouped in another cluster.
Genetic variability analysis
In general, phenotypic variances were higher than the corresponding genotypic variances for all the characters under study (
Table 5). The phenotypic variance was highest for total biomass (30610.20) followed by weight of tender shoot (41.64) and stalk yield (26.52). Similarly, the genotypic variance was also highest for total biomass (7680.81) followed by weight of tender shoot (36.36) and stalk yield (21.32). The degree of variability shown by different parameters can be judged by the magnitude of GCV and PCV. GCV showed that the extent of genetic variability in the population ranged from 4.66 (length of tender shoot) to 73.95 (stalk yield). PCV showed that the extent of genetic variability in the population ranged from 9.42 (length of tender shoot) to 82.49 (stalk yield). The estimates of PCV (
Table 5) were highest for stalk yield (82.49%) followed by leaf-stalk ratio (51.97%) and weight of tender shoot (44.14%), while lowest for length of tender shoot (9.42%) followed by leaf weight (9.80%) and leaf yield (15.43%). The estimates of GCV (
Table 5) were highest for stalk yield (73.95%) followed by leaf-stalk ratio (46.70%) and weight of tender shoot (41.25%), while lowest estimates were found for length of tender shoot (4.66%) followed by leaf weight (7.74%) and leaf yield (9.44%). The estimates of PCV (
Table 5) were of high magnitude (>20%) for leaf width, petiole length, internodal length, weight of tender shoot, stalk yield, total biomass, leaf-stalk ratio and harvest index, of moderate magnitude (10–20%) for leaf length and leaf yield and of low magnitude (<10.00%) for leaf weight and length of tender shoot. The estimates of GCV (
Table 5) were of high magnitude (>20%) for petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index, of moderate magnitude (10–20%) for leaf length, leaf width and total biomass and of low magnitude (<10.00%) for leaf weight, length of tender shoot and leaf yield. In general, the magnitude of phenotypic coefficients of variation (PCV) was higher than the corresponding genotypic coefficients of variation (GCV) for all the twelve characters under study (
Table 5). The magnitudinal differences between the estimates of GCV and PCV were highest for total biomass (15.26) followed by leaf length (7.11) and leaf width (6.26).
The estimates of heritability (
Table 5) were of high magnitude (>60%) for leaf weight, petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index, of moderate magnitude (30–60%) for leaf length, leaf width and leaf yield and of low magnitude (<30%) for length of tender shoot and total biomass. The estimates of genetic advance as percent of mean (
Table 5) were of high magnitude (>20%) for petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index, of moderate magnitude (10–20%) for leaf length, leaf weight, leaf yield and total biomass and of low magnitude (<10%) for length of tender shoot. High estimates of heritability (>60%) coupled with high genetic advance as percent of mean (>20%) were observed for petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index. The characters like petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index recorded high genetic advance as percent of mean coupled with high heritability estimates.
Overall, the analysis of variance revealed considerable variability among the landraces for the majority of the leaf yield and its components under study. Further, the results of the genetic parameters also indicated considerable variability in the material. There was considerable variation in the coefficient of variation, heritability and genetic advance of various quantitative traits under study offering ample scope for selection. There was considerable divergence among the landraces as evident from the genetic diversity analysis.
DISCUSSION
One of the main reasons for the under-utilization of germplasm, according to curators, breeders and other users of plant genetic resources, is the lack of adequate passport, characterization and evaluation data: people cannot use genetic resources that lack essential information. In addition, such information is necessary for proper management of the resources in the gene banks by gene bank managers. Therefore, the accurate documentation of information about the origin, characterization and performance of germplasm is essential for effective conservation and use. Characterization and evaluation are important to provide breeders, growers and consumers, with information about certain properties of newly collected genotypes.
Characterization of landraces
Characterization of genetic resources refers to the process by which accessions are identified, differentiated or distinguished according to their character or quality (traits) (
Merriam-Webster 1991). Characterization of each sample involves a careful description of the special characteristics that are inherited, easy to score and expressed consistently in all environments (
Rubenstein and Heisey 2003). Characterization on the basis of qualitative traits provides information on diversity within and between genotypes. Since most of the traits recorded during characterization are those that can be seen, the person responsible for managing the germplasm material is best placed to carry out the work of documenting these characteristics (
De Vicente et al. 2005). Many of the characteristics that are recorded on individual accessions can serve as diagnostic descriptors for the accessions (
Rubenstein and Heisey 2003). Such diagnostic characters help gene bank curators keep track of an accession and check for the genetic integrity over a number of years of conservation (
Rubenstein and Heisey 2003). This enables the identification of unique genotypes essential for curators of gene banks. Hence, characterization of newly collected germplasm is a necessary requirement for crop improvement, use and conservation of plant genetic resources.
Basella alba L. features green-stems and deep-green leaves, while
Basella rubra L. is known for its purplish-stem and deep-green leaves with pink veins. The striking morphological difference between
Basella alba L. and
Basella rubra L. is the colour of the edges of the leaves and the stem. Accessions with green leaf margin colour were recognized as
Basella alba L., while RNIS-4 with red leaf margin colour was recognized as
Basella rubra L. The accessions belonging to these two species were identified with the help of Economic Botanists from National Bureau of Plant Genetic Resources Regional Station, Rajendranagar. Botanical characterization primarily revealed that there were two species
Basella alba L. (RNIS-1 RNIS-2 RNIS-3 RNIS-5) and
Basella rubra L. (RNIS-6) under cultivation in South India. The purple form,
B. rubra L., is less preferred to the green type
B. alba L., regardless of their nutritional value (
Edema and Fakorede 1978).
Six landraces of Indian spinach characterized in this study showed a broad variation for most of the qualitative traits (
Table 2), which allows for the identification of promising landraces of Indian spinach. The apparent variation in qualitative traits could probably be due to the fact that the genotypes used in this study were the indigenous landraces and hence distinctly variable or diverse with respect to qualitative traits. Landraces with twining but initially bushy growth habit are locally called as ‘
mattu bacchali’, while those with twining or procumbent growth habit are locally called as ‘
teega bacchali’ in Andhra Pradesh, India. Twining growth habit is the commonest growth habit. Twining plant type is advantageous to perennial leaf production since it would allow maximum and uniform exposure or distribution of all leaves and other vegetative parts for better interception of sunlight. This would result in an increase in dry matter production and a subsequent increase in yield. Moreover, there is less chance of tender shoots and leaves touching the ground or soil thereby causing leaf rot as in case of procumbent growth habit. The difference between the procumbent and circumnutating stem forms was quite distinct particularly in terms of biomass since the circumnutating form showed reduced laminar area and weight but with long internodes and minor stem circumference, which is otherwise perfectly suited for circumnutation. Of the six landraces, the landraces RNIS-1 and RNIS-4 with twining growth habit could be exploited for commercial cultivation on supports. The landraces with twining growth habit are often grown on supports like stakes or trellises or pandals. On reaching a height of 30 cm, the plant is usually supported by sticks (
Lucas 1988). The three types of staking-individual, pyramidal, and trellising could be adopted, but for optimum yield, a trellis or stick table of about 30 cm above the surface of the bed should be constructed. However, for individual staking to be effective, the stakes must be stout and at least 2 m tall. The landraces RNIS-2 and RNIS-3 with twining but initially bushy growth habit could be exploited for pot culture for urban vegetable cultivation. The landraces RNIS-5 and RNIS-6 with procumbent growth habit could be exploited for ground culture. The plants of twining growth habit are exceedingly vigorous and do better with support than those of procumbent growth habit when sprawling on the ground to keep the foliage clean.
Evaluation goes deeper than characterization. It may require special biometrical techniques and usually include agronomic performance, yield and biotic and abiotic stresses, such as drought or pest. These traits are important to plant breeders and researchers in crop improvement. Such evaluation may also use DNA-based methods to analyze a plant’s genetic diversity (
Rubenstein and Heisey 2003;
De Vicente et al. 2005). The evaluation descriptors, although contributing to some extent to identifying an accession, are more interesting than characterization descriptors because of their value in crop improvement. In general, effective evaluation is possible when there is close institutional and personal interaction between curators and breeders or other crop improvement scientists, and where breeding objectives are reflected in evaluation programs (
Rubenstein and Heisey 2003;
De Vicente et al. 2005). Evaluation is primarily carried out by users, in multidisciplinary teams that include breeders, entomologists, pathologists and agronomists (
De Vicente 2005). A successful variety in any vegetable crop must meet minimal criteria for numerous traits that are potentially valued in the markets. Superiority for multiple ‘yield’ and ‘quality’ traits is essential for economic sustainability of a variety. Consumer purchases of
Basella are enthused based on ‘quality’ traits inherent to the leaves such as size, shape and color. Thus, yield is partly about producing tonnage, but also about the proportion of the crop that can be harvested and brought to market in a condition and at a price acceptable to the consumer.
From the analysis of variance (
Table 3), it is evident that highly significant differences among the landraces were observed for majority of the characters under study indicating presence of sufficient amount of variability in the germplasm under study. Such wide variation indicated the scope for improving the population for these characters. Non-significant differences within replications for almost all traits except harvest index suggested that the landraces have enough variability for almost all the traits to carry out further genotypic studies. Generally, the significant differences (
P<0.01) revealed among the aforementioned morpho-agronomic traits may be due to environmental influences on the genotypes as well as differences in the genetic potential of the different landraces of Indian spinach. This indicates the role of environmental factors as well as differences in the genetic makeup of different landraces in leaf yield determination of Indian spinach. The non-significant differences observed in the landraces for leaf length, length of tender shoot, leaf yield and total biomass indicates that the genetic components of the genetic material are intact. It follows, therefore, that any improvement sort must be directed at the other characters except leaf length, length of tender shoot, leaf yield and total biomass.
In conventional breeding programs, the choice of parents, in general, is based on the general principle that the parents under selection should have a high mean performance for the desirable traits. Hence, the breeders are in absolute need of desirably high or low mean value depending upon the character, which is considered as a main criterion for effective selection forever. In
Basella, of the twelve quantitative traits under study, high mean values are desirable for leaf length, width, weight and yield, weight of tender shoot, total biomass, leaf-stalk ratio and harvest index, while low mean values are desirable for petiole length, internodal length and stalk yield. Due reduction in internodal length adds the more number of leaf production points in plant. High leaf-stalk ratio and harvest index are the key aspects. Harvest index is not directly a yield contributing trait but is considered important parameter for genetic improvement of genotypes. After analyzing the mean performance of 6 different Indian spinach landraces (
Table 4), it is concluded that the two landraces RNIS-2 and RNIS-4 remained superior in terms of leaf-stalk ratio and harvest index. It is, therefore, recommended that these genotypes can be brought forward to evaluate the yield constituency in various ecological zones across the Andhra Pradesh State. Upon assessing yield stability through multi-location trials, these genotypes may be used for large-scale cultivation if found suitable. Evaluation of eleven germplasm lines of the Indian spinach (
Basella) revealed maximum leaf weight per plant in IIHR-1 (160.5 g), followed by IIHR-18 (111.6 g) and IIHR-3 (98.3 g) (
Varalakshmi and Devaraju 2010).
A plant breeder is usually interested in accessions which possess some desired quality traits for incorporation in breeding programs. Quality is often defined from either a product orientation or a consumer orientation. Quality is a measure of how much the end-user values a product. The term quality implies the degree of excellence of a product or its suitability for a particular use. Quality is a human construct comprising many properties or characteristics. Leaf quality plays an important role in marketability of leafy vegetables. What can leafy vegetable growers do to manage the quality of their produce? One of the first steps leafy vegetable growers can take to ensure good quality is variety selection. What can leafy vegetable breeders do to assess the quality of their varieties? When new leafy vegetable germplasm have been collected, they should be evaluated in variety trials based on certain external leaf characteristics to decide their quality.
In
Basella, both stem and leaves are used in culinary practice in southern parts of India (
Saroj et al. 2012). The succulent young leaves and stems are consumed as a vegetable in this crop. Accordingly,
Basella is harvested by periodical shoot pickings. In general, bunches of fresh young tender shoots are marketed for fresh consumption of
Basella. For marketing, ten young tender shoots of 30 cm length are bunched and tied with a rope or thread. In quality breeding, the issue that leafy vegetable breeder encounters is how to assess quality. Ideally, the way it is assessed in the breeding program should reflect the quality that the consumer will perceive. Because the consumers are the ultimate users of the produce of any crop and possess valuable traditional knowledge, due consideration must be given to involve consumers’ views and expectations at some point during any evaluation program. Accordingly, during exploration survey consumer groups were also interviewed at local vegetable markets to determine the external quality traits that they consider as acceptable. The qualitative characters based on which most consumers determine the quality of
Basella were stem length (short/long), stem straightness (straight/curved), stem thickness (thin or thick) stem shape (oval or ovate) and branch color (green or purple), leaf size (small, medium or large), leaf shape (oval or ovate), leaf color (green or light green or dark green or red). In local markets, shoot quality plays an important role in marketability. Shoot quality is mainly related to the stem straightness, length, shape and colour and intact leaf size, shape and colour. The tender shoots intended for market must mostly be straight, short, thin and green. Leaf colour is commonly used measure of leaf quality. A specific greenness and leaf size are also required, but they are often arbitrarily indicated. Size is another factor that affects market acceptance of the leaf that is produced. External amount and intensity of surface colour on a leaf of any cultivar is of prime importance to its appeal in the marketplace. For example, light green colored and medium sized leaves are the most preferred quality traits. In fact, the quality traits like greenness and size (length and width) of the leaves are associated with
Basella genotype. In the surveyed local markets, local landraces with green and round stalk possessing leaves with green/dark green colour, oval/ovate shape, entire leaf margin, green leaf margin colour, acuminate leaf apex are acceptable/desirable qualitative traits of Indian spinach. A high level of variability was observed among the accessions in the quality. On the whole, the results indicated a high level of variability among the accessions in the quality and the possibility to use these landraces to improve the agro-economic and quality traits during breeding programs. RNIS-2, RNIS-3 and RNIS-6 were among the landraces that had acceptable quality traits.
The determination of genetic diversity of accessions is extremely important in breeding of crop plants. Genetic divergence analysis estimates the extent of diversity existed among selected genotypes. Precise information on the nature and degree of genetic diversity helps the plant breeder in choosing the diverse parents for purposeful hybridization. The value of a germplasm collection depends not only on the number of accessions it contains, but also upon the diversity present in those accessions. A small set of accessions of Indian spinach was utilized for divergence analysis in the present study owing to the fact that it is commercially cultivated in only few tracts of Andhra Pradesh and Orissa. Hence, it is indispensable to scrutinize and exploit this natural genetic diversity of
Basella for crop improvement.
Ward (1963) describes a class of hierarchical clustering methods including the minimum variance method. Ward’s minimum variance method tends to join clusters with a small number of observations, and it is strongly biased toward producing clusters with roughly the same number of observations. It is also very sensitive to outliers (
Milligan 1980). Hierarchical clustering following Ward’s minimum variance method revealed the presence of wide range of diversity in agro-economic traits offering a great scope for improvement of
Basella. These studies have shown that accessions from the same geographical region may differ genetically as well as phenotypically and also in adaptability. The pattern of clustering showed more or less distinct relationship with the geographic origin of landraces. Geographical origin was found to be a good parameter of genetic divergence.
Genetic variability analysis is helpful to know about the nature and extent of variability that can be attributed to different causes, sensitive nature of the crop to environmental influences, heritability of the characters and genetic advance that can be realized in practical breeding in evolving varieties to various environmental conditions. Genetic variability is essential in order to realize response to selection pressure. Perusal of data in
Table 5 shows a considerable difference between PCV and GCV values for all the characters studied. This indicates presence of greater environmental influence on expression of all these characters and selection may not be effective in improvement of
Basella. This also indicates that direct selection is not effective in these characters and that heterosis breeding can be resorted to for further improvement. Similar observations were made by earlier researcher in
Basella (
Varalakshmi and Devaraju 2010). Since genotypic coefficient of variation compares the relative amount of variability among attributes, it could, therefore, be deduced that stalk yield, leaf-stalk ratio and weight of tender shoot had higher amount of exploitable genetic variability among the attributes. It also signifies that there is greater potential for favorable advance in selection in these attributes when compared to others. High degree of genetic variability for most of the characters in the present investigation offers a greater scope for effective selection.
In general, the magnitude of phenotypic coefficients of variation was higher than the corresponding genotypic coefficients of variation for all the twelve characters under study (
Table 5) indicating environmental influence on expression of these characters. However, the differences between PCV and GCV were narrow indicating low environmental influence in the expression of these characters. The magnitudinal differences between the estimates of GCV and PCV were highest for total biomass (15.26) followed by leaf length (7.11) and leaf width (6.26).
Varalakshmi and Devaraju (2010) also observed relatively higher magnitude of PCV than GCV for leaf weight, stem weight, petiole length, leaf length, leaf breadth and total plant weight in
Basella. Presence of this high variability for the above parameters can form basis for effective selection of superior lines in
Basella. For other characters, the PCV and GCV values were close to one another, implying that genotype contributed more to the expression of these characters than environment, suggesting greater possibilities of improvement through selection. With the help of GCV alone, it is not possible to determine the extent of heritable variation. Thus the estimates for heritability indicate effectiveness with which selection may be expected to exploit existing genetic variability.
The observed variability is a combined measure of genetic and environmental causes, whereas genetic variability alone is heritable. For improvement of leaf yield in
Basella direct selection is often misleading. The genetic variability is heritable from generation to generation. Heritability and genetic advance is a useful tool for breeders in determining the direction and magnitude of selection. Yield and yield components, in general, are polygenic in nature and are subjected to different amount of non-heritable variation (
Lush 1940). Effectiveness of selection is dependent not only upon the nature, extent and magnitude of genetic variability present in material but also on the extent to which it is heritable. Heritability gives the information on the magnitude of inheritance of quantitative traits, while genetic advance will be helpful in formulating suitable selection procedures. Heritability in conjunction with genetic advance has a greater role to play in determining the effectiveness of selection of a character (
Johnson et al. 1955).
The ratio of genetic variance to the total variance i.e., phenotypic variance is known as heritability. Heritability in broad sense is the ratio of genotypic variance to total variance in non-segregating population (
Hanson et al. 1956). Heritability estimates gives a measure of transmission of characters from one generation to the next and the consistency in the performance of progeny in succeeding generations and depends mainly on the magnitude of heritable portion of variation. Heritability is the only component which is transmitted to the next generation. Heritability estimates of quantitative characters play an important role in expressing the reliability of variance value as a selection guideline to the plant breeder during the succeeding generations. High values of heritability for leaf weight, petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index indicated that though the characters are least influenced by the environmental effects, the selection for the improvement of such characters may not be useful, because broad sense heritability is based on total genetic variance which includes both fixable (additive) and non-fixable (dominance and epistatic) variances. Such high heritability values in yield and its related characters were also reported in Indian spinach (
Varalakshmi and Devaraju 2010). The high heritability, therefore, implies that these yield attributes are controlled genetically, signifying high potential for improvement through selection. The moderate estimates of heritability for leaf length, leaf width and leaf yield indicating that these characters are moderately influenced by environmental effects and genetic improvement through selection will be moderately difficult due to masking effects of the environment on the genotypic effects.
The estimates of heritability alone fail to indicate the response to selection. Therefore, heritability estimates appear to be more meaningful when accompanied by estimates of genetic advance and genetic advance as percentage over mean (
Johnson et al. 1955). The estimates of genetic advance as percent of mean (
Table 5) were of high magnitude (>20%) for petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index, of moderate magnitude (10–20%) for leaf length, leaf weight, leaf yield and total biomass and of low magnitude (<10%) for length of tender shoot. High estimates of heritability (>60%) coupled with high genetic advance as percent of mean (>20%) for petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index revealed that most likely the heritability is due to additive gene effects and selection may be effective. Such value of high heritability and high genetic advance may be attributed to the action of additive genes (
Panse 1957). The characters like petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index recorded high genetic advance as percent of mean coupled with high heritability estimates, indicating that these traits were under the strong influence of additive gene action, and hence simple selection based on phenotypic performance of these traits would be more effective. Similar kind of results in
Basella was also reported by earlier researcher (
Varalakshmi and Devaraju 2010). Low heritability and low genetic advance as percent of mean values were observed for the character length of tender shoot. This indicates that this character is highly influenced by environmental effects and selection would be ineffective. Similar results were also reported by other researcher in
Basella (
Varalakshmi and Devaraju 2010).
The morphological evaluation and characterization revealed considerable variability among the six landraces. Genetic diversity analysis revealed that landraces from the same geographical region differed genetically as well as phenotypically. Based on mean performance, two landraces RNIS-2 and RNIS-4 were superior in terms of leaf-stalk ratio and harvest index as well as in other important attributes related to yield. Upon assessing yield stability through multi-location trials, these genotypes may be used for large-scale cultivation if found suitable. Leaf weight, petiole length, internodal length, weight of tender shoot, stalk yield, leaf-stalk ratio and harvest index had high estimates of heritability coupled with high genetic advance as percent of mean. Hence, these characters need to be given more emphasis in selection as these are expected to be controlled by additive genes. The breeder should adopt suitable breeding methodology to utilize both additive and non-additive gene effects simultaneously, since varietal development will go a long way in the breeding programs especially in case of Indian spinach. The results also indicated the possibility to improve total biomass and quality thereby farmer’s income through selection programs. The results indicated that landraces of Indian spinach traits of high biodiversity and genetic resources are suitable for the breeding. There is a need to continue work in the area of nutritional analysis, which is required as an evaluation tool in varietal selection.
ACKNOWLEDGMENTS
The senior author is highly grateful to the National Bureau of Plant Genetic Resources Regional Station, Hyderabad for sharing the germplasm of Basella with the Vegetable Research Station, Dr. Y.S.R. Horticultural University, Rajendranagar.
Fig. 1DIVA-GIS mapping of collection sites of landraces of Indian spinach from Andhra Pradesh and Orissa.
Fig. 2Phenotypic variability in the plants (top row), tender shoots (middle row) and leaves (bottom row) of landraces of Indian spinach.
Fig. 3Ward’s minimum variance dendrogram showing clustering of landraces of Indian spinach.
Table 1Passport data of the various landraces of Indian spinach.
Table 1
|
Accession ID |
Collector No. |
Common name |
Botanical name |
Vernacular name |
Collection site |
|
|
Geo-reference |
Village |
Mandal |
District |
State |
|
|
Latitude (°N) |
Longitude (°E) |
Altitude (m) |
|
RNIS-1 |
SNTV-25 |
Indian Spinach |
Basella alba L. |
Mattu bacchali
|
18.77 |
84.41 |
35.05 |
Peddaveedhi |
Palasa |
Srikakulam |
Andhra Pradesh |
|
RNIS-2 |
SNTV-38 |
Indian Spinach |
Basella alba L. |
Mattu bacchali
|
18.36 |
83.87 |
28.65 |
Bavajipeta |
Srikakulam |
Srikakulam |
Andhra Pradesh |
|
RNIS-3 |
SNTV-51 |
Indian Spinach |
Basella alba L. |
Mattu bacchalli
|
18.31 |
83.57 |
66.14 |
Chipurupalli |
Chipurupalli |
Vizianagaram |
Andhra Pradesh |
|
RNIS-4 |
SNTV-68 |
Indian Spinach |
Basella rubra L. |
Erra bacchali
|
18.59 |
83.37 |
131.37 |
Patha Bobbili |
Bobbili |
Vizianagaram |
Andhra Pradesh |
|
RNIS-5 |
SNTV-79 |
Indian Spinach |
Basella alba L. |
Bhaji
|
18.58 |
82.91 |
1009.80 |
Malliput |
Pottangi |
Koraput |
Orissa |
|
RNIS-6 |
SNTV-86 |
Indian Spinach |
Basella alba L. |
Bhaji
|
18.63 |
82.59 |
605.33 |
Lamtaput |
Lamtaput |
Koraput |
Orissa |
Table 2Qualitative traits of six landraces of Indian spinach.
Table 2
|
Character |
Landrace |
|
|
RNIS-1 |
RNIS-2 |
RNIS-3 |
RNIS-4 |
RNIS-5 |
RNIS-6 |
|
Growth habit |
Twining |
Twining (Initially bushy) |
Twining (Initially bushy) |
Twining |
Procumbent |
Procumbent |
|
Stem colour |
Red |
Green |
Green |
Dark red |
Light red |
Green |
|
Stem shape |
Round |
Round |
Round |
Angular (3) |
Angular (3) |
Angular (3) |
|
Leaf colour |
Dark green |
Light green |
Light green |
Dark green |
Dark green |
Light green |
|
Leaf shape |
Ovate |
Ovate |
Ovate |
Oval |
Oval |
Ovate |
|
Leaf margin |
Entire |
Entire |
Entire |
Entire |
Entire |
Entire |
|
Leaf margin colour |
Green |
Green |
Green |
Red |
Green |
Green |
|
Leaf apex |
Acuminate |
Acuminate |
Acuminate |
Acuminate |
Acuminate |
Acuminate |
|
Petiole colour |
Green |
Green |
Green |
Red |
Green |
Green |
|
Flower colour |
Pink |
Light pink |
Pink |
Pink |
Pink |
Light pink |
Table 3Analysis of variance for various agro-economic traits in Indian spinach.
Table 3
|
Mean squares |
|
|
|
Character |
Replications (3) |
Genotypes (5) |
Error (10) |
|
Leaf length (cm) |
0.736 |
2.014 |
0.658 |
|
Leaf width (cm) |
0.101 |
1.183*
|
0.296 |
|
Leaf weight (g) |
0.005 |
0.014**
|
0.002 |
|
Petiole length (cm) |
0.003 |
0.528**
|
0.005 |
|
Length of tender shoot (cm) |
16.243 |
24.423 |
12.388 |
|
Internodal length (cm) |
0.305 |
2.780**
|
0.099 |
|
Weight of tender shoot (g) |
2.768 |
114.353**
|
5.281 |
|
Leaf yield (g/shoot) |
2.802 |
2.747 |
0.984 |
|
Stalk yield (g/shoot) |
3.239 |
69.161**
|
5.205 |
|
Total biomass (g/plant) |
25126.050 |
45971.820 |
22929.390 |
|
Leaf-stalk ratio |
0.368 |
2.544**
|
0.187 |
|
Harvest index |
0.060*
|
0.069**
|
0.009 |
Table 4Mean performance of six landraces for various agro-economic traits in Indian spinach.
Table 4
|
Landrace |
Leaf length (cm) |
Leaf width (cm) |
Leaf weight (g) |
Petiole length (cm) |
Length of tender shoot (cm) |
Internodal length (cm) |
Weight of tender shoot (g) |
Leaf yield (g/shoot) |
Stalk yield (g/shoot) |
Total biomass (g/plant) |
Leaf-stalk ratio |
Harvest index |
|
RNIS-1 |
5.69 |
3.62 |
0.76 |
1.07 |
38.55 |
2.21 |
11.54 |
7.81 |
4.31 |
547.67 |
1.83 |
0.68 |
|
RNIS-2 |
5.26 |
3.65 |
0.77 |
1.04 |
41.43 |
2.76 |
11.31 |
8.05 |
3.17 |
532.33 |
2.62 |
0.73 |
|
RNIS-3 |
4.16 |
2.91 |
0.78 |
1.03 |
43.31 |
2.84 |
10.48 |
7.10 |
2.78 |
569.67 |
2.59 |
0.69 |
|
RNIS-4 |
4.73 |
2.95 |
0.74 |
1.00 |
46.79 |
2.80 |
10.47 |
7.45 |
2.77 |
473.33 |
2.77 |
0.73 |
|
RNIS-5 |
6.37 |
3.89 |
0.82 |
1.82 |
45.00 |
3.95 |
18.21 |
8.55 |
10.39 |
495.67 |
0.83 |
0.47 |
|
RNIS-6 |
5.99 |
4.54 |
0.93 |
1.87 |
42.78 |
4.82 |
25.71 |
9.79 |
14.04 |
814.67 |
0.75 |
0.38 |
|
S. Em |
0.43 |
0.29 |
0.03 |
0.04 |
1.86 |
0.17 |
1.21 |
0.52 |
1.20 |
79.80 |
0.23 |
0.05 |
|
CD (5%) |
NS |
0.99 |
0.09 |
0.13 |
NS |
0.57 |
4.18 |
NS |
4.15 |
NS |
0.79 |
0.17 |
Table 5Genetic parameters for various agro-economic traits in Indian spinach.
Table 5
|
Character |
Variance |
Coefficient of variation (%) |
Heritability (%) |
Genetic advance (5%) |
Genetic advance as percent of mean |
|
|
Phenotypic |
Genotypic |
Phenotypic |
Genotypic |
|
Leaf length (cm) |
1.11 |
0.45 |
19.64 |
12.53 |
41.00 |
0.88 |
16.47 |
|
Leaf width (cm) |
0.59 |
0.30 |
21.36 |
15.10 |
50.00 |
0.79 |
21.98 |
|
Leaf weight (g) |
0.01 |
0.00 |
9.80 |
7.74 |
62.00 |
0.10 |
12.59 |
|
Petiole length (cm) |
0.18 |
0.17 |
32.46 |
31.96 |
97.00 |
0.85 |
64.84 |
|
Length of tender shoot (cm) |
16.40 |
4.01 |
9.42 |
4.66 |
25.00 |
2.04 |
4.75 |
|
Internodal length (cm) |
0.99 |
0.89 |
30.85 |
29.27 |
90.00 |
1.85 |
57.22 |
|
Weight of tender shoot (g) |
41.64 |
36.36 |
44.14 |
41.25 |
87.00 |
11.61 |
79.40 |
|
Leaf yield (g/shoot) |
1.57 |
0.59 |
15.43 |
9.44 |
37.00 |
0.97 |
11.89 |
|
Stalk yield (g/shoot) |
26.52 |
21.32 |
82.49 |
73.95 |
80.00 |
8.53 |
136.58 |
|
Total biomass (g/plant) |
30610.20 |
7680.81 |
30.58 |
15.32 |
25.00 |
90.44 |
15.80 |
|
Leaf-stalk ratio |
0.97 |
0.79 |
51.97 |
46.70 |
81.00 |
1.64 |
86.43 |
|
Harvest index |
0.03 |
0.02 |
27.75 |
22.99 |
69.00 |
0.24 |
39.22 |
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