Most Bt transgenic rice events have an underlying grain cost depending on the insect pressure in the field. This study was conducted (1) to determine if the cry1Ac/bar genetically modified (GM) rice (designated Agb0101) based on a Korean japonica rice cultivar has any underlying grain cost and (2) to develop cry1Ac/bar GM rice lines with yield performance similar to those of Korean elite cultivars via crossbreeding. A three-year field experiment showed that Agb0101 had a high underlying grain cost equivalent to 18% grain yield loss, and this cost was mainly due to the grain number per panicle. Moreover, it was found that the cry1Ac/bar transgene was inherited as a single dominant gene. BC₁F₄―F₅ crossbred progeny derived from an anther culture of Agb0101―showed phenotypic resemblance to non-transgenic Korean elite cultivars, resulting in a decrease in the grain yield cost of Agb0101 from 27% to 10%. These results suggest that Bt-GM rice-oriented cross-fertilization with a non-GM elite cultivar followed by two- or threefold selection is a feasible method to minimize or remove the underlying grain cost of the Bt transgenic insect-resistant rice line.

Hybrid sterility is the major obstacle that can act as a barrier to genetic recombination and limits favorable gene transfer during inter-subspecific crosses in rice. However, hybrid sterility can be overcome by utilization of wide-compatible varieties (WCV). In the present study, two F₂ populations generated from crosses between a wide-compatibility line (HWC-line) and two Korean varieties, Dasan and Hwacheong were evaluated for eight agronomic traits. A total of 157 molecular markers consisted of 116 STS, 40 SSR and 1 FNP were used to create genetic linkage maps spanning all 12 chromosomes. Twenty-one main-effect QTLs (M-QTLs) were identified in HWC-line/Dasan (HD) population. These loci are populated with two QTLs for culm length, one for spikelet per panicle, one for spikelet fertility, four for grain length, five for grain width, five for grain shape, and three for 100 grain-weight. In HWC-line/Hwacheong (HH) population, 17 QTLs were detected including two QTLs for culm length, one for panicle length, one for spikelet fertility, five for grain length, three for grain width, three for grain shape, and two for 100-grain weight. Of the total 34 QTLs found in the two F₂ populations, 9 QTLs associated with culm length, grain length, grain width and grain shape were newly identified in this study. These QTLs will be useful for further understanding the genetic basis of agronomic traits and for developing markers for selection in rice breeding. In addition, HWC-line could be used as a bridge for inter-subspecies crosses overcoming hybrid sterility.

Citations

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• QTL Analysis for Yield and Grain-Related Traits Using the Recombinant Inbred Lines Derived from a Cross between ‘Boramchan’ and ‘Pecos’
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  Kelvin Dodzi Aloryi, Nnaemeka Emmanuel Okpala, Aduragbemi Amo, Semiu Folaniyi Bello, Selorm Akaba, Xiaohai Tian
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