Marker assisted backcrops breeding in rice for drought tolerance

Abstract

Rice {0ryza sativa L.) is one of the most important food crop grown across the globe. The crop is cultivated in diverse environments ranging from uplands to deep water ecosystems. Drought is one of the major constraints for rice production in rainfed lowlands. In the present scenario of climate change, the frequency of drought is more likely to increase in the future, making drought resistance in rice varieties indispensable. During the era of post-green revolution, many locally adapted traditional rice varieties (TRVs) were replaced by high yielding varieties (HYVs) that thrive best in the irrigated ecosystem. Most of these HYVs sutTer heavy yield loss even under mild water deficit conditions. Hence, improving drought tolerance of high yielding varieties is imperative. Considering this, the study 'Marker assisted backcross breeding in rice for drought tolerance,' was executed with an objective to improve drought tolerance in high yielding rice variety Ptb 39 (Jyothi; J) using Ptb 30 (Chuvannamodan; Ch) as donor parent, through marker assisted backcross breeding. Jyothi is a popular high yielding rice variety of Kerala derived from the cross between Ptb 10 and IR 8. Chuvannamodan is an improved landrace, recommended for ''Modan^ i.e., upland cultivation owing to its drought tolerance ability. Morphological characterisation of both the varieties was done at Regional Agricultural Research Station, Pattambi, during 2018. Chuvannamodan registered a higher vegetative growth than variety Jyothi. The plant height and the number of productive tillers were 141 cm and 33 respectively in Chuvannamodan, while, in comparison, it was 91 cm and 17 in Jyothi. It was also observed that Chuvannamodan flowered earlier (Days to 50% flowering: 76 days) than variety Jyothi (Days to 50% flowering: 93 days). However, Jyothi out-performed Chuvannamodan with respect to the yield traits like number of filled grains per panicle (Ch: 71 and J: 104), iOOO-grain weight (Ch: 27.00 g and J: 28.30 g), and grain density (Ch: 1.09 g/cm^ and J: 1.11 g/cm^). The sterility in Chuvannamodan and Jyothi was 11.40 per cent and 18.40 per cent respectively. The water mining traits like root length, root volume, root dry weight and root to shoot ratio were higher in variety Chuvannamodan. The root length, root volume, root dry weight and root to shoot ratio of Chuvannamodan was respectively 109cm, 96cm"\ 31.60g and 0.31, while, it was 68cm. 32cm^,14.40g and 0.24 respectively in variety Jyothi. The genetic polymorphism study between Jyothi and Chuvannamodan was I studied using 120 SSR markers. Forty-seven markers were found to be n, polymorphic between the two genotypes. Among these polymorphic markers, 24 are reported to be linked to drought tolerance traits. Forty five F1 seeds were obtained by hybridizing variety Jyothi (as female parent) and Chuvannamodan (as male parent). Staggered sowing of the two varieties was done at weekly intervals for this purpose. Only six Fj seeds germinated. The test for confirmation of hybridity was conducted in these plants along with the parents. The polymorphic markers RM3825 and RM263, which are reported to be linked to drought traits were used for hybridity testing. Two plants, P5 (Plant No.5) and P6 (Plant No.6), were confirmed to be true hybrids as they were found to be heterozygous for the parental alleles. The hybrids (P5 and P6), were then backcrossed to the recurrent parent Jyothi to produce BCiFi seeds (15 Nos.). Simultaneously, selfing of the Fis to generate F2S (300 Nos.) was also done. In order to advance further the marker assisted backcross breeding programme aimed at imparting drought tolerance to Jyothi, the BC1F1s produced need to be genotyped further to identify progenies with resistant alleles for drought tolerance. The F? population can be forwarded to develop RJLs (Recombinant inbred lines) that would enable mapping of qualitative traits and quantitative trait loci related to drought tolerance. The F2S can also serve as the base population for the development of advanced breeding lines through pedigree selection.