Marker assisted selection for heat tolerance in rice (Oryza sativa L.)

Abstract

Rice is highly susceptible to heat stress, particularly during the reproductive and ripening stages. In the major rice growing tracts of Kerala viz., at Palakkad, Kole and Kuttanad, the temperature tends to rise up to 40 ºC or more during the second/third crop. Consequently, high temperature induced sterility has become a serious problem. To tackle this, high yielding varieties coupled with heat stress need to be developed. As most of the prevalent high yielding rice varieties in Kerala including Uma are highly susceptible to heat stress. It is therefore, essential to impart heat tolerance to such varieties which are cultivated to a very large extent. Marker assisted selection (MAS) has been identified as a dependable, reproducible and time saving strategy to confirm the presence of desirable gene and to quicken the breeding cycle. A study conducted for the identification of SSR markers linked to the genes for heat tolerance in rice through bulked segregant analysis approach using F3 population of the cross Uma x N22 revealed that microsatellite marker, RM5749 was tightly linked to spikelet fertility trait under heat stress. The F4 population (59 nos.) raised from seven F3 lines that were found tolerant to heat stress comprised the base population for the present study. They were characterised morphologically and heat tolerance was scored under natural heat stress in the field conditions based on IRRI spikelet fertility classification. In the 26 F4 lines that registered more than 75 per cent spikelet fertility, foreground selection was done using RM5749. All the 26 F4 plants registered an amplicon corresponding to the heat tolerant parent N22. Background selection of these 26 lines was done using 35 markers found polymorphic between the parents Uma and N22. Seventy five F5 plants were evaluated for morphological characters. Among these, nine F5 plants (Plant nos.16.1.4, 16.1.5, 16.1.6, 31.2.3, 31.2.4, 31.2.5, 31.5.1, 31.6.6, and 31.6.9) with high spikelet fertility (60-70 %) were selected and genotyped using RM5749. These lines were further genotyped using the 35 polymorphic background markers. All the nine F5 plants recorded 54-64 % similarity to Uma genome. The highest spikelet fertility percentage was observed in plant no.16.1.5 (70.78 %) while the highest recovery of the parental genome of Uma was found in plant no. 31.2.5 (64.28 %).

Backcrossing of the seven selected heat tolerant lines of F4 (lines 12, 13, 15, 16, 31, 41, and 45) with Uma as male parent resulted in production of BC1F1 seeds. However, the seedlings raised from these seeds did not survive under field conditions. The results obtained thus indicated that the nine lines selected in the present study are to be evaluated in further generations morphologically inorder to isolate genotypes with tolerance to heat stress.