Analysis Of QTLs,Epistatic Effects And Q×E Interaction Effects Associated With The Resistance To Ultraviolet-B Radiaton In Rice (Oryza Sativa L.)

The depletion of the stratospheric ozone layer due to the emission of chlorofluorocarbons and other trace gases has resulted in increased solar ultraviolet-B(UV-B:280-320nm)radiation on the earthe' s surface, which would affect the agricultural production and the growth of plants. This has been one of popular studies on the change of climate over the world. In this study, we used a recombinant inbred lines population consisting of 123 lines (RILs) from a cross between Dular (an sensitive type parent introduced from India) and Lemont (an resistant type parent from USA) with 109 pairs of SSR markers to construct a genetic linkage map .RILs and both parents were grown under visible light with or without supplemental UV-B radiation in plastic pot in the two years, 2005 and 2006．In order to evaluate UV-B resistance, we used the inhibitory rates of the plant height(IPH),the root length(IRT),the dry weight of root parts(IDWRP),the dry weight of shoot parts(IDWSP),the chlorophyll content (ICC) and the number of tillering(INT)as index . The population of RILs exhibited a wide range of variation in these traits. The software QTL Mapper1．0 was applied to analyze quantitative trait loci (QTL), including main QTL effects,digenic epistasic effects and QTL interactions with environment. The main results are as follows:(1) Using the inhibitory rates of the plant height(IPH) :one additive QTLs was detected on chromosomes 2, individually explaining 37．8% of the phenotypic variations;three pairs of additive×additive epistasis were also detected, which contributed to 15．76% of the total phenotypic variations in 2005．There were three additive QTLs, which were qIPH1-a,qIPH1-b,qIPH1-c both on chromosomesl, individually accounting for 18．41%,12．12% and 11．32% of the phenotypic variation respectively, two pairs of additive×additive epistasis were examined, which contributed to 12．59% of the total phenotypic variations in 2006, of which qIPH1-b had significant Q×E interaction effects , accounting for 3．45% of the phenotypic variations; two pairs of additive×additive epistasis also detected, performing significant Q×E interaction effects ,which contributed to 20．49% of the total phenotypic variations in the two yeaes.(2) Using the inhibitory rates of the root length (IRT) as evaluated index, two additive QTLs of qIRL2 and qIRL9 were detected on chromosomes 2 and 9 respectively, individuall explaining 10．02% and 13．00% of the phenotypic variations respectively; no additive×additive epistasis existed in 2005．There were one additive QTLs of qIRL3-a on chromosomes 3, , accounting for 10．41% of the phenotypic variation, two pairs of additive×additive epistasis contributing to 11．29% of the total phenotypic variations were detected in 2006．Among them, only qIRL3-a was found to have significant Q×E interaction effects , accounting for 1．67% of the phenotypic variations; two pairs of additive×additive epistasis, contributing to 16．60% of the total phenotypic variations.(3) Using the inhibitory rates of the dry weight of root parts(IDWRP) as index, two additive QTLs of qIDWRP2-a and qIDWRP8-a were mapped on chromosomes 2 and 8 respectively, explaining 10．00% and 13．82% of the phenotypic variations respectively; three additive×additive epistasis were identified, the variations explained by epistatic effects were collectively 15．27% in 2005．qIDWRP6-a and qIDWRP6-b both located on chromosomes 6 were detected , explaining 10．00% and 11．00% of the phenotypic variations; four additive×additive epistasis were identified, contributing to 33．20% of the total phenotypic variations in 2006．No significant Q×E interaction effects was detected for additive QTLs ;but three pairs of additive×additive epistasis were examined which contributed to 10．77% of the total phenotypic variations.(4) Using the inhibitory rates of the dry weight of shoot parts(IDWSP) for the evoluation, two additive QTLs of qIDWSP3-a and qIDWSP3-b were mapped on chromosomes 3 , accounting for 13．00% and 10．00% of the phenotypic variations respectively, threeadditive×additive epistasis were identified , the variations explained by epistatic effects were 11．72% in 2005．Only qIDWSP6-a was identified and individually explained 10．00% of the phenotypic variations; two pairs of additive×additive epistasis contributing to 13．14% of the total phenotypic variations exisited in 2006．Althouth no ignificant Q×E Interaction effects was detected for additive QTLs, two pairs of additive×additive epistasis were identified, which contributed to 9．04% of the total phenotypic variations.(5) Using the inhibitory rates of the chlorophyll content(ICC) in 2006 as an indice, only one additive QTLs of qICC3-a lacated on chromosomes 3 was detected, and it explained 22．27% of the phenotypic variations, at the same time, four additive×additive epistasis were identified, but epistatic effects was small.(6) Using the inhibitory rates of the number of tillering(INT) to evaluate the effect in 2006, it found that there were one QTL that was qINT2-a located on chromosomes 2 associated with INT , which accounted for 41．22% of phenotypic variations; and two additive×additive epistasis contributing to small percentage of the phenotypic variations.