Dissection of additive, epistatic effect and QTL × environment interaction of quantitative trait loci for sheath blight resistance in rice.

A recombinant inbred line (RIL) population from a cross between 'HH1B' and 'RSB02' (a deep-water rice variety with resistance to sheath blight) was planted in two locations for four different growing seasons. Seven traits were used to evaluate the disease severity, namely disease rating (DR), lesion length (LL), lesion height (LH), relative lesion length (RLL), relative lesion height (RLH), plant height (PH) and heading date (HD). Based on a linkage map of 163 simple sequence repeat (SSR) markers, a total of 37 QTLs were mapped on nine chromosomes. Additionally, 32 epistatic QTLs were identified, distributed on all the 12 chromosomes. The contribution of a single QTL's additive and epistatic effect was of low magnitude for most cases (from 0.39% to 24.62%). Among QTL × environment interaction test, 28 additive QTLs and six pairs of epistatic interactions were involved. Correlation analysis showed that DR had significant positive correlations with LL, RLL and RLH, but had a negative correlation with PH, two of six QTLs controlling DR were mapped in the same chromosome regions as the QTLs controlling PH. The alleles which can enhance disease resistance and increase PH are from the resistant parent 'RSB02', indicating that PH has certain effect on sheath blight resistance in the present study.