Detection and verification of QTLs associated with heat-induced quality decline of rice (<i>Oryza sativa</i> L.) using recombinant inbred lines and near-isogenic lines

Abstract

Decline in the apparent quality of rice (Oryza sativa L.) grain due to high temperatures during ripening recently became a major concern in many areas in Japan. The occurrence of white-back kernels (WBK) is one of the main problems of heat-induced quality decline. We identified QTLs associated with the occurrence of WBK using recombinant inbred lines (RILs) and verified their effects using near-isogenic lines (NILs). The QTL analysis used F7 and F8 RILs derived from ‘Hana-echizen’ (HE), which is tolerant to high temperature, × ‘Niigata-wase’ (NW), which is sensitive to high temperature. Four QTLs were identified on chromosomes 3, 4, 6, and 9 (qWB3, qWB4, qWB6 and qWB9). To verify the effects of qWB6 and qWB9, we developed two NILs in which qWB6 or both were introduced from HE into the NW background. The HE allele at qWB6 significantly decreased WBK under multiple environments. The combination of qWB6 and qWB9 in an F2 population derived from a cross between a NIL and NW showed that the NW allele at qWB9 significantly decreased WBK if the qWB6 allele was HE. These results will be of value in marker-assisted selection for the breeding of rice with tolerance to heat-induced quality decline.

Countermeasures for heat damage in rice grain quality under climate change

“…Based on the regularity of starch accumulation as described in the above section (Nagato & Kobayashi, 1959), the appearance of dehulled grains can be objectively evaluated using a chalky rice grain predictor that is capable of determining the number of milky-white grains effects of QTLs for white-back grain using near-isogenic lines (Kobayashi et al, 2013;Wada et al 2015). These findings will accelerate development of heat-tolerant variety to decrease white-back and basal-white grains under high temperature.…”

Molecular physiological aspects of chalking mechanism in rice grains under high-temperature stress

“…Microscopic observation showed that chalking occurs at the belly, back, base, or center parts of the grains. Although highly effective quantitative trait loci (qWB6, qWB9) associated with the occurrence of white-back kernels have been identified (Kobayashi et al, 2013), the precise mechanism controlling the localization of chalking remains unclear. The imbalance of starch biosynthesis and degradation might be generated by the spatial expression of the genes responsible.…”

Breeding efforts to mitigate damage by heat stress to spikelet sterility and grain quality

“…Kobayashi et al (2007) detected three QTLs on chromosomes 3, 4, and 6 using F 2 and F 3 populations derived from a cross between Hana-echizen and niigatawase. An nIL carrying a QTL on chromosome 6 (qWB6) introduced from Hana-echizen into the niigatawase background was developed (Kobayashi et al, 2013). This nIL carrying qWB6 significantly decreased WBCG at 27.3-31.1 °C during grain filling.…”

“…This nIL carrying qWB6 significantly decreased WBCG at 27.3-31.1 °C during grain filling. In addition to qWB6, Kobayashi et al (2013) Gene profiling by comprehensive expression analyses could be useful to narrow down the candidate genes in high-resolution linkage mapping for WBCG.…”