Marker-assisted breeding of a LOX-3-null rice line with improved storability and resistance to preharvest sprouting.

KEY MESSAGE: Breakage of the tight linkage between rice seed lipoxygenase - 3 and easy preharvest sprouting trait led to breeding of lines with few stale flavors after long storage and desirable preharvest sprouting resistance. Lipoxygenase-3 (LOX-3) is involved in the production of volatile constituents in stored rice, and the development of stale flavor is delayed in LOX-3 null rice. In the process of breeding new LOX-3-null lines with long storability, we found a close association between LOX-3 and preharvest sprouting resistance. To determine whether this relationship was due to the tight linkage of two genes or the pleiotropic effect of LOX-3, we performed marker-assisted selection using a BC3F3 population derived from crosses between LOX-3-present/preharvest sprouting-resistant lines and LOX-3-null/preharvest susceptible lines. In one individual, a recombination event occurred 13 kb downstream of LOX-3 (RM15750) and a significant quantitative trait locus, namely qPHS3, for easy preharvest sprouting trait (LOD = 10.4) was detected in an 842-kb region between RM15711 and RM15768. Using BC3F4 and BC3F5 populations, we succeeded in selecting LOX-3-absent and preharvest sprouting-resistant lines with only a 393-kb introgressed chromosome segment from the donor line for LOX-3-null at the LOX-3 locus on chromosome 3. This result indicated that the LOX-3 gene and the locus affecting preharvest sprouting are distinct. The selected line was named 'Hokuriku 244'. Sensory testing of rice grains with and without LOX-3 confirmed that stale flavor production in LOX-3-null rice during storage was lower than in normal LOX-3 rice. These results indicated that rice varieties with little stale flavor after long storage and preharvest sprouting resistance had been selected.