Inhibitory effect of chemical combinations on seed germination and pre-harvest sprouting in hybrid rice

Pre-harvest sprouting (PHS) is a primary cause of decreases in quality and economic value in rice seeds. This study examined the inhibitory effects of four combinations of maleic hydrazide, eugenol and uniconazole on rice PHS and seed quality. After the four treatments, delayed grain germination was observed compared with the control, mean germination time was prolonged by 17.5 % and germination index was decreased by an average of 18.2 %. Activity of alpha-amylase was significantly reduced, by 26.7-83.5 %, during grain germination and early seedling growth. We then used qRT-PCR to further analyze the mRNA expression levels of four genes involved in alpha-amylase biosynthesis. The expression of OsAMY3B and OsAMY3E was significantly down-regulated by the four combinations of chemicals. In field trials, each of the four combinations resulted in a significantly lower sprouting rate and sprouting index compared with the control. In addition, freshly harvested rice seeds showed no significant differences in the mean germination time or germination index between the four combination treatments and the control. After 1 month of storage, there was still no significant difference between the four combination treatments and the control with regard to the mean germination time and germination index. These results suggest that the selected combinations strongly inhibited the seed germination speed and PHS of rice in the field. However, these combinations had no inhibitory effects on the final germination percentage and showed no negative effect on seed quality after short-term storage. The combinations of inhibitors used in this study can be applied to decrease the PHS damage caused by high temperatures and moist weather during the production of hybrid rice.