Inhibitory effect of eugenol on seed germination and pre-harvest sprouting of hybrid rice (Oryza sativa L.)

Pre-harvest sprouting (PHS) is a constrain problem in hybrid rice production. The present study was conducted to investigate the inhibitory effect of eugenol on seed germination and PHS of hybrid rice variety (Qian You 1). The results showed that seed germination speed and the activities of α-amylase were inhibited by eugenol pre-soaking and these effects enhanced with the increasing of eugenol concentrations; while seedling growth was not negatively affected. In field trials, eugenol application caused a significant decline in PHS as compared with control, whereas no sustained inhibition in post-harvested seed germination was observed. The HPLC analysis indicated that eugenol raised the internal ABA content by 1-4 times more than control, and seeds treated with eugenol had relatively lower OsABA8OH2 and higher transcript levels of OsNCED2 expression during early stages of seed imbibitions. In addition, seed germinated faster after GA₃ application than eugenol alone, and seed endogenous ABA content decreased obviously. It suggested that eugenol strongly delayed seed germination and the PHS in the field, which might be mainly due to the increased ABA contents caused by eugenol. However, the phenomenon of delayed germination and high ABA content caused by eugenol could be effectively recovered by exogenous GA₃.