Seed germination responses to temperature and water availability in weedy rice

Weedy rice is one of the main agricultural weeds infesting transplanted and direct-seeded rice cultures across Japan. However, the environmental factors that facilitate its proliferation are largely unknown. This study investigated the effects of temperature and water availability on seed germination of Japanese weedy and cultivated rice strains differing in degree of seed dormancy and after-ripening. This information could help predict weedy rice infestation and design efficacious control measures.

The germination responses of weedy rice to temperature and water availability varied among strains and after-ripening duration. The germination rate varied inversely with the degree of dormancy, increased with water availability, and fluctuated between low and high temperatures. The shallow-dormant tropical japonica-derived strawhull weedy rice (TRJ) germinated at 10 °C unlike the temperate japonica-derived weedy rice strains, namely, the intermediate-dormant blackhull (BH) and the deep-dormant strawhull (SH). Seeds of all plant strains germinated below the permanent wilting point of clay loam soil, but the germination rates were higher for TRJ and BH than for cultivated rice. SH germination was more synchronous with rice than the other weedy rice strains.

This study has confirmed the overall robustness of germination cold tolerance at 10 °C in TRJ, high germinability at low-water availability and high temperature in TRJ and BH, and relatively more synchronous germination between SH and cultivated rice in seeds grown in different years. These observed characteristics are considered advantageous to the coexistence of weedy rice with cultivated rice. © 2022 Society of Chemical Industry.