Germination of weedy rice in response to field conditions during winter

Weedy rice is a problematic weed that infests paddy fields worldwide. Differing populations, with variable physiological and morphological traits, characterize this weed. In particular, seed dormancy makes its control difficult. The objective of this study was to evaluate the germination behavior of five Italian weedy rice populations (two awnless, two awned, and one mucronate) after exposure of seeds to different field storage conditions (flooding, burial, and dry soil surface) during winter in two sites (Grugliasco and Vercelli). Seed samples were taken from each population, storage condition and site, every 15 days for Petri dish germinability testing. The two sites displayed slightly different germination patterns, which were probably due to the differing climatic conditions. One of the awned populations showed the highest (always exceeding 80%) and fastest germination percentage in all field conditions and sites, compared to the other four populations. While flooding promoted germination in one awnless population, it delayed germination in two others (one awned and one awnless), attaining only 20% germination after more than 100 days. In all populations, burial delayed germination while seed placement on the soil surface enhanced it. Our study indicated that autumn tillages that promote weedy rice seed burial should be discouraged; spring tillages that expose seeds to the soil surface and cause their depletion should be encouraged. The tested technique of winter flooding can also improve weedy rice control, despite its varying efficacy among populations. Cycles of flooding and drying followed by spring tillage might improve weedy rice seed control.