Weedy rice de-domesticated from cultivated rice has evolved strong resistance to seed ageing

Weed seeds generally have stronger ageing resistance than crops, allowing them to maintain their persistence in the field. Weedy rice (Oryza sativa), de-domesticated from cultivated rice (Oryza sativa L.), has become a pernicious weed in Chinese rice fields in recent years. Whether weedy rice rapidly evolved strong resistance to seed ageing in the process of de-domestication, thereby contributing to its persistence in the paddy field, requires investigation. Accordingly, the seeds of weedy rice populations and their co-existing rice varieties were collected from 61 regions of China and germinated after incubation at normal (25 degrees C) and artificial accelerated ageing (50 degrees C) conditions, for four consecutive years (2013-2016). The results showed that the seed-ageing resistance of weedy rice was higher than that of its coexisting rice cultivars. The high temperature treatment and seed viability tests showed that weedy rice seeds had only weak dormancy in the first year (2013). Furthermore, a negative correlation was found between germination and latitude. At about 35 degrees N, naturally selected weedy rice formed two distinct groups. This implies that indica-japonica differentiation might affect the ageing resistance of weedy rice and the coexisting cultivated rice. After dividing the weedy and cultivated rice into indica and japonica types, the germination percentage of the indica-type was higher than that of the japonica type. These results indicate that weedy rice may have evolved new resistance to seed ageing that may be helpful in formulating prevention and control strategies for this problematic weed.