Better performance of germination in hyperosmotic solutions in conspecific weedy rice than cultivated rice

Abstract

Weeds and crops that grow together often confront similar types of environmental stress, especially drought stress. Weedy rice (Oryza sativa f. spontanea) and cultivated rice (O. sativa L.) provide a unique pair consisting of a weed and a conspecific model crop that can be used to study the drought tolerance of plants across a large distributional range. The investigation on weedy rice's damage to paddy fields showed that it was more serious in dry direct seeding than water direct seeding. Compared with water direct seeding, the seeds of cultivated rice and weedy rice in dry direct seeding will absorb water and germinate under the condition of insufficient soil moisture. Our hypothesis is that weedy rice seeds have evolved stronger germination ability than coexisting cultivated rice under water stress, so that they can obtain more growth space in the early stage in dry direct seeding and thus obtain higher fitness. Seeds of weedy rice populations and coexisting rice cultivars were collected from 61 sites across China and were germinated with 20% polyethylene glycol-6000 to simulate drought stress. Two drought response indices, which assessed germination rate and germination index, plus one germination stress tolerance index, indicated significantly greater drought tolerance in weedy rice populations than in coexisting rice cultivars (P < 0.01). Drought tolerance for the three indexes were indica weedy rice > indica rice cultivars, japonica weedy rice > japonica rice cultivars, and indica weedy rice > japonica rice cultivars. These results indicate that weedy rice populations show stronger drought stress tolerance than coexisting rice cultivars at various sites, specifically during the seed germination period. Furthermore, Pearson's correlation found that drought response of weedy rice populations and coexisting rice cultivars were significantly different with these environmental factors: latitude, altitude, annual mean precipitation, mean annual temperature, mean precipitation in the sowing month, mean temperature in the sowing month, and sowing methods. Weedy rice shows different patterns of drought tolerance variation across geographical (latitude and altitude) and environmental (precipitation) gradients compared to coexisting rice cultivars. This study suggests that weedy rice might have evolved new drought tolerance and could provide a useful source of genetic resources for improving drought tolerance of crop cultivars and breeding direct seeded cultivars to reduce the usage of seeds in direct seeding.

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

“…Based on the geographical distribution of rice planting areas in China, 61 weedy rice populations and their co‐existing rice cultivars were collected from 2009 to 2012 (Figure ; Wang et al, 2019). The latitude, altitude and sowing method of each sampling site are recorded in Table .…”

How Can Weedy Rice Stand against Abiotic Stresses? A Review

“…A recent study has predicted a possible occurrence of water scarcity for about 13 Mha of irrigated wetland rice in Asia by 2025 and that another 22 Mha of irrigated dry season rice will suffer economically from issues connected to water scarcity, such as limited availability of resources to access water [26]. As a response to these conditions, the adoption of direct dry seeded rice in Asia is gaining importance, as it requires less water than flooded seeding or transplanting [27,108]. A more widespread adoption of direct dry seeding will increase weed competition, especially for some species, such as weedy rice, whose growth is suppressed or limited by flooding water [27].…”

“…A study conducted in China on 61 weedy rice populations and coexisting rice cultivars collected in an equal number of sites and tested for germination under drought conditions found that weedy rice was much more tolerant to drought than cultivated rice in all the sites [108]. Moreover, the authors showed that indica weedy rice and japonica weedy rice populations were more tolerant to drought, in terms of germination, than their respective indica and japonica rice cultivars; indica weedy rice was also much more tolerant than the japonica rice varieties [108].…”

“…A study conducted in China on 61 weedy rice populations and coexisting rice cultivars collected in an equal number of sites and tested for germination under drought conditions found that weedy rice was much more tolerant to drought than cultivated rice in all the sites [108]. Moreover, the authors showed that indica weedy rice and japonica weedy rice populations were more tolerant to drought, in terms of germination, than their respective indica and japonica rice cultivars; indica weedy rice was also much more tolerant than the japonica rice varieties [108]. A possible explanation for the higher tolerance of weedy rice to drought, and to other abiotic stresses, compared to cultivated rice, is that the domestication process of the cultivars has led to a higher allocation of resources for reproduction than for traits that are useful to counteract abiotic stresses, as already demonstrated for weedy and cultivated sunflowers [109].…”

Competition between Rice and Weedy Rice under Different Water Regimes

“…In Asia, about 13 Mha of irrigated lowland rice by 2025 and another 22 M ha of irrigated dry season rice will possibly experience water scarcity due to limited availability and accessibility of water resources (Korres et al 2016). To address this, the adoption of direct dry-seeded rice in Asia is encouraged, as it requires less water than wet seeding or transplanting (Korres et al 2016;Wang et al 2019). However, more widespread adoption of direct dry seeding will expectedly increase weed competition, especially in weed species that are normally suppressed by flooding of water (Korres et al 2016).…”