| Direct seeding of rice is a light production method,which has shown a trend of not pushing from the main rice areas in China in recent years because it can significantly reduce labor input.However,there are problems such as serious weed damage and uneven seedling growth in current direct rice production,which seriously affect food security production.It is important to improve the uniformity of seedling emergence in direct-seeded rice to ensure complete seedlings to solve the problems of uneven seedling growth and difficult weed control.In this study,we selected common commercial varieties of direct-seeded rice produced in the same batch,and investigated the effects of seed development(expressed by seed fullness)and field environmental factors represented by different inundation depths(commonly caused by potholes in the field due to rough tillage)on seed germination and seedling growth under direct-seeded conditions,with a view to providing theoretical guidance for direct-seeded rice variety selection and cultivation management.The main research results are as follows:(1)The morphological index parameters,mainly seed projected area,showed poor consistency among all nine commercial rice varieties of the same batch.The seed morphological plumpness was defined by the ratio of the standard deviation of the seed projected area to the mean value,and the highest coefficient of variation(CV= 13.6%)was found for the seed morphological fullness of Huanghuazhan,and the lowest coefficient of variation(CV = 10.6%)was found for the seed morphological fullness of Liangyou 287.The results of germination experiments showed that there were significant inter-varietal differences in germination traits such as germination potential,germination rate,germination index,vigor index and germination uniformity of rice seeds.Rice varieties with smaller coefficients of variation in seed morphological plumpness had higher vigor indices and would also exhibit higher germination uniformity.Further direct seeding tests showed that the coefficient of variation of seed morphology plumpness correlated with the growth traits of direct seeded rice seedlings.(2)There were significant varietal differences in the effect of rice plumpness on seedling growth of direct-seeded rice.The acquired rice commercial seeds were classified into three different plumpness levels according to the seeds’ sinking in different concentrations of saline water,and the seedling growth and growth dynamics of seeds with different plumpness levels after direct seeding were analyzed and compared.The results showed that there were significant varietal differences in the effects of seed plumpness on seedling growth-related indexes.For Liangyou287,Lvdao Q7 and Jinkesimiao1,the higher the seed plumpness(seed specific gravity),the number of leaves,tillers,plant height and shoot biomass of seedlings showed a decreasing trend,and some indicators reached statistically significant levels at 15 to20 days after emergence.Seed plumpness had no significant effect on tiller number and plant height of Ezao18 seedlings,but it had significant effect on seedling shoot biomass at 15 days to 20 days.(3)Submergence depth significantly affected seedling growth of direct-seeded rice,and it was consistent among the tested varieties.There was no significant difference in seedling growth-related traits between dry direct seeding and 0 cm submergence in the tested varieties.Before seedlings emerged from water,seedling growth was significantly slower in the 4 cm and 8 cm submergence treatments than in the non-submergence treatments.After the seedlings emerged from the submerged 4cm treatment,the difference between the growth indexes of the seedlings and those of the submerged 0 cm treatment disappeared rapidly and surpassed each other,while the shoot biomass,plant height,and number of tillers per plant of rice seedlings under the submerged 8 cm treatment were always lower than those of the submerged 0 cm treatment during the test period.Under 4 cm and 8 cm submergence,seedlings of Liangyou 287 and Ezao 18 emerged from the water at 15 days and 20 days after sowing,respectively,while seedlings of Lvdao Q7 and Jinkesimiao 1 emerged from the water at 20 days and 25 days after sowing,respectively.The depth of submergence affected the stalk morphology of seedlings,showing that the deeper the submergence,the lower the height of rice plants and the thinner the stems.In addition,this study also found that the depth of submergence significantly affected the morphology of aeration tissue in the root system and stem of rice.(4)Seed plumpness and submergence depth interacted with each other to significantly affect the seedling growth of rice,and there were differences among varieties.At 10 days after seeding,seed plumpness and submergence depth interacted only with plant height,but only with tillering number per plant at 15 days after seeding.From 20 days to 25 days after seeding,seed plumpness and submergence depth interactively affected the number of leaves per plant,tillering number per plant,plant height and shoot biomass of rice.In summary,the results of this study showed that both seed plumpness and field submergence treatments affected seedling emergence and seedling growth uniformity in direct-seeded rice,but there were large varietal differences.The plumpness screening of rice seeds before sowing would be beneficial for seedling emergence and seedling growth of direct seeded rice.It is worth noting that proper submergence(e.g.,4 cm submergence depth in this study)can promote seedling growth of direct-seeded rice and facilitate the formation of a neat seedling population. |
