| Direct-seeded rice is a one of techniques for coping with the rice production transformation based on labor saving,high resource use efficiencies and easy to full mechanization.Nevertheless,poor crop establishment of direct-seeded rice is one of the major constraints to wide adoption of direct-seeded rice,particularly in areas prone to flooding after sowing or where fields are not level result in waterlogging stress.Previous reported that seed pelleting is an effective,practical and facile technique to enhance crop establishment under unfavorable environmental conditions.However,few work has been done regarding the effects of pelleting treatments on seeds germination and early seedlings growth and its relative mechanisms in direct-seeded rice under waterlogging conditions.A series of experiments were conducted(1)to determine the effective seed pelleting formulae and pelleting times(the weight ratio of pelleting agents to rice seeds)for direct-seeded rice under waterlogging conditions;(2)to explore the physiological and biochemical mechanisms underlying the waterlogging tolerance induced by seed pelleting with CaO2;(3)to examine the effects of seed pelleting treatments on seed germination,the early growth of seedlings,yield and its components in wet direct-seeded rice(WDSR)system under waterlogged field conditions.The results obtained as followed:(1)We havd selected pelleting treatments with CaO2,which can notably increase the seed germination and the early seedling growth of direct-seeded rice under waterlogging stress.Moreover,the average seed germination percentages of the pelleting treatments were 38.4 % higher than the naked seeds.And the shoot length,root length,shoot FW,and root FW increased by 130.0%,71.9%,147.8%,137.4%,respectively,compared with naked seeds control.Forthermore,the optimum weight ratios of CaO2 to dry seeds were found to be in the range of 0.6:1-1:1 based on seed germination and seedling growth performance under waterlogging conditions.(2)The mechanisms of seed pelleting with CaO2 enhanced the seed germination and the early seedlings growth in WDSR under waterlogging conditions:(1)The surrounding oxygen content of the seeds increased as a result of CaO2 react with water release O2,which improved the seed emergence and early growth of seedlings under waterlogging stress.An increase in the pelleting time from 3:1 to 5:1 at the content of CaO2 10%,resulted in an increase in the amount of oxygen released from CaO2 by 126.5%.(2)The ?-amylase activities and total amylase activities of rice seeds or seedlings increased by 345.5% and 201.1% under waterlogging stress,respectively,compared with naked seeds control.(3)The pyruvate decarboxylase(PDC)and alcohol dehydrogenase(ADH)activities of rice seeds or seedlings decreased by 73.0% and 90.8% under waterlogging stress,respectively,compared with naked seeds control.(3)Results from the field experiment showed that CaO2 pelleting treatments significantly improved the seed germination an early seedling growth.On average,the seed germination percentages of the pelleting treatments were 33.9 % higher than the naked seeds.And the shoot length,root length,shoot FW,and root FW increased by 66.7%,35.2%,181.9%,215.8%,respectively,compared with naked seeds control.In comparison to the yield of naked seeds,the yields of the pelleting treatments increased by 11.9%-23.2%,which were attributed to higher panicles per m2 than naked seeds control.Conclusively,in comparison to the naked seeds,seed pelleting with CaO2 notably accelerated starch degradation and decreased anaerobic respiration of rice seeds or seedlings.The seeds pelleting treatments enhanced the stress tolerance of rice seeds under waterlogging conditions,significantly improved the seedling establishment and increased the rice yield of WDSR under waterlogging stress.Considering the compressive strength and the sinking in the mud,the formulae of with 10% CaO2 at a pelleting time of 5 or with 20% CaO2 at a pelleting time of 3 are recommended in practical production. |
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