Changes Of Vigor, Physiology, Biochemistry And Storability During Hybrid Rice Seed Maturity And The Effect Of Dehydrating Agent Application

Hybrid rice seed production plays a great role during agricultural production in China. If accelerating dehydration during seed maturation of hybrid seed production, it will be benefit for reducing seed broken when harvesting mechanically, avoiding pre-harvest sprouting and aftercrop production. Seed vigor, physiology, biochemistry and storability varied a lot at different maturity stages, it is important to study their change regulation and get a suitable seed harvest time. In present study, two hybrid rice varieties, Qianyou No1and Y Liangyou689were used to investigate changes of vigor, physiology, biochemistry and storability during hybrid rice seed maturity and the effect of dehydrating agent application. The main results were as follows:The viability and vigor of different maturation stages in hybrid rice seeds were studied. For Qianyou No1, seeds harvesting at13to28DAP (days after pollination) all had high germination percentage and germination energy, while the quality of seedlings harvesting at13DAP and16DAP were low. For Y Liangyou689, seeds harvesting at16to34DAP had high germination percentage and germination energy, while the seeds harvesting at16DAP had low quality seedlings. After the mean fuzzy subordinate function values of germination percentage, germination energy, germination index, vigor index and mean germination time, root number, root length, shoot length, seedling weight were analyzed, it was found that Qianyou No1hybrid rice seeds harvesting at19to28DAP and Y Liangyou689hybrid rice seeds harvesting at19to34DAP had a higher viability and vigor.The changes of testa layer, pericarp layer and aleurone layer were observed during seed maturation progress of Qianyou No1and Y Liangyou689using scanning electron microscope (SEM). The thickness of aleurone layer sustained decline after10DAP, and the thickness of testa and pericarp layer was raised firstly and then declined. The changes of seed length, width, thickness, thousand-seed weights, weights of thousand-embryo and endosperm were studied, and their linear regression relationships with seed germination percentage, germination energy, germination index, vigor index, mean germination time were analyzed respectively. It was found that most of the physical parameters of seeds harvested at19DAP had no significant changes in Qianyou No1. The seed width, thickness, thousand-seed weights of fresh and dry seeds and the thickness of testa and pericarp layer were all significantly related with seed viability and vigor. For the variety Y Liangyou689, most of the physical parameters of seeds harvested at19DAP had no significant changes. The seed width, thickness, thousand-seed weights of fresh and dry seeds, weights of thousand-embryo and endosperm and the thickness of testa and pericarp layer were all significantly related with seed viability, seed width and thousand-embryo weights also significantly related with seed vigor.The starch granules development of Qianyou No1and Y Liangyou689were observed using SEM. With the maturity of seeds, the number of starch granules became larger, starch arrangement was from loose to neat and tight. The changes of seed moisture content, the contents of total soluble sugar, soluble protein, total starch, stachyose, raffinose, sucrose, glucose and fructose, the activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and catalase (CAT), the contents of ABA and GA3and the relative transcriptions of64SHsp18.0and Os03g0267200genes were studied, and their linear regression relationships with germination percentage, germination energy, germination index, vigor index, mean germination time were analyzed respectively. It was found that most of the parameters changed sharply at19DAP. For Qianyou No1, the content of GA3, total soluble sugar, soluble protein, raffinose and stachyose were all significantly related with seed viability and vigor. For the variety of Y Liangyou689, the seed moisture content, the content of ABA and GA3, total starch, soluble protein, raffinose, stachyose and sucrose, the activities of POD, CAT and APX were all significantly related with seed viability. The content of total starch, soluble protein, raffinose, stachyose and sucrose, the activities of POD, CAT and APX, relative transcriptions of64S Hsp18.0and Os03g0267200genes were all significantly related with seed vigor.The torelance of hybrid rice seeds harvested at different maturation stages to accelerated aging were studied. The relationship between the torelance to accelerated aging and the content of GA3and ABA were also studied. For Qianyou No1, seeds harvested at19DAP, the seed viability and vigor had no significant changes after accelerated aging for9days. Seeds harvested from22to25DAP, the seed viability and vigor all declined significantly after accelerated aging for9days. For Y Liangyou689, seeds harvested from22to25DAP, the seed viability and vigor had no significant changes after accelerated aging for9days. Seeds harvested at28DAP, the seed viability and vigor all declined significantly after accelerated aging for9days. The tolerance to accelerated aging was significantly improved after the seeds were presoaked with GA3. After soaking with ABA, the seed viability and vigor all significantly decreased however there were no significant changes before and after accelerated aging.The effects of spraying dehydrating agent on the changes of seed moisture content, vigor, physiology and biochemistry in hybrid rice were studied. Dehydrating agent F significantly reduced seed moisture content by5.3%when the seeds were harvested6days after application of desiccants, further investigation found there was no harmful influence on thousand-seed weights and quality. It suggested that suitable dehydrating agent could be used in hybrid rice production before harvest.The content of sucrose was highly related with dehydration during seed maturity, and there were no significantly relationship between other oligosaccharides and seed dehydration. The relative transcriptions of64S Hspl8.0gene was apparently down-regulated in the control of un-spraying dehydrating agent when the seed dehydration was fast, while the relative transcriptions of64S Hsp18.0gene obviously up-regulation after the application of dehydrating agent.