Differences And Regulation Of Preharvest Sprouting Rate In Different Early And Middle Rice Varieties At Maturity

With global climate change,extreme weather such as high temperature and heavy rainfall has become more frequent.Under the influence of climate change,the phenomenon of preharvest sprouting in continuous rainy days during the mature period seriously reduces the yield and quality of rice.Most of the previous studies focused on the resistance and genetic mechanism of preharvest sprouting during rice maturity,but few studies on the regulation of panicle sprout through cultivation measures.Under the condition of artificial humidification,the effect and mechanism of different nitrogen fertilizer management and chemical regulation measures on preharvest sprouting were investigated.Six early rice varieties Ezzao 18(EZ18),Zhongzao 39(ZZ39),Xiangzaoxian 45(XZX45),Zhuliangyou 39(ZLY39),Liangyou 287(LY287),Liangyou42(LY42)and six middle rice varieties Huanghuazhan(HHZ),Yangdao 6(YD6),Huangkexiang 2(HKX2),Liangyou 6326(LY6326),Feng Liangyou 1 hao(FLYX1),Quanyou Yuenong Simiao(QYYNSM).In the field environment,different nitrogen treatments were set(Conventional Fertilization: CF,Low Nitrogen: LN),and the plants were transferred into the plants before heading,and artificially humidification at maturity stage(AH: Artificial humidification).In the yellow ripening stage,medium rice varieties were sprayed with paclobutrazol(PP333),exogenous ABA(ABA),paclobutrazol +ABA(P+A)and water(CW: Clear water).The preharvest sprouting rate and related indexes of rice at maturity were investigated.The main results are as follows:1.An artificial humidification method was established to evaluate the preharvest sprouting of rice: controlling humidity more than 80 percent at the maturity stage can significantly improve the panicle sprout rate of early and middle rice varieties.Among the early rice varieties,LY42 and LY287,which had high preharvest sprouting rate,increased by 124 percent and 67 percent,respectively,compared with the natural environment.FLYX1 and LY6326,which had high preharvest sprouting rate,increased by 103 percent and 195 percent,respectively,compared with natural environment.2.There were significant genotypic differences in the preharvest sprouting rate of different early and middle rice varieties at maturity stage,and the preharvest sprouting rate of early rice varieties was higher than that of middle rice varieties.Among the tested early rice varieties,LY42 and LY287 had the highest preharvest sprouting rate,which was 1.69 percent and 4.57 percent,respectively.The varieties ZZ39 and XZX45 had lower preharvest sprouting rate,which was 1.69 percent and 4.57 percent,respectively.The preharvest sprouting rate of FLYX1 and LY6326 were 7.49 percent and 3.29 percent,respectively.The preharvest sprouting rate of HHZ and YD6 were 3.01 percent and 1.43 percent,respectively.3.The grain water content,soluble sugar content,α-amylase and β-amylase activities of early and middle rice varieties with high preharvest sprouting rate increased,while the ABA content decreased significantly.Among the early rice varieties with high panicle sprout rate,LY42,its grain water content,soluble sugar content,α-amylase activity andβ-amylase activity increased by 10 percent,115 percent,286 percent and 62 percent,respectively,compared with ZZ39 with low panicle sprout rate,while ABA content decreased by 3 percent.Compared with YD6 with low panicle germination rate,the grain water content,soluble sugar,α-amylase activity and β-amylase activity of FLYX1 with high panicle germination rate increased by 7 percent,100 percent,95 percent and 5percent,respectively,and the ABA content decreased by 5 percent.4.Low nitrogen treatment significantly increased the preharvest sprouting rate of early and middle rice varieties at maturity stage.Under low nitrogen treatment,the preharvest sprouting rate of early rice variety LY42 was the highest,reaching 50.73 percent,which increased by 55 percent compared with conventional fertilization.Under the low nitrogen treatment,the preharvest sprouting rate of ZZ39 was the lowest,reaching2.75 percent,which was 62 percent higher than that of conventional fertilization.Under low nitrogen treatment,the preharvest sprouting rate of rice variety LY6326 was the highest,reaching 10.40 percent,which increased by 163 percent compared with conventional fertilization.Under low nitrogen treatment,the preharvest sprouting rate of HHZ was the lowest,up to 1.24 percent.5.Under artificial humidification treatment,spraying paclobutrazol,ABA and paclobutrazol+ABA significantly reduced the preharvest sprouting rate at mature stage of medium rice varieties.Under the conventional fertilization treatment,the preharvest sprouting rate of medium rice was decreased by 41 percent compared with that of clean water by spraying paclobutrazol;the preharvest sprouting rate of medium rice was decreased by 51 percent compared with that of clean water by spraying ABA;the preharvest sprouting rate of medium rice was decreased by 49 percentcompared with that of clean water by spraying paclobutrazol +ABA.Under the low nitrogen treatment,the preharvest sprouting rate of medium rice was reduced by 54 percent compared with that of clean water by spraying paclobutrazol;the preharvest sprouting rate of medium rice was reduced by 51 percent compared with that of clean water by spraying ABA;the2022preharvest sprouting rate of medium rice was decreased by 46 percent compared with that of clean water by spraying paclobutrazol +ABA.In conclusion,artificial humidification significantly increased the preharvest sprouting rate of early rice and middle rice,and early rice was more prone to preharvest sprouting than middle rice.There were preharvest sprouting rate differences among different early rice and early rice varieties.The grain water content,soluble sugar content,α-amylase and β-amylase activities of early rice and middle rice varieties with high preharvest sprouting rate increased significantly compared with those before preharvest sprouting,while ABA content decreased significantly.Low n treatment significantly increased the preharvest sprouting rate of early and middle rice varieties at maturity stage.Under artificial humidification treatment,foliar spraying paclobutrazol,ABA and paclobutrazol +ABA significantly reduced the preharvest sprouting rate at mature stage of medium rice varieties.