The Difference In Yield Formation And Grain Quality Of Direct Seeded Rice Under The Different Seeding Date

The rice planting pattern in the Sichuan Basin is diversified,and the connection of crop rotation is complicated.The harvesting period of the previous crop limits the sowing date and variety selection of the direct seeding rice.In this study,through the sowing date experiments of different hybrid rice varieties with various growth periods,the direct seeding rice varieties satisfying the demand of complex crop rotation were screened,and the physiological basis of high yield and stable yield such as yield formation,spikelet differentiation and degradation and flowering and filling of direct seeding rice under different sowing dates were explored.And the difference in characteristics,as well as the impact on rice quality,the optimal sowing date of direct seeding rice in the Sichuan Basin was proposed,which provided theoretical basis and technical support for realizing high yield and stable yield of direct seeding rice.The main findings are as follows:The yield performance of hybrid rice varieties at different maturity stages under various sowing dates showed that the effects of sowing date,variety and interaction between the two on rice yield were extremely significant.The early seeding(April15)rice yield was Zhongjiazao 17(early maturity)<Fyou 498(late maturity)<Fuyou 838(medium maturity),on the other sowing date,rice yields were Zhongjiazao 17(early maturity)<Fuyou 838(medium maturity)<Fyou 498(late maturity).The yield of early maturity varieties was the lowest,and it continued to increase with the delay of sowing date.The yield of mid-maturity and late maturity varieties increased first and then decreased with the delay of sowing date.The mid maturity variety Fuyou 838 sowed on April 30 obtained the highest yield,and the late maturity variety Fyou 498 had the highest yield with the sowing period on May 15.The effect of delayed sowing on the yield of different late maturity hybrid rice varieties showed that the average yield of rice was the highest on May 15 th,followed by May30 and the lowest on June 14.The primary factor for high rice yield during the sowing period on May 15 was the seed setting rate,which was 32.77% and 20.18% higher than the sowing date on May 30 and June 14,respectively.The number of filled grains per panicle also showed certain advantages,but there was little difference in the number of grains per panicle.At the latest sowing date of June 14,Fyou 498 had a significant advantage over the remaining late maturity varieties in terms of effective panicle number and 1000-grain weight.Although the seed setting rate and the number of grains per panicle decreased,the yield was still higher than the other varieties.The comparison of photosynthetic production efficiency of hybrid rice varieties with different growth periods showed that the net photosynthetic rate,stomatal conductance,intercellular carbon dioxide concentration and apparent mesophyll conductance of direct seeding rice under different sowing dates were Zhongjiazao 17>Fuyou 838>Fyou 498.Direct seeding rice had the highest photosynthetic capacity during the heading stage at the sowing date on May 15.Too early or late sowing will reduce the photosynthetic capacity after the heading.From the perspective of photosynthetic production efficiency of different late maturity hybrid rice varieties,the net photosynthetic rate and stomatal conductance of rice at jointing stage were May 15 > May 30 > June 14,at heading stage were June 14 > May 30 > May15 th.The net photosynthetic rate of flag leaves of Chuanyou 8377 was lower than other varities at jointing stage,heading stage and 15 d after heading,performing weak photosynthetic production ability.Shanyou 908 had a certain advantage in net photosynthetic rate,and the photosynthate production ability was strong.The accumulation and transport of different types of hybrid rice varieties in growth periods showed that the dry matter accumulation at jointing stage decreased with the delay of sowing date,and the dry matter accumulation at maturity increased gradually,while the dry matter accumulation at the heading stage showed a parabolic trend,reaching the maximum on May 15.From the point of view of variety,the dry matter accumulation of early maturity varieties decreased gradually with the delay of sowing date,and the medium maturity and late maturity varieties did not show strong regularity.The three varieties all reached the maximum dry matter accumulation at the heading stage on May 15.Screening the differences among the sowing date of different late maturity varieties,the dry matter accumulation at the heading stage and the maturity stage decreased with the delay of the sowing date;the dry matter accumulation from the heading stage to the maturity stage and harvest index reached the maximum on May 30.On May 15 th,the post-anthesis dry matter accumulation was the least,but the harvest index was higher than the latest sowing date of June 14.The dry matter accumulation of Chuanyou 727 and Chuanyou 8377 at maturity was the highest with sowing date of May 30,while the dry matter accumulation of other varieties decreased with the delay of sowing date.The harvest index of Chuanyou 727 gradually decreased with the delayed sowing date,while the maximum harvest index of the other four variet branches.With the delay of sowing date,the number of secondary branches increased significantly.The spikelet differentiation number of secondary branches on April 30,May 15 and May 30 was significantly higher than that on April 15,with growth rates of 4.2%,12.2%,and 24%,respectively.The spikelet degradation rate of secondary branches was the lowest on May 15 th,which was 16.4%,23.7%,and 27.2% higher than the sowing dates of April 15,April 30,and May 30,respectively.From the effect of sowing date on the anthers and pollen physiological characteristics of late maturity hybrid rice,with the delay of sowing date,the proportion of full dehiscence anthers in total anthers gradually decreased,and the proportion of partially cracked anthers increased.With the proportion of full indehiscence anthers increased rapidly,making the anther cracking coefficient smaller overall.On June 14 th,only the cracking coefficient of Fyou498 reached 0.8,the other varieties were all below 0.8.Among them,Chuanyou 727 had the lowest cracking coefficient of only 0.74.The length of filament,pollen grain diameter and anther width on the sowing date of May 30 were significantly higher than those on May 15 and June 14,and the lowest were on June 14.The anther length and pollen dyeability of May15 were the most advantageous.The filament length and anther length of Luyou 908 and the anther width of Fyou 498 were significantly higher than those of other rice varieties.In terms of pollen grain diameter and pollen dyeability,Fyou 498 and Chuanyou 8377 had the most advantages.The comprehensive analysis showed that there was a significant positive correlation between the yield and the total number of spikelets,and the spikelet number of secondary branches(r2= 0.42** and 0.44**),filament length,anther length and width were also positively correlated with yield.but the seed setting rate was negatively correlated with total spikelets,secondary branch differentiation and secondary spikelet differentiation(r2=-0.37*-0.44*).As for the number of secondary branches differentiation and pollen staining rate,there were significant positive correlations(r2=0.37* and 0.82**).There was a significant positive correlation between seed setting rate and pollen staining rate(r2=0.73**),while 1000-grain weight had a significant positive correlation with anther length(r2=0.46**).The effect of sowing date on the quality of late maturity hybrid rice showed that on the latest sowing date of June 14 th,rice was significantly higher than the first two sowing dates in terms of roughness,whole milled rice rate and gel consistency.However,it is at a disadvantage in terms of chalkiness and chalkiness.On the sowing date of May 15,the fine rice rate and protein content of Qyou 5 were higher than other varieties,and the amylose content,whiteness and chalkiness of rice were lower than other varieties.On the sowing date ies was outstanding sowed on May 30.From the difference among sowing dates of different varities with varied growth periods,with the delay of the sowing date,the total number of spikelets and the number of existing spikelets increased significantly.The delay of the sowing date was conducive to the differentiation of spikelets and reduced the degradation of spikelets.Compared with the sowing date of April 15 th,the number of total spikelet differentiation,the total number of spikelets,the spikelet number of secondary branches and the number of secondary branches differentiation were 14.42%,13.8%,23.63% and 10.79% higher than the other sowing dates,respectively.The maximum number of spikelets of early maturity varieties appeared in the sowing date of May 30,whiule the maximum number of spikelets of medium maturity and late maturity varieties appeared on April 30 and May 15,respectively.The difference among sowing dates of different late maturity varieties showed that the differentiation and degradation of total spikelets were mainly affected by secondary branches,and the sowing date had no significant effect on the differentiation and degradation of firstof May 30,the whiteness and chalkiness of Luyou 908 were higher than those of other varieties.On the sowing date of June 14,the fine rice rate of Luyou 908 was the highest,and the whiteness of Chuanyou 8377 rice was the lowest.