| A study was conducted in Zhenhua village(32.15N,119.83E),Youfang Town,Yangzhong County,Jiangsu Province in 2020 and 2021.Three type rice(early-maturing late japonica rice(ELJR),late-maturing medium japonica rice(LMJR),medium-maturing medium japonica rice(MMJR))were used as materials,and three seeding dates including May 10(S1),May 20(S2)and May 30(S3)were set to research the yield and components,growth of photosynthetic material,population structure,lodging resistance,rice quality,and starch physicochemical properties of different type japonica rice varieties under mechanical transplanting.The study aimed to clarify the differences of yield,quality and related physicochemical and ecological characteristics of different type japonica rice varieties and provide theoretical basis and technical support for the scientific selection of suitable seeding dates for different types japonica rice varieties in Yangtze river in southern Jiangsu.The main results are as follows:1.Along with the delayed seeding date,there was no significant difference in the number of panicles,the number of grains per panicle gradually decreased and the differences between S1 and S3 were significant or highly significant,the 1000-grain weight showed an increasing trend,and the overall difference between S1 and S3 was significant or highly significant.Some varieties had significant or highly significant differences between S2 and S3,and the seed setting rate showed an increasing trend.In terms of yield,the yield decreased with the delay of seeding date except for ELJR.Compared with S1,the yields of different type japonica rice varieties had no significant changes under S2.Compared with S2 and S1,the yields of ELJR and LMJR decreased significantly or highly significantly under S3,and the yield of MMJR was significantly lower than that of S1 but not significantly different from that of S2.Along with the delayed seeding date,the number of tillers in the tillering-hearty-period of different type japonica rice varieties increased and the number of tillers in the jointing,heading,and mature stages showed a decreasing trend,with a significant or highly significant decrease in the effective panicle percentage.Along with the delayed seeding date,the dry matter accumulation and photosynthetic potential of various types of japonica rice showed a decreasing trend from seeding to jointing stage,jointing to heading stage and heading to maturity stage.At the same seeding date,the dry matter accumulation and total dry matter accumulation of ELJR and LMJR were similar from heading to maturity,both higher than those of MMJR.Along with the delayed seeding date,the dry matter accumulation ratio,population growth rate and net assimilation rate showed the same trend,with S3>S2>S1 from seeding to jointing stage,jointing to heading stage,and S1>S2>S3 from heading to maturity stage.It could be seen that under early seeding conditions,the higher dry matter accumulation ratio,population growth rate and net assimilation rate of rice from heading to maturity stage were important characteristics of its high yield.2.The LAI index,Leaf length and leaf width of the upper three leaves(sword leaf,inverted two leaf and inverted three leaf)of various types of japonica rice showed a trend of S1>S2>S3,while the drooping angle showed an opposite trend.Under the same seeding date,the LAI index showed as ELJR>LMJR>MMJR,and the drooping angle showed as MMJR>LMJR>ELJR.The leaf length and width of LMJR and MMJR were similar,and were significantly smaller than that of ELJR.Along with the delayed seeding date,the light transmittance and root bleeding intensity of various types of japonica rice showed a decreasing trend.At heading stage,milk ripening stage and wax ripening stage,the root bleeding intensity was manifested as ELJR>LMJR>MMJR.3.Along with the delayed seeding date,the plant height and center of gravity height of various types of japonica rice showed a decreasing trend,with no significant difference in relative center of gravity height.The wall thickness of stem,dry weight of unit internode and breaking resistance of basal I1,I2,and I3 internodes showed a decreasing trend,while bending moment and lodging index showed an upward trend.The plant’s lodging resistance ability was significantly reduced.For different types of japonica rice,the relative gravity center height was shown as ELJR>LMJR>MMJR under the same seeding date.The stem thickness,stem wall thickness,dry weight of unit internode and breaking resistance were shown as MMJR>ELJR>LMJR,while the lodging index showed the opposite trend.For different basal internodes,the lodging index showed I3>I2>I1,and the bending force and bending moment showed an opposite trend.4.In terms of quality,along with the delayed seeding date,the processing quality and appearance quality of various types of japonica rice were better for the higher brown rice rate,milled rice rate and head milled rice rate,and lower chalky rice rate and chalkiness degree.The postponement of seeding date increased the amylose content and protein content,shortened the gel consistency,debased the taste value,peak viscosity,trough viscosity,breakdown and final viscosity,increased the setback and pasting temperature,deteriorated the taste quality.The processing quality,appearance quality of various types of japonica rice and the taste quality of EL JR and MMJR were not significantly different between S1 and S2,but were significantly or highly significantly different from those of S3.There were significant or highly significant differences in the taste quality of LMJR under the three seeding dates.For S1,S2 and S3,the brown rice rate,milled rice rate,head milled rice rate showed that LMJR>ELJR>MMJR.Taste value showed that ELJR>LMJR>MMJR.Chalky rice rate,chalkiness degree and protein content showed that MMJR>LMJR>ELJR.Compared with japonica soft rice,milled rice rate,head milled rice rate,chalky rice rate and chalkiness degree of late-maturing medium non-soft japonica rice,and milled rice rate,head milled rice rate and taste value of medium-maturing medium non-soft japonica rice were less affected by the seeding date.Correlation analysis found that the milled rice rate and head milled rice rate were significantly negatively correlated with daily mean temperature during the grain filling stage,and the chalky rice rate,chalkiness degree were significantly positively correlated with daily maximum temperature and daily mean temperature.Protein content was significantly negatively correlated with daily maximum temperature and daily mean light hours,and taste value was significantly positively correlated with daily mean temperature and accumulated temperature during the grain filling stage.5.Along with the delayed seeding date,more small starch particles adhering to the large particles,and whose surface were unsmooth.The starch diffraction patterns of various types of japonica rice at different seeding dates were all A-type,indicating that the seeding date did not change the crystallinity type of starch,but the relative crystallinity of starch decreased when seeding date was delayed.As the seeding date was postponed,the infrared ratio of starch at 1045/1022cm-1 increased,the surface order of starch increased,the number of small and medium starch particles significantly or extremely significantly increased,and the number of large starch particles significantly or extremely significantly decreased.In terms of starch thermodynamic properties,the values of enthalpy,peak temperature,initial temperature,and final value temperature showed a decreasing trend with the delay of seeding time,while the regenerative enthalpy and regenerative value showed an opposite trend.6.Comprehensive analyses indicate that,along the Yangtze river in southern Jiangsu,from the perspective of high yield,the suitable sowing date for each maturity-type japonica rice under mechanically transplanting is from May 10 to May 20.From the perspective of the coordination of high yield and good quality,early-maturing late japonica varieties sown around May 10th have the best taste quality with high yield,and late-maturing medium japonica rice varieties can be sown around May 10th to achieve the coordination of high yield and good quality,and medium-maturing medium japonica rice varieties have the highest yield and best taste quality when sown around May 10th. |
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