| Mechanic cultivation is an important development direction in rice production.Mechanic transplanting density has an important impact on rice yield and quality,but the effect of spacing on the yield and grain quality of rice with good taste is not clear.The representative rice cultivars with good taste quality in Jiangsu Province,Nanjing 9108,Nanjing 5055 and Nanjing 46 were used in this study.The effects of plant spacing of 10 cm,12 cm,14 cm,16 cm,18 cm on the yield and quality of the rice cultivars above were studied under the condition of fixed row spacing of 30 cm.The effect of halving the panicle fertilizer(50%of nitrogen application rate of normal panicle fertilizer)on the yield and quality of rice cultivars with good taste was also investigated.The main results are as follows:1.With the increase in plant spacing,the number of panicles,the rate productive tillers,the seed setting rate and the yield of Nanjing 9108,Nanjing 5055 and Nanjing 46 increased first and all reached the highest with plant spacing of 12 cm,and then decreased.However,the plant spacing had no significant effect on the 1000-grain weight,and the number of grains per panicle increased with the increase in plant spacing.According to the curve equation of yield and plant spacing,the suitable planting spacing of the above three rice cultivars with good taste quality ranged from 10.5-12 cm.2.Increasing the plant spacing will lead to the deterioration of the processing quality of rice cultivars with good taste quality.The variation of chalkiness character with plant spacing varies with varieties.The amylose content and setback value of rice were decreased first and then increased with the increase in plant spacing,while the gel consistency and breakdown value were opposite.The total starch content increased with the increase in plant spacing,and the protein content was not significantly different between 12-18 cm but decreased significantly when the plant spacing was set to 10 cm.The appearance quality and cooking and eating quality of rice were the best when the planting spacing was set to 12 cm.3.The contents of endogenous hormones and key enzymes envolved in starch synthesis in grains of three rice varieties increased first and then decreased with the advancement of grain filling time after heading.Increasing plant spacing might cause the first decrease and then the increase of granule-bound starch synthase(GBSS)activity,the contents of zeatin+zeatin nucleoside(Z+ZR),indole acetic acid(IAA)and abscisic acid(ABA)in the early and mid-grain filling stage(12-16 d after heading),which was consistent with the trend of amylose accumulation in the middle and late filling stage(12-32 d after heading);The activity of ADP-glucose pyrophosphorylase(AGP)increased continuously,which was the same as the total starch accumulation trend in the middle and late filling stage.The starch branching enzyme(SBE)activity showed no obvious change.The rate of amylose accumulation increased with higher GBSS activity in the grains during the early to mid-grain filling stage of all three cultivars,which is similar to the change relationship between grain AGP and the total starch accumulation rate.Correlation analysis showed that the average contents of Z+ZR,IAA and ABA in grains in the middle stage of grain filling was significantly or extremely significantly and positively correlated with the mean value of GBSS activity,positively correlated with the average value of AGP activity,and had no significant correlation with SBE.The average accumulation rate of amylose and total starch content in the middle stage of grain filling and its final content were significantly or extremely significantly and positively correlated with the average values of GBSS and AGP activities and the average contents of Z+ZR,IAA and ABA.The correlation with SBE was different with varieties and did not reach the significant level.The maximum and average contents of Z+ZR and IAA in the middle and late stages of grain filling were significantly or extremely significantly and positively correlated with protein content,however,the breakdown value,gel consistency and taste value were negatively correlated.4.When the plant spacing was set at 12 cm,the reduction of panicle fertilizer to half of the normal nitrogen application had no significant effect on the yield.But when the plant spacing was set at 18 cm,the reduction of panicle fertilizer decreased the number of grains per panicle significantly,which led to a significant decrease in yield.Under the same panicle fertilizer application,increasing the plant spacing could enhance the amylose content of all three rice varieties,and had no significant effect on protein content,but reduced the gel consistency,breakdown value and taste value;Under the same mechanic transplanting spacing,the reduction of panicle fertilizer had no significant effect on the rates of milled and head milled rice,but the chalkiness,amylose content,setback value and protein content decreased to different degree,however,the gel consistency and breakdown value were reversed,and the rice taste value was significantly improved.In addition,under the condition of halving the panicle fertilizer,the effect of plant spacing on the average activities of GBSS and AGP,the average contents of Z+ZR,IAA and ABA,and the amylose and total starch in the grains of all three cultivars was basically the same as that of normal nitrogen application in the early and mid-grain filling stage(12-16 d after heading).Under the same plant spacing condition,the above indexes were significantly lower than normal nitrogen application after halving the panicle fertilizer.The above results showed that with the row spacing fixed at 30 cm,setting the plant spacing between 10.5-12 cm can improve both the yield and quality of rice.The reduction of panicle fertilizer helps to stabilize the yield,and also helps to improve the cooking and eating quality of rice cultivars with good taste.But at the same time,the protein content of rice is also reduced.In addition,the cooking and eating quality of rice with good taste had a close relationship with Z+ZR,IAA and ABA contents and GBSS and AGP activities in the middle stage of grain filling,and had no significant correlation with SBE activity.Therefore,appropriately reducing the planting distance under mechanic transplanting can adjust the relevant endogenous hormone content and key enzyme activity of starch synthesis in the grain of rice varieties with good taste,and further optimize the cooking and eating quality of rice varieties with good taste. |
PDF Full Text Request