Identification And Evaluation Of Resistant Starch Content In Brown Rice Of Rice Germplasms And Preliminary Study On Its Nitrogen Level Regulation

Rice is the staple food of Chinese people for their daily nutrients and energy.Resistant starch(RS)is a functional starch of rice to decrease blood sugar and blood lipids,enhance mineral absorption and regulate body weight;and it is also a raw material and ingredient of functional foods to alleviate metabolic syndrome.Thus,RS combined nutrition and function,has widely focused and increasingly loved in agriculture,food and medicine industries;and which has become highlight for research and development.In this dissertation,1196 rice germplasms with the same period of duration in 2021 field planting were used as the experimental materials and their RS content in brown rice were identified,evaluated and screened;the selected rice germplasms with extreme RS content as the materials in the different planting seasons of 2022 field experiment were analyzed the genotypic differences of RS content in their brown rice;which shall provide the rich materials for genetic improvement of RS rice.R223 with highest RS content was used as material in the pot planting to preliminarily explore the regulation of RS formation and accumulation under three N levels of 120 kg/hm~2,180 kg/hm~2and 240 kg/hm~2;which provided theoretical basis and technical support for the application of N fertilizer in high-RS rice cultivation.The main research results are as follows:1.The RS content of brown rice among 1196 rice germplasms had significant or highly significant genotypic differences.The RS content of brown rice in rice germplasms ranged from 0.95%-19.16%,with the average of 7.38%and variational coefficient of40.79%;the RS content of brown rice in early rice germplasms ranged from2.69%-16.65%,with the average of 8.32%and variational coefficient of 36.30%;the RS content of brown rice in medium rice germplasms ranged from 1.39%-16.96%,with the average of 6.88%and variational coefficient of 44.48%;the RS content of brown rice in late rice germplasms ranged from 0.95%-19.16%,with the average of 7.01%and variational coefficient of 38.09%.The average RS content of brown rice in early rice germplasms were highly greater than those in medium and late rice,but the genotypic difference of RS content in medium rice was greater than that of early and late rice.The mean RS content of brown rice in japonica rice was significantly lower than that of indica rice,the mean RS content of brown rice in glutinous rice was significantly lower than that of non-glutinous rice,and the RS content of black,red and purple brown rice weren’t significantly different,but they existed extremely significant differences than that of light-yellow brown rice.Twenty-five rice germplasms with extreme RS content were selected,and the highest RS content in brown rice of R223 reached 19.16%.2.The RS content of brown rice among the 25 rice germplasms in different planting seasons had significant or highly significant genotypic differences.The RS content of brown rice in 25 rice germplasms showed significant inter-annual differences;and RS content of early,medium and late rice germplasms in 2021 were significantly higher than those in the corresponding planting seasons of 2022.Except for RS content of a few rice germplasms in the current season were lower than those in the other two seasons,the RS content of most early and late rice germplasms in the corresponding planting season of2022 were higher than those in the other two seasons.The RS content of most medium rice germplasms in the middle and late seasons were higher.3.Nitrogen level could significantly or extremely significantly regulate the RS formation and accumulation of brown rice in rice germplasm R223 with high RS content.The measured agronomic traits,yield traits,chlorophyll content,soluble sugar content and gluten content of R223 increased with increasing nitrogen levels,while RS content,starch content and starch synthase activity decreased with increasing nitrogen levels.The correlations of RS content and other indicators except seed starch,5d AH leaf Chl and starch content showed significant or highly significant.So,the RS accumulation amount of brown rice in R223 was the highest under the 120 kg N/hm~2level in high-RS rice cultivation.