Minor Effect Of RFT1,Hd1 And Ghd7 On Heading Date And Yield Traits In Rice

Heading date is controlled by major and minor quantitative trait locus（QTLs）.Major QTL mainly affects the regional and seasonal adaptability of rice cultivars,while minor QTL fine-tunes the heading date in the same or similar ecological regions,and plays a key role in making full use of natural resources or avoiding stress.In this study,NIL populations that segregated in the region of Hd17-RFT1or Hd1 and Ghd7 were constructed to study their genetic effects on heading date and yield traits using Zhenshan 97 and Milyang 46 as the parents.The purpose was to provide a theoretical basis for the genetic mechanism of transition from major effect to minor effect.At the same time,a total of 220indica rice accessions from southern China including 128 improved varieties and 92 landraces were used to analyze the allelic variations of RFT1,Hd1 and Ghd7 in different ecological types and their relationship with heading date and photoperiod sensitivity.This study provided a genetic basis for clarify the genetic mechanism of variety adaptability in southern China.The main results are as follows:1.Minor effect of RFT1 on heading date and yield traits in riceOne NIL-F₂ population and one NIL population which segregated in the region of Hd17-RFT1under the early-heading genetic background were developed using Zhenshan 97 and Milyang 46 as the parents,and were planted in Hangzhou,Zhejiang Province.Results showed that the Milyang 46 allele could promote heading date.Additive effects on heading date ranged from 0.84 days to 1.21 days,explaining 10.46%to 18.62%of the phenotypic variations.Meanwhile,the analysis of yield traits in two-year’s trials using the NIL population showed that the Milyang 46 allele in target region could promote heading date and had a slight negative effect on yield traits.Moreover,in the two populations only segregated in the Hd17 region,no significant variations on heading date were detected.It was confirmed that the effect of the region Hd17-RFT1 is not from Hd17.In summary,the Milyang 46 allele of RFT1 could further shorten the growth period of early-season varieties with slight penalty in grain yield.2.Minor effect of Hd1 and Ghd7 on heading date and yield traits in riceOne NIL population that segregated in the regions of Hd1 and Ghd7 in the genetic background of functional Milyang 46 was constructed using Zhenshan 97 and Milyang 46 as the parents.This population was planted in Hangzhou,Zhejiang Province and Lingshui,Hainan Province.In Hangzhou trail,the results showed that the functional Hd1 promoted and delayed heading date when Ghd7 was the nonfunctional allele and the functional allele,respectively.This result indicated that the dual function of Hd1 was affected by Ghd7.The ability to delay heading date of the functional Ghd7 was stronger when Hd1 was the functional allele than when Hd1 was the nonfuctional allele.This indicated that the functional Hd1 could enhance the function of Ghd7.In Hangzhou trail,Hd1 and Ghd7 each showed minor effect on heading date when the other one was the nonfuctional allele.The additive effects on heading date were 2.20 days and 2.00 days,respectively.In Lingshui trail,Ghd7 both showed minor effects on heading date whether Hd1 was the functional allele or not.The additive effects on heading date were 2.20 days and 1.30 days,respectively.This minor effect of Hd1 and Ghd7 was also detected in yield traits.3.Genotype characteristics of RFT1,Hd1 and Ghd7 for rice varieties in Southern ChinaA total of 220 indica varieties from southern China were tested,the result showed that allele frequencies of RFT1,Hd1 and Ghd7 were very different in various ecotypes.For RFT1,two alleles were similar distribution in the improved varieties and the landraces.For Hd1 and Ghd7,Hd1ghd7accounted for the highest propotion in the improved varieties,and were discovered in only four landraces.The frequencies of Hd1Ghd7 were the highest in late-season rice of both the improved varieties and the landraces.It showed that most of the late-season rice carried functional Hd1 and Ghd7.In two-locations’trails,the genetic effect of RFT1 on heading date was only significant in Lingshui,Hainan,however,the effect direction was opposite in the improved varieties and the landraces.There was a significant effect for Hd1 in both locations.Among the landraces,the functional Hd1 promoted and delayed heading date in Lingshui trail and Hangzhou trail,respectively.However,the functinal Hd1promoted heading date in both locations in the improved varieties.The functional Ghd7 delayed heading date in both the two trails,and the effect was strong in the improved varieties and was weak in the landraces,respectively.In summary,it showed that Hd1 and Ghd7 play important roles in regional and seasonal adaptability of indica varieties in southern China.