| Rice is the main source of food for more than half of the world's population,and also ranks first in China's food crops.However,due to the frequent occurrence of low temperature in recent years,rice yield is decreasing year by year.Therefore,improving cold tolerance of rice has always been the direction of breeding experts.Brassinolide(BR),as the sixth major hormone,plays a certain role in promoting plant growth regulation and stress resistance.Based on the cold tolerance identification and genetic theory,it is of great significance and value to screen cold tolerant rice germplasms and locate cold tolerant related genes by QTL combined with BR.At present,there are considerable opinions on cold tolerance of rice at home and abroad,but because different experimental materials,rice growth period and identification methods can not comprehensively analyze cold tolerance genes of rice,the final cold tolerance genes are not comprehensive,so we should select high-quality cold tolerant rice materials to carry out cold tolerance identification in the most suitable growth period.To select the most cost-effective technology to obtain cold-tolerant genes.In this study,140 recombinant inbred lines constructed from Dongxiang wild rice and Shennong 265 were used to identify cold tolerance of rice seedlings.The simplified genome sequencing method combined with SNP loci was used to preliminarily locate the QTL.The main results are as follows:(1)Through the experiments of temperature gradient and BR concentration gradient of cold treatment,the optimum temperature of cold treatment for rice was 10 C,and the optimum concentration of BR was 0.1 micromol/L.(2)The variation of each trait of 140 backcross recombinant inbred lines was quite different,the average number of panicles was 12,mostly more than 10;the average seed setting rate was 93%,mostly more than 90%,indicating that most of the inherited Shennong265 was in this population;the average plant height was 95.32 cm,and the 1000-grain weight was concentrated in 25-27.Combining the above results,it showed that most of the 140 backcross recombinant inbred lines were similar to Shennong 265 and had good agronomic traits.The coefficient of variation of rice seedling stage ranged from 1.00 to 2.00.The selected cold tolerance indexes were wilting rate and dead seedling rate.The corresponding distribution frequencies were 85% and 69% respectively,which indicated that the two indexes were sensitive to cold stress.It can be used to accurately and objectively evaluate cold tolerance of rice germplasm at seedling stage.(3)For rice seedling stage,low temperature treatment was divided into cold treatment(not sprayed BR)and cold treatment + BR spraying.After 7 days of cold treatment at 10 C,the growth resumed.The wilting rate and seedling death rate were measured.The coldtolerance level was divided into 1,3,5,7 and 9 grades.After cold treatment,31,69,34,7 and0 grade 1,5 and 9 grade 9 materials were obtained.After BR treatment,55 first-grade materials,54 third-grade materials,28 fifth-grade materials,3 seventh-grade materials and 0ninth-grade materials were obtained.Among them,the wilting rate increased by 30,decreased by 57,unchanged by 53,increased by 23,decreased by 54 and unchanged by 63.According to the classification of cold-resistant grade,9 materials with strong cold-resistance were screened out,including T38,T57,T58,T62,T63,T100,T110,T111 and T131,and 3materials with very weak cold-resistance were T18,T48 and T140.(4)Using GBS method,140 backcross recombinant inbred lines were sequenced.The results showed that the distribution of base content was normal and the quality of sequencing data was high.The ratio of all samples ranged from 73.74% to 99.59%.After SNP detection,lines with individual deletion rate over 0.7 and SNP deletion rate over 0.2 or lines with minimal allele greater than 0.05 were removed to ensure that the results were consistent with the requirements of QTL mapping.The high quality SNP can continue the research of QTL mapping. |
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