Studies On Identification And Evaluation Of Chilling-tolerance And Association Analysis In Melon Germplasm

Chilling stress is a one of major limiting factors of melon production in northern cold regions. To breed chilling tolerance germplasm is an effective way for improving chilling tolerance in melon. Excavation of chilling tolerance gene resources is an important prerequisite for cultivation of chilling tolerance germplasm, and establishing a high accuracy and stability of identification of chilling tolerance evaluation system is an important condition for the breeding of chilling tolerance. With the development of molecular biology and widely used in agriculture, identifying and screening marks related to chilling tolerance has promoted melon breeding l ow temperature process to provide evidence for molecular marker assisted selection of chilling tolerance breeding in melon. As a starting point to identification of chilling tolerance conditions and identification methods in this study, we analyzed and compared the variation of different cold stress of each index with comprehensive screening of low temperature stress and time suitable for identification of chilling tolerance in melon,and systematically utilized multivariate analysis methods to evaluate chilling tolerance during germination and seedling stages,which aim to establish a reproducible and operability of identification of chilling tolerance evaluation system. The chilling tolerance of natural population 247 melon accessions has been evaluaed by me ans of identification of relevant valid indexes by using established melon chilling tolerance evaluation methods and screened low temperature stress. The use of genome-wide association study to study natural populations genome-wide scan by population structure, linkage disequilibrium,genetic relationship analysis of natural populations. Moreover, association analyses of the molecular data obtained by high-throughput sequencing technology and phenotypic data about chilling tolerance evaluation were conducted to screen chilling tolerance traits significantly associated SNP. The major results obtained were as follows:(1) By comparing traits related chilling tolerance of 14 melon varieties under different low temperature stress during germination stage, screening suitable temperature of identification of chilling tolerance for low temperature stress is 18℃, and to determine the relative germination rate, relative germination potential, relative germination index, relative radicle length and relative germination weight and relative vigor index can be used as indexes of chilling tolerance in germination stage.(2) By comparing traits related chilling tolerance of 14 melon varieties under different low temperature stress and time during seedling stage, screening suitable condition of identif ication of chilling tolerance for low temperature stress is 4℃ for 8h and 7℃ for 16 h, and to determine the relative conductivity, MDA content, proline content and peroxidase activity, soluble sugar content and superoxide dismutase activity can be used as indexes of chilling tolerance in seedling stage.(3) Principal component analysis combined membership function evaluation method can accurately evaluate chilling tolerance of melon, and a mathematical evaluation model for chilling tolerance in melon germplasm has been established by regression analysis: Y=0.1197+0.3150X2+ 0.0257X3-0.2458X8-0.0076X11, then four main indexes related to the chilling tolerance were screened, which were relative germination potential, relative germination index, MDA and soluble sugar content.(4) The chilling tolerance strength of the 247 melon germplasm have been evaluated by chilling tolerance evaluation system, and these melon germplasm have been divided by cluster analysis into strong resistance to high resistant, resistant, middle resistance, low resistance and sensitive types, and we screened out 34 high resistant in melon germplasm.(5) Genome-wide association study has been performed between 12937 SNPs and valuation value of chilling tolerance in 247 melon germplasm by mixed linear model under conditions of controlling population structure and relationship between materials, and detected 6 SNP site significantly associated with chilling tolerance in melon, which are located on chromosome 2, 3 and 12, and can explain 9.11% to 13.38% phenotypic variation.