Genetic Analysis And Genome-wide Association Mapping Of Plant Architecture And Powdery Mildew Resistance Traits In Melon (Cucumis Melo L.)

Melo (Cucumis melo L.) is a world-wide planting horticultural crop with high diversity. Many agronomic traits such as plant architecture traits, powdery mildew resistance, cracking resistance traits are very important to melon cultivation. And deep dissection and utilization of the important genetic variations is essential to melon industrial development. In this study, melon as experimental materials, genetic analysis of melon agronomic traits has been carried out. Genome-wide association studies (GWAS) was used to study the traits of plant architecture and resistance to powdery mildew with simplified genome sequencing and single nucleotide polymorphisms (SNP) genotyping technique, which provide a reference for melon breeding and follow-up research. The main research contents and results are summarized as follows:1. The melon agronomic traits, internode length (INL), lateral branch length (LBL), main-stem diameter (MSD), leaf area (LA), external color (ECOL) was analyzed in four generations (P1, P2, F1 and F2) of melon, using the Hami melon varieties ’AM-5’and muskmelon varieties’RE-19’. The study found that external color was quality trait, controlled by a single gene. And the others were quantitative traits controlled by multiple genes. A mixed major gene plus polygene inheritance model was used to analyze the four quantitative traits. The results showed that INL and LBL fitted two additive-dominance major genes plus additive dominance polygene mode, MSD fitted two additive-dominance epitasis major genes plus additive-dominance polygene mode, and LA fitted additive -dominance polygene mode.2. Genome-wide association studies (GWAS) was used to study the five traits with restriction association site DNA sequencing (RAD-seq) and SNP genotyping technique by the parents and 147 Individual plant of the F2 population from’AM-5’ x’RE-19’. GWAS for INL showed that the identified SNPs were located in the chromosome 1 and 10. GWAS for LBL showed that the identified SNPs were located in the chromosome 1,4 and 8. GWAS for LA showed that the identified SNPs were located in the chromosome 1,3,4,8,11 and 12. The SNPS, from the region (16265415bp- 31301063bp) in the chromosome 1,were associated with the traits of INL, LBL and LA. GWAS for the external color (ECOL) showed that the identified SNPs were located in the chromosome 10. The SNPs, from the region (3453384bp-5647302bp) in the chromosome 10, were associated with the traits of ECOL.3. Six generations (P1, P2, Fi, B1, B2 and F2) of melon, from the parents of muskmelon variety’RE-33’and inbred lines’MOIN-10’, was used to analyze fruit cracking resistance and powdery mildew resistance. The results showed that powdery mildew resistance was quality traits controlled by a single gene. And fruit cracking resistance were quantitative traits controlled by multiple genes. A mixed major gene plus polygene inheritance model was used to analyze fruit cracking resistance. The study found the genetic model E-0, incorporating two additive-dominance-epitasis major genes plus an additive-dominance polygene mode, was the best-fitting genetic model for fruit cracking resistance. The heritabilities of the major genes in the B1,B2 and F2 populations for fruit cracking resistance were 46.24%,59.19% and 57.98%, respectively, and the heritabilities of polygenes for the trait were 21.26%,2.02% and 9.74%, respectively. Genetic variances in B1, B2 and F2 accounted for 67.51%,61.19% and 67.73% of phenotypic variance, respectively, showing that fruit cracking resistance was controlled by genetic factors, although under environmental influence. In melon breeding, it would be most efficient to conduct selection for cracking resistance in early generation.4. Individual plant of the F2 population, from’RE-33’×’MOIN-10’,was classified as resistant or susceptible group. Genome-wide association studies (GWAS) was used to study the traits of resistance to powdery mildew with type IIB restriction site associated DNA (2b-RAD) sequencing and SNP genotyping technique. The powdery mildew resistance gene, from’RE-33’,was located in region (135976bp-1418829bp) in the chromosome 2.