Genetic Analysis And Mapping Of Gene Associated With Gummy Stem Blight(GSB) Resistance In Melon(cucumis Melo)

Melon(Cucumis melo)is widely cultivated all over the world,with a variety of types.China has 460 thousands hectares melon cultivation in 2015.Gummy Stem Blight(GSB)is a major limited disease that affacets quality and production of melon,which can infect leaf,stem and fruit.Plants display necrosis spot and even die after GSB infection.Although chemical and agricultural operations can control GSB,the development of GSB-resistance cultivar is considered to be one of the most successful,economical and effective approachs to control the disease severity.In this study,we try to elucidate the genetic characteristic of GSB-resistance gene,construct a high-density genetic map based on single nucleotide polymorphisms(SNPs)and map candidate genes associated with GSB-resistance in melon.The main results are as follows:1.Genetic characteristic of GSB-resistance in melonThe inbred lines HS and XH were crossed to generate F2 populations.Afterward,the HS(20 individuals),XH(20 individuals),F1(25 individuals)and F2(219 individuals)were inoculated with GSB.All the HS lines and F,were found to be resistant to GSB,whilst the XH was susceptible to GSB.The segregation ratio of the GSB responses of the F2 generation were found(165 resistant and 54 susceptible)to be 3:1 ratio,indicating that GSB-resistance is controlled by a single dominant allele in melon.2.Construction of an ultra-dense density genetic map in melonWe employed the F2 populations(150 individuals)from the cross between XH and HS to construct genetic map in melon.The parents lines of XH and HS were resequenced by Illumina HiSeqTM 2500,26× covering genomedepth in average.150 individuals of F2 were resequenced by Illumina HiSeqTM 2500,2× covering genome depth in average.Finally,we constructed an ultra-dense density genetic map which spanned 1987.06 cM in length with 0.18 cM average distance and consisted of 1,188,159 SNPs that were grouped into 13,275 bins.The map is benefiting for re-anchoring genome scaffolds of melon,of which over 91%scaffolds were anchored onto the 12 chromosomes,and 90%of them are oriented.3.Mapping and functional analysis of GSB-resistance gene candiadtesBased on the ultra-dense density genetic map,we mapped a GSB-resitance trait locus in a 106kb region in CM3.5_scaffold00018 of chromosome 12.In total,8 genes were annoated in this region.According to annotation,expression patterns and non-synonmous SNP,we proposed that MELO3C012987(Avr9/Cf-9 rapidly elicited protein 146 homolog),MELO3C012991(Protein SEC13 homolog)and MELO3C012992(GATA transcription factor 9)are probably as GSB-resistance gene candiadtes in melon.