Major QTL Analysis Of Melon Oblate Fruit

Melon（Cucumis melo L.）is an important economic crop of Cucurbitaceae and is widely cultivated worldwide.Because of its unique aroma,fresh and juicy,rich in nutrition,it is loved by consumers.China is a big producer of melon,and its cultivation area and yield rank first in the world.Melon fruit shape is an important factor affecting consumer choice and an important trait affecting fruit quality.The shape of melon fruit is various,such as snake,oval,oblate,etc.,among which the oblate melon fruit transverse diameter is generally larger than the fruit longitudinal diameter and has a certain market share.Clarifying the genetic law of melon oblate fruit and exploring the related genes can provide important data support for the fine mapping,molecular mechanism research and fruit shape diversity breeding of melon oblate fruit in the future.In this study,the long fruit shape melon material M4-101 was used as the male parent（P₁）,and the oblate melon material M4-16 was used as the female parent（P₂）to prepare the F₁generation.The F₁generation was self-crossed to obtain the F₂generation separation population.The two parents,F₁and F₂generation groups were sowed.After the fruit was ripe,the length and width of the mature fruit were investigated,and the fruit shape index was calculated.The dominant-recessive relationship between the long fruit shape and oblate shape traits of melon and the separation of the fruit shape index in the F₂generation group.In the F₂segregating population,20 long-fruit-shaped and 20 oblate-shaped individuals were selected to construct two extreme mixed pools of long-fruit-shaped and oblate-shaped individuals.BSA-seq sequencing analysis was performed on the parents and extreme pools.The chromosome segment controlling the gene of melon oblate fruit trait was obtained,and the In Del marker was developed in the target segment.The selected polymorphic primers were used to genotype the F₂segregation population,and Rqtl（Version 4.2.2）was used for QTL analysis to obtain the main QTL regulating the gene of melon oblate fruit.（1）The fruit shape index of the male parent M4-101 was1.84±0.11,and the fruit shape index of the female parent M4-16 was 0.94±0.03.The fruit shape index of the F₁generation was in the range of 1.29±0.09,which was biased towards the male parent.The field statistical data of fruit shape index,fruit length and fruit width of F₂generation were analyzed.All traits showed normal distribution in the segregating population,showing the genetic characteristics of quantitative traits.（2）In the F₂population,melon fruit length was significantly positively correlated with melon fruit width and fruit shape index,and the correlation coefficients were 0.435**and 0.770**,respectively.Fruit width and fruit shape index showed a significant negative correlation coefficient of-0.231**.（3）Twenty flat round fruits and 20 long fruit fruits were selected from 172 F₂populations to construct long fruit-flat round extreme mixed pools.The results of BSA-seq analysis showed that chromosome segments that may be linked to oblate fruits were detected on chromosomes 3（22,836,883-25,573,518 bp interval,about 3.0 Mb）,6（8,123,728-28,480,009 bp interval,about20.0 Mb）and 9（19,022,366-21,289,897 bp,about 3.0 Mb）.Based on the resequencing data of the two parents,a total of 32 polymorphic In Del molecular markers were developed in the above intervals to genotype the F2 population,and genetic linkage analysis was carried out in combination with phenotypic data.The genetic linkage map of melon was drawn by QTL Ici Mapping V3.3 software.The map consisted of three linkage groups corresponding to chromosomes3,6 and 9 of melon.The map included 32 markers covering 72.72 c M genetic distance,with an average distance of 2.27 c M between markers.A major QTL locus was detected in the18.215,807-21,080,671 bp interval on chromosome 6,with a LOD value of 7.37 and a contribution rate of 17.9%.Combined with the published melon fruit shape integration map,the locus was named Cm FS6.3,and no fruit shape-related QTL locus was detected on chromosomes 3 and 9.