Preliminary Location Of QTL For Fruit Firmness Of Melon

Melon(Cucumis melo L.)is a Cucurbitaceae crop with a wide range of planting areas in the world.Its rich nutritional value and unique flavor are favored by the majority of consumers.Fruit firmness is an important index of melon quality,which has great influence on fruit size,shape and transportation.The varieties with high fruit hardness have long storage and transportation resistance,long edible period and shelf life,low sensitivity to cracking,and good marketability;the fruits are too soft and taste bad,and are not resistant to storage and transportation,which are easy to cause fruit cracking,lead to disease invasion and yield reduction,affect the external visual value of fruits,reduce the marketability of fruits,and restrict the healthy development of melon industry.Therefore,the study of fruit firmness is of great significance for the improvement of important characters of melon varieties and the cultivation of melon varieties with storage and transportation tolerance.In this study,M2-10 was used as the experimental material F₁,BC₁P₁,BC₁P₂backcross population,F₂and F₃segregation population were obtained.The distribution of fruit firmness in the field was investigated.The candidate regions related to fruit firmness were screened by SLAF-seq sequencing combined with BSA grouping method.The major QTL genes of fruit firmness were further located by using larger F₃families combined with SSR molecular markers The results are as follows:1.Record and measure fruit firmness 30 days after self pollination,investigate and analyze the genetic law of melon fruit firmness and the distribution trend of F₂and F₃.The results showed that:the average firmness of P₁(M2-10)was 10.8±1.24,and that of P₂(ZT00091)was 3.2±0.32.The difference between parents was significant.The average firmness of F₁was 8.7±1.15,which was between parents and tended to P₁;the average firmness of BC₁P₁and BC₁P₂were 6.3±0.68 and 5.7±1.31,respectively;the average firmness of F₂was 5.3±1.12,which was less than the average firmness of parents.The hardness of BC₁P₁,BC₁P₂and F₂showed continuous distribution.The fruit firmness of F₂and F₃populations had a wide range of genetic variation,and the firmness values showed a partial normal distribution of continuous changes.It can be judged that melon fruit firmness was a quantitative trait controlled by multiple genes.The results showed that the fruit firmness of melon was B-2 model,and its heredity was controlled by two pairs of major genes,and showed two pairs of additive dominant major genes.2.SLAF-seq(specific locus amplified fragment sequencing)technology was used to sequence the parents and F₂of extremely hard fruit mixed pool(20 hard fruits with firmness value greater than 9.5)and extremely soft fruit mixed pool(20 soft fruits with firmness value less than 3.2).A total of 18.53 Gbp data was obtained,and the effective data was 18.39 Gbp after filtering The average sequencing depth of each sample was 11.03×,and the genome coverage was 98.09%.The QTL loci controlling fruit firmness were located between 18996333?23870331 on chromosome 2 and 49380?28751254 on chromosome 5.3.Based on slaf-bsa sequencing,142 F₃families(10 strains in each family)were used to further locate melon fruit firmness in the candidate interval,and to explore SSR molecular markers linked to melon fruit firmness.The results showed that the QTL ff2.1 on chromosome 2was located on scaffold00030 1366537?1505146 between cmssr07709 and cmssr07734,with LOD value of 3,80,phenotypic contribution rate of 28.14%,and additive effect of 1.82;on chromosome 5,with LOD?5.5,ff5.1 was located on scaffold00043 715989?716227 between cmssr13509 and cmssr13423,with LOD value of 17.44,phenotypic contribution rate of 38.44%,and additive effect of 0.85.