Fine Mapping Of Immature Fruit White Color Gene And Inheritance Studying Of Fruit Firmness In Cucumber

The immature fruit skin color in cucumber has became one of the most important external traits which affcts its commodity value. Cross was made between white parent H4(P2) and green parent Q1(P1). The F1 generation was selfed and backcrossed to generate segregating generations F2, BCP1(F1×P1) and BCP2(F1×P2). The inheritance of immature fruit color has been studied previously in our laboratory using the methods of color difference meter and visual grading. It showed that the number of green plants and white plants in F2 had a ratio of 3:1, and 1:1 in BCP2 while the fruit colors of BCP1 were all green. The result proved that the white character was hidden in the green one being regulating by 1 gene. Co-dominant maker SSR15312 was found and it showed that the gene which controlled immature fruit skin color was in chromosome 3. In this study, the cucumber fruit skin color gene was fine mapped based on that primary mapping. At the same time, the firmness of immature fruit flesh was measured by hardmeter with the method of conjoint analysis to study the inheritance of cucumber firmness. The main results were as following:1. Using all white plants(882) of the F2 segregating population(3,916) as materials and using the method of BSA, I originally found 2 markers H2-2 and Q4-2 closely linked with the target gene from 8 SSR makers and 39 new CAPS markers near the co-dominant marker SSR15312. Q4-2 was co-segregative with the target gene and it was located on the left side of SSR15312 while H2-2 was on the right.2. 128 new CAPS were developed from far to near. they covered 1300 kb on the left side of SSR15312. Specific makers Q88、Q400-31 and Q138 were found in turn. SNP sites were found in PCR products of Q400-31 by sequencing and Q138 was co-segretative with the target gene. Finally, the target gene was corresponded to the end of chromosome 3 with the flanking makers Q400-31(0.3c M) and SSR15312(0.2c M). The physical distance between Q400-31 and SSR15312 was 467 kb based on the whole genome sequence of cucumber and there were 2 co-segregative CAPS makers Q4-2 and Q138 located on the left side of SSR15312 with the physical distance of 150 kb and 206 kb, respectively.3. Softberry and the BLAST of NCBI were both used to predict and analyse the candidate genes with the results of gene prediction and comments provided by GUGI. 66 candidate genes were predicted in this area including 4 genes related to the synthesis and transport of chloroplast.4. Co-segregative CAPS maker Q139 was found in candidate gene Csa3G904080 and the genome sequencing results of those 4 candidate genes indicated that there were 3 different amino acids between two parents in the gene Csa3G904080. Csa3G904080 was located between Q4-2 and Q138, and it dominates the synthesis of pyruvate kinase isozyme G. At the same time, the result of QRT-PCR indicated that the expression levels of Csa3G904080 in green parent was obviously higher than the white one.5. The inheritance of fruit flesh firmness in cucumber conformed to the additive pattern(A-2 model), no dominance and epistatic efficts existing. The major gene has a lower heritability with 3.66 % in F2 while the heritability and environmental effect of polygene were higher, so it is difficult to carry out the breeding of cucumber fruit firmness.