Genetic Analysis And Gene Localization Of Female Flower Related Traits In Melon (cucumis Melo L.)

Melon (Cucumis melo L.),2n=2x=24, is a very important economically horticultural crop worldwide, belonging Cucurbitaceae family. The land area cultivated melon in China is first widely and production is first in the world. Andromonoecy is a widespread sexual system in cultivar melon characterized by plants carrying both male and bisexual flowers, only which can fruit. So, producing melon-generation hybrid through emasculation by measures cost higher than conventional varieties 12-30 times. And used gynoecious without emasculation will save labor, reduce the price of produced seeds. So, in order to provide the basis for breeding melon gynoecious line, genetic analysis of the gynoecious and femle sex related traits, days of first female flower(DFF), rate of female flower(RF), maximum number of female in secondary branches(MNF), node number of first female flower(NFF), were studied, and mapping their genes.In this study, the homozygous monoecious line 3-2-2 (AAGG) from China, thin-skinned, was crossed with the homozygous gynoecious line WI998 (AAgg), thick-skinned from USA to get six generations(P1,P2,F1,F2,BC1P1,BC1P2), which were used to reseach the genetic analysis of gynoecious and NFF. The results were as follows:F1 plants were all monoecious. The segregation ratio of monoecious and gynoecious was 3:1 in F2 population. The segregation ratio of monoecious and gynoecious is 1:1 in BC1P1 population. Monoecious phenotype was conferred by the dominant allele of the gynoecious (g) gene, whereas recessive homozygous plants are gynoecious. Number of plants of NFF was continues distribution in F2 population, so inheritance of NFF was quality trait.The F1 between 3-2-2 and WI998 was self-pollinated to produce F2 progeny, which were then self-pollinated by single-seed descent (SSD) to obtain 185 F6:7 recombinant inbred lines (RILs). The data of DFF,RF,MNF,NFF were collected in F6:7/spring and F6:7/autumn. Inheritance model of major gene plus polygene for RILs population was used to the data analysis. The results were as follows:RF and MNF traits did not have these models of the corresponding gene effect. The optimal model for DFF was two major genes plus additive polygene model (E₁₈) in spring and autumn. hmg2 was 77.05%,72.38% in spring and autumn, respectively. hpg2 was 22.44%,27.52% in spring and autumn, respectively. The optimal model for NFF was two major genes plus additive polygene model (E₁₈) in spring, hmg2 was 79.17%, hpg2 was 20.83%, respectively. And model E₁₇ was optimal for NFF in autumn, hmg2 was 61.94%, hpg2 was 36.77%, respectively.1219 simple repeated sequences (SSRs) markers were used to amplify parental DNA for polymorphism detection.215 (17.6%) were polymorphic between two parental lines and were used in linkage analysis in RILs population. The resulting genetic map consisted of 18 linkage groups spanning 937.1 cM with a mean marker interval of 4.4 cM. This melon genetic map framework was SSR codominant markers, providing the basis for map integration and trait mapping.The segregation ratio of RF and MNF was 1:1 in RIL population, respectively. RF and MNF phenotype was conferred by an allele of the RF (rf) and MNF (mnf) gene, respectively. Based on the RILs linkage map and RE and MNF data, the g and SSR markers MU8294₁ were mapped near the rf locus at 0.6 cM and 2 cM in linkage group 1, respectively, and RF minimum gene (rf2) were mapped; the SSR markers MU11132 and CMBR078 were mapped near the mnflocus at 0.3 cM and 5.8 cM in linkage group 1, respectively.Based on the RILs linkage map and sexual type data, the SSR markers NR3 and MU8294₁ were mapped near the g locus at 1.2 cM and 2.6 cM in linkage group 1, respectively. Marker NR3 was the closest to the g gene identified, and can be useful in breeding programs, using marker-assisted selection procedures to screen for sexual type in melon.Based on the RILs linkage map, the QTL analysis of the female sex related traits was done in F6:7families between two seasons. The results were as follows:1. Five QTL were detected for four female sex related traits(DFF,NFF) in F6:7/autumn and F6:7/spring. QTL appeared relatively aggregation of sites in LG1.2. One QTL were detected for DFF trait in spring and autumn, respectively(adff1.2, LOD=6.81, R2=32.40%, spring; qdff1.1, LOD=5.82, R2=39.20, autumn), R2 >10%, both additive values were negative.3. Three QTL were detected for NFF trait in spring and autumn. Two QTL (qnff7.1, R2=6.78%, LOD=2.17; qnff8.1, R2= 11.04%, LOD=2.36) in LG7 and LG8 in spring, both additive effect values were negative(-0.22,-0.29). qnff1.1 detected for NFF trait in autumn and qdff1.2 detected for DFF trait in spring in the LG1 same region.In this study, the construction of genetic maps and gynoecious localization provide a theories basis for construction of the high-density genetic linkage map and melon gynoecious lines molecular marker assisted breeding. In addition, genetic analysis and QTL mapping of female-related traits contribute to more comprehensive understanding melon female development.