Melon crop is of significant economic importance in Brazil mainly because it is an export product. Rio Grande do Norte and Ceará are the major producer states where the occurrence of yellow mosaic, caused by the ZYMV virus, represents a problem. The most efficient way to control this disease is by using resistant varieties. The access PI414723 is the only source of resistance used in breeding programs. Its resistance is controlled by at least one locus, called Zym-1, which is located on chromosome II and linked to the microsatellite marker CMAG36. However, in addition to this gene, the literature suggests the existence of at least another locus, Zym-2, but still with an uncertain chromosomal position. Preliminary studies carried out by our group indicated that Zym-2 is located on chromosome X, but further analyses with more markers are necessary to define its position with greater statistical precision. This project aims to assemble a genetic map with ten SSR markers loci located on chromosome X based on genotypic data from an F2 population of 300 individuals derived from the cross between PI414723 and the susceptible 'Védrantais' cultivar. The same population will be phenotyped for ZYMV resistance by quantifying viral titers using the quantitative PCR method. The genotypic and phenotypic data will be used to increase the number of markers around the Zym-2 locus. Candidate resistance genes will then be identified by aligning the linkage map with the sequence of chromosome X.
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