Abstract
The objective of this work was to construct linkage maps of 'Pêra' sweet orange [Citrus sinensis (L.) Osbeck] and 'Cravo' mandarin (Citrus reticulata Blanco) using RAPD markers and the pseudo-testcross strategy. The parents were chosen according to the resistance/susceptibility to citrus variegate chlorosis (CVC). The segregation of 176 markers was analyzed in 94 progeny of F1 hybrids, which were obtained from controlled crossings. The linkage map of 'Pêra' sweet orange had 117 markers defined by 12 linkage groups, which spanned 612.1 cM. Only six markers could not be linked to the linkage group and 48.7% of the markers showed segregation distortion. The linkage map of 'Cravo' mandarin had 51 markers defined by 12 linkage groups, which spanned 353.3 cM. Only two markers did not link to the groups and 15.7% showed segregation distortion. The construction of linkage maps is relevant to future mapping studies of the inheritance of CVC, citrus canker and leprosis.
Highlights
IntroductionCitrus breeding programs present biological limitations due to the heterogeneity of the genus, polyembryonic nature, long reproduction cycle, sterility, incompatibility and endogamy depression
According to Food and Agriculture Organization (FAO, 2002), Brazil is the largest producer of citrus in the world, and ‘Pêra’ sweet orange (Citrus sinensis (L.) Osbeck) is the variety of highest commercial importance.Citrus breeding programs present biological limitations due to the heterogeneity of the genus, polyembryonic nature, long reproduction cycle, sterility, incompatibility and endogamy depression
The genetic linkage map of ‘Pêra’ sweet orange had 117 markers defined in 12 linkage groups, which spanned 612.1 cM
Summary
Citrus breeding programs present biological limitations due to the heterogeneity of the genus, polyembryonic nature, long reproduction cycle, sterility, incompatibility and endogamy depression. The literature does not provide information on the nature and manner of the genetic inheritance of some traits of economic importance (Grosser & Gmitter Junior, 1990). Linkage maps are the bases for advanced genetic studies; they allow a better understanding of the inheritance, identification and isolation of the genes. Cloning of genes will be facilitated by well-defined genetic maps in many species. Some genetic characteristics of citrus as the haploid chromosomes number of 9, the high polymorphism, the production of fertile interspecific and intergeneric hybrids and the small genome size (1C = 0.62 pg) favor the construction of linkage maps (Gmitter Junior et al, 1996)
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