A family of 63 citrus intergenemic backcross hybrids was used for this study. The parents and hybrids were multiplied by rooted cuttings, with 6 uniform replicates selected per hybrid, and each plant was inoculated with citrus nematodes (Tylenchulus semipenetrans) 5 times over 2 mo. The number of nematode female larvae per gram of fine fresh root was determind 2 mo after the last inoculation. The phenotypic variation of the hybrids was continuous and wide-ranged, from 8.0 females· g-1 of root tissue (resistant parent Swingle citrumelo=15.6) to 620.0 females· g-1 of root tissue (susceptible parent LB 6-2=540.5). Bulked segregant analysis (BSA), using RAPD fragments, was conducted with 2 DNA bulks of individuals from the extremes of the phenotypic distribution. Three hundred twenty primers were screened and 5 were found to generate repeatedly single RAPD fragments specific to the resistant bulk. The segregation of resistance-associated fragments among the individuals was examined, and the linkage between these markers and potential nematode resistance loci was estimated.
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