ARS | Publication request: RAPD LINKAGE MAP OF THE GENOMIC REGION ENCOMPASSING THE ROOT-KNOT NEMATODE MELOIDOGYNE JAVANICA RESISTANCE LOCUS IN CARROT

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 22, 1999
Publication Date: N/A

Interpretive Summary: Carrot production around the world is threatened by the attack of nematodes in the soil. Genetic resistance to nematodes is an excellent way to continue carrot production without pesticides, most of which will be outlawed within five years. We have found a naturally occurring source of genetic resistance in a Brazilian carrot, Brasilia, which resists one of the most economically important nematodes, Meloidogyne javanica, found in the southern U. S. and other warmer areas of the world. This paper reports four molecular genetic markers close to the nematode resistance gene. This is important in vegetable seed industry and public carrot breeding programs since these markers can be evaluated rapidly and inexpensively. This makes them important in facilitating the genetic resistance gene into new carrot varieties.

Technical Abstract: Inheritance studies have indicated that resistance to the root-knot nematode (Meloidogyne javanica) in carrot inbred line, Brasilia-1252, is controlled by the action of one or two (duplicated) dominant gene(s). A systematic search for randomly amplified polymorphic DNA (RAPD) markers linked to Mj-1 was carried out using bulked segregant analysis (BSA). Altogether 1000 ten-mer primers were screened with 69.1% displaying scorable amplicons. A total of approx 2400 RAPD bands were examined. Four reproducible markers (OP-C2 1700, OP-Q6 500, OP-U12 700, and OP-AL15 500) were identified, in coupling phase linkage, flanking the Mj-1 region. The genetic distances between RAPD markers and Mj-1 locus, estimated using an F2 progeny of 412 individuals from Brasilia 1252 x B6274, ranged from 0.8 to 5.7cM. The low number of markers suggests a reduced amount of genetic divergence between the parental lines at the region surrounding the target locus. Nevertheless, the low rate of recombination indicated these markers could be used as landmarks for positional cloning of the resistance gene(s). These RAPD markers could be used to increase the Mj-1 frequency during recurrent selection cycles and in backcrossing programs to minimize linkage drag in elite lines employed for development of resistant F1 hybrids.