TABLE CONTENTS

Breeding for Resistance to Root-knot Nematodes in Vegetable Crops
Roberts, P.A.
Department of Nematology, University of California, Riverside, CA 92521, USA
Most vegetable crops are hosts for one or more common root-knot nematodes (Meloidogyne
spp.), and suffer yield loss from infection. Several important crops have natural sources of
host resistance in the crop species or in wild relative species. Opportunities and challenges
for breeding effective resistance into commercial varieties differ between crops based on the
genetics and specificity of the resistance. Examples from breeding and analysis of resistance
in carrot, bean crops, and tomato are used to describe the nature of resistance, its specificity
with respect to species and populations of Meloidogyne, the process required for successful
introgression of resistance genes, and challenges related to incidence and selection of
nematode virulence. In carrot, major dominant gene resistance is available and is being bred
into elite fresh market varieties via a combination of intense phenotypic selection and use of
co-dominant flanking STS markers for indirect selection. In lima bean, three independent
genes for resistance to root galling and nematode reproduction provide a broad-based
resistance to M. incognita and M. javanica, but require a gene pyramiding approach in
resistance breeding. In both cowpea and tomato, single major gene resistance used for many
years in commercial varieties has been highly effective but has led to selection of virulent
nematode populations able to break resistance. In these crops plants, second generation
resistance genes are available that block virulent populations, but they require breeding into
elite varieties.
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