Root-Knot Nematode Resistance Genes in Tomato and Their Potential for Future Use

Abstract

The gene Mi, which confers resistance to several species of root-knot nematode, is present in many modern tomato cultivars. Recent cloning of this gene revealed that it encodes a member of the plant resistance protein family characterized by the presence of a putative nucleotide binding site and a leucine-rich repeat. Analysis of transgenic plants revealed the unexpected result that Mi also confers resistance to potato aphids. Although highly effective in many conditions, Mi fails to confer resistance at high soil temperature, and Mi-virulent nematode isolates have been identified in many areas of the world. These findings have stimulated efforts to identify new sources of root-knot nematode resistance. Resistance genes that differ from Mi in properties and genetic position have been identified in Lycopersicon peruvianum. These genes, as well as the cloned Mi gene, provide a resource for broadening the base of root-knot nematode resistance in tomato and other crops.

Pre-inoculation with arbuscular mycorrhizal fungi suppresses root knot nematode (Meloidogyne incognita) on cucumber (Cucumis sativus)

“…Inoculation with the RKN had significant effects on shoot Mg, Cu, and Zn concentrations (Table 2) and frequently increased shoot Mg and Cu concentrations but decreased Zn concentrations irrespective of the AM fungal isolate present. Root knot nematode infection often reduces plant growth and yield (Sasser and Freckman 1987;Williamson 1998) and decreases nutrient uptake (Patel et al 1988), and infested plants show deficiencies of N, Mg, Fe, B, Cu, and Zn (Good 1968) due to root damage by RKN and subsequent prevention of water and nutrient uptake by the roots (Gaillaud et al 2008). The increased shoot length in infested plants could be a temporal response of plants to M. incognita infestation which might be driven by the carbon drain due to the RKN infestation.…”

Thermal requirements for the embryonic development and life cycle of Meloidogyne hispanica

“…At 30 and 35°C M. hispanica development was similar on both tomato cultivars because the tomato Mi-1.2 gene only confers resistance at soil temperatures below 28°C for some Meloidogyne spp. (Williamson, 1998). The ability of M. hispanica to develop and reproduce at 30°C on the resistant tomato cv.…”

PERSPECTIVES ONPLANT ANDSOILNEMATOLOGY

“…Their polyploidy (diploid to tetraploid, but typically triploid) apparently resulted in conserved genetic diversity, yet in some manner enables them to adapt to very different environments and hosts. For example, repeated exposure to the resistant Mi gene in tomato under greenhouse conditions gives rise to virulent populations of Meloidogyne, but this occurs infrequently in the field (105). Continuous deployment of the Rk resistant gene in tobacco in given fields results in the development of resistance-circumventing populations or host races of M. arenaria or M. incognita (6).…”

“…As with the C. elegans genome project, research on the molecular genetics of parasitism and host resistance requires enormous inputs. Recent progress in these areas (4,24,33,37,41,90,105) often involved international collaboration. This shift is due, in part, to the limited number of nematologists, the need for multidisciplinary inputs to address very complex issues, and downsized programs (including graduate research).…”