Relationships between Meloidogyne incognita resistance genes in Lycopersicon peruvianum differentiated by heat sensitivity and nematode virulence

Abstract

Resistance to Meloidogyne incognita (Kofoid and White) Chitwood in clones of Lycopersicon peruvianum (L.) Mill. PI 126443-1MH, 270435-2R2 and 2704353MH, their F1, a field-produced F2, and their test-cross (TC1) populations, was evaluated based on egg masses and eggs produced on root systems. Reactions to M. incognita isolates differing in virulence to gene Mi were determined at 25°C (Mi expressed) and 32°C (Mi not expressed). PI 126443-1MH, 270435-2R2, 270435-3MH, and their F1 progenies were resistant to Mi-virulent and Mi-avirulent isolates. At 32°C with a Mi-avirulent isolate and at 25°C with a Mi-virulent isolate, four TC1 generations segregated into resistant: susceptible (R∶S) ratios close to 3∶1. These results indicated resistance to Mi-(a)virulent M. incognita isolates is conferred by different non-allelic dominant genes in PI 126443-1MH, 270435-2R2 and 270435-3MH. The F2 progeny of PI 126443-1MH x EPP-1, challenged with Mi-avirulent M. incognita at 32°C and with Mi-virulent M. incognita at both 25°C and 32°C, segregated with a ratio of 3∶1 (R∶S), indicating expression of a single dominant resistance gene in PI 126443-1MH in each case. In dual screenings on clones of the same individual plants from the TC1 and F2 segregating populations, some individual plants were susceptible at 32°C to a Mi-avirulent isolate but resistant to the Mi-virulent isolate, and vice versa, suggesting that different but linked genes confer heat-stable resistance to Mi-avirulent M. incognita and resistance to Mi-virulent M. incognita. We propose the symbol Mi-5 for the gene in PI 126443 clone 1MH and the symbol Mi-6 for the gene in PI 270435 clone 3MH which both confer resistance to Mi-avirulent M. incognita isolates at high temperature. We propose the symbol Mi-7 for the gene in PI 270435 clone 3MH and the symbol Mi-8 for the gene in PI 270435 clone 2R2 that both confer resistance to the Mi-virulent M. incognita isolate 557R at moderate (25°C) temperature. The novel resistance genes are linked and reside in a genomic region in each parental clone that is independent from the Mi locus.

The heat-stable root-knot nematode resistance gene Mi-9 from Lycopersicon peruvianum is localized on the short arm of chromosome 6

“…Several L. peruvianum accessions have been identified to possess heat-stable resistance (Ammati et al 1986;Veremis and Roberts 1996b). L. peruvianum is cross-incompatible with cultivated tomato, L. esculentum, thus impeding efforts to introgress the resistance.…”

TheMi-9Gene fromSolanum arcanumConferring Heat-Stable Resistance to Root-Knot Nematodes Is a Homolog ofMi-1

“…For example, new sources of root-knot nematode resistance have been identified in accessions of S. peruvianum (Ammati et al, 1985(Ammati et al, , 1986. Inheritance studies of some of these new resistance traits have revealed the presence of additional genes that segregate independently of Mi-1 (Cap et al, 1993;Veremis and Roberts, 1996b). These genes were distinguished according to resistance phenotype at high temperature or resistance to Mi-1-virulent nematode isolates Roberts, 1996a, 1996b).…”

Fine mapping of the nematode resistance gene Mi-3 in Solanum peruvianum and construction of a S. lycopersicum DNA contig spanning the locus

“…However, Veremis and Roberts (1996) suggested that the two phenotypes were controlled by linked genes, Mi-3 and Mi-5. Possible explanations for the discrepancy with our results include differences in the backgrounds of the parental lines or resistance assay procedures.…”

“…The resistance gene, Mi-3, which confers resistance to Mi-1-virulent root-knot nematode strains, has been mapped to the short arm of chromosome 12 (Yaghoobi et al 1995;Huang et al 2004). In addition, Mi-3, or a closely linked gene, confers resistance at temperatures above 30°C (Yaghoobi et al 1995;Veremis and Roberts 1996).…”

“…Root-knot nematode resistance has been reported in several accessions of the diverse wild species S. peruvianum (Cap et al 1993;Yaghoobi et al 1995;Veremis and Roberts 1996;Veremis et al 1999). Some of these sources carry genes that confer resistance to nematodes that are virulent on strains carrying Mi-1.…”