Inheritance of heat-stable resistance to Meloidogyne incognita in Lycopersicon peruvianum and its relationship to the Mi gene

Abstract

The inheritance of heat-stable resistance to the root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, was studied in crosses between different accessions and clones of Lycopersicon peruvianum L. F1, F2 and BC1 generations were evaluated for their index of resistance based on numbers of eggs and infective second-stage juveniles (J2) per gram of root, and the segregation ratios were determined in experiments carried out at constant soil temperatures of 25 °C and 30 °C. L. peruvianum P.I. 270435 clones 3 MH and 2R2 and P.I. 126443 clone 1 MH, all heatstable resistant, were crossed with L. peruvianum P.I. 126440 clone 9 MH, which is susceptible at both 25 °C and 30 °C. All F1 progeny were resistant at 25 °C and 30 °C; F2 and BC1 generations at 25 °C gave resistant: susceptible (R∶S) ratios of 15∶1 and 3∶1, respectively, which suggests that resistance is conditioned by two independently assorting genes. However, at 30 °C, R∶S ratios of 3∶1 and 1∶1 were observed for the F2 and BC1 generations, respectively. These results indicate that heat-stable resistance is conferred by a single dominant gene expressed at 30 °C, while the second resistance gene is heat unstable and not expressed at 30 °C. P.I. 270435 clones 2R2 and 3 MH and P.I. 126443 clone 1 MH were crossed with P.I. 128657 clone 3 R4 (source of gene Mi), which is resistant at 25 °C but susceptible at 30 °C. All of the F1 progeny were resistant at 25 °C and 30 °C.TC1 progeny of 270435-2 R2 x 128657-3 R4, 270435-3 MH x 128657-3 R4 and 126443-1 MH x 128657-3 R4 crossed with susceptible 126440-9 MH were all resistant at 25 °C and segregated in a 1∶1 ratio at 30 °C. These results also suggest that the heat-stable resistance is monogenic and that it is non-allelic to gene Mi. The non-segregation of TC1 progenies at 25 °C, suggests that the heat-unstable resistance factor in L. peruvianum P.I. 270435 clones 2 R2 and 3 MH and in P.I. 126443 clone 1 MH is allelic to or the same as gene Mi. We propose the symbol Mi-2 for the gene in P.I. 270435 that confers heat-stable resistance to M. incognita.

Selection forMeloidogyne incognita virulence against resistance genes from tomato and pepper and specificity of the virulence/resistance determinants

“…nematodes virulent on Me3-resistant peppers were not able to reproduce on Mel-resistant peppers). Concordant observations had already been made for tomato, in which resistance was found against selected Mi-virulent M. incognita isolates (Roberts et al, 1990), and later identified as partly due to the gene Mi-2 (Cap et al, 1993). Very recently, a new resistance locus was identified in Lycopersicon peruvianum, and this gene, designated Mi-3, was shown to confer resistance against a M. incognita strain that can infect plants carrying Mi (Yaghoobi et al, 1995).…”

Genetic and physical localization of the root-knot nematode resistance locus Mi in tomato

“…Upon digestion with either SacI or BamHI, the band from the resistant parent was cleaved into two fragments, while that of the susceptible parent was not cleaved. Because additional root-knot nematode resistance genes that are unlinked to Mi have been identi®ed in L. peruvianum (Cap et al 1993;Yaghoobi et al 1995;Veremis and Roberts 1996a), F2 progeny were assayed to con®rm segregation of nematode resistance with Milinked markers from the resistant accession.…”

“…L. peruvianum is a heterogeneous species, with accessions and individuals within accessions diering in marker alleles as well as in nematode resistance (Miller and Tanksley 1990;Yaghoobi et al 1995). Several different root-knot nematode resistance genes have recently been identi®ed within accessions of this species (Cap et al 1993;Yaghoobi et al 1995;Veremis and Roberts 1996b, c). We developed a population of plants segregating for resistance due to Mi and identi®ed recombinants with crossovers near Mi by using PCR-based anking markers.…”

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).…”