Abstract
Resistance conferred by the Mi-1 gene from Solanum peruvianum is effective and widely used for limiting root-knot nematode (Meloidogyne spp.) yield loss in tomato (Solanum lycopersicum), but the resistance is ineffective at soil temperatures above 28 degrees C. Previously, we mapped the heat-stable resistance gene Mi-9 in Solanum arcanum accession LA2157 to the short arm of chromosome 6, in a genetic interval as Mi-1 and the Cladosporium fulvum resistance gene Cf2. We developed a fine map of the Mi-9 region by resistance and marker screening of an F2 population and derived F3 families from resistant LA2157 x susceptible LA392. Mi-1 intron 1 flanking primers were designed to amplify intron 1 and fingerprint Mi-1 homologs. Using these primers, we identified seven Mi-1 homologs in the mapping parents. Cf-2 and Mi-1 homologs were mapped on chromosome 6 using a subset of the F2. Cf-2 homologs did not segregate with Mi-9 resistance, but three Mi-1 homologs (RH1, RH2, and RH4) from LA2157 and one (SH1) from LA392 colocalized to the Mi-9 region. Reverse transcriptase-polymerase chain reaction analysis indicated that six Mi-1 homologs are expressed in LA2157 roots. We targeted transcripts of Mi-1 homologs for degradation with tobacco (Nicotiana tabacum) rattle virus (TRV)-based virus-induced gene silencing using Agrobacterium infiltration with a TRV-Mi construct. In most LA2157 plants infiltrated with the TRV-Mi construct, Mi-9-mediated heat-stable root-knot nematode resistance was compromised at 32 degrees C, indicating that the heat-stable resistance is mediated by a homolog of Mi-1.
Highlights
Resistance conferred by the Mi-1 gene from Solanum peruvianum is effective and widely used for limiting root-knot nematode (Meloidogyne spp.) yield loss in tomato (Solanum lycopersicum), but the resistance is ineffective at soil temperatures above 28°C
We identified Mi-1 homologs in the Mi-9 donor S. arcanum accession LA2157 that cosegregate with the heat-stable nematode resistance
We report that the heat-stable rootknot nematode resistance gene Mi-9 is a homolog of Mi-1
Summary
Resistance conferred by the Mi-1 gene from Solanum peruvianum is effective and widely used for limiting root-knot nematode (Meloidogyne spp.) yield loss in tomato (Solanum lycopersicum), but the resistance is ineffective at soil temperatures above 28°C. Tomato (Solanum lycopersicum, formerly Lycopersicon esculentum; Peralta and Spooner, 2005) is a highly susceptible host of several species of root-knot nematodes and incurs yield losses from root-knot infection in warm temperate to tropical regions as well as in greenhouse and other controlled environment production systems. Nematode Resistance Gene Mi-9 Is a Homolog of Mi-1 root-knot nematode R genes, having been described in other crop species, including alfalfa (Medicago sativa; Griffin, 1969), sweet potato (Ipomoea batatas; Jatala and Russell, 1972), and cotton (Gossypium hirsutum; Carter, 1982)
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