Characterization of tomato mosaic virus and search for its resistance in Solanum species

Abstract

Tomato mosaic virus (ToMV) is a consistent problem threatening tomato production worldwide, including Pakistan. In this paper, we report characterization of a ToMV strain from naturally infected tomato in Pakistan and response of 128 diverse tomato genotypes to identify potential resistance sources in Solanum and its related wild species that can be incorporated into breeding programs. Upon ToMV inoculation, local necrotic lesion developed within 1 wk on plants of Nicotiana tabacum var. xanthi, N. tabacum var. glutinosa, Chenopodium album and Datura alba except N. tabacum var. K-399 which showed systemic mosaic symptoms. Coat protein (CP) sequence of ToMV strain (GenBank accession No. MG975645) in present study showed a high level of similarity with the sequence of different ToMV strains submitted in GenBank NCBI. Of 128 tomato genotypes inoculated with ToMV-Pak in controlled conditions, 13 were highly resistant, three resistant, 24 tolerant, 62 susceptible and 26 highly susceptible against ToMV. Among highly resistant germplasm, one genotype (LO6170 with unknown ToMV-resistant gene) and 11 genotypes with ToMV-resistant gene (Tm-22) belonged to cultivated Solanum lycopersicum whereas one genotype (LA0111) belonged to the wild species, S. arcanum. Presence of Tm-22 in the 11 highly resistant genotypes was confirmed using CAPS marker in PCR. Of resistant genetic resources, LB2 belonged to S. lycopersicum, LO6122 to S. arcanum and LO4166 belonged to S. pimpinellifolium. Presence or absence of ToMV in all the tested genotypes plants was confirmed using ELISA and its absence in symptomless highly resistant genotypes with negative ELISA results were further confirmed using RT-PCR. Resistant genotypes of S. lycopersicum identified in the present study can be easily used for heterosis and recombination breeding aiming to develop high yielding and ToMV tolerant cultivars. However, wild genotypes resistant to ToMV can be used in a wide hybridization breeding programme with cultivated S. lycopersicum keeping in view the genetic barriers and appropriate pattern of crossing.