Resistance to western flower thrips, Frankliniella occidentalis (Pergande), a vector of tomato spotted wilt tospovirus in wild Lycopersicon species

Tomato spotted wilt tospovirus (TSWV) is transmitted by the western flower thrips (WFT), Frankliniella occidentalis. Host plant resistance offers the best long-term strategy for TSWV management. A comparison of mechanical and thrips inoculation of TSWV across selected Lycopersicon accessions resulted in systemic infection in all accessions except Lycopersicon Peruvianum. However, rate of infection varied within and between inoculation methods. Lycopersicon peruvianum, L. chilense and L. pennellii were least susceptible to TSWV. With thrips inoculation, infection rates were significantly lower on L. hirsutum f. glabratum and cultivars 'Anahu', 'Manzana and Rey de los Tempranos. Thus, mechanical inoculation was most useful in identifying direct resistance while thrips inoculation indicated the importance of vector mediated components of TSWV resistance. Field evaluation of tomato accessions indicated significant differences in WFT landing on individual flowers but not on unit leaf. Cultivar 'Anahu' was infected with TSWV at the seedling stage while cv 'Pearl Harbor', L. parviflorum and L. hirsutum succumbed only after flowering. Field resistance to TSWV was observed in L. chmielewskii, L. chilense, L. hirsutum f. glabratum, L. peruvianum, L. pimpinellifolium and cultivar 'Rey de los Tempranos'. Our results indicated that susceptibility of accessions to TSWV and behavioral complexities at thrips/plant interface are more important in influencing the incidence of TSWV on tomatoes under field conditions than landing behavior or direct resistance to insect colonization. 'Thumbtack assay' bioassay to determine antixenosis revealed very high antixenosis to WFT nymphs in L. hirsutum, L. hirsutum f. glabratum and L. pennellii and moderate antixenosis in L. chmielewskii and L. chilense'. Leaf choice assay indicated highest feeding preference for L. peruvianum and least for L. hirsutum. Significant negative relationship between antixenosis and extent of feeding damage was observed across all accessions. Flowers did not exhibit any resistance to WFT. Evidences based on antixenosis, feeding preference and feeding damage to Lycopersicon leaves (as observed under scanning and transmission electron microscope) suggest that complex multiple resistant components are involved in limiting thrips transmission of TSWV.