Evaluation of tomato cultivars for resistance to Tuta absoluta (Lepidoptera : Gelechiidae)

Abstract

Cultivated tomato, Solanum lycopersicum L., is the second-most important herbaceous vegetable after potato, both in the world and South Africa. It is cultivated in all nine provinces of South Africa with an estimated annual gross value of over R2 billion. However, the introduction of the tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), during late 2016, brought uncertainties for the tomato industry. Tuta absoluta causes significant crop losses due to its leaf-mining activity. The current pest management tactics rely on chemical control, which cannot be sustained indefinitely. Host plant resistance is a valuable component of any integrated pest management strategy. It affects important life history parameters of herbivorous species through antixenosis and antibiosis, or a combination of these two resistance mechanisms. The aim of this study was to evaluate tomato accessions for resistance to T. absoluta. In doing so, behavioural responses of T. absoluta were determined and morphological characteristics (leaf trichome type and density) responsible for resistance identified. The accessions included four commercially available cultivated accessions viz. Moneymaker, Commander, Emerald and Esty, one interspecific cross (L. lycopersicum × L. habrochaites f. glabratum, accession PI 134417, and two wild species (L. habrochaites f. typicum, accession LA 1777 and L. habrochaites f. glabratum, accession PI 134417). To determine the feeding preference of T. absoluta larvae, third-instar larvae were used for larval feeding bioassays conducted under laboratory conditions at 26 ± 1 oC, 65 ± 5% RH and 14L: 10D photoperiod. Larvae showed equal preference for the cultivated accessions, LA 1777 and the Cross. Wild accession PI 134417 was significantly less preferred when compared to cultivated accessions. The results for larval development times showed that neonate larvae had difficulty in establishing (antixenosis) and developing (antibiosis) on LA 1777, PI 134417 and the Cross. Only a few larvae were able to complete their life cycles on wild accession LA 1777 and none was able to do so on PI 134417 and the Cross. Cultivated accessions were suitable host plants for T. absoluta as larvae had shorter development times when compared to LA 1777. The mass of pupae reared on this accession and the cultivated accessions showed no significant difference despite the low survival rate on LA 1777. Female moths showed low preference for wild accessions. When the extent to which T. absoluta larvae can feed on these accessions was quantified under semi-field conditions, larvae showed similar responses as when under laboratory conditions, except for the Cross, which was not included. The morphological characteristics assumed to be responsible for resistance to T. absoluta in wild accessions and the Cross is most likely the presence of glandular trichome type 4, which was not present in cultivated accessions. Despite the high density of trichome type 4 observed on LA 1777, T. absoluta resistance in this study was most likely related to the kind of exudates produced, rather than density. Further studies are required to understand the mechanisms of resistance that are present in the wild accessions and the Cross.