Exploring wild tomato germplasm for resistance to Tuta absoluta

Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) is native to South America and has rapidly spread in various countries, becoming one of the major threats to tomato crop (Solanum lycopersicum L.). Its range is constantly expanding, spacing up to the North-Western Himalayan Region of India and in the sub-Saharan Africa area. Although this species has a tremendous potential to develop resistance against many insecticides, its control still relies largely on molecules such as organophosphates, pyrethroids, spinosad and diamides. Sustainable control, either based on the use of predators (i.e mirid bugs) and eggs parasitoids (i.e. Trichogrammatidae) or mating disruption (also combined), has been successful only in specific conditions. In this context, the exploitation of resistance traits from wild relative species could offer another sustainable alternative to synthetic insecticides. It is noteworthy that crop wild relatives harbour an abundant supply of resistance genes for biotic and abiotic stresses. We studied two wild tomato backgrounds, Solanum pennellii (acc. LA0716) and Solanum habrochaites (acc. LA1777), using the corresponding populations of introgression lines (ILs and ILSHs) obtained by crossing the processing tomato inbred varieties M82 and E6203 to the wild accessions LA0716 and LA1777, respectively. These lines are expected to exert defence mechanisms able to hamper the attraction and the larval feeding of T. absoluta. Pest resistance of these wild tomato accessions has been related to naturally occurring allelochemicals present in leaf glandular trichomes such as acyl sugars, 2-tridecanone, or sesquiterpenes, especially zingiberene. We have selected a panel of five lines of both IL populations, and have carried out bioassays to compare their effect on T. absoluta to identify genes putatively involved in resistance to this invasive pest. The number of eggs laid over time unit was used as a measure of adult attraction, while antixenosis/antibiosis was measured by recording survival, development time and pupal weight of feeding larvae on tomato leaves. Our work showed that several ILs exhibit an intermediate resistance level, prompting further studies to characterize the specific gene/s involved. Nonetheless, breeding programmes could benefit from these preliminary results.