Resistance to Thrips tabaci in onion wild relatives, and the role of intraspecific thrips diversity in overcoming resistance

Onion ( Allium cepa L.) is one of the most important horticultural crops worldwide, and Thrips tabaci is the main pest on it. It is a polyphagous, often insecticide-resistant, cryptic species with two main phylogenetic groups characterized by host range and reproductive modes: arrhenotokous and thelytokous. Host plant resistance, mainly antibiosis-type, is a promising solution for preventing or reducing T. tabaci population build-up. Resistant sources are absent in onion germplasm, but present in wild relatives. We determined the resistance mechanisms present in resistant (R) and moderately resistant (MR) onion wild relatives, and whether arrhenotokous and thelytokous (heteroplasmic or non-heteroplasmic) T. tabaci differ in overcoming this resistance. Oviposition rate, survival rate of T. tabaci immature stages, and length of the immature period from L1 to pupae were determined on R, MR, and susceptible Allium genotypes infested with arrhenotokous and thelytokous populations. The R species, A. prostratum , A. komarowii , and A. flavescens, block the cycle of arrhenotokous and thelytokous T. tabaci in the L1 or L2 stage. Allium prostratum showed antibiosis, while A. flavescens and A. komarowii showed antibiosis and antixenosis. The MR species, A. angulosum , A. senescens , and A. eduardii, partially impede the life cycle through antixenosis and antibiosis. Heteroplasmic and non-heteroplasmic thelytokous T. tabaci did not statistically differ, and they overcome the MR mechanisms better than arrhenotokous T. tabaci . Arrhenotokous showed a higher oviposition rate and lower survival (as specialists) than the thelytokous (generalists). Some of the identified sources, especially Allium prostratum , may be suitable for introgressing resistance into cultivated onion .