Characterization of Solanum habrochaites-based Resistance Against the Tomato-Potato Psyllid

The tomato-potato psyllid (TPP), Bactericera cockerelli, vectors the phloem-limited bacteria Candidatus Liberibacter solanacearum (Lso), the causative agent of economically important plant diseases in Solanaceae species including the tomato vein-greening and potato zebra chip. The appearance of TPP-Lso in potato, tomato, and pepper fields has resulted on millions of dollars in losses. As a result, in the absence of commercial resistant cultivars to both the vector and the pathogen, growers have dramatically increased pesticide use to control the vector. In tomato (Solanum lycopersicum), resistance against the insect vector has been recently reported in wild relative specie S. habrochaites. The objective of this project was to characterize S. habrochaites based resistance to ultimately introgress it into cultivated tomato. In order to study inheritance and characterize resistance, the backcross recombinant inbred lines representing the genome of S. habrochaites accession LA17777 in S. lycopersicum background were obtained from the Tomato Genetics Resource Center at UC-Davis and screened for adult mortality and fecundity. The introgression lines consist of a core set of 57 lines that provide good genome representation with a minimum number of segments in each line. The RIL, susceptible tomato cv MoneyMaker and resistance source S. habrochaites LA17777 were infested with two adult males and two females in a no-choice test using clip cages. Adult survival and fecundity (total number of eggs and nymphs) was recorded 10 days after. No alive adults and nymphs were found in LA17777, and only 3 eggs were found in one of the replicated plants. Unfortunately, no single RIL showed the same level of resistance as the source. However, lower fecundity and survival as compared to susceptible control was observed in seven RILs, suggesting that resistance in LA17777 involves more than one gene. Four of those RILs had overlapping chromosome introgressions on chromosomes 5 and 8, therefore it was concluded that at least five introgressed segments located in chromosomes 2,3,5,6, and 8 contributed to resistance. Furthermore, the resistance factor on chromosomes 2 appear to contribute to reduced fecundity but does not affect survival, while segments in chromosomes 3, 5, and 8 contribute to both adult increased mortality and lower fecundity. Finally, introgression on chromosome 6 contributes to adult increased mortality, however higher number of eggs were observed. Identified introgression lines carrying resistance factor(s) will be crossed with advanced tomato breeding lines to develop resistant population(s).