ASHS 2025 Conference

Recently, Impatiens necrotic spot virus (INSV), transmitted by the western flower thrips (Frankliniella occidentalis), has emerged as a major limiting-factor in lettuce production, causing up to 100% yield losses in California. Florida, the third-largest lettuce-producing state in the US, following California and Arizona, cultivates approximately 11,000 acres of lettuce annually. While cases of INSV have not been reported in Florida lettuce, F. occidentalis is a common pest in many crops in Florida including lettuce, the virus poses a significant threat to lettuce crops if introduced. Since INSV is exclusively transmitted by thrips, effective thrips management is crucial to mitigate its impact. Currently, management of F. occidentalis mainly relies on pesticides, however, over-reliance on pesticides may lead to insecticide resistance and further raising environmental and health risks. An integrated pest management approach, incorporating thrips-resistant lettuce cultivars as a first line of defense, could provide a sustainable solution to mitigate the possible negative effects of INSV. The aim of this study was to identify lettuce germplasm with resistance to F. occidentalis. In no-choice experiments, 39 lettuce germplasms including commercial cultivars were evaluated for the resistance to F. occidentalis. These germplasms were planted under thrips-free conditions and plants were placed individually to thrips-proof container and infested with 7 female thrips when they developed 5-6 true leaves. The thrips colony was reared on Okeechobee cultivar, a cultivar susceptible to other sap-feeding insects, which was also used as control for the experiments. Fourteen days post-infestation, the number of larvae and adult thrips per plant. Experiments were conducted in an insectary room maintained at 25 ± 1 °C with a photoperiod of 16-hour light and 8-hour dark. Five replicates (plants) were conducted for each lettuce germplasm. Several germplasms, including breeding lines 50100, 70096, and 70882, cultivars such as Bambino, La Brillante, Manatee, Emperor, Hacienda, and Valmaine, as well as plant introductions (PI) 204707 and 251246, exhibited significantly less larvae (Alpha level 0.05) than Okeechobee, suggesting resistance to F. occidentalis. On the other hand, breeding line 60183 and Gator had significantly higher number of larvae thrips than Okeechobee suggesting high susceptibility to F. occidentalis. These findings highlight promising candidates for further identification of genomic regions responsible for resistance against F. occidentalis and to develop resistant lettuce cultivars that could be a first-line of defense against INSV. Since INSV has not been reported in Florida, this underscores the importance of proactive resistance breeding efforts to prevent potential outbreaks.