Evaluation of lettuce germplasm for resistance to Impatiens necrotic spot virus

Authors: Richardson, Kelley; Nayak, Santosh; Hasegawa, Daniel; Eriksen, Renee

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2023
Publication Date: 2/12/2024
Citation: Richardson, K.L., Nayak, S., Hasegawa, D.K., Eriksen, R.L. 2024. Evaluation of lettuce germplasm for resistance to Impatiens necrotic spot virus. Euphytica. 220. Article 33. https://doi.org/10.1007/s10681-023-03285-z.
DOI: https://doi.org/10.1007/s10681-023-03285-z

Interpretive Summary: Lettuce is one of the most valuable agricultural commodities in California, with a revenue of ~2.3 billion dollars in 2021. Impatiens necrotic spot virus (INSV) has become a major disease of lettuce in Monterey County and causes significant economic losses. The best way to control INSV is to plant completely resistant varieties, but none are available. In this paper, we present results of evaluation of 189 cultivars and breeding lines to identify resistant lines and assess stability of resistance in field and greenhouse experiments. Factors affecting thrips and lettuce relationships were also examined. We determined the red-leaf cultivar ‘Eruption’ was resistant with a high degree of stability.

Technical Abstract: Recently, Impatiens necrotic spot virus (INSV) has emerged as a major disease of lettuce in the Salinas Valley of California. This disease is caused by Impatiens necrotic spot virus, a member of genus Orthotospovirus. Under natural conditions, the disease is transmitted by western flower thrips from a sick plant to healthy plant. Both the virus and thrips have a broad host range that makes chemical control methods prohibitive and often ineffective to prevent the spread of this disease. Therefore, use of genetic resistance is the most sustainable control method; however, little is known about genetic sources of INSV resistance in lettuce. Lettuce germplasm (189 cultivars and breeding lines) was evaluated under natural infection conditions across four field experiments to identify resistant lines and assess stability of resistance under different inoculation methods in controlled conditions. Factors affecting thrips and host plant relationships were also examined. Results showed a significant variation (p < 0.0001) among lettuce cultivars for both INSV severity and incidence. INSV resistant germplasm was identified that belongs to different horticultural types and leaf color, including a red-leaf cultivar ‘Eruption’ with a high degree of genetic stability. Several factors can influence thrips-host plant relationships, including horticultural types, leaf color, and polyphenol concentration that contribute to INSV resistance. Overall, INSV resistant germplasm identified in this study provide valuable resources for breeding of INSV resistant lettuce cultivars.