Evaluation of lettuce germplasm for resistance to impatiens necrotic spot virus

Abstract

Recently, impatiens necrotic spot virus (INSV) has emerged as a major pathogen of lettuce in the Salinas Valley of California. The virus is a member of the genus Orthotospovirus, and under natural conditions, is transmitted by the tiny insect, western flower thrips. Due to the high efficiency of virus transmission, chemical management of thrips vectors is often ineffective in preventing the spread of the disease. Utilization of genetic resistance will be a critical component for managing the disease; however, little is known about genetic sources of resistance in lettuce. Here, we evaluated 189 lettuce lines under natural disease pressure in four field experiments to identify INSV resistant germplasm. The stability of resistance was also evaluated using different inoculation methods under controlled conditions. Our results showed a significant variation (p < 0.0001) among lettuce cultivars for both INSV severity and incidence. We identified INSV resistant germplasm that belongs to different horticultural types and leaf color, including a red-leaf cultivar ‘Eruption’ with a high degree of genetic stability. Moreover, we characterized several factors influencing thrips and host plant relationships, including horticultural type, leaf color, and polyphenol concentration. Overall, INSV resistant germplasm identified in this study provide valuable resources for breeding of INSV resistant lettuce cultivars.