Genetic and physiological determinants of lettuce partial resistance to Impatiens necrotic spot virus

Authors: Simko, Ivan; Hasegawa, Daniel; PENG, HUI - University Of California; Zhao, Rebecca

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2023
Publication Date: 6/8/2023
Citation: Simko, I., Hasegawa, D.K., Peng, H., Zhao, R.B. 2023. Genetic and physiological determinants of lettuce partial resistance to Impatiens necrotic spot virus. Frontiers in Plant Science. 14. Article 1163683. https://doi.org/10.3389/fpls.2023.1163683.
DOI: https://doi.org/10.3389/fpls.2023.1163683

Interpretive Summary: Impatiens necrotic spot virus (INSV) is a major pathogen currently threatening lettuce production in the coastal areas of California. The virus is transmitted by the western flower thrips. We have tested a almost 500 lettuce accessions for disease incidence in 12 field experiments performed over seven years. This set of accessions was also assessed for thrips feeding damage, the rate of plant development, and the content of chlorophyll and anthocyanins to determine their effect on resistance to INSV. In addition, recombinant inbred lines from two biparental mapping populations were also evaluated in field experiments. The mean disease incidence in 14 field experiments ranged from 2.1% to 70.4%. A highly significant difference in disease incidence was observed among the tested accessions, with the overall lowest DI detected in the red color cultivars, Outredgeous Selection, Red Splash Cos, Infantry, Sweet Valentine, Annapolis, and Velvet. Accessions with lower disease incidence values a had slower plant development, higher anthocyanin content, less thrips feeding damage, and lower chlorophyll content. We have identified 16 loci associated with disease incidence, with the most frequently detected locus located on chromosome 2. The work highlights the genetic basis of partial resistance to INSV and reveals the relationship between resistance, the host physiology, and the thrips vector. Results of this study are an important steppingstone towards developing cultivars with increased resistance against INSV.

Technical Abstract: Impatiens necrotic spot virus (INSV) is a major pathogen currently threatening lettuce (Lactuca sativa L.) production in the coastal areas of California. The virus is transmitted by the western flower thrips (Frankliniella occidentalis Pergande). We have tested a diversity panel of almost 500 lettuce accessions for disease incidence (DI) in 12 field experiments performed over seven years. This set of accessions was also assessed for thrips feeding damage (TFD), the rate of plant development (PD), and the content of chlorophyll (SPAD) and anthocyanins (ACI) to determine their effect on resistance to INSV. In addition, recombinant inbred lines (RIL) from two biparental mapping populations were also evaluated for DI in field experiments. The mean DI in 14 field experiments ranged from 2.1% to 70.4%. A highly significant difference in DI was observed among the tested accessions, with the overall lowest DI detected in the red color cultivars, Outredgeous Selection, Red Splash Cos, Infantry, Sweet Valentine, Annapolis, and Velvet. Multiple linear regression models revealed a small, but significant effect (p < 0.005) of the four analyzed determinants on DI. Accessions with lower DI values a had slower plant development (PD, r = 0.352), higher ACI content (r = - 0.284), lower TFD (r = 0.198), and lower SPAD content (r = 0.125). Genome-wide association mapping (GWAS) revealed 13 QTLs for DI located on eight out of the nine lettuce chromosomes (the exception was chr. 8). The most frequently detected QTL (qINSV2.1) was located on chr. 2. Several of the QTLs for DI were in the same genomic areas as QTLs for PD, ACI, and SPAD. Additional three QTLs for DI on chr. 5 and 8 were identified using linkage mapping performed on two biparental mapping populations. The work highlights the genetic basis of partial resistance to INSV and reveals the relationship between resistance, the host physiology, and the thrips vector. Results of this study are an important steppingstone towards developing cultivars with increased resistance against INSV.