Inheritance of partial resistance to isolate VdLs17 of Verticillium dahliae within Lactuca spp.

Authors: Nayak, Santosh; Richardson, Kelley

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2023
Publication Date: 12/1/2023
Citation: Nayak, S., Richardson, K.L. 2023. Inheritance of partial resistance to isolate VdLs17 of Verticillium dahliae within Lactuca spp. Plant Disease. 107(12):3868-3876. https://doi.org/10.1094/PDIS-09-22-2194-RE.
DOI: https://doi.org/10.1094/PDIS-09-22-2194-RE

Interpretive Summary: Lettuce is one of the most valuable agricultural commodities in California, with a revenue of ~2.3 billion dollars in 2020. Verticillium wilt disease imposes a serious threat to lettuce production and often results in near-total loss. It is caused by three races (race 1, 2, and 3). Among these, race 1 is predominate across major lettuce growing regions of California. Incidence of race 2 is reported from limited fields, whereas incidence of race 3 is unknown. Race 1 resistant varieties have been bred and released, but nothing has been identified to date which provide complete resistance to race 2. The present study was designed to understand the complex genetics of race 2 resistance in lettuce using a population from two partially resistant accessions and to determine if favorable genes could be combined. Our results indicate that resistance to race 2 is controlled by two major genes. However, inhibitory gene interaction and environmental factors create a challenge for combining favorable genes from partially resistant germplasm.

Technical Abstract: Lettuce (Lactuca sativa L) production is greatly threatened by Verticillium wilt caused by three pathogenic races (race 1, 2, and 3) of the soilborne fungus Verticillium dahliae. Race 1 is predominant and resistant varieties have been bred and released that provide full protection conferred by the Vr1 gene. However, heavily relying on race 1 resistant cultivars could shift the population towards resistance-breaking isolates and impact durability of plant resistance. This study was conducted to determine the inheritance pattern of race 2 (VdLs17) resistance in lettuce using 258 F2:3 progeny generated from a cross between two partially resistant accessions 11G99 (L. serriola) and PI 171674 (L. sativa). Experiments were performed in three controlled environments across three years using a randomized complete block design. Segregation analysis was conducted to determine the inheritance pattern of race 2 resistance in this population. The results indicate that the inheritance of V. dahliae race 2 resistance followed a genetic model of two major genes with additive-dominance-epistatic effects. Transgressive segregants were infrequent but observed in both directions, indicating that favorable and adverse alleles are dispersed in both parents. Combining favorable alleles of these two partially resistant parents appears to be challenging because of epistatic effects and a significant role of environment on disease severity. The probability of capturing favorable additive genes could be maximized by generating and evaluating a large population and making selection at late generation. This study provides valuable insights on the inheritance pattern of V. dahliae race 2 resistance in lettuce that would be helpful in designing the most efficient breeding strategy and highlights controlled environment conditions ideal for evaluating Verticillium wilt severity.