Identification of transgressive segregants for resistance to race 2 isolate of Verticillium dahlia in F2:3 segregating generation of lettuce

Authors: Nayak, Santosh; Richardson, Kelley

Submitted to: American Society of Horticulture Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/7/2021
Publication Date: 8/7/2021
Citation: Nayak, S., Richardson, K.L. 2021. Identification of transgressive segregants for resistance to race 2 isolate of Verticillium dahlia in F2:3 segregating generation of lettuce. American Society for Horticultural Science Annual Conference, August 5-9, 2021, Denver, Colorado.

Interpretive Summary:

Technical Abstract: Lettuce (Lactuca sativa L.) is one of the most important leafy vegetable crops in the USA, more specifically in the Salinas Valley of California which alone contributes approximately 50% of national production. Lettuce commercial acreage is greatly threatened by verticillium wilt caused by two races (Race 1 and 2) of the fungus Verticillium dahliae Kleb. Resistance to Race 1 is governed by a single dominant gene (Vr1) and effective in many commercial cultivars. In contrast, resistance to Race 2 is known to be polygenic and only a few accessions have been identified that provide partial resistance i.e. a reduction in disease incidence and severity. Therefore, the development of improved lettuce germplasm with a high level of resistance to Race 2 is imperative. This study was conducted to identify transgressive segregants in progeny from a cross between the two most Race 2 resistant accessions: PI 171674 (L. sativa) and 11G99 (L. serriola). Fifty-four F2:3 families were screened for resistance against Race 2 isolate of V. dahlia (VdLs17). The experiment was conducted in a randomized complete block design under two controlled environments: greenhouse and growth room. Disease resistance was assessed as vascular discoloration severity (VDS) of taproot using a 0 to 5 scale (0=no vascular discoloration, 5=100% vascular discoloration) at 13 weeks after sowing. The results showed a significant variation (p < 0.05) among entries for VDS across two environments as well as within each environment. As expected with a genetic background of two resistant parents, VDS data of F2:3 families were skewed to the lower end of the rating scale and 37% families showed a lower VDS than both parents. Entries did not perform differently under greenhouse and growth room conditions, but roots with higher symptom severity were observed in the growth room. Progeny were selected based on a lower VDS and other traits such as leaf color, leaf shape, bolting, and flowering. We continue to evaluate 258 F2:3 families to identify potential transgressive segregants.