Location: Crop Improvement and Protection ResearchTitle: Genetics of resistance in lettuce to races 1 and 2 of Verticillium dahliae from different host species Author
|Sandoya, German - University Of California|
|Gurung, Suraj - University Of California|
|Short, Dylan - University Of California|
|Subbarao, Krishna - University Of California|
|Michelmore, Richard - University Of California|
Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2016
Publication Date: 12/23/2016
Citation: Sandoya, G.V., Gurung, S., Short, D.P., Subbarao, K.V., Michelmore, R.M., Hayes, R.J. 2016. Genetics of resistance in lettuce to races 1 and 2 of Verticillium dahliae from different host species. Euphytica. 213:20. doi: 10.1007/s10681-016-1813-0.
Interpretive Summary: Verticillium wilt is a destructive disease of lettuce caused by the soil dwelling fungus Verticillium dahliae. Complete or high level resistance to race 1 strains of the disease is conditioned by the single dominant gene Verticillium resistance 1 (Vr1) found in the cultivar La Brillante. In addition to La Brillante, multiple morphologically diverse sources of resistance have been identified as resistant to race 1. It is not known if these additional cultivars are resistant due to the presence of Vr1 or a new gene. In this study, we determined that the resistance in these different lettuce cultivars is either due to the Vr1 gene or a different gene that is located close to Vr1 on the plant chromosome. These findings indicate that the cultivars evaluated in this study are essentially equivalent sources of race 1 resistance. The Vr1 gene offers no resistance to race 2 strains of Verticillium wilt. Only partial resistance to race 2 is available in a few Plant Introductions (PIs). Partially resistant plants are not immune to the disease, but exhibit fewer symptoms than currently used cultivars. This research determined that partially resistant PIs exhibit similar levels of resistance to race 1 and race 2 strains when tested in greenhouse and field experiments. Verticillium wilt is a disease of many crops, some of which are routinely grown in rotation with lettuce. Strains of the fungus isolated from these rotational crops can exhibit differences in aggressiveness on lettuce. Cultivars with Vr1 and PIs with partial resistance were challenged with several race 1 and 2 strains originating from crops other than lettuce. These studies found that cultivars with Vr1 are resistant to race 1 strains regardless of the crop the strain originates from; similarly, the partially resistant accessions were effective against race 1 and 2 strains from hosts other than lettuce. Nevertheless, there were specific fungal strain-lettuce host combinations that resulted in unexpectedly high levels of resistance or disease and warrant further study. Although race 1 currently predominates in the major lettuce production area of the Salinas Valley, CA, breeding lettuce for resistance to V. dahliae should take both races into account by combining genes for partial resistance with Vr1.
Technical Abstract: Race 1 resistance against Verticillium dahliae in lettuce was originally shown in the cultivar La Brillante to be conditioned by a single dominant gene (Verticillium resistance 1, Vr1). Multiple, morphologically diverse sources of germplasm have been identified as resistant to race 1. In this study, allelism tests indicated that resistance in these different lettuce cultivars is closely linked or allelic to the Vr1 gene. The Vr1 gene is defeated by race 2 isolates of V. dahliae. Only partial resistance to race 2 isolates is available in a few Plant Introductions (PIs). Greenhouse and field experiments conducted with these PIs demonstrated partial resistance to V. dahliae race 1 as well as race 2 isolates from lettuce. Cultivars resistant to race 1 and PIs with partial resistance to race 2 were challenged with several race 1 and 2 isolates originating from hosts other than lettuce. This indicated that cultivars resistant to race 1 and the breeding lines derived from them would also be resistant to race 1 isolates from other hosts; similarly, the partial resistance would be effective against race 1 and 2 isolates from hosts other than lettuce. Nevertheless, there were specific interactions that warrant further study. Although race 1 currently predominates in the major lettuce production area of the Salinas Valley, CA, breeding lettuce for resistance to V. dahliae should take both races into account.