Distribution of races and virulence factors of Bremia lactucae in the main lettuce production area in Brazil

Abstract

Lettuce downy mildew, caused by Bremia lactucae, occurs throughout São Paulo, the main lettuce production state in Brazil, during winter due to low temperatures and high humidity. Thus, the aim of this work was to monitor the races and virulence factors in São Paulo’s B. lactucae population from 2003 to 2015, and to compare the results with similar studies in other countries. Data from 582 isolates collected from Lactuca sativa cultivars in 33 municipalities of São Paulo were analyzed. Seventeen virulence patterns (races) were identified. Only few races have been stable over the years. The virulence factors v1, v2, v3, v4, v5/8, v7, v10, v11, v12 and v13 have always been present since the first screening in 2003 while the factors v6, v14, v15, v16, v36 and v37 were found in varying frequencies. The population diversity in São Paulo increased over time with five new races emerging in 2014 and 2015. However, the virulence factors identified are the same as previously described in other areas. The races of São Paulo state are similar to the new races from Australia, California, Europe and Japan, grouping in the same clade by analysis the virulence patterns. The genes Dm17, Dm18, R38 and the resistance factors of the cultivars Balesta and Bellisimo can be recommended as source of resistance to the pathotypes characterized to date in São Paulo.