Advances in plum breeding for resistance to Xylella fastidiosa in Brazil
Xylella fastidiosa, the causal agent of plum leaf scald, was introduced in Brazil in the 1960s, leading to the death of most plum orchards. Lately, with the identification of medium resistance cultivars, such as Laetitia and Fortune, plum cultivation resumed its importance. However, infected orchards are generally short-lived, which increases production costs. This bacterium is widespread in the main producing regions due to the presence of insect vectors (leafhoppers) and native hosts. A plum breeding program has been developed since 1990 in Santa Catarina State, Brazil, focusing on leaf scald resistance. Initially, resistant materials from Argentina and Florida were used as sources of resistance. These materials are infected with the bacterium but the symptoms are mild or not visible. After generations of crosses made to combine leaf scald resistance and fruit quality some genotypes showed resistance levels even higher than the resistant parentals. Some plum selections are not infected in the field but transmission occurs when grafted over infected plants. Apparently, there is a mechanism that interferes in the transmission by insect vectors (leafhoppers). One example is the cultivar Zafira, recently released. It was observed that the leafhopper Sibovia sagata has a clear preference for feeding on Laetitia compared to Zafira. In the field, the number of vector insects captured in yellow adhesive traps placed within the canopy of Zafira is much lower than in Fortune, suggesting the presence of repellent compounds. More recently, plum genotypes apparently immune have been identified. They are negative for Xylella by PCR tests even when grafted over infected trees. These materials will be used in future crosses for more durable resistance and possibly immunity to the disease.
Dalbó, M.A., Menezes-Netto, A.C., Bruna, E.D., Thomazi-Kleina, H. and May-de-Mio, L.L. (2021). Advances in plum breeding for resistance to Xylella fastidiosa in Brazil. Acta Hortic. 1322, 19-24
Prunus salicina, disease resistance, plum leaf scald