Direct and cross-pathogenicity of Phytophthora palmivora against cacao, papaya, and peach palm

Phytophthora palmivora is a plant pathogen that affects cacao, papaya and peach palm, which are often intercropped in Bahia, in the Northeast of Brazil. The objectives of this study were to find answers to the following questions: Is there variability in the aggressiveness of pathogen isolates to their respective hosts? Can isolates derived from one host infect another? A total of 150 P. palmivora isolates derived from cacao (85), papaya (36), and peach palm (29) were inoculated on leaf discs of their respective hosts to study pathogenicity. For cacao, two clones were used. Inoculum was applied to leaf discs of cacao, peach palm, and papaya at a concentration of 3 × 10 5 zoospores/mL, and evaluations were performed, respectively, 7, 5, and 4 days later. Twelve, seven, and five isolates taken from cacao, papaya, and peach palm, respectively, were inoculated on leaf discs of the three hosts to determine cross-pathogenicity. The aggressiveness of the isolates against their respective hosts was variable and all 24 isolates caused lesions on the leaf discs of the three hosts. Isolates from one host were observed to infect others as well. Isolates from cacao, papaya, and peach palm were highly aggressive against their own host, although a few isolates from other hosts were among the most aggressive against these three hosts.