Corynespora Leaf Spot of Papaya (Carica papaya L.) in Puerto Rico

Abstract

The fungus Corynespora cassiicola (Berk. & Curt.) Wei, causal agent of "greasy spot" or "papaya decline" in St. Croix, was found invading papaya plants of both Solo and Puerto Rican varieties in the Gurabo and Isabela Substations and in the Solis field in the Main Station. Plants of both varieties in the field appeared severely affected by the fungus as evidenced by heavy spotting on the foliage and the stems and by premature defoliation of the trees. Pathogenicity tests conducted with three isolates of the fungus isolated from Gurabo (Gurabo isolate), from Isabela (Isabela isolate), and from diseased-papaya plants from St. Croix (Santa Cruz isolate), proved that it is highly pathogenic to both Solo and Puerto Rican papayas. Optimum temperature and optimum pH for growth of the fungus, as well as the best medium for growth and sporulation, were determined. Cultural characteristics, response to varying temperatures, morphology, and symptoms expressed by inoculated plants of both papaya varieties were similar for all three isolates studied.