|Crop Knowledge Master||Fungi|
|fruit spot on papaya (Plant Disease Pathogen)|
Wayne Nishijima, Extension Plant Pathologist
Department of Plant Pathology
University of Hawaii at Hilo
This Guignardia sp. has been described as occurring only on papaya in Hawaii.
The disease is characterized by usually numerous, circular to oval, sunken greenish-black lesions up to about 15 mm diameter. Lesions expand in diameter very slowly but the fungus may grow deep into the flesh causing a black, firm discoloration.
This disease is caused by an unidentified Guignardia sp. Occurrence of the disease has been sporadic but heat stress from postharvest quarantine treatments has been implicated as a predisposing factor. The disease was most common on fruits that were double hot water treated using the original schedule of 40 min at 42ûC followed by 20 min at 49ûC. Its occurrence was drastically reduced when the first stage treatment time was reduced to 30 min. The disease occasionally occurs when the time between the second hot water dip and tap water shower to cool fruits to near ambient is delayed longer than 3 min.
Ascospores of Guignardia citricarpa Kiely are found in the airspora of papaya orchards year round in Hawaii at a spore density of 1-10 ascospores/m3. Ascospores are ellipsoid to fusiform, hyaline, single-celled, often curved and measured 12-21 x 4-8 µm. Ascospores were characterized by a slight swelling near the center of the spore. It is unknown whether this species is the cause of this disorder.
Control of this disease requires close monitoring and accurate control of postharvest quarantine heat treatments. Any excessive heating times or temperatures or the delay of cooling may result in the fruits overheating and predisposing them to this disease.
Alvarez, A.M., and Nishijima, W.T. 1987. Postharvest diseases of papaya. Plant Dis. 71:681-686.
Zimmer, R. 1969. Air-spora studies of certain fungus pathogens of papaya and passion fruit in Hawaii. M.S. Thesis, Univ. of Hawaii, Honolulu, Hawaii, 42 pp.