|Crop Knowledge Master||Fungi|
|(Plant Disease Pathogen)|
(In:Wayne Nishijima's papaya compendium)
Department of Plant Pathology
University of Hawaii at Hilo
Colletotrichum gloeosporioides is known to infect a wide variety of hosts. However, this summary deals specifically with its affects on papaya. Information about the host range of this fungus may be found in other summaries discussing this organism.
This disease is regularly seen in the field on ripe or overripe fruits they are not a serious problem with unrefrigerated fruit sold in the local markets. It is most important on fruits that are refrigerated and exported to overseas markets.
The first symptoms of papaya anthracnose are round, watersoaked, and sunken spots on the body of the ripening fruit. Lesions may become as large as 5 cm in diameter. Pinkish-orange areas are formed by the conidial masses that cover the lesion center and are frequently produced in a [concentric ring pattern].
Symptoms also may appear as irregular to circular spots 1 to 10 mm in diameter, sharply defined, occasionally slightly depressed and reddish-brown in color. These lesions are referred to as "chocolate spots." As the fruit ripens, these spots rapidly enlarge (up to 20 mm in diameter), to form the characteristic circular sunken lesions.
Colletotrichum gloeosporioides also causes anthracnose on papaya leaves.
Colletotrichum gloeosporioides Penz. a facultative parasite belongs to the order Melanconiales. The fungus produces hyaline, one- celled, ovoid to oblong, slightly curved or dumbbell shaped conidia, 10-15 µm in length and 5-7 µm in width. Masses of conidia appear pink or salmon colored. The waxy acervuli, that are produced in infected tissue, are subepidermal, typically with setae, and simple, short, erect conidiophores.
Isolations from the two different lesion types result in isolates of C. gloeosporioides indistinguishable culturally from one another. Each isolate is capable of producing the two different lesion types. The factors involved in influencing a single isolate to produce these different lesion types are not known.
The petioles of papayas support abundant development of C. gloeosporioides and its perfect stage, Glomerella cingulata. However, the petiole isolates, when used to inoculate fruits, do not cause typical anthracnose, chocolate spot, nor the gray-depressed lesions. Also, they do not produce the masses of pinkish-orange conidia on V-8 juice agar that are characteristic of the fruit isolates.
The pathogen initially infects intact, non-wounded immature green fruit in the field. Spores germinate and form appressoria on the fruit surface. The fungus, using its appressorium, enzymatically penetrates the cuticle and then remains as sub-cuticular hyphae until the post climacteric stage of fruit growth is attained. At this point, for reasons that are not understood, the fungus resumes growth and causes the characteristic symptoms. Thus, papaya anthracnose has a latent stage in its development that is similar to many other anthracnose diseases of tropical fruits.
Environmental conditions favoring the pathogen are high temperatures, 28ûC being optimal, and high humidity. Spores must have free water to germinate; germination is negligible below 97% relative humidity. Spores are only released from acervuli when there is an abundance of moisture. Splashing from rain is a common means of spread. Severity of disease is related to weather and the fungus is relatively inactive in dry weather. Sunlight, low humidity and temperature extremes (below 18ûC or greater than 25ûC) rapidly inactivate spores.
Primary inoculum can be disseminated by wind or rain.
Hot water dips at 48ûC for 20 min is an effective treatment for reducing anthracnose incidence. Although hot water dips do not completely eliminate anthracnose the reduction in disease is economically significant.
Orchard sprays applied at 14 - 28 day intervals, depending on rainfall, with an appropriate protective fungicide is commonly recommended. Although no known cultivars of papaya offer complete resistance to anthracnose the Hawaiian cultivar Sunrise Solo is more resistant than Kapoho Solo.
Postharvest fungicides, applied as a spray or dip, with a food-grade wax have also shown to be effective in reducing anthracnose. This is a common practice especially for fruits shipped to overseas markets.
Akamine, E. K., and Arisumi, T. 1953. Control of postharvest storage decay of fruits of papaya (Carica papaya L.) with special reference to the effect of hot water. Proc. Am. Soc. Hort. Sci. 61:270-274.
Bolkan, H. A., Cupertino, F. P., Dianese, J. C., and Taketsu, A. 1976. Fungi associated with pre and postharvest fruit rots of papaya and their control in central Brazil. Plant Dis. Rep. 60:605-609.
Burger, O. F. 1921. Variations in Colletotrichum gloeosporioides. J. Agric. Res. 20:723-735.
Dickman, M. B., Patil, S. S., and Kolattukudy, P. E. 1982. Purification, characterization, and role in infection of an extracellular cutinolytic enzyme from Colletotrichum gloeosporioides Penz. on Carica papaya L. Physiol. Plant Pathol. 20:333-347.
Dickman, M. B., and Alvarez, A. M. 1983. Latent infection of papaya caused by Colletotrichum gloeosporioides. Plant Dis. 67:748-750.
Hunter, J. E., and Buddenhagen, I. W. 1972. Incidence, epidemiology and control of fruit diseases of papaya in Hawaii. Trop. Agric. (Trinidad) 49:61-71.
Trujillo, E. E., and Obrero, F. P. 1969. Anthracnose of papaya leaves caused by Colletotrichum gloeosporioides Plant Dis. Rep. 53:323-325.
Wastie, R. L. 1972. Secondary leaf fall of Hevea brasiliensis: factors affecting the production, germination, and viability of spores of Colletotrichum gloeosporioides. Ann. Appl. Biol. 72:273-282.