|Crop Knowledge Master||Fungi|
|anthracnose fruit rot (Plant Disease Pathogen)|
Stephen A. Ferreira, Extension Plant Pathologist
Rebecca A. Boley, Educational Specialist
Department of Plant Pathology,CTAHR
University of Hawaii at Manoa
In Hawaii, this pathogen is known to affect watermelon, muskmelon, cantaloupe, winter squash (Cucurbita maxima), and bittermelon (Momordica charantia). Reported hosts from areas other than Hawaii are cucumbers, eggplant, gourd, sponge gourd (luffa), chayote, citron, and pumpkin.
Temperate, subtropical and tropical regions.
All aboveground plant parts are affected. Leaf spots first appear as yellowish or water-soaked areas that enlarge, turn brown, and become brittle. Leaf spots on watermelon turn black. Spots on petioles and stems are elongated and dark with a light center and can result in vine defoliation.
Fruit becomes susceptible to infection near the time of ripening. Cankers are the most noticeable symptoms on fruit. Cankers are circular, black, sunken lesions and often vary in size (both diameter and depth). Lesions expand rapidly in the field and during transit or storage and may coalesce to form larger ones. When moisture is present, the black center of the canker is filled with a gelatinous mass of pink (salmon-colored) spores (conidia). Cankers do not penetrate the flesh of the fruit, but can cause the fruit to be tasteless or bitter. Afflicted fruits are likely to be destroyed by soft rot organisms that gain entrance through the broken rind (the canker).
A synonym for Colletotrichum lagenarium is C. orbiculare (Berk. & Mont.) Arx. (some articles refer to this as the correct name and C. lagenarium as the synonym). Gloeosporium lagenarium is similar, if not identical, to C. lagenarium. The sexual or perfect stage (teleomorph) is Glomerella lagenarium.
C. lagenarium can infect a plant successfully at any stage of growth. When moisture is present, the spore germinates and a penetration tube enters the plant within three days. Invaded tissues die and form a canker followed by the production of spores which are then ready to repeat the infection process.
Colletotrichum produces conidia in acervuli (the canker). Masses of conidia attain a pink or salmon color. Conidia are released from the acervuli and come into contact with susceptible plant and/or fruit hosts and germinate when water is present and temperatures are optimal (20-32 C). The conidia germinate and penetrate host tissues directly.
The conidia (spores) are released and spread only when the acervuli are wet and are generally spread by splashing water and blowing rain or by coming into contact with insects, other animals (including humans), and tools. The fungus can overwinter as mycelium on or in seed and on residue from diseased plants in and on the soil. The fungus can also live in weeds of the cucurbit family.
Crop rotation, good drainage, the use of resistant varieties when available, and the destruction of wild cucurbits are important control practices. Seed treatment with mercuric chloride or other mercury compounds will destroy surface inoculum but does not affect any fungus under the seed coat.
Resistant cultivars reduce the rate of disease development. However, when conditions are favorable for the pathogen, even the most resistant cultivars can fall to severe epidemics. The use of resistant cultivars will also help decrease fungicide rates and doses. Cucumber varieties and their resistance include: Calico (highly resistant), Calypso (moderately resistant), Marketer (more susceptible), SMR-58 (more resistant than Marketer), and Earlipik 14 (susceptible) (Thompson and Jenkins, 1985a).
There is an increasing intrest in controlling or curbing disease incidence by immunizing plants to some bacterial, viral, and fungal plant pathogens (including C. lagenarium) by exposing them to C. lagenarium. Separate studies have reported that C. lagenarium can protect cucumber against 13 pathogens. Immunization is systemic and requires a 3-4 day lag period between inoculation and exposure to the pathogen followed by a booster inoculation to maintain protection through fruiting. Reportedly, C. lagenarium inoculated onto immunized plants does not reduce conidial germination, but reduces penetration of the pathogen into plant tissues.
A fungicidal trial from India (Prakash et. al., 1974) tested six fungicides. Benlate (0.2 %) and difolatan (0.3 %) provided the best control (applied at weekly intervals for five weeks, starting approximately 3 weeks after inoculation). Benlate treated plots also gave significantly higher yields than plots treated with other fungicides.
Agrios, G.N., ed. 1988. Plant Pathology, 3rd ed. Academic Press. New York. pp. 379-390.
Chupp, C. and A.F. Sherf. 1960. Vegetable diseases and their control. The Ronald Press Company, New York. pp. 295-299.
Ishida, N. and S. Akai. 1969. Relation of temperature to germination of conidia and appressorium formation in Colletotrichum lagenarium. Mycologia 61:382-286.
Kuc, J. 1990. Immunization for the control of plant disease. In Biological Control of Soil-borne Plant Pathogens. Edited by D. Hornby. CAB International, Redwood Press Ltd., Melksham, Wiltshire. pp. 355-373.
MacNab, A.A., A.F. Sherf, and J.K. Springer. 1983. Identifying diseases of vegetables. The Pennsylvania State University, University Park, PA.
Prakash, O., H.S. Sohi, and S.S. Sokhi. 1974. Studies on anthracnose disease of cucurbits caused by Colletotrichum lagenarium (Pass.) Ell. & Halst. and its control. Indian J. Horticulture 31:278-282.
Thompson, D.C., and S.F. Jenkins. 1985a. Influence of cultivar resistance, initial disease, environment, and fungicide concentration and timing on anthracnose development and yield loss in pickling cucumbers. Phytopathology 75:1422-1427.
Thompson, D.C., and S.F. Jenkins. 1985b. Pictorial assessment key to determine fungicide concentrations that control anthracnose development on cucumber cultivars with varying resistance levels. Plant Disease 69:833-836.
Wei, G., J.W. Kloepper, and S. Tuzun. 1991. Induction of systemic resistance of cucumber to Colletotrichum orbiculare by select strains of plant growth-promoting rhizobacteria. Phytopathology 81:1508-1512.
Xuei, X.L., U. Jarlfors, and J. Kuc. 1988. Ultrastructural changes associated with induced systemic resistance of cucumber to disease: host response and development of Colletotrichum lagenarium in systemically protected leaves. Can J. Bot. 66:1028-1038.