Cassava anthracnose disease is a major economic disease of cassava in the tropics (2). Infection can lead to a significant loss in planting materials and total field crop failure. The disease has been reported to be transmitted mainly by a bug (Pseudotheraptus devastans Dist) (1). Open pollinated seeds from 13 cassava (Manihot esculenta Crantz) genotypes, stored for 10 months after harvest in 1994, were used to investigate the presence of the cassava anthracnose disease fungus. Seeds, 200 from each genotype, were surface sterilized, cultured on potato dextrose agar (PDA), and incubated for 8 days, at 25 ± 2°C. Microscopic examination indicated that Colletotrichum gloeosporioides was one of the seed-borne fungi, with up to 40% incidence recorded in some genotypes. Seeds from five susceptible genotypes selected for seed transmission studies were planted in fine, steam-sterilized soils in jiffy pots and watered daily for seedling emergence. At a height of 10 to 15 cm, the seedlings were transferred to plastic pots (10.5 cm in diameter) filled with sterilized mixture of soil and sand (2:2, vol/vol). Pots were placed close to each other to obtain a thick plant canopy. Temperature of 25 to 32°C and humidity of 80 to 98% were maintained. After 45 days, some plants had cassava anthracnose symptoms, including defoliation, wilt, and necrotic lesions. Stems, leaves, and roots of infected plants were washed, surface sterilized, and plated on PDA for 5 to 7 days. Microscopic observation of the fungus showed conidia of C. gloeosporioides. The rest of the plants were monitored for 3 months under vector-free conditions for typical anthracnose symptoms. Mean maximum wilt and defoliation of 35 to 38% was recorded in some genotypes. Conidial suspensions of C. gloeosporioides were used in stem-puncture inoculations of young, healthy cassava plants. The typical anthracnose symptoms of stem necrosis were observed 2 weeks after inoculation, confirming isolates as C. gloeosporioides f. sp. manihotis. This is the first report of C. gloeosporioides f. sp. manihotis being seed-borne and seed-transmitted in cassava.
References: (1) B. Boher et al. Agronomie 3:989, 1983. (2) J. C. Lozano. PANS 20:30, 1974.
