Host selectivity of a 40kDa phytotoxic extract fromColletotrichum gloeosporioides(Phyllachoraceae) on yamDioscorea alata(Dioscoreace)

Abstract

Isolates of the fungal pathogen Deuteromycota, Melanconiales, Colletotrichum gloeosporioides (Penz and Sacc.) from yam, Dioscoreales, Dioscoreacceae, Dioscorea alata cultivar White Lisbon, and one each from Mangifera indica L (mango), Anthurium andreanum (Schott) (anthurium) and Citrus paradisi (grapefruit) were used for precipitation of phytotoxic secondary metabolites. These phytotoxic extracts decreased cell viability of yam, tomato, pepper and tobacco cell suspension cultures. Protein and carbohydrate fractions of the extract co-eluted during gel filtration chromatography and were present in amounts ranging from 26–46 μgmL-1 and 0.24–0.62 μgmL-1 respectively per gram of phytotoxin. Biochemical analyses of the phytotoxic extracts showed they contained mainly two sugars, mannose, and galactose which were both closely linked to a protein component containing large amounts of cysteine and glycine. This latter protein component was essential for disease induction in yam and is part of a relatively mid-range glycoprotein complex containing both N and O-glycosidic bonds, approximately 40kDa in molecular mass.