Cyanogenic acid content of cassava (Manihot esculenta Crantz.) leaves and tolerance to anthracnose disease caused by Colletotrichum gloeosporioides

Abstract

Anthracnose (caused by Colletotrichum gloeosporioides) is a fungal disease which attacks plant stem and leaves and it is expressed by excessive defoliation leading to low yield and even plant death. This study was carried out to determine the relation between cyanogenic (HCN) content of leaves from four cassava (Manihot esculenta) cultivars (one local cultivar: CV1 = LMR; three improved cultivars: CV2 = 92/0326, CV3 = 81/00110, CV4 = W94/009) and their tolerance to anthracnose disease. Disease severity and incidence, HCN content of leaves, percentage of defoliation and inhibitory effect of HCN extract (in vitro) were evaluated. HCN content was determined by titration using a solution of 0.02 N AgNO3. Disease severity was high in cultivars CV1 and CV3 (21.38 and 17.79 % respectively) with low levels of HCN (0.44 and 0.59 mg.g-1 respectively), and low in cultivars CV2 (5.50 %) and CV4 (5.31 %) with high levels of HCN (1.23 and 1.77 mg.g-1 respectively). HCN extracts had inhibited 51.16 % of Colletotrichum gloeosporioides. A direct relation existed between HCN content in cassava leaves and their tolerance to anthracnose disease. The capacity of cassava to synthesize HCN can be used in selection programs to obtain cassava cultivars resistant to anthracnose disease.

Keywords: Anthracnose, cassava cultivars, Colletotrichum gloeosporioides, cyanogenic acid, host resistance

Cameroon Journal of Experimental Microbiology Vol. 4 (2) 2008: pp. 89-96