Morphological and Biometric Diversity of <i>Colletotrichum capsici</i> Isolates, Causal Agent of Cowpea Brown Blotch Disease (<i>Vigna unguiculata</i> (L.) Walp) in the Sudano-Sahelian Zone of Cameroon

Abstract

Cowpea [Vigna unguiculata (L.) Walp] is an important legume in the midst of about 170 species of its genus because it is an important source of protein and other essential nutrients for humans and animals. Its production faces many constraints such as the cowpea brown blotch disease caused by Colletotrichum capsici which contributes in wet conditions of the field to losses ranging from 42% to 100%. This study was conducted to identify Colletotrichum capsici isolates responsible for cowpea brown blotch disease and to determine their diversity in the Sudano-Sahelian zone of Cameroon. Identification and isolation were made from cowpea organ samples on the Potato Dextrose Agar (PDA) medium and, morphological and biometric characteristics such as: the colony color, the mycelium shape, the abundance of acervules, the presence or absence of saltations, the mycelial growth rate, the conidia length and width were used to assess the diversity. The results obtained indicate that 55 Colletotrichum capsici isolates have been identified in the Sudano-Sahelian zone of Cameroon. Statistical analysis showed that there is a significant difference between isolates. Isolates showed multiple colony colours and were brown coloured as presented by 36.36% of isolates, compact mycelium is found in 56.36% of isolates, 56.36% of isolates have abundant acervulis, and saltations were absent in 45.45% of C. capsici isolates. The mycelial growth rate is between 6.69 mm/d and 12.33 mm/d. The principal component analysis (PCA) made indicated that there are differences between the observed and measured characteristics. The Hierarchical Ascending Classification (HAC) was done and 10 morphotypes of C. capsici in the Sudano-Sahelian zone were identified.