Evaluation of neem (Azadirachta indica) seed and ginger (Zingiber officinale) as potential control agents of yam (Dioscorea rotundata Poir.) tuber rot fungi

Abstract

Yam is an important crop which serves as a source of income to small-holder farmers as well as a foreign exchange earner. Among the constraints faced by yam farmers are pests and diseases, especially deterioration caused by microbes during storage. Since over dependence on pesticides is being discouraged, neem seed and ginger extracts were evaluated as potential control agents against rot-causing fungi. The study was conducted in the Spanish laboratory, at the Faculty of Agriculture, University for Development Studies, Nyankpala Campus. Isolations were made from rotted yam tubers sampled from the Tamale Central market with potato dextrose agar (PDA) as the growth medium. Growth inhibition of the isolates was determined by growing pure cultures on PDA plates amended with 2 ml each of ethanol and aqueous extracts of neem seed and ginger as well as carbendazim. A pathogenicity test proved that Aspergillus flavus, A. niger, A. ochraceus and Penicillium digitatum isolated from the rotted tubers were responsible for the rot. A. niger had a significantly higher (p < 0.05) occurrence (40%) than the others. Growth inhibitions by carbendazim and ethanol extracts of neem seed and ginger were comparable but significantly higher (p < 0.05) than the aqueous extracts of neem seed and ginger as well as the control. However, the aqueous extracts of neem seed and ginger had a significantly higher (p < 0.05) inhibition than the control. For instance, growth inhibition of A. niger by carbendazim, ethanol neem seed and ginger extracts were 70.5, 69.6 and 65.5%, respectively, while inhibition by aqueous neem seed and ginger extracts were 33.9 and 24.8%, respectively. Since aqueous extracts of neem seed and ginger significantly inhibited (p < 0.05) growth of the rot-causing fungi, they can be used as surface protectants of stored tubers.