Isolation, Identification and Cross-Infection of Pathogens Responsible for Postharvest Spoilage in Yam And Cocoyam Across Markets in Awka, Anambra State Nigeria

Abstract

Postharvest loss of food is highest during storage, which is caused by a number of fungi pathogens. This study aims to isolate and identify the disease-causing pathogens associated with yam and cocoyam in markets across Awka. Diseased yam (Dioscorea rotundata) and cocoyam (Xanthosoma sagittifolium) samples was collected from four different markets: Eke-Awka, Nkwo-Amaenyi, Amawbia, and Amansea all in Awka, Anambra State, Nigeria. Samples were taken to the Department of Botany laboratory, Nnamdi Azikiwe University, Awka for culturing, isolation, identification and cross-inoculation. Proximate analysis was also done on the fresh and diseased yam after cross-infection to determine the difference and effect of spoilage in the nutritional composition. Based on physical observation of the growth of the fungi on the yam and cocoyam specimens, the several fungal species isolated include: Aspergillus niger, Aspergillus flavus and Rhizopus stolonifer for both yam and cocoyam samples and Fusarium oxysporum and Aspergillus terreus for yam only, while cocoyam also had Phytophthora parasitica and Fusarium solani. The percentage occurrence of fungi pathogens on the diseased yam and cocoyam samples collected from different markets across Awka showed that most of the fungi had 100% occurrence. The pathogenicity test result for the yam sample showed that A. flavus had a higher pathogenicity on the fresh yam samples when compared with R. stolonifer. Aspergillus niger, Aspergillus terreus and Fusarium oxysporum showed no significant difference in their pathogenicity on the fresh yam sample. For cocoyam, Phytophthora parasitica and Fusarium solani had higher pathogenicity at later days. The Aspergillus species showed a slow but steady increase in their pathogenicity. The result of the pathogenicity of cross-infection of fungi pathogens isolated from the diseased yam samples on the fresh cocoyam samples showed that the pathogenicity of the fungi pathogens and the number of days were significantly different (P<0.05), while that of the pathogenicity of cross-infection of fungi pathogens isolated from the diseased cocoyam samples on the fresh yam samples also showed that the pathogenicity of the fungi pathogens and the number of days were significantly different (P<0.05). Results of the percentage proximate composition assay showed that diseased yam and cocoyam have lower ash content compared to healthy counterparts. Healthy yam has the highest carbohydrate content while diseased yam and cocoyam had lower carbohydrate levels respectively. Results obtained in this study obviously showed that cross-infection of fungi pathogens isolated from diseased yam and cocoyam samples could induce rot on healthy yam samples or cocoyam samples. Thus, cross-infection was ascertained to be possible in this study amongst the crops.