Prevalence And Characterization of Avocado Fruit Fungal Diseases in Embu County, Kenya, And the Efficacy of Aloe Secundiflora Crude Extracts in Their Control

Abstract

Avocado production faces various constraints that include common post-harvest fungal diseases. Most of these diseases are difficult to control using cultural measures while use of chemicals leads to pathogen reistance in addition to being harmful to human and environment. The objective of this study was therefore to determine the prevalence of the fungal avocado fruit diseases in Embu County, isolate and characterize the causal pathogens and test the efficacy of Aloe secundiflora extract in the diseases. Questionnaires were administered to a total of 120 respodents to gather additional information on avocado production, marketing and management. The stores and avocado bags were randomly identified and the fruits assessed for the prevalence of fungal avocado diseases. Aloe leaves were collected in the field and phytochemical analysis done using standard procedures. The efficacy of Aloe secundiflora extract against the avocado fungal diseases was done in the laboratory using a Completely Randomized Design. The extracts were then assessed for antimicrobial activity against Colletotrichum gloeosporioides (scab disease), Sphaceloma perseae (anthracnose) and Cercospora purpurea (Cercospora spot). In the results, chemicals were widely used to control the pathogens. The mean percentage prevalence of scab, cercospora spot and anthracnose diseases was 36.4%, 35.15% and 35.0%, respectively, among the markets, although anthracnose was highly prevalent within each market. Four avocado varieties were commonly sold with Fuerte and Puebla being the most susceptible to the fungal diseases. There were significant variations in the morphological characteristics of the pathogen isolates. The aloe extract revealed the presence of steroids, phenolics, flavonoids, saponins, terpenoids and phenolics. The extract prepared using ethanol had a high inhibitory activity against C. gloeosporioides (15.59mm) and Cercospora purpurea (7.22mm), while hexane solvent extract had minimal antimicrobial activity (10.53 and 5.22mm respectively). Aloe crude extract is therefore a potential antifungal agent against C. gloeosporioides and Cercospora purpurea.