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 has increased exponentially worldwide due to increased demand for the fruit in the food, pharmaceutical, cosmetic, and oil industries. However, avocado production faces various constraints that include post-harvest losses due to pests and diseases, which contribute about 83% of yield losses. Fungal diseases are the most prevalent and are difficult to control using cultural methods, while continuous use of chemicals can lead to pathogen resistance and have adverse effects on humans and the environment. The main 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 (Aloe) crude extract in the management of the fungal diseases. Aloe was selected because of its wide medicinal use and local availability. A descriptive cross-sectional survey design was carried out in six purposefully selected avocado markets in the study area to assess the prevalence of fungal diseases of avocado fruit. A structured questionnaire was administered to gather information on avocado production, marketing, and management. A total of 100 respondents were interviewed. The stores and avocado bags were randomly selected. The fruits in the bags were assessed to determine the prevalence of fungal avocado diseases. Experiments were then carried out in the laboratory to isolate and characterize the pathogens. Aloe leaves were collected in the field, and phytochemical analysis of the crude extracts was done. The efficacy of the crude extract against the pathogens was tested in the laboratory using a Complete Randomized Design (CRD). The data were subjected to an analysis of variance (ANOVA) using Scientific Analysis System version 9.4 Software. Significant means were separated using LSD at p < 0.05 significant level. Results on the demographic characteristics of the respondents showed that the majority were above 30 years of age, with more women than men, and had a primary level of education. More than 50% sourced avocado fruits from their own farms and were able to identify disease symptoms themselves. The main methods of harvesting were both handpicking and hook, and the product was mainly stored in sacks. More than 40% of the respondents used chemicals to control fruit diseases. Three fungal pathogens were isolated and characterized: Colletotrichum gloeosporioides (anthracnose), Cercospora purpurea (cercospora spot), and Sphaceloma perseae (avocado scab) and their mean percentage prevalence was 29.00%, 25.98% and 31.44%, respectively. The commonly sold varieties were Hass, Fuerte, Puebla and the local varieties, with Hass being the most preferred variety. Fuerte and Puebla were the most susceptible to these diseases. There were variations in the morphological characteristics of the pathogen isolates: C. gloeosporioides had a white to grey smooth mycelia, concentric zonation and sizes ranging from 3.0 - 5.0 μm in width and 10.3 - 18.2 μm in length. Sphaceloma perseae had a white and yellow layered mycelium with sizes ranging from 3.0 - 5.0 μm in width and 10.3 - 18.2 μm in length, while C. purpurea had a leathery grey to brown conidia of 2 - 5 μm in width and 20 -34 in length. Phytochemical analysis of the aloe-ethanol extract revealed the presence of steroids, phenolics, flavonoids, saponins, and terpenoids, but phenolics were only present in the hexane extract. The mean zone of inhibition for the ethanol and hexane extract against C. gloeosporioides was 13.50 mm and 9.36 mm, respectively, while for Cercospora purpurea was 4.72 mm and 4.32 mm, respectively, but no effect on S. perseae at any concentration. Vendors should therefore be trained on proper handling of avocado fruits to reduce post-harvest losses. Aloe secundiflora extracts can be integrated with other methods of managing avocado fungal diseases to reduce over-reliance on chemical fungicides.