Anthracnose disease of avocado contributes to a huge loss of avocado fruits due to postharvest rot in Kenya. The causal agent of this disease has not been clear but presumed to be Colletotrichum gloeosporioides as reported in other regions where avocado is grown. The fungus mainly infects fruits causing symptoms such as small blackish spots, “pepper spots,” and black spots with raised margin which coalesce as infection progresses. Due to economic losses associated with the disease and emerging information of other species of fungi as causal agents of the disease, this study was aimed at identifying causal agent(s) of the disease. A total of 80 fungal isolates were collected from diseased avocado fruits in Murang'a County, the main avocado growing region in Kenya. Forty-six isolates were morphologically identified as Colletotrichum spp. based on their cultural characteristics, mainly whitish, greyish, and creamish colour and cottony/velvety mycelia on the top side of the culture and greyish cream with concentric zonation on the reverse side. Their spores were straight with rounded end and nonseptate. Thirty-four isolates were identified as Pestalotiopsis spp. based on their cultural characteristics: whitish grey mycelium with black fruiting structure on the upper side and greyish black one on the lower side and septate spores with 3-4 septa and 2 or 3 appendages at one end. Further molecular studies using ITS indicated Colletotrichum gloeosporioides, Colletotrichum boninense, and Pestalotiopsis microspora as the causal agents of anthracnose disease in avocado. However, with this being the first report, there is a need to conduct further studies to establish whether there is coinfection or any interaction thereof.

Colletotrichum gloeosporioides is a serious postharvest pathogen of avocado fruits worldwide. Kenya lacks any registered fungicides for the management of the disease. Nevertheless, farmers commonly use commercially available fungicides such as Bayleton 25WP (Triadimefon 250 g/Kg), Milraz 76WP (Propineb 70% and Cymoxanil 6%), and Copper oxychloride 500WP for disease management. The efficacy of these fungicides against C. gloeosporioides is not known. The purpose of this study was therefore to test the inhibitory effect of these fungicides against 46 C. gloeosporioides isolates from avocado fruits collected from varieties grown at different agroecological zones in Murang'a County, a popular avocado-growing region in Kenya. Mycelial growth rate and sporulation for each isolate were measured in vitro on PDA plates amended with different concentrations of the fungicides. Plates were arranged in a completely randomized design with three replications per treatment. All fungicides were effective in vitro but there were significant differences in sensitivity among isolates. Bayleton had the highest mycelial inhibition followed by Milraz, while copper oxychloride had the lowest mycelial inhibition rates, ranging from 81% to 88%. However, copper oxychloride was more effective in inhibiting sporulation. The inhibitory effect of each fungicide was concentration-dependent, where twice the recommended concentration had the highest inhibitory effect, followed by the recommended concentration. Our results show that the fungicides used by farmers against C. gloeosporioides, the causal agent for anthracnose, are effective. We, however, recommend further field tests in different avocado-growing areas so as to validate their efficacy against various isolates and under different environments.

Avocado production is severely affected by anthracnose disease in the field and after harvest worldwide. This disease causes losses in the field due to fruit abortion and as post-harvest disease affecting quality and quantity during marketing and storage. The management of this disease has been through the use of chemicals that toxify human beings and contaminate the environment. So, the development of alternative bio-pesticide, which is environment-friendly, is imperative. Therefore, this study was carried out to find an alternative to fungicides currently being used in the control of Colletotrichum gloeosporioides. This was achieved by evaluating the effectiveness of plant extracts from tree marigold (Tithonia diversifolia) and garlic (Allium sativum) in the inhibition of Colletotrichum gloeosporioides in vitro. The antifungal activity of the extracts was determined by the evaluation of their effectiveness in inhibiting the fungal mycelial growth and sporulation on PDA media. Fungicide, Atracol 70WP used to control the disease, was used for comparison purposes. Data obtained were analysed by ANOVA and Fishers mean separation test using Gestart version 6 software. Concentrations of 80 g/l of Allium sativum and 120 g/l of Tithonia diversifolia were significantly effective as antracol fungicides at 2 g/l which is the recommended rate by the manufacturer in inhibiting mycelial growth and sporulation of Colletotrichum gloeosporioides. However, further studies are recommended to evaluate the effectiveness of the extracts under field conditions.