Characterisation Of Colletotrichum Gloeosporioides And Effectiveness Of Management Strategies Of Anthracnose Disease Of Avocado In Murang’a County, Kenya

ABSTRACT

Avocado (Persea americana Mill) is a fruit commercially grown worldwide. Its production is affected by anthracnose disease which causes huge loss of avocado fruits both at farm level and in storage. Management of anthracnose disease worldwide has been mainly through use of fungicides. In Kenya, farmers use fungicides such as bayleton, milraz and Copper oxychloride which are not registered for controlling anthracnose in avocado. Despite this, the disease has continued to cause significant fruit losses of up to 40% as a post-harvest disease. This study was conducted to evaluate avocado production and anthracnose disease management practice; determine the incidences of anthracnose disease in avocado in Murang‘a County; determine the morphological and genetic characteristics of the Colletotrichum gloeosporioides; determine the pathogenicity of the representative isolates of the fungus on avocado varieties (Fuerte and Hass) and determine the inhibitory effect of selected fungicides on C. gloeosporioides isolates in vitro. A completely randomized block design was used in the laboratory tests while questionnaires were used during surveillance. The data on incidence, latent and surveillance was analysed descriptively into histograms and percentages using IBM SPSS version 21 software. Cultural and morphological data was analysed through ANOVA and Fisher's LSD to compare means using Genstart version 6 while molecular data was analyzed through PCR, sequencing (sanger sequencing), alignment (Bio edit software version 7.2.1 and phylogentics relationship of sequences using MEGA 7.0.18. Surveillance on anthracnose disease incidence and the control strategies adopted by farmers was done in the three agro-ecological zones upper midland (UM) 2, 3 and 4 where avocado is grown. The survey revealed that agro- ecological zone 2 had the highest disease incidence of 24.3% followed by zone 3 with 15% and lastly zone 4 with 9.6%. Farmers controlled the disease by pruning, sanitation and use of fungicides not registered for use in avocado. Eight percent of the farmers used fungicides while 30.2% used pruning strategy. Morphological and molecular studies identified C. gloeosporioides, C. boninense and Pestalotiopsis microspora as the causal agents of anthracnose. Further studies on C. gloeosporiodes showed a signicant difference (P≤0.05) among isolates in mycelia diameter and size of conidia. Both Hass and Fuerte fruit varieties were susceptible to all C. gloeosporioides isolates. Diameter of lesions on unripe Fuerte varieties four days after inoculation were not significantly different (P≥ 0.05) ranged from 7.33 -10.00 cm while in unripe Hass it was 6.33-7.33cm. However, lesions on ripe, Fuerte variety 2 days after inoculation ranged 10-17cm while ripe Hass was 9.67cm - 12.33cm. Hass variety was more tolerant to the disease as compared to Fuerte variety. The fungicides Bayleton, Milraz and Copper oxychloride significantly (P≤0.05) inhibited mycelial growth and sporulation of C. gloeosporioides invitro. Farmers should be encouraged to use cultural methods and field sanitation as management strategies to reduce loses and should be trained on strategies in handling, harvesting and storage. They should also be encouraged to grow Hass variety which is tolerant to anthracnose as compared to Fuerte variety. Field studies on the effectiveness of fungicides Bayleton, Milraz and copper oxychloride on anthracnose disease of avocado is recommended.