Identification of Stem End Rot Fungal Pathogens on Avocado Fruits and Efficiency of Fungicides and Trichoderma spp. in Murang’a County, kenya
Loading...
Date
2021
Authors
Wanjiku, Mwaura Elizabeth
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
Avocado (Persea americana Mill.) is a commercially important fruit cultivated in
tropical and sub-tropical climates. In Kenya the fruit is cultivated for both local
and export market, significantly contributing to the country’s GDP. The
production of avocado fruits in Kenya is limited by fruit diseases among others.
Stem end rot (SER) is an economically important post-harvest disease of avocado
fruits contributing to losses of the fruits at the farm level, during storage and on the
shelves. The causal agents of the disease in Kenya are not clear, but
Botryosphaeriaceae spp. are most important causal agents of avocado SER in
other parts of the world where the fruit is grown. This study was conducted to
evaluate avocado production and SER disease management; determine the
incidence of SER on avocado fruits in Murang’a County; identify the SER fungal
pathogens, determine the efficacy of selected fungicides and the inhibitory effect
of selected Trichoderma species against the SER fungal pathogens of avocado
fruits. A structured questionnaire was administered by face-to-face interview with
farmers while colony growth and conidia characteristics were used in
morphological identification of the pathogens. Two fungicides, (Green Cop
500WP (Copper oxychloride 500g/Kg) and Milraz 76 WP (Propineb 70% +
Cymoxanil 6%) were used in the in vitro inhibitory study while four Trichoderma
spp. (T. asperellum, T. harzianum, T. atroviride and T. virens) were tested against
the most isolated SER pathogens on post-harvest ‘Hass’ avocado fruits. The
survey revealed that 84% of the farmers preferred ‘Hass’ avocado fruits, 85%
intercropped the avocado fruits with food crops, while 88% of the farmers used
organic manure only to replenish the soils. Majority of the farmers (62%) used
grafted seedlings while 27% of the farmers top worked the old trees. Most farmers
(84.6%) did not adopt the recommended field management practices, and none of
the farmers used fungicide in the management of SER. Avocado fruits from the
market and orchard had SER disease incidence of 52.08 % and 45.70 %
respectively. Lasiodiplodia theobromae, Neofusicoccum parvum, Nectria
pseudotrichia, Fusarium solani, Fusarium oxysporum, Fusarium equiseti and
Geotrichum candidum were identified as the causal agents of SER on avocado
fruits. Lasiodiplodia theobromae was the most frequently isolated pathogen
followed by, N. parvum, N. pseudotrichia and F. solani respectively. All the
fungicides significantly (P≤0.05) inhibited mycelial growth of the four pathogens.
In both in vitro study and on post-harvest avocado fruits T. atroviride had highest
efficacy against N. parvum, N. pseudotrichia and F. solani while T. harzianum had
the highest efficacy against L. theobromae. This study has identified the causal
agents of stem end rot disease of avocado fruits in Kenya. Trichoderma atroviride
and T. harzianum present a potential alternative to synthetic fungicides against
SER diseases of avocado fruits, and the possibility of using them at a commercial
level should be explored.
Description
A Thesis Submitted in Fulfillment of the Requirements for the award of the Degree of Doctor of Philosophy in Plant Pathology in the School of Agriculture and Enterprise Development, Kenyatta University, May 2021
Keywords
Identification, Stem End Rot Fungal Pathogens, Avocado Fruits, Efficiency of Fungicides, Trichoderma spp., Murang’a County, kenya