Abstract
Demand for organic avocado fruits, together with stringent food safety standards in the global market, has made producers to use alternative, safe, and consumer-friendly strategies of controlling the postharvest fungal disease of avocado fruits. This study assessed the in vitro efficacy of Trichoderma spp. (T. atroviride, T. virens, T. asperellum, and T. harzianum) against isolated avocado stem-end rot (SER) fungal pathogens (Lasiodiplodia theobromae, Neofusicoccum parvum, Nectria pseudotrichia, and Fusarium solani) using a dual culture technique. The Trichoderma spp. were also evaluated singly on postharvest “Hass” avocado fruits. Spore suspension at 5 × 104 conidial/ml of the Trichoderma spp. was applied on the avocado fruits at three time points, twenty-four hours before the fungal pathogen (preinoculation), at the same time as the fungal pathogen (concurrent inoculation), and 24 hours after the fungal pathogen (postinoculation). In the in vitro study, T. atroviride showed the highest mycelial growth inhibition against N. parvum (48%), N. pseudotrichia (55%), and F. solani (32.95%), while T. harzianum had the highest mycelial growth inhibition against L. theobromae. Trichoderma asperellum was the least effective in inhibiting the mycelial growth of all the pathogens. Similarly, T. virens showed the highest mycelial growth inhibition against N. pseudotrichia at 45% inhibition. On postharvest “Hass” fruits, T. atroviride showed the highest efficacy against N. parvum, N. pseudotrichia, and F. solani in all the applications. Trichoderma virens and T. harzianum were most effective against all the pathogens during postinoculation, while Lasiodiplodia theobromae was best controlled by T. virens, T. harzianum, and T. asperellum during postinoculation. Both T. atroviride and T. harzianum present a potential alternative to synthetic fungicides against postharvest diseases of avocado fruits, and further tests under field conditions to be done to validate their efficacy. The possibility of using Trichoderma spp. in the management of SER on avocado fruits at a commercial level should also be explored.
Highlights
Avocado (Persea americana Mill.) is one of the economically most important subtropical fruit crops worldwide and a major foreign exchange earner in Kenya [1, 2]
Trichoderma virens and T. harzianum were most effective against all the pathogens during postinoculation, while Lasiodiplodia theobromae was best controlled by T. virens, T. harzianum, and T. asperellum during postinoculation
All the Trichoderma species reduced the mycelial growth of the four (L. theobromae, N. parvum, N. pseudotrichia, and F. solani) avocado Stem-end rot (SER) pathogens. e highest mycelial growth inhibition of L. theobromae was produced by T. harzianum (54.57%) followed by T. atroviride (36.28%)
Summary
Avocado (Persea americana Mill.) is one of the economically most important subtropical fruit crops worldwide and a major foreign exchange earner in Kenya [1, 2]. In the year 2017, 300 MT of avocado fruits were exported from Kenya, contributing USD 50.5 million to the GDP [3]. Avocado fruits are cultivated in a wide range of agroecological zones for both domestic and commercial purposes [4]. The consumption of avocado fruit is associated with improved overall diet quality [2, 5]. Stem-end rot (SER) disease causes losses of avocado fruits in all avocado-growing regions of the world. Members of the Botryosphaeriaceae family (Diplodia mutila, D. pseudoseriata, D. seriata; Dothiorella iberica; Lasiodiplodia theobromae; and Neofusicoccum australe, N. nonquaesitum, and N. parvum) have mainly been associated with SER on avocado fruits. Other pathogens reported to cause the disease include Colletotrichum gloeosporioides or C. fructicola and Diaporthe foeniculacea Phomopsis perseae, yronectria pseudotrichia, Advances in Agriculture
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