CONTROL OF LASIODIPLODIA THEOBROMAE ON AVOCADO IN EGYPT

Abstract

This study was performed during 2015-2016 seasons to identify fungal species associated with dieback, grafting failure process during vegetative propagation in commercial nursery and stem-end rot of avocado(Persea americana Mill.).Lasiodiplodia theobromae (syn. Botryodiplodia theobromae, Diplodia natalensis) was the most pathogenic as well as the most frequently isolated fungi whereas, the other isolated fungi (Alternaria solani, Fusarium moniliforme, F. solani, Aspergillus niger and Rhizopus stolonifer) were negligible. Hass and Fuerte were the most susceptible cultivars to dieback and stem-end rot diseases, followed by Eitinger, Duke and Reed, while Bekon and Benkerton recorded the lowest percentages of infection. Hass and Fuerte were susceptible to grafting failure process. All tested fungicides suppressed completely the avocado dieback infection when shoots were sprayed at the same time of inoculation with L. theobromae, followed by 7 days pre inoculation. On the other hand, spraying the avocado shoots 7 days post inoculation with L. theobromae was the least effective treatment in controlling the disease under greenhouse conditions. Dipping the scions in the tested fungicides before dipping it in spore suspensions of L. theobromae during grafting increased the percentage of success of grafted seedlings. Dipping avocado fruit after harvest in the tested fungicides before placing mycelial agar discs (5 mm diameter) of L. theobromae into a hole on the pedicel (stem) that was made with a 5-mm-diameter cork borer reduced the infection of stem-end rot. Generally, KemaZed, Amistar Top,Topsin M70 and Occidor were the most effective in controlling the avocado three diseases. This study confirms that stem-end rot and failure grafting followed by dieback of avocado can be initiated by fungus causing branch dieback and stresses the importance of controlling branch dieback.