Isolation and characterisation of pathogenic and non-pathogenic fungi associated with avocado plants showing dieback symptoms in Indonesia

The avocado (Persea americana Mill.) is a high value fruit crop in Indonesia. This exotic commodity is affected by dieback disease, an unrecorded disease in the country that threatens the production. The objectives of the present study were to characterise the pathogen and culturable non-pathogenic fungi associated with the dieback disease of avocado plants. Fungal isolates were collected from branches of avocados showing dieback symptom in the Standard and Instrument Tropical Fruit Applied Institute (SITFAI) experimental orchards during 2022-2023. A total of 17 fungal isolates selected from 73 fungal isolates isolated from three location were characterised morphologically, molecularly, phylogenetically, and by pathogenicity tests. The fungal isolates were tested for their pathogenicity to the local variety of avocado with two stages and three replications. The identification of the fungal species was conducted on the morphological characteristics and molecular analysis obtained from the internal transcribed spacer (ITS), the 28S region of the ribosomal DNA, and translation elongation factor 1 (TEF1). The results revealed that the artificial inoculation of Avo7 and Avo3.2 isolates, identified as Lasiodiplodia theobromae, caused necrosis and wilt symptoms on the avocado seedlings. Several fungal species from the Botryosphaeriaceae, Eurotiomycetes, and Sordariomycetes groups were found alongside the pathogen responsible for causing the dieback symptoms in the avocados. The most frequently isolated genera were fast growing, Botryosphaeriaceae (58.9%), followed by Penicillium spp. (20.5%), Pestalotiopsis spp. (15.1%) and Colletotrichum spp. (5.4%). The information in this article should be used as new insights about the incidence of dieback disease caused by L. theobromae and proper management strategies against dieback disease on avocado need to be developed.