Resumo

BIBIANO-FLORES, Abraham et al. Neem oil ( Azadirachta indica: Meliaceae) as biofumigant of root pathogenic fungi in avocado rootstocks (Persea americana var. drymifolia: Lauraceae). Rev. Int. Contam. Ambient [online]. 2026, vol.42, 55584.  Epub 05-Jun-2026. ISSN 0188-4999.  https://doi.org/10.20937/rica.55584.

Wilt of avocado (Persea americana var. drymifolia) rootstocks, associated with root-parasitic fungi, causes the loss of between 60 and 100% of plants in nurseries in the state of Morelos, Mexico. Conventional management involves fumigating substrates with metam-sodium, which poses risks to human and environmental health. Biofumigation with neem oil (azadirachtin) represents an ecological alternative to avoid this problem. The objectives of this research were: (1) to determine the etiology of root rot of avocado rootstocks based on Koch’s postulates; (2) to evaluate in vitro the effective dose 50% (ED50) and 90% (ED90) of neem oil against the causal microorganisms; and (3) to compare the biofumigant effect of azadirachtin and metam-sodium on the colony forming units (CFU) density of native bacteria and fungi in a conventional organic substrate. Root rot in avocado rootstocks was caused by Fusarium sp., Rhizoctonia sp., Ilyonectria sp., Pythium sp., and Phytophthora cinnamomi. Except for Pythium sp., neem oil also inhibited the in vitro growth of these pathogens (ED50, 1 mL/L); in contrast, the ED90 values varied by microorganism species (1.86 to 4.85 mL/L). It also limited sporulation and viability, as well as the size of conidia and phialides. Azadirachtin reduced the CFU density of native bacteria and fungi, but not of actinobacteria, in the evaluated substrates. Neem oil as a biofumigant represents a sustainable strategy for root rot management on avocado rootstocks.

Palavras-chave : plant nursery management; wilting; subED₉₀; azadirachtin.

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