Plant oil concentrations and lipid constituents shape temperature-dependent antifungal activity against Lasiodiplodia laeliocattleyae in cacao

The aim of this study was to evaluate the protective efficacy of castor ( Ricinus communis L.), neem ( Azadirachta indica A. Juss.), and physic nut ( Jatropha curcas L.) oils at concentrations of 0, 10, 20, 30, and 40% against the phytopathogen Lasiodiplodia laeliocattleyae (Sibilia) A. Alves. The oils were evaluated in vitro for their inhibitory effect on pathogen growth, using the synthetic fungicide iprodione as a positive control, and in vivo for their protective effect on cacao pods (CCN-51) artificially inoculated with the pathogen under controlled conditions. A completely randomized design was used in both experiments, and data were analyzed using two-way ANOVA and multivariate analysis. The oils exhibited distinct lipid profiles. Neem oil was characterized by higher concentrations of α-linolenic, γ-linolenic, linoleic, arachidic, palmitic, and stearic acids, while castor and physic nut oils showed contrasting compositions dominated by eucalyptol, elaidic acid, linolelaidic acid, oleic acid, and petroselinic acid. In vitro , highly significant differences were observed among treatments, days, and their interactions at both 25 and 28 °C ( P < 0.0001). At 25 °C, vegetable oils increased mycelial inhibition by approximately 86–129% relative to their respective negative controls but remained 38–50% less effective than Iprodione. At 28 °C, the 10% concentration was the most effective oil treatment, approximately doubling the inhibition obtained with the fungicidal control and markedly exceeding the negative control and higher oil concentrations ( P < 0.0001). In vivo , none of the vegetable oils consistently reduced pod rot severity relative to the negative control, whereas Iprodione reduced the affected area by approximately 77–82%, depending on temperature ( P < 0.0001). Overall, the vegetable oils showed concentration- and temperature-dependent antifungal activity in vitro , particularly at 10%, but this activity did not translate into consistent disease suppression in vivo , where Iprodione remained the most effective treatment.