Identification and fungicide sensitivity of Phytophthora nicotianae for controlling pineapple heart rot in Thailand

Importance of the work: Pineapple heart rot caused by Phytophthora spp.can lead to substantial yield losses and significant economic impacts for pineapple growers.This highlights the need for accurate identification of the causative agent and effective control measures.Objectives: To identify and characterize Phytophthora isolates, evaluate fungicide sensitivity and assess fungicide effectiveness in pineapple field trials.Materials and Methods: Pineapple heart rot samples were collected for pathogen isolation.Phytophthora isolates were identified using morphological and molecular methods.Fungicide sensitivity was evaluated based on in vitro assays, with field trials being used to assess the efficacy of four fungicides.Disease incidence and severity were monitored and analyzed using two-way analysis of variance.Results: Four fungal isolates (PHY-01 to PHY-04) were identified, with PHY-02 matching Phytophthora nicotianae morphologically and phylogenetically.Pathogenicity assays confirmed PHY-02 as the causal agent of pineapple heart rot.In fungicide sensitivity tests, dimethomorph achieved 100% mycelial growth inhibition at concentrations of 100 mg/L and 1,000 mg/L, with a half maximal effective concentration (EC 50 ) value of 0.17 mg/L.Metalaxyl was effective at higher concentrations (EC 50 : 5.3 mg/L).Fosetyl-Al and phosphonic acid showed no efficacy.The field trials demonstrated that dimethomorph (9.5 mL/L) was most effective, reducing disease severity to 1 after 45 d, compared to 3 in control plots.Metalaxyl and fosetyl-Al provided moderate control, while phosphonic acid was less effective.Main finding: Phytophthora nicotianae was confirmed as the cause of pineapple heart rot.The results demonstrated dimethomorph's superior efficacy for disease control, advancing effective fungicide use and integrated management strategies for pineapple cultivation.