Fusarium Heart Rot: A New Disease of Pineapple in the Philippines

Abstract


Pineapple is among the major export commodities in the Philippines. A species of Fusarium was found to be consistently associated with diseased leaves collected from pineapple plantations in Polomolok, South Cotabato and Davao City. There are no published reports of Fusarium heart rot of pineapple in the Philippines. Hence, this study was conducted to prove the pathogenicity of the fungus on pineapple following Koch’s postulates and to test the efficacy of Fosetyl-Aluminum products against the fungus under laboratory condition. Microscopic examination of infected leaves and trapping of the suspected pathogen from infested soils were conducted. The pathogen isolated was identified based on its cultural and morphological characteristics. For the bioassay, the treatments used were as follows: T1 – untreated; T2 – 2.25g/L water (Fosetyl-al, Brand X); T3 – 5g/L water (Fosetyl-al, Brand X); T4 - 2.25g/L water (Fosetyl-al, Brand Y); T5 – 5g/L water (Fosetyl-al, Brand Y); T6 – 2.25g/L water (Fosetyl-al, Brand Z) and T7 – 5g/L water (Fosetyl-al, Brand Z). The experiment was laid-out in Completely Randomized Design (CRD) with three replications at three plates per replicate. The data were statistically analyzed using the Analysis of Variance and treatment means were compared using Tukey’s Honest Significant Difference. Symptoms of the disease included water-soaked lesions which later turned brown necrotic tissues at the base of infected pineapple leaves. In advanced cases, margins of infected tissues became dark brown to black and dried-up while advancing portions became soft rotted tissues. The isolated fungus produced cottony white aerial mycelia on the cut surface of the tissues planted on Potato Sugar Agar (PSA) medium. Mycelia were hyaline and septated. Macroconidia are slightly curved, sickle-shaped with three or more septations. Microconidia are single-celled. Pure cultures showed white cottony growth which turned light purple after eight days of incubation in full strength PSA. Abundant chlamydospores were formed after two months of incubation. Baiting from infested soil using young pineapple leaves revealed micro- and macroconidia similar to those isolated from infected pineapple leaves. Inoculation and re-isolation of the fungus showed similar symptoms with the original diseased specimens and isolate, respectively. Based on the cultural and morphological characteristics, the fungus associated with heart rot disease of pineapple was identified as Fusarium sp. similar to the genus Fusarium described by Quimio (1983). Results of the bioassay showed that Fosetyl-al Brand Z at 2.25g and 5.0 g/L water and Fosetyl-al Brand X at 5.0 g/L significantly inhibited the growth of Fusarium sp. infecting pineapple leaves up to 94.38-100% inhibition after nine days of incubation.

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