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A bud rot disease, referred to as "pudricion del cogollo" or PC (for its name in Spanish), is a major disease of oil palm in four production areas of Colombia. Even though the disease has been studied for more than 40 years in Central and South America, the causal agent remained unknown (1). Infection first develops in the palm heart (cogollo) above the meristematic zone. Initial external symptoms appear as necrotic lesions on the sides of the spear leaf (youngest, unexpanded leaf) and the sizes of the lesions remain static as tissues emerge, expand, and mature. Under favorable environmental conditions (temperature around 26°C and relative humidity above 80%), further rotting of the heart eventually destroys the bud. A baiting technique with papaya and cocoa fruits was successfully used to trap the causal agent from symptomatic spear leaf tissue collected from the provinces of Nariño and Santander (2), where the disease is severe. Small, triangular-shaped pieces were removed from healthy fruits that had been surface sterilized, and a corresponding piece of diseased oil palm tissue was inserted into the hole and sealed with the removed fruit tissue. The whole fruit was wrapped with plastic and incubated at 25°C. Once the fruit traps showed initial necrotic symptoms, fruit tissue from the advancing point of the lesions was plated on Phytophthora-selective media. Four isolates of Phytophtora palmivora, all A2 mating type, were obtained during this study and each presented similar white and depressed mycelium when grown on oatmeal agar (OMA) medium. Papillated, ellipsoidal sporangia with short pedicels had an average size of 37.1 (breadth) × 52.8 μm (length). Chlamydospores averaged 35.1 μm in diameter and were similar to those observed in diseased palm tissue. DNA from the Phytophthora isolates was used as a template for PCR using ITS1/ITS4 primers. BLASTn analysis of the ITS sequences (GenBank Accession No. GQ398157) showed 99.9% homology with P. palmivora. The sequences of the four isolates were identical. For pathogenicity testing, cultures were grown on OMA. Two milliliters of distilled water containing 40,000 sporangia were injected into the base of the spear leaf of 105 nursery palms; the same number of palms was injected with 2 ml of distillated water as controls. Initial PC symptoms were observed 3 to 4 days after inoculation on 85% of inoculated palms and 15% of these palms developed typical bud rot symptoms under favorable conditions. No symptoms were observed on the controls. The presence of Phytophthora was confirmed by light microscopy and P. palmivora was reisolated from symptomatic palms with the fruit-baiting technique. The presence of Phytophthora in the four Colombian growing areas was also confirmed using Agdia (Elkhart, IN) immunostrips followed by DNA extraction from the Immunostrip wick and ITS sequencing to confirm the species. To our knowledge, this is the first report of P. palmivora causing PC on oil palm in Colombia. References: (1) H. de Franqueville. Exp. Agric. 39:225, 2003. (2) G. Sarria et al. Rev. Palmas, Colombia. 29(3):31, 2008.
Torres et al. (Tue,) studied this question.