First Report of Fruit Basal Rot by Ceratocystis paradoxa on Coconut in Taiwan.

Abstract

Since 2005, coconut fruits (Cocos nucifera L.) harvested from trees in southern Taiwan have shown symptoms of a fruit rot disease. The disease occurs only on harvested coconut fruits and is more serious during warmer seasons. Principal symptoms are blackening of the exocarps, mesocarps, and then the endocarps of coconut fruits from pedicel end or wounds on fruits. A fungus was consistently recovered from diseased fruits. Colonies on potato dextrose agar (PDA) were white, becoming black 1 to 2 days later, with a strong fruity aroma. The fungus produced two asexual spores, including phialospore-type conidia, which were hyaline to mid brown, cylindrical to somewhat oval and thick walled when mature, 8.5 to 16.0 × 4.7 to 6.7 μm, released from phialides measuring 80.0 to 155.0 × 5.0 to 7.8 μm, and chlamydospores, which were oval, black, 13.4 to 25.0 × 8.9 to 12.5 μm, and formed in short chains from specialized hyphal tips. Perithecia were produced after 2 months by mating isolates on coconut exocarp placed on PDA. Perithecia were brown, globose, 280 μm in diameter, with a 1,100-μm long neck. Ascospores generally were ellipsoid, but some were unequally bent, 12 × 3 μm. The temperature for hyphal growth of this fungus was 25 to 30°C, with a growth rate of 3.3 cm per day. It did not grow at temperatures lower than 10°C or higher than 35°C. On the basis of these characteristics, this fungus was identified as Ceratocystis paradoxa (Dade) C. Moreau (anamorph Thielaviopsis paradoxa (de Seynes) Höhn) (1). The internal transcribed spacer (ITS) region of mycelial DNA of two isolates was amplified with ITS5 and ITS4 primers and the PCR products were sequenced (GenBank Accession Nos. GU358207 and GU358206). BLAST analysis of both sequences showed 99% sequence similarity with C. paradoxa strain WIN(M) 925 (Accession No. DQ318203). Two of the isolates (BCRC 34425 and BCRC 34426) were deposited in the Bioresource Collection and Research Center, Hsinchu, Taiwan. Twenty-four detached healthy coconut fruits were inoculated by placing spore suspensions (1 × 105 spores/ml) of eight wild type isolates onto wounds created by removing the calyx. Symptoms similar to those observed in the field developed on inoculated fruits after incubating at room temperature for 10 days, but did not develop on six fruits that were wounded but not inoculated. The same pathogen was reisolated from the inoculated fruits but not the control fruits. C. paradoxa has been reported as causing disease of coconut fruits in Brazil (2), but to our knowledge, this is the first report of the disease in Taiwan.