Archivio Journal of Plant Pathology

Abstract:

In December 2013, irregular spots with gray centers, dark brown edges and chlorotic halos were observed on the old leaves of bananas of cv. Williams (AAA, Cavendish) in Guangxi province (China), with an incidence of 15% to 30%. Small pieces of diseased leaf tissues were surface-sterilized in 75% ethanol for 30 s followed by 2 min in 0.1% HgCl2, rinsed in sterile water, plated on potato dextrose agar (PDA) and incubated at 28oC in darkness. A single-spore culture had initially an olive or dark green mycelium with granular surface and white edges which, over time, turned almost black. Asci containing 8 ascospores, were clavate or cylindrical, stipitate, and measured 35.6-43.6×8.5-10.6 μm. Conidia measured 7.2-11.8×4.0-6.3 μm, and were obpyriform or nearly elliptic. Single spore cultures of the isolate were obtained and used for molecular identification. The internal transcribed spacer (ITS) region of rDNA was amplified and sequenced by utilizing the primers ITS4/ITS5 (2). The ITS region of the isolate (Accession No. LM994823) was 629 bp in length. BLAST analysis of the sequences showed a 99% homology with two Phyllosticta capitalensis isolates (accession Nos KM979840 and JQ743587). Pathogenicity was conducted using healthy banana plants with five or six leaves, approximately 30 cm in height. Nine plants were used for each treatment and three leaves of each plant were artificially inoculated. Mycelial plugs were placed on the surface of the leaves, whereas controls were treated only with agar plugs. All the treated plants were covered with plastic bags for 2 days and incubated at 28oC, 75% relative humidity (RH) and with a 12-h photoperiod. After 7 days, typical lesions identical to those observed on the field-grown plants appeared on the inoculated plants, whereas control plants remained healthy. The re-isolated fungus was identified as P. capitalensis by morphology and molecular analysis. P. capitalensis is generally considered an endophyte or saprophyte, within a wide host range and distributed in different plants (Wulandari et al., 2010; Wong et al., 2012). However, it is a weak plant pathogen which was the causal agent of plant diseases in few cases (Wikee et al., 2013). To our knowledge, this is the first report of P. capitalensis causing freckle disease of banana in China.