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First report of alternaria rot caused by Alternaria alternata on peach in ecuador

Abstract:

Alternaria alternata is a ubiquitous plant pathogen that can cause rot symptoms on stone fruits. Alternaria rot has been previously described in peach orchards from China, Japan, Hong Kong, Libya, Mexico, Australia, and the United States (Kim et al. 2005). In September 2015, brown spots were observed on several fruits of peach (Prunus persica L.) var. Diamante in an experimental orchard from the National Institute of Agricultural Research in the province of Pichincha, Ecuador, where up to 80% postharvest yield losses were reported. Twenty fruits that showed a single lesion were collected, surface sterilized for 1 min in 0.5% sodium hypochlorite, and placed in moist chambers until cottony mycelia was observed growing over the rotting tissue. Fungal isolates were obtained by plating mycelia on potato dextrose agar amended with 50 ppm of chloramphenicol. Five peaches rendered axenic cultures of white mycelium that turned greenblack with time. These cultures were identified morphologically as Alternaria sp. using a taxonomic key (Barnett and Hunter 1972). The other 15 peaches showing rot symptoms were infected mostly by Monilinia fructicola. Microscopic characteristics of Alternaria sp. included brown conidiophores holding chains of septatedconidia in acropetalous manner and conidia were ovoid or elliptical, 11 to 25 (17) µm long, 5 to 10 (7) µm wide, with one to three transverse septa and none or one longitudinal septum. One of the isolates (UFAH00014) was identified molecularly by sequencing the internal transcribed spacer region (ITS) and a small fragment of the elongation factor 1 alpha gene (EF1a) with primers ITS4ITS5 (White et al. 1990) and EF1a983EF1a2218 (Kurtzman et al. 2008), respectively. BLAST results showed 100% identity of the ITS sequence with A. alternata sequence HM013812.1 and 99% identity of the EF1a sequence with A. alternata sequence KP334736.1. Sequences of 584 bp for ITS (KU866390) and 993 bp for EF1a (KU886569) were uploaded to GenBank. To test Koch’s postulates, 10 µl of a 1.5 × 103 conidia/ml suspension of isolate UFAH00014 were inoculated on three wounded and three unwounded healthy peaches var. Diamante. Peaches were placed in a moist chamber at 27 ± 2°C; two noninoculated peaches were incubated under the same conditions as control. Wounded and unwounded inoculated peaches showed a firm, brown, circular, shallow rot over the surface at the third day, and at the fifth day, gray cottony mycelia was observed. Mycelia were recovered, cultured, and identified as A. alternata. This is the first report of alternaria rot caused by A. alternata in peach orchards in Ecuador, a disease that significantly contributes to severe postharvest losses.