Postharvest Black Spot Disease in Broccoli Caused by Alternaria brassicicola

Abstract

Broccoli in markets frequently suffers from black spot disease and rapidly turns yellow, thus losing commercial value. To clarify the causal pathogen, we isolated micro-organisms from infected broccoli and examined them for their pathogenicity using an inoculation assay. The pathogenic isolates obtained were further examined and identified using morphological and molecular characteristics. For molecular analyses, the nucleotide sequences of ribosomal DNA internal transcribed spacer regions were determined, and specific gene sequences were amplified using PCR. The highly pathogenic isolate obtained was identified as Alternaria brassicicola HLYB-4. Vegetative hyphae of the isolate slowly elongate and produce spores, even during cold storage (5 °C). Optimal hyphal growth was observed at 25 °C. Both ethylene production and chlorophyll degradation of diseased broccoli increased after infection with this isolate, promoting senescence of florets. However, higher temperatures (35 °C) severely restricted growth of the pathogen.