Pyricularia zingiberi, a causal agent of diamond shape leaf spot disease of ginger in Indonesia

Abstract

Ginger is an economically important commodity of Indonesia. A diamond shape leaf spot disease has been reported in ginger cultivation areas. The aim of this study was to determine the causal agent of the disease. Two isolates were obtained by a single conidia isolation method on Pyricularia typical conidia, followed by propagation on a PDA medium. The conidial suspensions were sprayed onto leaf of white and red ginger types for pathogenicity test. The inoculated plants were placed at room temperature with 80%-90% air humidity for 48 hr, then put back in the green house. The fungal identity was determined based on its morphological characteristic and confirmed by molecular characterization through DNA extraction and amplification using ITS5 and ITS4 primers. The optimal growth temperature of the fungus was assayed by planting each isolate onto PDA medium, then incubated at 4 level temperatures. The same temperature levels was also tested on conidial germination, on WA medium. The artificial inoculation showed both isolates infected all types of ginger, but red ginger showed lower in disease severity. Morphologically, both isolates are corresponding to Pyricularia zingiberi. The fungus grows optimally between 25 °C and 31 °C. PCR analysis supported the morphological observation results.