The occurrence and identification of powdery mildew on melon in Java, Indonesia

Abstract

Powdery mildew is a serious disease and causes considerable decline in production and fruit quality of melon (Cucumis melo L.) grown in Java, Indonesia. The fungal species that cause powdery mildew in Indonesia have never been reported. Therefore, the lack of knowledge about the biology of these fungi will inhibit in the handling of the eradication of powdery mildew further. A survey was conducted in 58 locations of melon cultivation in Central Java, East Java and West Java to study the occurrence of powdery mildew in Java. Powdery mildew species involved in the disease development were identified morphologically based on the anamorph characters such as the mycelium/hyphae, germ tube, appressoria, conidia and fibrosin bodies. In order to confirm the identification, the complete ITS (internal transcribed spacer) region of rDNA of powdery mildew species was amplified using ITS 1 and ITS 4 primers, sequenced directly and compared with sequences from the GenBank. Twelve isolates of powdery mildew species were collected from 58 melon cultivations in Java. Based on the morphological characters, the powdery mildew species had similarity characters to Podosphaera xanthii (Castagné) U. Braun & N. Shishkoff (syn. Podosphaera fusca (Fr.) U Braun & N Shishkoff). Molecular characterization of ITS rDNA produced 562 bp to 704 bp sequences. Homology search from the Genbank showed that the powdery mildew species in Java had 98 % to 99 % similarity to a sequence from the USA and it confirmed that the identity of powdery mildew species in Java as P. xanthii.