Archivio Journal of Plant Pathology

Abstract:

The bottle gourd (Lagenaria siceraria, family Cucurbitaceae) is a medicinal plant (Sirohi and Sivakami, 1991) widely cultivated throughout India. In December 2014, powdery mildew symptoms were observed on L. siceraria in different fields of the Odisha state (India), i.e. circular white mycelial patches 1 to 2 mm in diameter on the upper surface of the leaves, which coalesced and developed into larger circular or irregular spots on both leaf surfaces. Infected leaves dried and eventually dropped. Conidiophores were 110-220×11-13.5 µm in size and produced 3 to 5 immature conidia in chains with a crenate outline. Foot cells were 40-75 µm long, straight, cylindrical, slightly constricted at the basal septum. Conidia were hyaline, ellipsoid-ovoid, 25-40×17-22 µm in size and had distinct fibrosin bodies. These morphological traits suggested this fungus to be a species of the genus Podosphaera, likely corresponding to Podosphaera xanthii (Braun and Cook, 2012). For confirmation, the internal transcribed spacer (ITS) region of rDNA from conidia was amplified with primers ITS 1/ ITS 4 and sequenced according to Babu et al. (2015). The resulting 182 bp sequence (GenBank accession No. KU376473) was analysed by BLAST homology search against GenBank database revealing 100% similarity with P. xanthii (KX061106, KR779870). Pathogenicity was determined by inoculating conidial suspension onto young leaves of five healthy potted L. siceraria in a greenhouse at 25-28ºC (>80% humidity). Five non inoculated plants served as control. Symptoms like those shown in the field developed 5-7 days post inoculation only on inoculated plants from which P. xanthii was reisolated. To our knowledge, this is the first report of P. xanthii as the cause of powdery mildew disease on bottle gourd in India.