First report of anamorphic Podosphaera on Gerbera jamesonii in India

Gerbera jamesonii (Asteraceae) is an ornamental plant grown in the Northeastern states Karnataka and Maharashtra, India. It is an important cut flower, considered suitable for both export and domestic markets due to its ability to withstand long transportation (Aswath & Rao, 2006). Powdery mildew symptoms were observed on the leaves of G. jamesonii during April 2008 in an experimental field of ICAR Research Complex for NEH Region, Barapani, Meghalaya, India. Almost all the plants in the field were infected. Symptoms were more prominent on upper leaves, which later turned necrotic.  Surveys conducted in nearby areas revealed the widespread occurrence of this pathogen. Voucher specimens have been deposited in the herbarium collection of the ICAR Research Complex for NEH Region (ICARHNEH- 84) and Martin-Luther-Universität, Institut für Biologie, Bereich Geobotanik, Herbarium, Germany (HAL 2328 F.).

Light microscopy revealed the presence of ectophytic mycelium and indistinct appressoria, which was confirmed by scanning electron microscope (SEM). Catenate conidia with fibrosin bodies were also observed, excluding the possibility of Golovinomyces (previously Erysiphe) cichoracearum, which is reported on this host from India(Farr & Rossman, 2009). Foot cells of conidiophores (39-58 x10-12 µm) were followed by two or three shorter cells, terminated with ellipsoidal conidia (20-24 x 18-22 µm) produced in chains (Figs. 1, 2). The basal septum of the conidiophore was adjacent to the mycelium. Germ tubes developed laterally without any distinct appressoria (Fig. 2). Smooth wrinkles were evident on the conidial surface through SEM. No perfect stage was found to be associated with this fungus. These characteristics confirm the identity as the anamorphic Podosphaera sp. (Cook et al., 1997). Major host expansion and genetic divergence of this genus has been reported on Asteraceae (Hirata, 2000). There is a possibility that this species belongs to P. xanthii (Braun et al., 2001). Pathogenicity was confirmed by dusting conidia on healthy, potted G. jamesonii plants with uninoculated plants serving as controls. Inoculated plants developed symptoms after a week, whereas control plants remained healthy. Podosphaera has been reported on gerbera from China, Japan, Romania, Korea, Brazil and Australia (Farr & Rossman, 2009). To our knowledge, this is the first record of powdery mildew caused by Podosphaera sp. on G. jamesonii in India.