Screening for powdery mildew (Erysiphae polygoni DC.) resistance in mungbean (Vigna radiata (L.) Wilczek) using excised leaves

Abstract

A simple, reliable method for assessing powdery mildew reaction on excised mungbean leaves has been developed and used for screening germplasm accessions. Third trifoliate leaves from 21–25 day old field-grown plants were cultured in enamel trays filled with tap water at 21±1°C, 12 h/day photoperiod (4136 lux/m² from incandescent and white fluorescent light). After 9–12 days such leaves showed rooting from petiole and substantial root growth followed. Excised leaves could be maintained upto 40 days. Leaves were sprayed with conidial suspension (3·5×10⁶ conidia/ml) of a local isolate of powdery mildew fungus. In susceptible types, powdery mildew lesions appeared 8–10 days after inoculation, enlarged and coalesced to cover the entire leaf area in 20 days. Fifty five germplasm accessions were tested using this method; all except 7 RUM accessions were susceptible. These RUM accessions showed resistant reaction even after two reinoculations. They were also resistant in the field under natural powdery mildew infection.