The tomato powdery mildew fungus Oidium neolycopersici.

UNLABELLED: summary Pathogen: Powdery mildew fungus; Ascomycete although sexual stage is yet to be found; an obligate biotroph. IDENTIFICATION: Superficial mycelium with hyaline hyphae; unbranched erect conidiophores; conidia, ellipsoid-ovoid or doliform, 22-46 x 10-20 microm, lack fibrosin bodies; conidia formed singly, rarely in short chains of 2-6 conidia; appressoria lobed to multilobed, rarely nipple-shaped. Pseudoidium species. HOST RANGE: Broad, reported to attack over 60 species in 13 plant families, particularly members of the Solanaceae and Curcubitaceae. SYMPTOMS: Powdery white lesions on all aerial plant parts except the fruit. In severe outbreaks the lesions coalesce and disease is debilitating. Agronomic importance: Extremely common in glasshouse tomatoes world wide but increasing in importance on field grown tomato crops. CONTROL: Chemical control and breeding programmes for disease resistance.