Components of Slow Mildewing in Oat Powdery Mildew Caused by Blumeria graminis F. Sp. avenae

Powdery mildew of oat (Blumeria graminis f. sp. avenae) is the most deleterious foliar disease of cultivated oat, particularly in cooler regions. Slow mildewing, a partial resistance behaves genetically as a quantitative trait and can be assessed by comparing with mildew development on a highly susceptible cultivar grown under the same conditions. The slow mildewing components (disease severity, AUDPC and infection rate) under field conditions were studied in 15 moderately susceptible along with highly susceptible check (HJ-8) selected from panel of 303 field screened oat genotypes. The lines were categorized into slow mildewing categories based on terminal disease severity and AUDPC values. The AUDPC values of these lines ranged from 475 (JPO-45) to 1775 (HJ-8) and infection rate ranged from 0.053 to 0.144, being minimum in JPO-45 and maximum in HJ-8. All the tested lines gave 3 or 4 infection type under greenhouse evaluation and were designated as moderately susceptible and susceptible genotypes. Three oat lines showing moderately susceptible reactions, along with HJ-8 were selected to carry out experiment on slow mildewing in greenhouse. Among all the selected lines, the incubation period varied between 3-4 days and latent period between 4-5 days, i.e. maximum of 4 and 5 days, as compared to minimum of 3 and 4 days in HJ-8, respectively. After 11 days of inoculation, countless conidiophores bearing conidia were produced on all the lines except in IG-03-203. The size of powdery mildew colony was recorded and maximum colony size 3.87 mm was observed in HJ-8 followed by 2.87, 3.37 and 3.30 mm in IG-03-203, JPO-20 and KRR-AK-06, respectively.