Field and Growth Chamber Evaluation of Powdery Mildew Disease on Deciduous Azaleas

• Published in: HortScience Vol. 45; no. 5; pp. 784 - 789
• Main Authors: Long, Michael C, Krebs, Stephen L, Hokanson, Stan C
• Format: Journal Article
• Language: English
• Published: Alexandria, VA American Society for Horticultural Science 01-05-2010
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; cultivars; disease resistance; disease severity; Erysiphe; Erysiphe azaleae; field experimentation; Fundamental and applied biological sciences. Psychology; genetic resistance; germplasm screening; growth chambers; leaf area; methodology; nursery crops; ornamental woody plants; plant pathogenic fungi; powdery mildew; Rhododendron; Ohio; Minnesota; Evaluation; Don; Horticulture; Disease; Mycosis; disease resistance breeding; Woody plant; Pentanthera G; Infection; Field; Deciduous plant; Disease resistance; Sensitivity resistance; Growth chamber; Dicotyledones; Angiospermae; Genetic improvement; Spermatophyta; Rhododendron subgen; Ericaceae; Rhododendron
• ISSN: 0018-5345; 2327-9834
• DOI: 10.21273/hortsci.45.5.784

Forty-one deciduous azalea (Rhododendron subgen. Pentanthera G. Don) cultivars were assessed for powdery mildew (PM) resistance in a two-location, 3-year field trial. Disease severity (percent leaf area affected) on abaxial leaf surfaces was used to rate the level of field resistance. This measure was proportional to (r = 0.83) but higher than estimates from corresponding adaxial surfaces. Eleven of these cultivars (27%) appeared to be highly resistant under field conditions, i.e., evidence of PM on the leaves was zero or near zero. Twenty-three of the cultivars evaluated in the field experiment were also evaluated in a growth chamber experiment. In contrast to the field study, PM was more severe on the adaxial leaf surface in the growth chamber but still highly correlated with the abaxial response (r = 0.93). Based on adaxial disease scores, no cultivars in the growth chamber experiments were completely resistant. Growth chamber disease ratings based on either leaf surface were predictive of field performance (r2 = 0.62), suggesting use of the chambers could serve as a low-cost, off-season, early selection component of a deciduous azalea PM resistance breeding program.