ARS | Publication request: Variation in fungicide sensitivity between two field populations of Sclerotinia sclerotiorum

Submitted to: Proceedings of the International Sclerotinia Workshop
Publication Type: Abstract Only
Publication Acceptance Date: May 15, 2009
Publication Date: December 15, 2009
Citation: Attanayake, R., Johnson, D., Porter, L., Chen, W. 2009. Variation in fungicide sensitivity between two field populations of Sclerotinia sclerotiorum. Proceedings of the International Sclerotinia Workshop.

Technical Abstract: Sclerotinia sclerotiorum (Lib.) de Bary is a ubiquitous, necrotrophic pathogen. It causes white mold on more than 400 plant species including economically important crops such as potato, canola, soybean, pea, chickpea and lentil. Extensive studies have been carried out on S. sclerotiorum. This study is designed to investigate the effect of different cultural practices and cropping histories on fungicide sensitivity of S. sclerotiorum. A total of 57 isolates (26 isolates from a commercial potato field and 31 isolates from a commercial dry pea field) were used in the comparison. Fungicide application and irrigation was a regular practice in potato production, whereas no fungicides or irrigation were used in dry pea production. Variation in sensitivity among the isolates to the fungicide benomyl [methyl-1-(butylcarbamoyl)-2-benzimidazole carbamate] was measured in triplicates in PDA plates amended with six different concentrations (0.0, 0.025, 0.05, 0.1, 0.2 to 0.4 µg a.i./ml of agar). Agar plugs of 5 mm diameter from the edge of an actively growing colony of each isolate were placed in the middle of a 9 cm plate and colony diameters were determined 36 hr after inoculation. The experiment was repeated once. Highest variation in colony diameter and percent inhibition was found at 0.2 µg a.i./ml concentration. At this concentration, the pea field population showed greater variance (0.927) than did the potato population (0.735), suggesting that the potato population is more adapted to fungicide selection than the pea population. Population differentiation (QST value) was 0.492. These isolates are being assessed for variation at 12 microsatellite loci to estimate genetic differentiation at neutral markers between the two populations.