Screening of Soybean and Sunflower Cultivars for Escape Resistance to Sclerotinia Sclerotiorum Under Field Conditions

Abstract

Ten soybean cultivars and 21 sunflower cultivars were screened for escape resistance, i.e., tolerance towards increasing sclerotinia disease potential, from 2017 to 2021, in sequentially planted field experiments. Cultivars were randomised and planted in multiple rows, where plants were either artificially inoculated and naturally infected. A modified Finlay-Wilkinson regression analysis was used to determine escape resistance response types based on the relationship between observed disease incidence (%) within a cultivar and disease potential. Sclerotinia disease potential is defined as the mean disease incidence across all cultivars within a planting date, in either artificially inoculated or naturally infected plots per crop. Three cultivar reaction types were identified, i.e., high escape resistance to increasing sclerotinia disease potential ( b > 1), low escape resistance to increasing sclerotinia disease potential ( b < 1), and linear relationship with changing sclerotinia disease potential ( b ≈ 1). The sclerotinia disease potential required to initiate disease onset and the rate of response after onset were also determined. Low levels of escape resistance to sclerotinia were recorded in all but two soybean cultivars and four sunflower cultivars where b > 1.30 and onset potentials of > 10.00%. The regression approach can be used to quantify a cultivars’ escape resistance, if an adequate number of disease potentials are included. Planting cultivars with a b > 1.00, a high onset potential and subsequent low response rate could contribute to reducing the risk of sclerotinia diseases.

Keywords: Sclerotinia, soybean, Sunflower, cultivar evaluation, escape resistance