Effects of temperature and duration of preconditioning cold treatment on sclerotial germination of Claviceps purpurea

Abstract

Claviceps purpurea is an important ovary-infecting pathogen that replaces seed with sclerotia in Kentucky bluegrass grown for seed. Sclerotia overwinter in the soil and germinate in the spring to produce ascospores that infect grass seed ovaries. To better understand environmental conditions affecting ascospore production, the effects of preconditioning cold treatment and subsequent incubation temperature on germination of sclerotia were determined in growth chambers under controlled conditions. Preconditioning cold treatment was essential for germination only in treatments where the incubation temperature was high (at least higher than 20°C). At lower incubation temperatures (10 to 20°C), preconditioning also played a role in improving sclerotial germination. Preconditioning at 4°C (in darkness) for 4 to 8 weeks followed by incubation at 10 and 20°C (cycle of 12 h each of darkness and light), or constant 15°C (cycle of 12 h each of darkness and light), was optimal for ergot germination. When sclerotia were preconditioned for 4 weeks or longer, number of incubation days required for initiation of germination was not affected by temperature in the range from 10 to 25°C (cycle of 12 h each of darkness and light), although the duration of germination (or the progress speed of germination) was still affected by temperature. A simple model was developed based on laboratory results and validated with historic spore trap data collected from various Kentucky bluegrass fields in Oregon (Willamette Valley, central Oregon, and Grande Ronde Valley). The prediction model could predict ascospore onset well and explained 55% of variation in the data.