Environmental Factors for Germination of Sclerotinia sclerotiorum Sclerotia

Abstract

Basal stalk rot of sunflower is an economically important and rather unique disease among crops that are susceptible to Sclerotinia sclerotiorum. This disease is the result of myceliogenic germination of sclerotia whereby the vegetative hyphae infect the sunflower below the soil level. In contrast, sunflower head rot and similar diseases of susceptible crops result from carpogenic germination to produce airborne ascospores that infect above ground senescent or wounded tissues. Research was initiated on several factors reported to affect sclerotia germination as a prelude to genomic investigations of myceliogenic and carpogenic germination. Specifically, the effects of inoculum development temperature, sclerotia development temperature, conditioning temperature, conditioning of hydrated and desiccated sclerotia, and the duration of sclerotia desiccation on germination strain Sun-87 sclerotia were reevaluated. As reported previously, we were not able to use conditioning temperature from -20°C to 30°C to differentiate myceliogenic and carpogenic germination for either hydrated or desiccated sclerotia. Besides conditioning temperature, inoculum production temperature, sclerotia formation period and temperature, and desiccation failed to distinguish the two forms of germination. The high level of variability for sclerotia germination between experiments indicates the critical nature of repeating all experiments aimed at understanding factors that influence sclerotia germination. Thus, other methods will be required to discover a reliable and non-confounded method that clearly differentiates myceliogenic and carpogenic germination of S. sclerotiorum.