Environmental factors for germination of Sclerotinia sclerotiorum sclerotia

Authors: Foley, Michael; Dogramaci, Munevver; West, Mark; Underwood, William

Submitted to: Journal of Plant Pathology & Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2016
Publication Date: 11/3/2016
Citation: Foley, M.E., Dogramaci, M., West, M.S., Underwood, W.R. 2016. Environmental factors for germination of Sclerotinia sclerotiorum sclerotia. Journal of Plant Pathology & Microbiology. doi:10.4172/2157-7471.1000379.

Interpretive Summary: Sclerotinia is a serious fungal plant pathogen of many broadleaf crop and non-crop plants. It produces resting structures called sclerotia such that the pathogen can maintain a quiescent state in the soil in the absence of suitable hosts or conditions favorable for germination. Sclerotinia is the causal agent of two distinct disease in sunflower called basal stalk rot and head rot. Stalk rot is unique among host plants in that it results from germination of sclerotia in the soil follow by root invasion of hyphae. In contrast, the second and common mode of germination leads production of airborne ascospores that ultimately cause head rot. Little information exists on environmental factors that regulate the two modes of sclerotial germination. To pursue future genomic investigations on sclerotia germination, we sought to reexamine some environmental factors that purportedly were able to induce the two forms of germination such that there was no overlap between the two forms. However, we were not able to use conditioning temperature, inoculum production temperature, sclerotia formation period and temperature, or desiccation to distinguish the two forms of germination.

Technical 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. We initiated research on several factors reported to affect sclerotia germination as a prelude to genomic investigations of myceliogenic and carpogenic germination. Specifically, we reevaluated 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. As reported previously, we were not able to use conditioning temperature from -20 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 differentiate myceliogenic and carpogenic germination of S. sclerotiorum.