Garajová, Žofia (2018) Understanding the impacts of temperature and soil moisture on the germination of Sclerotinia sclerotiorum sclerotia. PhD thesis, University of Warwick.

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Abstract

Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic fungal pathogen causing Sclerotinia disease in a variety of crops all over the world. Infection of most host plants is through airborne ascospores released from mushroom-like apothecia, produced following carpogenic germination of soilborne sclerotia. Disease control relies mostly on fungicides to kill the ascospores and but efficacy is dependent on the correct timing of the limited number of allowed sprays.

Temperature and soil moisture are critical factors affecting carpogenic germination of S. sclerotiorum sclerotia with previous work suggesting a two-stage process; a “conditioning” phase (Stage 1, S1) requiring cold temperatures followed by a “germination” phase (Stage 2, S2) requiring warmer temperatures. Little is known about the conditioning process, and isolates within and between different geographic locations, vary in their individual temperature requirements. This study aimed to further investigate the effect of temperature and moisture on carpogenic germination of S. sclerotiorum sclerotia and model these underlying processes.

Extensive controlled environment experiments identified clear differences in the temperature requirements of sclerotia from two UK S. sclerotiorum isolates (L5, L6) for carpogenic germination. Differences in optimum conditioning requirements were apparent in S1 and S2. Furthermore, a two temperature optima, “spring” and “summer” were identified for isolate L6, explaining a possible adaptation of an UK isolate to initiate further cycles of infection within a single year.

Examination of the effect of a dry period during the S1 conditioning phase significantly limited and delayed germination, while dry periods introduced in S2 arrested germination but germination quickly resumed after moist conditions were restored.

Sclerotia of S. sclerotiorum isolate L5, exposed to various temperatures regimes were also examined microscopically for the presence of primordia (apothecial initials). Primordia were observed in sclerotia incubated at 11 - 20°C as early as 7 days, and the number increased with time and temperature; however, no germination was observed in sclerotia at 20°C without conditioning. In contrast, primordia were not observed until after 70 days at 4°C. When sclerotia were conditioned at 4°C for 28 days and transferred to 17°C, primordia and stipe germination was observed 14 days after transfer.

Data from these controlled environment experiments led to the formulation of a new model for carpogenic germination of S. sclerotiorum sclerotia, whereby conditioning and germination phases run in parallel rather than sequentially with each associated with low and high temperature respectively. Rates of conditioning and germination for times to 10, 25, 50, 75 and 90% sclerotial germination were determined for 8 temperatures in a first step of model parameter optimisation, which informed the shape of the temperature response curve with rate functions combining linear and logistic parts of the curve fitted to times to 10% germination.

The utility of a potential model to forecast germination of S. sclerotiorum sclerotia in the field is discussed.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QK Botany S Agriculture > SB Plant culture
Library of Congress Subject Headings (LCSH):	Sclerotinia sclerotiorum, Field crops -- Diseases and pests, Germination, Sclerotinia sclerotiorum -- Effect of temperature on, Soil moisture
Official Date:	September 2018
Dates:	Date Event September 2018 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Mead, A. (Andrew) ; Clarkson, John
Sponsors:	BASF SE
Format of File:	pdf
Extent:	xxiv, 314 leaves : illustrations
Language:	eng

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