Influence of matric potentials on carpogenic germination of sclerotia ofSclerotinia sclerotiorum. I. Development of an inclined box technique to observe apothecium production

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Abstract
A 4.1-m-long inclined box with five longitudinal compartments was filled with fine sandy loam and distilled water was added at the lower end. Due to capillary rise, steady state saturated and unsaturated flow of soil water, vapor movement in the soil atmosphere, and a controlled steady rate of evaporation from the soil surface, constant soil matric potentials between 0 and -15 bars were obtained in the box. The angle of inclination was reduced above the middle of the box to fit the moisture characteristic curve of the fine sandy loam. After soil moisture had reached equilibrium, sclerotia of Sclerotinia sclerotiorum pre-treated at -15 bars for 1 month at 5°C and non-pretreated sclerotia were placed at 2 cm intervals on the surface of the soil and at 1 cm depth. At about 15°C germination started after 2 weeks. There was no interaction between matric potential and speed of germination. The largest number of apothecia was produced near field capacity (-0.11 to -0.40 bar). However, apothecia developed between 0 and -4 bars. When exposed to light periodically 56% of all stipes at the soi surface formed apothecia.