To identify potential new soil treatments for control of Sclerotinia disease and to assess the impact of pathogen diversity.
The ascomycete fungus Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic homothallic pathogen affecting many economically important crops (Hegedus and Rimmer, 2005), with a wide host range of over 400 plant species (Boland and Hall, 1994) and a world-wide distribution (Purdy, 1979). Lettuce, oilseed rape, beans, peas, potatoes and carrots are among the crops susceptible to Sclerotinia disease, with infection levels varying year to year due to seasonal environmental conditions (Saharan and Mehta, 2008).
Due to the large host range the symptoms caused by S. sclerotiorum vary, but the white fluffy mycelial growth is an early symptom. Pale or dark brown lesions may be seen on the base of stems of herbaceous plants, often quickly covered by white mycelium, or infection may begin on a leaf and move into the stem (Saharan and Mehta, 2008). Multiple genotypes of S. sclerotiorum have been identified in the UK, with one genotype being found more frequently than the rest, at different locations and on different crops It is thought that the genotypes vary in their aggressiveness (Clarkson et al., 2008).
The long term survival structures for S. sclerotiorum are small black resting bodies called sclerotia (Willetts and Wong, 1980), capable of germinating carpogenically to produce apothecia (Bolton et al., 2006) or myceliogenically to produce hyphae which can attack plant tissues directly (Bardin and Huang, 2001). Carpogenic germination is affected by many environmental factors (Phillips, 1987) and apothecia are usually produced after canopy closure in crops as the high soil moisture required for apothecia production is maintained to an extent by shading (Bolton et al., 2006). The longevity of sclerotia is variable, being influenced by many factors including time and depth of burial (Duncan et al., 2006), and soil fumigants (Merriman, 1976). The number of sclerotia produced by S. sclerotiorum on different plant tissues is also variable and is an important factor in determining the inoculum levels in soil following an infected crop. An infected cabbage head was found to produce 250 to 500 sclerotia, (Leiner and Winton, 2006) while an infected carrot root produced up to 30 (Jensen et al., 2008).
A relative of S. sclerotiorum, S. subarctica has been recently identified in the UK (Clarkson et al., 2010) after previously only being found in Norway on wild hosts (Holst-Jensen et al., 1998) and on vegetable crops in Alaska (Winton et al., 2006). The symptoms caused by S. subarctica are very similar to S. sclerotiorum and therefore may be undetected in crops in the UK. Further work is required to establish distribution of this species in the UK, on both crops and wild hosts (Clarkson et al., 2010).
DUNCAN, R. W., DILANTHA FERNANDO, W. G. & RASHID, K. Y. 2006. Time and burial depth influencing the viability and bacterial colonization of sclerotia of Sclerotinia sclerotiorum. Soil Biology and Biochemistry, 38, 275-284.
biology, ecology and disease management. Dordrecht ; London: Springer,.