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My Research

Aims

To identify potential new soil treatments for control of Sclerotinia disease and to assess the impact of pathogen diversity.

 

Background

Sclerotinia sclerotiorum

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).

 Sclerotinia subarctica

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).

 

 

References

BARDIN, S. D. & HUANG, H. C. 2001. Research on biology and control of Sclerotinia diseases in Canada1. Canadian Journal of Plant Pathology, 23, 88-98.

BOLAND, G. J. & HALL, R. 1994. Index of Plant Hosts of Sclerotinia sclerotiorum. Canadian Journal of Plant Pathology-Revue Canadienne De Phytopathologie, 16, 93-108.

BOLTON, M. D., THOMMA, B. P. H. J. & NELSON, B. D. 2006. Sclerotinia sclerotiorum (Lib.) de Bary: biology and molecular traits of a cosmopolitan pathogen. Molecular Plant Pathology, 7, 1-16.

CLARKSON, J. P., CARTER, H. E. & COVENTRY, E. 2008. Diversity of Sclerotinia sclerotiorum from agricutural crops and meadow buttercup in the UK. Journal of Plant Pathology, 90, 2.405.

CLARKSON, J. P., CARTER, H. E. & COVENTRY, E. 2010. First report of Sclerotinia subarctica nom. prov. (Sclerotinia species 1) in the UK on Ranunculus acris. Plant Pathology, 59, 1173-1173.

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.

HEGEDUS, D. D. & RIMMER, S. R. 2005. Sclerotinia sclerotiorum: When “to be or not to be” a pathogen? FEMS Microbiology Letters, 251, 177-184.

HOLST-JENSEN, A., VAAGE, M. & SCHUMACHER, T. 1998. An approximation to the phylogeny of Sclerotinia and related genera. Nordic Journal of Botany, 18, 705-719.

JENSEN, B., FINCKH, M., MUNK, L. & HAUSER, T. 2008. Susceptibility of wild carrot (Daucus carota ssp. carota ) to Sclerotinia sclerotiorum. European Journal of Plant Pathology, 122, 359-367.

LEINER, R. H. & WINTON, L. M. 2006. Differential production of sclerotia by isolates of Sclerotinia sclerotiorum from Alaska. Canadian Journal of Plant Pathology, 28, 435-440.

MERRIMAN, P. R. 1976. Survival of sclerotia of Sclerotinia sclerotiorum in soil. Soil Biology and Biochemistry, 8, 385-389.

PHILLIPS, A. J. L. 1987. Carpogenic Germination of Sclerotia of Sclerotinia sclerotiorum: A Review. Phytophylactica, 19, 279-283.

PURDY, L. H. 1979. Sclerotinia sclerotiorum: History, diseases and symptomatology. host range, geographical distribution and impact. Phytopathology, 69, 875-880.

SAHARAN, G. S. & MEHTA, N. 2008. Sclerotinia diseases of crop plants

biology, ecology and disease management. Dordrecht ; London: Springer,.

WILLETTS, H. & WONG, J. 1980. The biology of Sclerotinia sclerotiorum, S. trifoliorum, and S. minor with emphasis on specific nomenclature. The Botanical Review, 46, 101-165.

WINTON, L. M., KROHN, A. L. & LEINER, R. H. 2006. Genetic diversity of Sclerotinia species from Alaskan vegetable crops. Canadian Journal of Plant Pathology, 28, 426-434.

 

 

Main Supervisor:

Dr John Clarkson

john dot clarkson at warwick dot ac dot uk

 

 

Collecting sclerotia from carrot crops