Sclerotinia trifoliorum. [Descriptions of Fungi and Bacteria].

A description is provided for Sclerotinia trifoliorum. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Trifolium spp., also Medicago sativa and other herbaceous leguminous forage crops including Anthyllis vulneraria, Lathyrus spp., other Medicago spp., Melilotus spp. and Vicia spp. including V. faba (on this host causing 'Bean rot'; the causal agent of which has often been referred to as S. trifoliorum var. fabae Keay) and V. saliva. Although approximately 100 hosts have been recorded for this pathogen there is often a lack of conclusive evidence that S. trifoliorum and not another Sclerotinia species is to blame. DISEASE: Rot, called variously: Stem rot, Crown rot, Brown patch of lawns, Clover sickness, Clover canker. Symptoms include leaf rot, petiole rot and stem rot. Initial leaf spotting may be followed by these more severe rot symptons. The foliage usually turns grey-green as though scalded, then may wither and the rot may spread. In lucerne the leaves may be totally destroyed by the pathogen, but it takes a long time to reach the root system through the comparatively thick stem. TRANSMISSION: The development of apothecia occurs in the autumn. Ascospores infect the leaves, and rotting of the clover plants sets in the following early spring. The fungus is able to complete its entire life-cycle as a saprophyte. Spread from plant to plant takes place chiefly along affected petioles, but the pathogen may grow about 2 cm over the soil from a nutritional base. The fungus can persist in the crown of the plant throughout the summer until harvest. Sclerotia may germinate to produce apothecia and ascospores which may infect emergent shoots; sclerotial germination is favoured by light, well-aerated soils and a temperature between 10° and 20°C. Mycelium and ascospores remain viable (in a dry state) for seven months, sclerotia buried in the soil survive for more than seven years. In vitro conidia will infect clover plants. GEOGRAPHICAL DISTRIBUTION: Africa: Egypt; Asia: China, India, Israel, Japan, Korea; Australasia & Oceania: Australia (NSW, Viet., Tas., W.A.), New Zealand; Europe: Austria, Belgium, Bulgaria, Czechoslovakia, Denmark, Eire, Finland, France, Germany, Greece, Hungary, Italy, The Netherlands, Norway, Poland, Romania, Sweden, Switzerland, UK, USSR; North America: Canada (Alberta, British Columbia, Manitoba, Que, PEI), USA (widespread), Mexico; Central & South America: Chile (see CMI Distribution Maps of Plant Diseases No. 274).