Evaluation of red clover (Trifolium pratense L.) resistance to Sclerotinia crown and root rot (Sclerotinia trifoliorum) in the laboratory and field conditions

Red clover (Trifolium pratense L.) is very productive in the first two years of harvest but afterwards it tends to thin out dramatically and finally die. In Lithuania, the main disease causing this problem is Sclerotinia crown and root rot (Sclerotinia trifoliorum Eriks.). The present study was aimed to determine red clover resistance to Sclerotinia crown and root rot in the laboratory and field conditions. Investigations were carried out at Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry. Resistance of red clover varieties and breeding lines to Sclerotinia crown and root rot was investigated in 2012-2014 in the field under natural and artificial infection conditions. Diploid (43: 20 varieties, 20 breeding lines, 2 wild ecotypes and 1 semiwild ecotype) and tetraploid (41: 24 varieties and 17 breeding lines) red clover was investigated. In the laboratory experiment, red clover seeds were treated with oxalic acid which is the main toxin of Sclerotinia spp. This experiment enabled us to evaluate seedling resistance to Sclerotinia crown and root rot. The same varieties and breeding lines as in the field experiment were investigated. The seedlings were treated with 0, 5, 7.5, 10, 15, 20 and 30 mM oxalic acid concentrations. The most resistant varieties were found to be 'Kaive', 'Kvarta', 'Arimaidiai', 'Skriveru tetra', 'Van', 'Ostro', 'Radviliai' and 'Jogeva 433', and breeding lines Nos. 2102, 1582, 2190, 2087 and 2739. The most sensitive varieties were 'Sara', 'Sabtoron', 'Britta', 'Triton' and 'Astra', and breeding lines Nos. 2297, 2268, 2093, 2296, 2300 and 2298.