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Evaluation of a diverse collection of red clover germplasm for susceptibility to clover rot (Sclerotinia trifoliorum) and other important traits

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Clover rot, caused by Sclerotinia trifoliorum or S. sclerotiorum, is animportant disease in European red clover crops. Little is known about the differencesin aggressiveness among Sclerotinia isolates from red clover. No completelyresistant cultivars are available and few previous studies have screened large redclover collections for resistance. Moreover, the relations between susceptibility toclover rot and architectural and biotic factors were never studied before. In thisstudy we compared the aggressiveness of 30 Sclerotinia isolates from 25 locationsin Europe. Aggressiveness was assessed on young plants from five cultivars withdifferent resistance. Additionally, we evaluated a diverse collection of 121 red cloveraccessions. Yield, branching, flowering date, susceptibility to mildew (Erysiphepolygoni), rust (Uromyces trifolii) and viral disease were scored on the field. Cloverrot susceptibility was determined by inoculating young plants with five aggressiveSclerotinia isolates. Our 30 isolates differed in aggressiveness. Red clover accessionsdiffered in susceptibility to clover rot, but no accession proved completelyresistant. Cultivars were more resistant than landraces and wild accessions.Tetraploid cultivars were more resistant than diploid cultivars. Clover rot susceptibilitywas not correlated with the degree of branching or plant yield. On the otherhand, late flowering and erectly growing accessions were less susceptible to cloverrot. Clover rot susceptibility was not correlated with susceptibility to rust or viraldiseases, but negatively with mildew susceptibility. The best way to improve resistancemay be to recurrently select for resistant plants among diverse cultivars andlandraces with lower susceptibility. Tetraploidisation of diploid populations with ahigher resistance level can provide an additional level of protection.
Book: Quantitative Traits Breeding for Multifunctional Grasslands and Turf
Pages: 55-60
Number of pages: 6
ISBN:978-94-017-9043-7