MOLECULAR KARYOTYPE OF THE PHYTOPATHOGENIC FUNGUS SCLEROTINIA-SCLEROTIORUM

Molecular techniques have been used to characterize different field is olates of Sclerotinia sclerotiorum, an ubiquitous phytopathogen, Chrom osomal DNA resolved by pulsed-field gel electrophoresis (PFGE) reveale d that S. sclerotiorum contains at least 16 chromosomes ranging from 1 .5 Mb to 4.0 Mb. The size of the haploid genome was estimated to be 43 .5 Mb, Six field isolates with different levels of virulence on sunflo wer germlings or green beans were differentiated by random amplificati on of polymorphic DNA (RAPD), and analysed by clamped homogeneous elec tric field electrophoresis. This analysis revealed few chromosome-leng th polymorphisms among these strains, Chromosomal DNA hybridization in dicated that the endopolygalacturonase-encoding pg1 gene is localized on the smallest chromosome of all the strains, whereas the ribosomal D NA mapped to different-sized chromosomes. The less-aggressive strain w as characterized by the presence of a supernumary small band, presumab ly consisting of dsRNA. In contrast to numerous other phytopathogenic fungi, this study reveals a strong karyotypic stability among the stra ins of S. sclerotiorum which may be preserved by the sexual mode of re production of this species.