Electrophoretic Karyotypes of Sclerotinia sclerotiorum

PATTERNS OF DESCENT IN CLONAL LINEAGES AND THEIR MULTILOCUS FINGERPRINTS ARE RESOLVED WITH COMBINED GENE GENEALOGIES

Clonal lineages in the filamentous ascomycete (fungi) Sclerotinia sclerotiorum were determined by analysis of genealogies of four loci: the intergenic spacer of the nuclear ribosomal repeat (IGS; approximately 4 kb), the translation elongation factor (EF-1α; approximately 300 bp), an anonymous region (44.11; approximately 700 bp), and the calmodulin gene (CAL; approximately 400 bp). Three of the four loci are physically unlinked. The combined analysis of the four loci provided the best estimate of phylogeny, which is consistent with a pattern of some recombination among clonal lineages against a background of predominant clonality. Comparison of gene genealogies with a phylogeny inferred from DNA fingerprints and a combined phylogeny of the entire dataset identified convergent or parallel changes in fingerprints. Analysis of the entire data matrix allowed us to resolve patterns of descent among clonal lineages that could not be inferred from fingerprints alone and to discern recent episodes of divergence that were not detected in gene genealogies. Prerequisites for applying this approach to other systems are a haploid context for inferring multiple gene genealogies (such as the mitochondrial genome) that indicate limited recombination and another data matrix that identifies recently evolved genotypes.

Highly variable minichromosomes and highly conserved endoglucanase genes in the phytopathogenic fungusMacrophomina phaseolina

Electrophoretic karyotype analysis of 17 different isolates of Macrophomina phaseolina revealed the presence of from zero to six minichromosomes (less than 2000 kilobases (kb)), with the smallest size observed being approximately 785 kb. Each isolate had a unique minichromosome pattern, whether from the same field or from different continents. The highly variable minichromosome pattern contrasts to the high degree of conservation found in the two endoglucanase genes (egl1 and egl2) harbored by M. phaseolina. Gene structure was conserved, as judged by Southern analysis, and restriction fragment length was conserved. Digestion of DNA with Sal1 resulted in a 2-kb fragment containing egl1, and a 4-kb fragment contained egl2. Conservation of restriction fragment length suggests that the portions of the genome harboring the endoglucanases are less subject to rearrangement, relative to minichromosome DNA.Key words: charcoal rot, cell wall degrading enzymes, cellulase.