|Kema, Gert - IPO-DLO, WAGENINGEN, NL|
Submitted to: International Congress of Plant Pathology Abstracts and Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 11, 1998
Publication Date: N/A
Technical Abstract: Analyses of 59 isolates of the septoria tritici blotch fungus Mycosphaerella graminicola from wheat plants in Minnesota, North Dakota, Indiana and Ohio using 20 RAPD primers revealed that almost every isolate had a unique genotype. Thus, sexual reproduction probably occurs commonly in these populations. The only exceptions were isolates from different lesions on the same leaf, which usually had identical genotypes. This pattern is consistent with epidemics initiated by ascospores, with subsequent spread on the same leaf by asexual pycnidiospores. Genetic analyses of more than 100 putative RAPD loci revealed that most behaved as simple Mendelian markers. Several loose linkage groups were identified that will be integrated into a more complete genetic map of M. graminicola. Most of the loci segregated for the presence or absence of a band. Knowledge of the genetic basis for each RAPD phenotype simplified scoring and ensured that only reliable bands were retained. Four loci segregated as if they had codominant alleles, i.e., each isolate possessed exactly one band within a certain size range. Putative alternative alleles at each locus were cloned and sequenced. In each case, the different bands were identical except for a single insertion or deletion of 20 - 60 base pairs. Thus, the bands were alternative alleles at single genetic loci. These loci were converted to sequence characterized amplified regions (SCARs) by designing specific primer pairs that amplified the variable regions. The SCARs eliminate problems with RAPDs due to longer primer lengths and increased specificity. Scoring is more reliable because the alleles differ in size rather than varying plus or minus. These markers are now available for analyzing genetic variability within populations of M. graminicola.