Submitted to: Septoria International Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 9/15/1997
Publication Date: N/A
Technical Abstract: RAPDs and isozymes are quick, cheap, and easy methods for assaying genetic variation within populations. Although RFLPs have proven extremely useful for studying populations of the Septoria pathogens, they are more expensive in time, labor, and materials. To test the utility of isozymes and RAPDs, isolates of the Septoria pathogens Mycosphaerella graminicola (n = 59) and Phaeosphaeria nodorum (n = 45) from wheat, and of Septoria passerinii (n = 22) from barley, were assayed for genetic variation using 29 isozyme systems and 20 RAPD primers. From seven to eleven isozyme systems worked well in each species. Four enzymes were polymorphic in M. graminicola and S. passerinii, and two in P. nodorum. The maximum number of alleles at any isozyme locus was four. Genotypic diversity (measured by the Shannon information statistic) ranged from 74% of the theoretical maximum in S. passerinii to 36% in M. graminicola and only 27% in P. nodorum. The high level of genotypic diversity in S. passerinii may indicate that sexual recombination is occurring in this species. Gene diversity analysis in M. graminicola revealed that 13% of the genetic variation was due to differentiation between the central Midwest and northern populations. This indicated a possible restriction on gene flow between winter and spring wheats. There was a high level of variability for most of the RAPD primers tested. Genetic analyses of RAPD polymorphisms in M. graminicola were performed using progeny isolates supplied by G. Kema (Wageningen, The Netherlands). Virtually all RAPD bands were inherited as single Mendelian markers. Most were unlinked, but three pairs of tightly linked markers and one loose linkage group of eight markers were identified. One RAPD primer produced unique bands that could be used for species identification.