Correlation between molecular and biological characters in identifying the wheat and barley biotypes of Stagonospora nodorum

Thirty-five isolates of Stagonospora nodorum from barley, wheat, and other hosts were identified as either the barley or wheat biotypes based on cultural characters and host specificity. Identification of the biotypes based on these phenotypic criteria was compared with genetic identification by analysis of restriction fragment length polymorphisms (RFLPs). Twenty-six probes randomly isolated from genomic DNA of a barley biotype isolate were used in the hybridization to differentiate the barley and wheat biotypes. Eighteen and 17 of the 26 probes detected no variation among 14 isolates of the barley biotype and 13 isolates of the wheat biotype, respectively, and unambiguously differentiated the two biotypes. Genetic distance, an estimate of accumulated number of allele substitutions per locus, is 2.286 between the barley and wheat biotypes. The genetic similarity was very high (>0.82) within each of the two biotypes and was very low (0.12) between the two biotypes. Clustering of the isolates based on individual hybridizing DNA bands correlated with biotype identification based on biological characters. The wheat and barley biotypes were then compared with isolates of Stagonospora avenae f. sp. triticea and an isolate of Stagonospora arenaria by hybridizing with 31 anonymous DNA probes (11 from a wheat biotype, 12 from a barley biotype, and eight from S. a. triticea). Two isolates of S. nodorum of unknown biotype, SN91-X and SNO38NY-89, used in a previous study, were considered to be the wheat biotype based on DNA banding patterns. Based on allele frequencies of the 31 RFLP loci, the estimated genetic distance between the barley biotype and the wheat biotype of S. nodorum was as great as between any of the two biotypes and S. a. triticea. Likewise, analysis based on discrete hybridizing bands showed that the barley biotype had a closer relationship with S. a. triticea than with the wheat biotype. Two probes from the barley biotype were specific for the barley biotype and did not detect any DNA bands in the wheat biotype. These barley biotype specific probes may be used as natural markers for identification of the barley biotype.