The seed-borne pathogen, Pyrenophora graminea is the causal agent of barley leaf stripe disease. Field trials were undertaken to investigate the impact of leaf stripe on barley yield in two growing seasons in Southern Syria, by comparing plots with and without artificial inoculation. Ten barley cultivars originating from widely dispersed areas were used. The overall response to leaf stripe differed with the differences in susceptibility levels of the cultivars. Grain yield, the number of tillers, kernel weight and plant biomass decreased as disease severity increased. Diseased plants had fewer tillers, and as a consequence a reduced grain yield per plant. High yield losses resulted from leaf stripe in susceptible cultivars in Arrivate, Furat 1, WI2291 and Arabi Abiad with 44%, 50%, 73% and 92%, respectively. The cultivar Banteng had the best level of resistance to the disease, and is a candidate donor for resistance in future breeding programmes. As leaf stripe can dramatically reduce barley yields under favourable conditions, the disease should be considered by crop improvement programmes in Mediterranean and similar environments.

Spot blotch, caused by Cochliobolus sativus, is a common foliar disease of barley. Information on the variability of virulence in C. sativus is essential for the production of spot-resistant barley cultivars. The virulence variability of isolates of this pathogen collected from different regions of Syria was evaluated using 10 differential barley genotypes originating from widely dispersed areas. Genotypes showed a continuous range of response from very susceptible to moderately resistant but none was immune to the disease. A cluster analysis indicated that the isolates had distinct differential virulence patterns within the three groups. A mean disease rating of 3.71 was the separation point between avirulent and virulent reactions. The data demonstrated that variation occurred in the virulence of and the resistance level to isolates and among genotypes, respectively. Isolate C41 exhibited distinct differential virulence patterns, high frequency and low variance in all genotypes. To incorporate adequate levels of resistance into future barley genotypes, disease evaluations should be made with C. sativus isolates that express the full spectrum of virulence found in Syria.

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The usefulness of IRAP (inter-retrotransposon amplified polymorphism) and ITS-RFLP (restriction of PCR-amplified internal transcribed spacers of the rDNA) markers in the analysis of 39 Pyrenophora graminea isolates was determined. Each marker system could discriminate between all of the isolates in detecting polymorphism, albeit with variable efficiency. IRAP and ITS-RFLP produced 85% and 77% polymorphic bands, respectively, with a corresponding mean polymorphic information content (PIC) of 0.38 and 0.36. The IRAP marker index ratio (2.41) was higher than ITS-RFLP (1.50). On one hand, the quality nature of data (QND) was higher for ITS-RFLP (0.169) than IRAP (0.093). However, correlation between both marker similarity matrices was significant (r = 0.34, p < 0.05). These findings suggest their combined use in phylogenetic analysis. To our knowledge, this is the first report of a comparison involving these two advanced DNA marker systems.