The virulence of 57 single colonies of Erysiphe graminis f. sp. hordei from Tunisia and Morocco was investigated using the Pallas near‐isogenic differential set. Virulence patterns in general were similar in both countries. Va8, Va10+Du2, V41/145, VLa and VRu2 appear to be common in the region. The resistance alleles Mla7 and Mla9, in combination with other resistances, were highly effective against the isolates tested. No virulence against mlo and Mla9 + k was detected in Tunisia. No virulence on Mla7 and Mla9 was detected in Morocco. The frequency of virulence against several resistances was significantly higher in Morocco than in Tunisia. On the other hand, virulence against other resistances was higher in Tunisia than in Morocco. Three isolates from Morocco infected mlo to an extent greater than previously described. All pathotypes were unique. An attempt is made to interpret the results by comparison with pathotype evolution in Europe.

Triticum dicoccoides, wild emmer wheat, Puccinia striiformis, yellow rust of wheat, stripe rust of wheat, temperature-sensitive genes, minor genes . SUMMARY Twenty-six selections of wild emmer collected at different sites in Israel and three entries obtained from Turkey were studied for the possible presence of temperature-sensitive genes controlling reaction to Puccinia striiformis . In tests carried out in Israel with a local P. striiformis isolate at two temperature regimes, 16 selections showed a change in infection rating toward resistance at the higher temperature regime . In comparable tests performed in the United States with a Montana P . striiformis isolate of different virulence pattern -including 14 of the same selections -ten entries displayed a temperature-sensitive reaction . Although slightly different temperature regimes were used in Israel and the United States, the results obtained were in general agreement . The shift toward resistance observed in the seedling tests at the higher temperatureprofile was also evident in the field in the mature plant stage with increasing spring temperatures .

No abstract

The response of barley Composite Cross XLI to selection for resistance to leaf rust was evaluated. Representative samples from eight cycles of recurrent selection were inoculated with an isolate of Pucdnia hordei Otth. in both the seedling and adult plant stage. Disease symptoms were evaluated 14 days after inoculation. The resistance in CC XLI increased with selection in the seedling stage from 15.1 to 20.5 %, and in the adult plant stage from 20.5 to 37.5 %, respectively. The largest gains in resistance were observed in the earlier cycles of recurrent selection. Significant fluctuations in percent resistant plants occurred between the years.

Transgressive segregation for higher resistance to stripe rust (Puccinia striiformis) was found in segregating populations of crosses of Triticum dicoccoides × Triticum aestivum and T. dicoccoides × Triticum durum. This indicates that additive "minor-effect" gene resistance to stripe rust can be transferred directly from the wild emmer (AABB) to cultivated tetraploid and hexaploid wheats. Since "major-effect" genes for stripe-rust resistance seem to be limited in number, Triticum dicoccoides appears to be a valuable currently untapped reservoir for additive genes which can be combined with genes existing in the tetraploid and hexaploid wheats.