PHYSIOLOGICAL SPEC'AllZATION IN Puccinia striiformis AND GENES CONDITIONING RESISTANCE TO YELLOW. RUST DISEASE IN CERTAIN WHEAT CUTUVARS IN EGYPT

The annual survey of wheat yellow rust races in 200212003 growing season
resulted in the presence of 10 physiological races of Puccinia striifonnis West. f. sp.
trifici. Races 198 E 150 and 198 F 148 were the highest virulence on some Yr's
resistance genes (differential varieties). On the other hand, race OEO was avirulent
on all differential varieties (Yr's resistance genes). Probable yr7 resistance gene
found in five tested commercial wheat varieties i.e. Sakha 8, Sakha 93, Sakha 94,
Giza 170 and Sids 4. Also, Yr SU postulated to be found in two tested wheat varieties
i.e. Sakha 93 and Giza 170. On the other hand, Sakha 69, Giza 160, Giza 168,
Gemmeiza 9 and Sids 1 probably lack Yr's resistance genes from tested near-
isogenic lines. However, postulation that Yr 7 exhibited the highest frequency (41.6%)
followed by Yr SU (16.6%), Yr 6, Yr 8, Yr 2+ (8.3%) for each. On the other hand, Yr
7+, Yr 3N. Yr CV. Yr SP, Yr SO and Yr 9+ were not represented in the tested near-
isogenic lines. Many of the cultivars studied can be combined into groups on the
basis of sharing the same genes for resistance. Some cultivars probably have Yr 7
and/or Yr SU and other cultivars contained Yr 8. It is likely that most of these cultivars
have genes in addition to those determined by this method as well as genes for adult
plant resistance.