EFFECTS OF ALIEN AND INTRASPECIES CYTOPLA SMS ON THE EXPRESSION OF MAJOR NUCLEAR GENES OF WHEAT RESISTANCE TO BROWN RUST .1. ANALYSIS OF F2RECIPROCAL HYBRIDS

The resistance of wheat reciprocal hybrid seedlings to two clones of b rown rust with different virulence is studied. The hybrids are obtaine d from crosses between isogenic lines of the cultivar Thatcher carryin g genes Lr1, Lr9, Lr15, Lr19 and alloplasmatic lines of the cultivar P enjamo 62 with cytoplasms derived from the species Triticum dicoccoide s var. fulvovillosum, Aegilops squarrosa var. typica, and Agropyron tr ichophorum. F2 hybrids between Th, its isogenic lines, and the euplasm atic cultivar Penjamo 62 are also analyzed. Reciprocal differences in the resistant/susceptible ratio in the F2 are revealed. These differen ces may be due to the specific effect of maternal cytoplasm on the exp ression of the major gene Lr. It is quite possible that it modifies th e expression of other genes located in original nuclear genomes of the cultivars Thatcher and Penjamo 62. Complementary interaction of these genes in a hybrid genome led to segregation of a certain proportion o f the resistant in the F2 phenotypes. Another mechanism of maternal cy toplasm control may involve its influence on the transmission of the r esistance genes located on different chromosomes of the nuclear genome . Pathogen virulence did not affect resistance only in cross combinati ons between isogenic lines and the alloplasmatic (trichophorum)-Penjam o 62 one or lines carrying the gene Lr9.