EXPRESSION OF BARLEY YELLOW DWARF VIRUS AND RUSSIAN WHEAT APHID RESISTANCE GENES IN AND FERTILITY OF SPRING WHEAT X TRITICALE HYBRIDS AND BACKCROSS LINES

The Barley Yellow Dwarf Virus disease (BYDV) and the Russian wheat aph id (RWA) Diuraphis noxia (Mordvilko) have caused significant losses to wheat and barley in several areas of the world. Important sources of resistance to both BYDV and RWA have been found in Triticale. Differen t generations of interspecific wheat x Triticale crosses were produced and the progenies were screened for BYDV and RWA tolerance. Plants wi th equal chromosome numbers showed different levels of fertility. A si gnificant correlation was observed between pollen fertility and seed s et in primary florets (r = 0.57). In general, pollen fertility, seed s et and the number of euploid plants (2n = 42) increased from one gener ation to the next. The expression of BYDV tolerance varied from popula tion to population. Additive effects were predominant in Fl and some b ackcross populations. A dominant effect of rye tolerance genes was als o observed in few populations. A monogenic trait or a quantitative (po lygenic) character would not agree with the observed segregation patte rns. The heritability of this oligogenic tolerance was quite different between populations and in many populations the tolerance genes were only partially expressed. Some transgressive segregation for tolerance and sensitivity was demonstrated. The genes controlling tolerance to RWA in Triticale lines, Muskox 658 and Nord Kivu were not expressed in advanced lines resistant to BYDV. This indicates that tolerance genes for BYDV and RWA in these lines are located on different chromosomes.