GENETICS OF RESISTANCE TO LEAF RUST IN THE COMMON WHEAT VARIETIES WEBSTER, LOROS, BREVIT, CARINA, MALAKOF AND CENTENARIO

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Abstract
Inheritance of seedling resistance to races 15 and 161 of leaf rust was investigated in the varieties Webster, Loros, Brevit, Carina, Malakof and Centenario. Backcross lines were developed in Thatcher and/or Prelude with leaf rust resistance derived from all the varieties except Brevit. The varieties and backcross lines were tested with nine races of rust. Webster was found to have the Lr2 gene which accounts for all of its resistance to the races used. Carina has an allele, Lr22, at the Lr2 locus, plus a gene tentatively assigned the symbol LrB, independent of the Lr2 locus which confers a type 2 reaction to races 15, 161 and probably several others. Resistance present in Loros is accounted for another allele, Lr24, at the Lr2 locus. Brevit also has an allele at the Lr2 locus which may be the same as that in Loros. In addition it probably has gene LrB conferring a type 2 reaction. Gene Lr1, which was independent of the Lr2 locus, accounts for all the detected resistance in Malakof. Centenario has the Lr1 gene and in addition has resistance to races 5 and 126a.The susceptible parents Thatcher and Prelude influence the dominance of the Lr2 alleles. The Lr22 allele in Carina x Prelude6 was partially dominant in crosses with Thatcher and completely dominant in crosses with Red Bobs. The Lr24 allele in Loros x Prelude6 was recessive in crosses with Thatcher and completely dominant in crosses with Prelude and Red Bobs.The expression of resistance of the Lr2 alleles to race 161 in Webster and Carina was different in crosses with Red Bobs than in those with Thatcher. In the crosses with Red Bobs one or more genes, which modified the degree of resistance to race 161, appeared to be segregating. This was not observed in crosses with Thatcher.