Backcross lines of gene LrT2 for resistance to leaf rust in the common wheat (Triticum aestivum L.) 'Thatcher' unexpectedly show improved resistance to stem rust compared with that of the recurrent parent. Genetic–cytogenetic evidence indicates that LrT2 is on chromosome 7D, which is known to carry the "suppressor" gene(s) that prevent the expression of stem rust resistance conferred by other genes in 'Canthatch'. Thus, LrT2 may be a nonsuppressing allele of the suppressor gene(s) or be closely linked to such an allele. LrT2 has been designated Lr34. Key words: Triticum, wheat, rust resistance.

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The common wheat (Triticum aestivum L.) cultivars Chinese Spring and Sturdy have adult‐plant resistance to leaf rust caused by Puccinia recondita Rob. ex Desm. To study the genetics of this resistance both cultivars were crossed and backcrossed to ‘Thatcher’, a leaf rust susceptible cultivar. The two cultivars or resistant selections from the above crosses were also crossed with backcross lines having Lrl2, Lr13, and Lr34 genes for adult‐plant leaf rust resistance. The backcross F2 families and F2 populations were grown in a field rust nursery artificially inoculated with a mixture of P. recondita isolates. The segregation for rust reaction of adult plants indicated that both cultivars have a combination of genes Lrl2 and Lr34. To assist in the identification of Lr34 in these cultivars, adult‐plant leaf rust resistance from each cultivar was transferred into Thatcher.

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