INHERITANCE OF RESISTANCE IN BARLEY TO SEVERAL PHYSIOLOGIC RACES OF THE SCALD FUNGUS

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Abstract
The genetics of resistance to races U. S. -1, U. S.-7, U. S.-8, and U. S.-9 of the fungus Rhynchosporium secalis, cause of scald in barley, was investigated in eight barley varieties. The scald reactions were classified into 5 types, 0 to 4, where type O was completely resistant and type 4 was fully susceptible. Five genes were identified, all dominant in their action. The barley varieties Atlas and Atlas 46 possessed the Rh2 gene which conditioned a type 1 reaction to race U.S. -1 and a type 2 reaction to U. S. -7 of R. secalis. In addition to the Rh2 gene, Atlas 46 had the Rh3 gene, which conditioned a type O reaction to races U. S.-1, U. S.-7, and U. S.-8. The varieties Turk and possibly Brier also possessed the same gene. A third gene, Rh4, conditioning a type O reaction to races U. S.-7, U. S.-8, and U. S.-9, was present in La Mesita, Trebi, and Osiris. This gene was closely linked with the Rh3 gene, with a recombination value of 1.0 [plus or minus] 0.78 percent. Modoc carried the Rh42 gene, an allele at the Rh4 locus, which conditioned a type O reaction to races U. S.-8 and U. S.-9 and a type 1 and type 2 reaction to races U. S.-l and U. S.-7, respectively. A gene, Rh5, conditioning a type 2 reaction to race U. S.-8, was present in Turk; it was independent of the Rh3 and Rh4 genes.

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