Resistance to scald (Rhynchosporium secalis) in barley (Hordeum vulgare L.).: II.: Diallel analysis of near-isogenic lines

Near-isogenic lines (NILs) in the BC7 generation for resistance to barley scald (Rhynchosporium secalis Oudem. J.J. Davis) have been developed with 'Ingrid' as the recurrent parent (RP). Starting from 23 differential varieties and a classical BC program with disease tests followed by selection for the RP phenotype, NILs from the following 9 sources have been selected for analysis: 'Turk', 'Brier', 'CI 8162', 'La Mesita', 'Hispont'. 'Atlas46', 'Modoc', 'Hudson' and 'Abyssinian'. The 9 NILs were crossed in a half-diallel design. The NILs, their F(1)s and F(2)s were tested along with the donors and RP against R. secalis isolates '4004' and '2' to understand the degree of resistance in each NIL, allelism/linkage and dominance relationships among the NILs. With isolate '4004'. 13 of the 36 crosses segregated in the F, generation. A common feature was that either 'Atlas 46'-NIL or 'Hudson'-NIL was one of the parents. Thus it seems that 7 out of the 9 lines are allelic, probably at the Rrs1 complex locus on chromosome 3H, one carries the Rrs2 locus on chromosome 7H and one is independent of both. Segregation with isolate '2' was harder to establish because of a weak resistance gene in the RP which acted additively with the other resistance genes and resulted in a narrower phenotypic range. Degree of dominance/recessiveness depended on the crosses as well as the isolate used. In general GCA effects were much stronger than SCA.