RECOMBINATION BETWEEN A CROWN RUST RESISTANCE LOCUS AND AN INTERCHANGE BREAKPOINT IN HEXAPLOID OAT

The oat (Avena sativa L.) cultivars, Steele and Dumont, differ by a ch romosome interchange. Two tightly linked or allelic crown rust resista nce genes (Pc-63 and Pc-38) are located on one of the segments involve d in the interchange. Recombinant chromosomes can result from crossing -over in the region between the crown rust resistance locus and the in terchange breakpoint. Our objectives were to use a diallelic duplicate locus to (i) identify recombinant BC1F1 genotypes with Pc-63 in the i nterchanged position, (ii) estimate the linkage relationship between t he crown rust resistance locus and the interchange breakpoint, and (ii i) recover duplication genotypes that possess four copies of Pc-63. Se gregation of BC1F2 families was used to detect recombination within an interchanged chromosome segment in F-1 interchange heterozygotes. Onl y 3/7 of the single crossover recombinant gametes could be recognized by duplicate dominant segregation in BC1F2 families. After inoculation of 145 BC1F2 families with a crown rust (Puccinia coronata Corda var. avenae W.P. Fraser & Ledingham) isolate avirulent on Pc-63 and virule nt on Pc-38, rye identified 11 recombinant families segregating 15R:1S . A 15:1 segregation ratio indicated Pc-63 recombined to an interchang ed position as a result of crossing-over between the crown rust resist ance locus and the interchange breakpoint Our data indicated Pc-63 was linked in repulsion and distal to the interchange breakpoint with 17. 7% recombination observed between the crown rust resistance locus and the breakpoint. Testcross segregation ratios confirmed that recombinat ion occurred and allowed identification of a true breeding duplication genotype that possessed four copies of Pc-63. Increasing the dosage o f Pc-63 did not alter the expected infection type conferred by a one o r two copies of Pc-63.