Figure 1.

Crossing scheme. For the three resistance genes, susceptible and resistance alleles are indicated in uppercase type and italics, respectively. A csr1-1 homozygous resistant plant was crossed with an axr1-3 homozygous resistant plant. A resulting F₁ plant was crossed with an ixr1-2 homozygous resistant plant. Four genotypes (generation 2) were expected from that cross. A resulting triple-heterozygous resistant-susceptible plant, i.e., a heterozygous plant at the three resistance loci, was isolated and selfed to produce the 27 expected genotypes described in Table 1. This cross design was replicated six times.