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Allelic and Nonallelic Interactions of af, st, and tl^w Genes in Pea¹

Interaction effects between alleles at one locus with other loci and with environments influence degrees of dominance and F₁ hybrid performance. To evaluate the effect of interactions among alleles, eight near-isogenic lines of pea (Pisum sativum L.) with the eight combinations of genes at the af, st, and tl^w loci were self-fertilized and intercrossed in a half-diallel design. Plants were grown at Portici, Italy, in a randomized complete block design with three replications; results were compared with a similar experiment at Norwich, UK. The afgene was partially dominant for number of fertile nodes, number of pods and seeds, and yield per plant. The three genotypes ranked in order: AfAf > Afaf > afar for each of these traits. The st gene was partially dominant for stipule weight, but Stst heterozygotes exceeded both the homozygous StSt and stst genotypes in both yield and yield components. The recessive homozygotes were the least productive genotypes for all but one character. The tl^w gene affected only leaf weight and number of basal branches, and showed overdominance for the latter trait. Since heterozygotes are morphologically very similar to dominant homozygotes, the mutant alleles studied can show pleiotropic effects also when the leaf phenotype does not vary or it varies slightly. Allelic interactions at one locus were influenced by the alle!ic state of the other two loci for number of fertile nodes and pods per plant, node of first flower, leaf weight, and number of pods at the first flowering node. The degree of dominance at the Af and St loci for plant yield varied with environment.

Key Words: Pisum sativum L. • Foliage types • Pleiotropism • Heterozygosity • Nonallelic interactions • Environmental effects

² Research geneticist, Vegetable Breeding Ctr., CNR, Portici, Italy; research geneticist; and professor of agricultural genetics, Inst. of Agronomy—Plant Breeding, Univ. of Naples, 80055 Portici, Italy.

Received for publication May 19, 1986.