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Production of F₁ Seed in Castorbeans by Use of Sex Genes Sensitive to Environment¹

By growing castorbeans, Ricinus communis L., in different environments, genotypes were obtained with both the N-pistillate gene for female racemes and environmentally sensitive genes for interspersed-staminate flowers. These genotypes were homozygous for the gene, but not always for the genes for interspersed-staminate flowers. With penetrance of the genes for interspersed-staminate flowers at a location having high summer te~nperatures, a July average of 91 F, plants were propagated by selfing or sibbing. With nonpenetrance at locations having lower summer temperatures, July averages of 75 to 83 F, F₁ hybrid seed was produced without roguing. Previous methods using the gene required roguing monoecious plants from the female parent, often involving more than 50% of the plants.

In test crosses, presence of interspersed-staminate flowers was recessive to absence. There was wide variation among genotypes tested for frequency of interspersed-staminate flowers, suggesting a polygenic system with considerable opportunity for selection.

² Research Agronomist (now stationed at the University of Arigona) and former Research Agronomist Crops Research Division, ARS, USDA, (now Farm Advisor, University of California).

Received for publication March 28, 1966.