Conditional lethality involving nuclear and cytoplasmic chlorophyll mutants in soybeans.

A conditionally lethal phenotype occurred when a nuclear chlorophyll mutant (y 20-k 2) was present with a cytoplasmic chlorophyll mutant (cyt-Y 2) in soybean (Glycine max [L.] Merr.). Nuclear mutant y 20-k 2, Genetic Type Collection Number T253, has yellow foliage, tan-saddle-pattern seed and is viable. The y 20-k 2 mutant cannot be separated by classical genetic tests into two separate components, y 20 (yellow foliage) and k 2 (tan-saddle-pattern seed). Mutant cyt-Y 2, T275, is inherited cytoplasmically, has yellow foliage, and is viable. The genotype cyt-Y 2 y 20-k 2/ y 20-k 2 is a conditional lethal; the genotype is lethal under field conditions, but plants survive under greenhouse conditions. This interaction is unique to y 20-k 2. This conditionally lethal genotype may be useful in molecular studies on the interaction between nuclear and plastid genomes.