Interactions among Loci Conferring Photoperiod Insensitivity for Heading Time in Spring Barley

The inheritance of extreme earliness for heading time, as measured by days to awn appearance (DAA), in «Super Precoz (2H)» (SP) a photoperiod-insensitive spring barley (Hordeum vulgare L.), was investigated in field studies under short daylengths at Davis, CA, and Ciudad Obregon, Sonora, Mexico, to obtain additional information on gene action. The DAA data from parental, F 1 , F 2 , F 3 , and F 4 generations indicated that extreme earliness in SP was conferred by a single locus when homozygous recessive. Data from 75F 3 families evaluated for DAA in a field study and by starch gel electrophoresis of seedling-plumule extracts indicated that the locus conferring extreme earliness was linked to Est1 and Est3 on the long arm of Chromosome 3 with ≃2% recombination