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 Obregón, 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 75 F 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 Est 1 and Est 3 on the long arm of Chromosome 3 with ≈2% recombination. The locus was assigned gene symbol Ea sp . The dominant allele Easp suppressed the recessive allele ea sp and permitted the expression of other unidentified Ea loci conferring relative lateness. Allelism tests indicated recessive epistatic interactions between the Ea sp locus and the Ea k and Ea 7 loci. The ea sp recessive homozygote suppressed numerous other Ea maturity loci and headed earlier than the other three recessive homozygotes (i.e., ea k , ea 7 , or ea c ), which were phenotypically similar.
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Gallagher et al. (1991) studied this question.