Genetic and cytogenetic analyses of the A genome of Triticum monococcum. II. The mode of inheritance of spring versus winter growth habit

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Abstract
The study on the mode of inheritance of spring versus winter growth habit in Triticum monococcum is the first in a diploid wheat species. The results are discussed in light of the information available on the genetics and cytogenetics of this character in Triticum aestivum. Two spring habit and six winter habit lines were used in these investigations. Statistical analyses of progenies in each of these lines clearly established the true-breeding nature of all eight lines with respect to days to heading. Analysis of F1 and F2 results of crosses between the two spring habit lines 68 and 293 showed the following: (i) neither line carries winter habit alleles at any of the major gene loci determining growth habit; and (ii) four of five minor allele pairs determine the phenotypic differences between them. Monohybrid F2 and testcross ratios in crosses between spring habit line 68 and each of the six winter lines lead to the following conclusions: (i) differences between spring and winter growth habit in each cross are due to alleles of one major gene; (ii) the allele for spring habit is completely dominant to that for winter habit in each cross; and (iii) all these lines are genotypically identical or very similar at all modifying gene loci. These results imply that only one major gene determines growth habit in this species. Diallel (critical) crosses among the six recessive lines indicate that complementation does not occur in any of the F1''s. Therefore, all these recessive genes represent mutations in the same gene. If these results are characteristic of all winter lines in Triticum monococcum, they permit the initial conclusion that only one major gene determines growth habit in this diploid species. This locus is in all likelihood the Vrn1 locus since it is the only one of the five major genes identified for growth habit, that is present in the A genome of Triticum aestivum. All six recessive lines respond to natural vernalization. This lends further suport to our initial conclusion. Because the six recessive lines head at five different times we conclude that a multiple allelic series occurs at this locus. Specifically, at least three and probably five recessive alleles responsible for different heading dates among the winter lines, and at least one dominant allele for spring habit, occur at this locus.