Expression of the R-r:Ecuador(1172) allele

R-r:Ecuador(1172) is a complex allele of the R locus that has been the subject of many recombination studies. Most of these studies have been done against a genetic background of the W22 inbred line. We have found that when our W22 R-r:Ecuador stocks are outcrossed, the specific features associated with the Ecuador allele (leaf, silk, pericarp color, etc.) are not always expressed; in fact some of our non-W22 lines of R-r:Ecuador cannot be distinguished from lines carrying other R-r alleles. Possible explanations include the loss by segregation of specific modifiers carried in W22, or the loss of structural components of the R locus required for tissue specific pigment production. Introduction of the Ecuador allele from these non-W22 stocks into plants homozygous for a3, a recessive intensifier of plant pigment, confirms that it is still fundamentally different from other R-r alleles. The enhancing effect of a3 on most other R-r alleles is minimal, and can be shown clearly only in the absence of B locus action (i.e., with b). The young leaves of a3 R-r:Ecuador plants are deep purple as they emerge from the whorl, but become progressively greener as they mature, so that at any one point in time, the plant appears continuously graded in anthocyanin pigmentation.

E. Derek Styles


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