Notes from a corner in Victoria
--E. D. Styles
A unique R1 allele? Although Stadler and Fogel initially described four different classes of R-r alleles, the only class that seems to have been easily distinguished from the rest was 'Class 4' (or 'Group D') R-r alleles, and that on the basis of a specific response to a plant color modifier. In later papers Stadler made a point of emphasizing that because of differences in expression in different tissues, it was virtually impossible to arrange different R-r alleles in any sort of continuous series. True as this may be, for convenience it is sometimes necessary to attach labels to particular R-r alleles that have unique enough features that allow them to be distinguished from other R-r alleles. One such R-r allele came into my stocks through the generosity of Ed Coe. In most pl stocks that I grow in Victoria, this allele determines green or near green anthers. It is not a 'Group D' allele, but sometimes I have mislabelled it as 'R-g' until for whatever reason I have crossed it with Pl, when it determines purple anthers as dark as any determined by the more predictable R-r alleles. As this allele seemed worthy of a special designation, and as it is in fact an 'R1' allele, I call it, as you may by now have guessed, 'E. Coe R1'. It is worth noting that the best expression of this allele in the anthers is 'restricted' to backgrounds that carry Pl. Any similarity to the terminology used by those working with inferior organisms is of course purely incidental.
Whp vs. whp. As with many others I am sure, I am trying to get parallel lines of stocks that, except for differences at the whp locus, are similar with respect to allelic variations at other flavonoid loci. The original reason for this attempt goes way back to when Ed Coe and I had the rather naive hope of being able to characterize the differences in expression of flavonoid genes in different inbred lines in terms of the known flavonoids. Apart from the fact that variations in the glycosidic patterns were more complex than thought, I at least had not recognized the difficulties in distinguishing possible effects of known differences between the inbreds (e.g., P-WW in K55 vs. P-WR in W22 and W23) from unknown specific or non-specific background effects. As Coe and his Coe-workers later found, K55 differs from other inbreds in carrying whp, and conceivably some of the differences we found between K55 and the other inbreds could have been due to differences at the whp locus. Of course there is no immediate way of testing that possibility except by evaluating the two alleles in backgrounds other than K55. Until recently I have not given much priority to the development of such lines, but have simply been saving those stocks that might one day yield testable comparisons. As I have gathered the whp C2 lines I need, I have noticed quite frequently a patchy or 'splotchy' anthocyanin phenotype in leaves of some whp C2 plants. In some families segregating for c2 and C2, the leaves of the c2 (whp) sibs shown necrotic patches in the same regions that their C2 (whp) sibs show anthocyanin patches. This patchiness is not present in r-g b lines, so that some R (or B) function seems to be involved. I am testing further to see what other genes may affect this phenotype (P, Pl, A1, bz1, etc.).
Defective Spm/En's at the P locus? In last year's Newsletter (page 111), I reported briefly on a P allele determining a 'grainy' pericarp that can mutate to a sectored form that in turn is capable of mutating to a stable P-RR. Although I have made no independent tests for Spm/En, I have traced back through my pedigrees, and it seems that I unwittingly introduced a non-defective Spm/En or Spm/En-like factor via a cross to a 'Rainbow Flint' stock. The original 'grainy' pericarp appears to result from the presence of a defective Spm/En(?) at the P locus that can be excised in the presence of the non-defective factor. Having satisfied my own mind as to the probable origin of this particular sectoring P allele, I then attempted to trace back through my pedigrees for the origin of another sectoring P allele that 'arose' in my stocks, distinguished by giving only very fine and infrequent pericarp sectors. As far as I can determine, this sectored form arose from a cross of the same 'Rainbow Flint' stock mentioned above, with a 'P-RW' allele from a Northwestern Dent source. This Northwestern Dent P-RW is a 'frustrating' P-RW because it maintains reasonably good pericarp expression in a Northwestern Dent background (where it segregates with a P-RR allele) but tends to 'lose' the pericarp expression when it is isolated from its partner P-RR or from its Northwestern Dent background. To all intents and purposes it becomes close to a 'P-WW' allele. Finding that a sectoring form can be derived by crossing it with a stock carrying a non-defective Spm/En or Spm/En-like factor, may be the clue that can lead to an understanding of the variable nature of this allele.
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