A new cherry allele at the R locus: r-ch(Hopi)

The symbol r-ch(Hopi) refers to an r allele isolated from a stock kindly supplied to us by the late Dr. Brink and tracing back to a Hopi Indian strain. Like other "cherry" accessions it leads to red pigmentation in seedling and plant tissues, while its presence together with the Pl factor in the plant genotype results in a deep purple pigmentation. In addition, following 24 hours of illumination, the colorless scutellum of r-ch(Hopi) seeds turns red and patches of pigment appear in the aleurone. Anthocyanin production in these seed tissues is a unique feature of this allele.

Plants of R-st o7/r-ch 07 genotype crossed by r-g o7 males yielded ears showing the following segregation:
 
  Stippled  Colorless
No. kernels +        o7 +          o7
4489 81     1676 2709    23

These results differ from expectation in two respects: (1) the R-O7 recombination amounts to 2.3%, a value much lower than the expected 26%; and (2) colorless kernels are found in the progeny of the testcross in excess of the expected value (61 vs. 50%), indicating a preferential transmission of the r-ch marked chromosome. Decrease of recombination in the R-O7 region and preferential segregation are observations consistent with an abnormal structure of the r-ch chromosome.

The "cherry" phenotype conditioned by r-ch(Hopi) could be accounted for by a genetic determiner found in some r accessions extracted from Bolivian populations (Gavazzi et al., 1985, in press) lying 1-2 units R distal and symbolized Sn (red scutellar node). The female parents of the previous cross would then be designated R-st sn o7/r-g Sn O7, and evidence in favour of the component structure of r-ch would be searched for among the stippled kernels in the progeny of these females crossed with r-g sn o7 males. Upon germination in the presence of light, parental stippled seeds would remain colorless in the scutellum tissues, while recombinants with an R-st Sn chromosome would quickly turn red. Accordingly, stippled kernels were germinated 48 hours in darkness, then transferred to light (20,000 lux) and scored 24 hours later for scutellum pigmentation.

The following results were obtained:
 
  + o7
Stippled kernels r1      nr r      nr
1752 29     47 3     1673

1r and nr refer to red and nonred scutellum as determined after 72 hours of germination

None of the 23 presumed R-st sn recombinants so far tested could be confirmed, all of them being R-st/r-ch contaminants.

Such negative results cannot be taken as evidence against the compound structure of r-ch(Hopi) considering that Sn lies 1-2 units R distal and that recombination in the R-O7 region appears dramatically reduced in the r-ch bearing chromosome.

Further testing is required to prove that the "cherry" phenotype of this r allele is due to Sn.

G. Gavazzi, M. L. Racchi and A. Gorrini


Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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