A new r mutant

In 1976, a selfed ear from the progeny of an outcross of a homozygous purple aleurone Mu plant to a purple aleurone stock segregated for sectored seeds. The sectored seeds had a pattern of aleurone color similar to that of R-st. In 1977 the sectored seeds were crossed as males to all of the aleurone testers. Only in crosses to the r tester did anything other than purple seeds result. The cross to r produced completely non-purple seeds or seeds with only one or two very small flecks of purple (near yellow seeds). Selfs or sibs of plants from sectored seeds resulted in ears that had predominantly sectored seeds with a few full colored purple and a few yellow or near yellow seeds.

In 1978, reciprocal crosses of plants from sectored seeds were made with r tester. Again, when sectored plants were used as males the outcross seeds were yellow or near yellow. However, the ears from the reciprocal cross (sector plants as females) produced ears with mostly sectored seeds and a few full-colored purple seeds and a few yellow or near yellow seeds. Twenty selfs of plants from yellow or near yellow seeds on homozygous sectored ears produced ears that showed the typical sectored pattern (i.e., mostly sectored seeds with occasional full colored and yellow or near yellow seeds). These same plants crossed as males to r testers gave mostly yellow seeds with an occasional near yellow one. Full colored purple seeds from homozygous sectored ears gave plants that when selfed produced the typical homozygous sectored ears. Outcrosses of plants from full colored seeds as males to r tester produce ears with predominantly yellow seeds and a few near yellows. The reciprocal cross gave ears with predominantly sectored seeds and a few full colored and yellow or near yellow seeds. To date, no true stable yellow or stable purple stock has been derived from this r-sector mutant.

In 1978, yellow seeds from homozygous sectored ears were selfed and crossed to a purple aleurone stock or reciprocally crossed to the purple aleurone line. All selfs gave homozygous sectored seeds. All outcrosses of the sector stock as males gave homozygous purple ears. All crosses with sector stock as female segregated 1:1 for purple and mottled seeds, typical of r mottling. The purple aleurone stock was heterozygous for R-scm2, an R allele that does not mottle when crossed as a male with a r stock. These results suggest that R-standard r-sec r-sec seeds are mottled and R-scm2 r-sec r-sec seeds are purple. This was confirmed by crossing plants from the purple and mottled seeds as males to r testers. The cross of the plants from mottled seeds gave the expected ears with mottled (R r r) and yellow seeds (r-sec r r). Also, homozygous sector plants pollinated by pollen from homozygous R-scm2 plants produced ears with only purple seeds.

In summary, this new r allele (r-sec) when homozygous shows an aleurone pattern similar to R-st. When outcrossed to r stocks as male, little or no pigmentation is observed. However, when crossed as a female with r tester stocks, the r-sec phenotype is observed. Homozygous r-sec ears have a few full color and colorless seeds but these phenotypes have not been found to be transmitted as yet. This new allele behaves like a recessive r when crossed with R stocks (i.e., R r-sec r-sec seeds are mottled while R R r-sec are purple).

Donald S. Robertson


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

Return to the MNL 54 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page