Experiments with id1

--B. Burr and Véronique Szabo

The mutation id1 causes the maize plant to prolong its vegetative stage and, in the field, turns it into a short day plant. We were interested in the mutation because it behaved as one might expect a phytochrome mutation to act. In this investigation we compared three alleles, mapped the mutation relative to RFLP markers, and examined the effect of the mutation on light dependent plant pigmentation.

We obtained the id1-R allele from the Maize Co-op and two other putative alleles from Bob Brawn while he was associated with CIBA-GEIGY. The alleles from Brawn were id-207 and id-Compeigne. Flowering can be prematurely induced in id-R homozygotes after only a week of 13 hour nights. Flowering could be induced in id-207 after about one month of short days, but short day treatment did not induce premature flowering in id-Compeigne homozygotes. Plants heterozygous for either id-207 or id-Compeigne were self-pollinated and crossed to induced id-R homozygotes. Selfed progeny and outcrossses from the same plant were then grown out to confirm that an id allele was present and test for allelism. Both id-207 and id-Compeigne were allelic with id1-R.

id1 has been reported to map on 1L in the vicinity of bz2. Since one of the phytochrome loci is nearby, we were interested to see if the two might map to the same locus. We obtained a segregating population from the Maize Co-op in which id had been crossed to inbred M14 and selfed. Three RFLP markers from this region, bnl17.06, bnl15.18, and ynh20, were tested on 24 plants in an F2 population. There were no recombinants with bnl17.06 which we estimate to map on 1L at position 99 or about 26 map units from phy1.

id1-R homozygotes, which appeared to be b, pl, r-g, were crossed to a B-S, pl, R-g stock and the heterozygotes were selfed. We examined two large F2 populations obtained in this fashion. Fully 3/4 of the id/id plants were sun-red and these plants showed no reduction in pigmentation in comparison with their normal sibs. We conclude that id1 has no effect on light dependent anthocyanin production.

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