Stocks and new factors
--G. F. Sprague
Due to poor health I have given up my field plantings. I have attempted to provide seed to the Coop of all my stocks which might have the most general interest. The following notes refer to several unfinished items which, hopefully, may be of interest to someone.
Dotted stocks. The dotted stocks involved in these studies involve Dt1, Dt2, Dt3 and Dt4 from the Maize Coop and Dt6, Dt7, Dt(a), Dt(b), Dt(c), Dt(d), Dt(e), Dt(f), Dt9 and Dt(n) derived from the earlier virus studies. Dt(b) may not be workable as it exhibits only 1 or 2 small dots per kernel. There are a few other instances where dotting appears to involve either the c or r alleles. These are not considered here.
Linkage relations for Dt(a) through Dt(n) have not been established. Two approaches have been used for allelism testing. Dt/Dt combinations have been produced and advanced to F2. Failure of segregation for non-dotted kernels would indicate the two parental types were alleles. On this basis none of the (a)-(n) parental types were allelic. Diallel crosses were also made among their true breeding non-dotted counterparts. Essentially all produced non-dotted F1 kernels. However when the non-dotted types were advanced to F2 they exhibited Dt:dt segregation. Proportions were quite variable with the dt class often exceeding 50%. With selection of the more heavily dotted kernels homozygous Dt/Dt types can be recovered in F3 or later generations.
These generalizations suggest some special types of reactivation or transposable element involvement. If transposable element or elements are involved they must differ from the typical trans-acting types such as Ac, Sm, Uq--as dt/dt crosses are non-dotted in F1.
After stabilization the Dt's recovered from dt/dt crosses may exhibit one of the parental dotting patterns (i.e. the Dt6 pattern from the dt1/dt6 cross) with or without its characteristic linkage pattern. This suggests either that patterns are conditioned by factors other than the Dt allele or the Dt allele has been transposed to a new site. The linkage relations of Dt(a) through Dt(n) are still unknown. Dt1, Dt2 and Dt6 are the best candidates for further exploration of this phenomenon and tests are underway.
Relevant stocks have been given to the Coop.
A new dwarf. A rosette type dwarf was found and tested against other recessive rosette dwarfs. No allelism was observed. In tests performed by B. O. Phinney this dwarf does not respond to gibberellic acid. Preliminary tests suggested it was allelic to an1. Test crosses were made with the an1-bz2-6923 deficiency stock from the Coop. The F1 seedlings were rosette dwarfs. However, this test was inconclusive as the deficiency stock shed poorly, increasing the possibility of contamination. Following a severe aphid infestation the F1 plants developed a soft rot and no progeny were obtained.
A gametophyte factor on chromosome 6. In the course of testing for allelism among the Coop's collection of glossy mutants, one cross exhibited an unexpected Y:y segregation. The numbers observed suggested either a gametophyte factor or a second y locus, similar to y1, conditioning the near absence of carotenoid pigments. F3 progeny tests supported the gametophyte assumption. The mean percentage of y kernels or segregating ears was 40.6. Other presumed instances of gametophyte factors include su and pr. These have been given to the Coop.
Green corn. Seed was obtained from a former County Extension Agent now located in Oklahoma who has a hobby of maintaining specialty corn. This type he calls his John Deere corn. The corn has aleurone which is an off color shade of green. A sample was supplied to Dr. E. D. Styles who indicated (personal communication) that the color was definitely in the aleurone, and that the anthocyanins are the normal acylated cyanidin glycosides present in Pr aleurones with no other flavonoids in easily detectable concentrations. Tests indicated the presence of an additional pigment, but this could not be resolved due to a lack of a colorless counterpart. Further work on identification will require additional material.
In crosses of "green" with the aleurone tester stocks the green color is so diluted in the F2 kernels as to make separations difficult and questionable.
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