Twins, pseudo-twins, and other seedling and kernel abnormalities in maize: a long term record
--Chase, SS; Kernan, P
In the search for parthenogenetic and androgenetic seedlings, starting at Ames in 1946 and continuing at DeKalb, many thousands of thousands of seedlings were examined by the senior reporter and colleagues. Many unusual individuals were preserved for drawing. Presented here are drawings, some representative of their class, a few directly depicting individuals. The frequency of ‘haploidy’ in maize, averaged among progenies, is about one per thousand seedlings. Many of the abnormalities reported here, found in progenies of normal maize (excluded here are abnormalities following mutagenic treatments or from known aberrant stocks), were less frequent; some were very rare indeed.
Fig I. Up-side-down embryo; faces base of ear. Common in Country Gentleman Sweetcorn; occasional generally. From second, usually sterile floret of pair.
Figs I.2&3 Back-to-back; and, side-by-side kernels and seedlings. Common in Country Gentleman Sweetcorn; occasional generally.
Fig II.1 Reversed embryo. Rare; a lethal. Embryo faces inwards. Can be ‘rescued’ by excision.
Fig II.2 Embryoless or germless. Occasional in some strains. Endosperm appears normal.
Fig II.3 Endospermless. Occasional in some strains; a lethal. Embryo can be ‘rescued.’
(Not shown) Heterofertilized kernels. First noted by Sprague. Occasional to frequent in some strains.
(Not shown) Kernel with embryos derived from twin embryo sacs. Observed only once.
Fig III.1.a Pseudo-twin. Seedlings forked at scutellar node, with two (mirror image) plumules. Occasional.
Fig III.1.b Pseudo-twin. Seedling forked below scutellar node, with two radicles. Occasional.
Fig III.1.c Pseudo-twin. Seedling with double plumules and double radicles. Rare.
Fig III.2.a Plumuleless. Root system only developing. Rare. (See: Evans & Kermicle, 2001).
Fig III.2.b Rootless. Plumule and scutellar node only developing. Rare. (Evans & Kermicle) Occasionally caused by insect damage. Seedling can be ‘rescued.’
Fig III.3.a Parthenogenetic monoploid (haploid). Frequency varies widely with genotype of pollinator and female parent (averaging about 1/1,000).
Fig III.3.b ‘Androgenetic’ or ‘paternal’ monoploid (haploid). Very rare in most genotypes (about 1/60,000). The terms ‘androgenetic’ and ‘paternal’ are qualified as the cytoplasm of these plants is derived from the female parent.
(Not shown) Parthenogenetic diploid. Originates by early chromosome doubling of a maternal monoploid or by derivation from an unreduced egg cell.
(Not shown) Parthenogenetic diploid. From a tetraploid parent (See: Randolph).
Fig III.4 Triploid. Occasional. (A few triploid plants can generally be found in any field of corn.) Formed by fertilization of an egg by an unreduced sperm; or by fertilization of an unreduced egg by a normal sperm.
(Not shown) Viviparous seedlings. Seedlings sprouting on ear; no dormancy.
Fig III.7.a Diploid/diploid twin. Rare.
Fig III.7.b Diploid/maternal monoploid twin. Rare.
Fig III.7.c Diploid/‘paternal’ monoploid twin. Very rare.
Fig III.7.d Triploid/maternal monoploid twin. Very rare indeed.
Fig III.7.e Maternal monoploid/maternal monoploid twin. Rare.
(Not shown) Maternal monoploid/‘paternal’ monoploid twin. Very rare indeed. (Gerrish, 1956)
(Not shown) Diploid/‘paternal’ monoploid twin. Very rare.
Fig III.7.h Maternal monoploid/diploid/maternal monoploid triplet. Very rare indeed.
Fig III.7.i Maternal monoploid/diploid/‘paternal’ monoploid triplet. Very rare indeed.
Fig III.7.j ‘Paternal’ monoploid/ diploid/‘paternal’ monoploid triplet. Seen once by Rhoades, once by Chase; also seen, as also many of the above twins and triplets, in ‘ig’ progeny.
Figs III.7.k.i&ii. Kernels with polyembryos. Two kernels seen; drawn here.