PNL Volume 15
Marx, G. A. NYS Agricultural Experiment Station, Geneva, NY USA
Indirect evidence obtained in 1981 and 19 82 ( 1,2) indicated that
the extreme dwarfing effect of _a is counteracted when na is combined
with la cryc (and presumably la. crys ). Thus, when na. is present
together with La and/or Cry, the plants are nana in phenotype, but when
na is combined with la cryc the plants are cryptodwarf. In effect, na is
hypostatic to le la cryc. This article offers direct confirmatory
evidence favoring this hypothesis.
Seeds from 29 individual na wlo F2 segregants from entries C281-308
and C281-309 [see (2)] were planted in greenhouse flats filled with
quartz sand and the resulting seedlings were scored for the marker wlo
and for plant stature. The na and WL 1329 parents were included as con-
trols. If the epistatic effect of na is overridden in an le. la cryc
background and if, as the F2 data showed, the cryc allele segregated in
F2, then it follows that some of na wlo F2 segregants should segregate
for cryptodwarf plants. The progeny tests Bear this out. Nineteen of
29 F3 progenies tested had one or more cryptodwarf plants (Table 1),
very close to the expected 2:1 ratio. Collectively, the segregating
progenies contained 197 nana plants and 53 cryptodwarfs. All ratios
must, of course, be interpreted in the light of the small size of the
individual progenies. All plants manifested the wlo phenotype, thus
verifying the classification for that gene in the F2 populations.
The F2 and F3 data together demonstrate that na is masked (at least
in a gross morphological sense) in the presence of la. cryc. By exten-
sion, the effect of na is modified by the dosage of alleles at La and
Cry. Hence, some of the F2 and F3 segregants that fit the description
of "compactum" may be the product of this gene interaction. In effect,
the action of na is partially overcome in certain gene combinations.
46 PNL Volume 15 1983
These findings affect the way in which internode length data are
interpreted, especially in attempting to fix the physiological basis for
gene action. It might be reasonable to assume that variation in height
of nana plants is a reflection of multiple alleles at the na locus when,
in fact, the cause is an indirect effect of allelic differences at the
La and/or Cry loci. Accordingly, since the allelic status at La. and Cry
affect the expression of differences at La and Cry would also affect
how gene action at the Na-na locus is measured and interpreted.
1. Marx, G. A. 1981. PNL 13:35-37.
2. Marx, G. A. 1982. PNL 14:47-49.
3. Potts, W. C. and J. B. Reid. 1983. Physiol. Plant, (in press).