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Inheritance of Cotyledon Number in Douglas-Fir
Note by Frank Sorensen
Abstract. Intraspecific crosses were made using five different pollen mixes on the same
Pseudostuga menziesii seed tree. At germination, it was found that average cotyledon
numbers of the progenies could be used to verify several hybrid parentages even though
average numbers differed by one cotyledon or less.
Cotyledon number has recently been used to
verify a hybrid between noble fir (Abies procera
Rehd.) and California red fir (Abies magnifica
A. Murr.). 1 For these species, cotyledon numbers
were different, ranging from 4 to 7 in noble fir
and from 7 to 11 in California red fir. Douglas­
fir (Pseudotsuga menzzestt (Mirb.) Franco)
cotyledon numbers range at least from three 2
to 113. Can this wide variability in cotyledon
number be used to confirm intraspecific crosses
in Douglas-fir? If so, genuine crosses could be
recognized early because cotyledon numbers
1 Silen, Roy R., Critchfield, William B., and
Franklin, Jerry F. Early verification of a hybrid
between noble and California red firs. For. Sci.
could be determined without damage to the
seedlings as soon as seedcoats are shed, or even
earlier if the seed can be sacrificed. In this report,
a small test, involving several crosses using a
common female parent, is described. Some pro­
genies did show significant differences in average
cotyledon number, thus verifying their diverse
hybrid parentages.
Materials and Methods
Female strobiles of a single tree at 4,400 feet m
the central Oregon Cascade Range were pol­
linated by the following:
1. A mixture from five trees growing at 4,000­
foot elevation about 1 mile east of the female
parent;
11: 460-462.
2
Personal observation.
'Greathouse, Thomas. Personal communica­
tion.
The au thor is Research Forester, Pacific
Northwest Forest and Range Expt. Sta., Forest
Service, U.S. Dept. of Agric. portland, Oregon
Manuscript received July 14, 1965.
volv,mc 12, number 2, 1966 I 175
TABLE 1. Average and range in cotyledon
number in seedlings from five intraspecific
crosses of Douglas-fir, by elevation of
parents.
Elevation of parents'
(feet) 4,400
4,400
4,400
4,400
4,400
wind pollinated
X 4,00()2
X 2,00()2
X 7002
X 2002
Cotyledons
Average Range of
number number
6.62
7.00
7.65
7.39
6.88
5-8
6-8
6-9
6-9
6--8
LSD. 05 based on ~he Duncan test is 0.44
cotyledon; LSD.o, is 0~58 cotyledon.
'Female parent, identified by altitude, is
listed first; male parents, similarly identified,
are listed afterward.
2 Pollen parentage is a composite or mix of
four to seven individuals, as described in the
text.
2. A mixture from four trees growing at 2,000­
foot elevation about 30 miles west of the female
parent;
3. A mixture from seven trees growing at
700-foot elevation about 40 miles west of the
female parent;
4. A mixture from four trees growing at 200­
foot elevation about 50 miles west of the female
parent.
17G I
Pore.~t Scitnc~
5. Wind-pollinated seeds were also collected
from the female parent.
Twenty-four germinated seeds from each cross
were planted, three per plastic pot following a
randomized block design in forest soil from the
central Oregon Coast Ranges. Pots were placed
in a growth c.hamber under a 16-hour photo­
period (light intensity about 1,100 foot-candles)
and a 16-hour thermoperiod (22°C day tempera­
ture, 10°C night temperature). Average seed
weights of the five lots were very nearly the same.
Number of cotyledons was counted 30 days after
planting. Cotyledon length, when measured, did
not differ among crosses.
Basic unit of observation for analysis of vari­
ance was average number of cotyledons per
seedling on three seedlings of one cross in a
single pot, except in one pot in which one germ­
minating seedling failed to develop cotyledons.
Results and Conclusions
Average cotyledon numbers for seedlings of the
five families are given in Table 1. An analysis
of variance was performed with 4, 7, and 28
degrees of freedom for crosses, replicates, and
error, respectively. The F-value was 9.02,
significant at the 1-percent level.
These results indicate rather strong control
of cotyledon number. In fact, genetic variance,
when expressed as a proportion of genetic plus
remainder variances, is equal to 0.53.
Thus, comparisons reveal that hybridi ty in
Douglas-fir can be confirmed at germination time
by average cotyledon number, even when: (1)
numbers on individual seedlings range from 5 to
9; and (2) average cotyledon numbers of crosses
vary from 6.6 to 7.6.