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ŠUMARSKI LIST 1-2/1966 str. 125     <-- 125 -->        PDF

NATURAL HYBRIDIZATION BETWEEN LOBLOLLY AND
SHORTLEAF PINES IN EAST TEXAS


(Contributed paper)
by


Dr. M. VICTOR BILAN*
School of Forestry, Stephen F. Austin State College, Nacogdoches, Texas, U.S.A.


Natural hybridization of loblolly pine (Pinus taeda L.) and shortleaf pine
(Pinus echinata Mill.) probably occurs throughout the southern pine region,
but it seems to be especially frequent on the western edge of the natural
range of these two species. While working in East Texas, Zobe l (1953)
reported on intermediate forms between loblolly and shortleaf pines which
could not be precisely classified as belonging to either species.


Loblolly pine seedlings grown from local seed in the Stephen F. Austin
State College forestry nursery show an unusually high degree of morphological
variation. Even when relatively uniform 1-0 seedlings are out-planted in
a uniform environment, some individuals grow more slowly than the rest of
the population. The slow-growers have usually dense and bushy crowns, the
stems are purplish, and the needles thin and twisted. Since the growth rate
and habit of these seedlings are similar to those of typical shortleaf pine, the
author believes that these individuals are natural hybrids of loblolly and
short leaf pines.


This supposition is supported by an experiment in an air-conditioned
greenhouse. Seeds collected from ten 45 to 50 year old open-pollinated
loblolly pines were germinated in petri dishes during the month of May and
then planted in individual 2-1/4-inch square jiffy pots filled with top-soil.
The labeled pots were arranged in 1 X 12 X 4-inch wooden flats on tables
in the greenhouse where temperatures ranged between 75°F and 85°F.
Relative humidity varied between 35 and 85 percent. The light intensity was
reduced by 20 percent with a nylon netting, and the photoperiod remained
natural.


Growth and development of individual seedlings in each of the ten
progenies (numbered I to X) were recorded periodically for one year. Some
variations were noted among all of the progenies, but especially striking
differences occurred between progenies IV and VI. While in July the average
height of progeny IV was 25 percent shorter than that of progeny VI, the
former outgrew the latter by the middle of October. By the end of November,
progeny IV was 15 percent taller than progeny VI; and by the middle of
February this difference increased to 25 percent.


* Travel to the meeting was partially supported by the National Science Foundation,
Grant GB-118.