DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1966 str. 126     <-- 126 -->        PDF

Most of progeny VI completed its seasonal height growth by the end of
August; 93 percent of seedlings developed terminal winter buds by the middle
of October and remained dormant until the end of February, whereas 74
percent of progeny IV continued to grow through the fall and winter. All
seedlings in progeny VI were typical of loblolly pine, while about three-
fourths of the plants in progeny IV resembled shortleaf more than loblolly
pine. The majority of progeny IV even had the root-collar crook characteristic
of shortleaf pine.


The author is convinced that at least part of progeny IV was natural
hybrid of loblolly and shortleaf pine. Experiments at the institute of Forest
Genetics at Placerville, California, demonstrated that crossability between
loblolly pine and shortleaf pine was 47 percent (Critchfield, 1962). The main
obstacle to profuse natural hybridization between these two species throughout
their natural range seems to be the difference in time of flowering.
Over several years, however, the author had observed that in Nacogdoches
County in East Texas, flovering of loblolly pine partially overlapped with
pollen dispersal of shortleaf pine. Also, the work by Dorman and Barber,
dealing with the time of flowering and seed ripening in southern pines, lists
Nacogdoches Country as the only one of the studied localities where periods
of pollen maturing of loblolly and shortleaf pines are overlapping for about
one week (Dorman and Barber, 1956). Thus, there is some evidence that the
chances of natural hybridization between these species are greater on the
western edge than in other areas of the southern pine region.


It is concluded that particular care should be exercised in provenance
testing of stands growing on peripheries of natural ranges of the tested
species. Provenance tests conducted in different temperature regimes might
supply conflicting results, and an inadequate representation of the tested
population might lead to erroneous conclusions.


PRIRODNA HIBRIDIZACIJA IZMEĐU PINUS TAEDA L. I
PINUS ECHINATA MILL. U ISTOČNOM TEKSASU


Prirodna hibridizacija Pinus taeđa L. i Pinus echinata Mili. vjerojatno se zbiva
kroz cijelo područje južnih borova, ali izgleda da je naročito česta na zapadnom rubu
prirodnog rasprostranjenja tih dviju vrsta. Dok je radio u istočnom Teksasu, Zobel
(1953) je obavijestio o prijelaznim oblicima između borova P. taeđa i P. echinata koji
se ne mogu tačno klasificirati da pripadaju bilo jednoj ili drugoj vrsti.


Sadnice od P. taeđa uzgojene iz lokalnog sjemena u šumskom vrtu sveučilišta
»F. Austin State College« pokazuju neobično visok stupanj morfološkog mijenjanja.
Čak i kada se relativno jednake sadnice 1—0 presade u jednoličnu okolinu, na terenu
neki individui rastu polaganije nego preostali dio populacije. Biljke sporog
rasta obično imaju guste i grmaste krošnje, stabla rumenkasta, a iglice tanke i uvijene.
Budući da su brzina rasta i habitus tih sadnica slični onima od tipičnog P. echinata,
autor vjeruje da su ti individui prirodni hibridi borova P. taeđa i P. echinata.


Tu predpostavku potkrepljuje i pokus napravljen u klimatiziranom stakleniku.
Sjeme sakupljeno sa deset 45—50 godina starih i slobodno oprašenih stabala P. taeđa
klijalo je u Petrijevim posudama za vrijeme mjeseca svibnja, a zatim su klijanci
presađeni u pojedinačne 2 1/4 palca (6.63 cm) kvadratične »Jiffy« lončiće koji su bili
napunjeni površinskim slojem zemlje. Etiketirani lončići poredani su u drvene
spremnice (12 x 12x4 palca odnosno 30 x 30 x 10 cm) na stolovima u stakleniku gdje
se temperatura kretala između 75° F i 85° F (24—29° C). Relativna vlaga zraka mijenjala
se između 35 i 85n/o. Intenzitet svijetla je smanjen za 20% pomoću najlonske
mreže, a fotoperiod je ostao prirodan.