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. |