DIGITALNA ARHIVA ŠUMARSKOG LISTA
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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. |
| 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. |
| ŠUMARSKI LIST 1-2/1966 str. 127 <-- 127 --> PDF |
Rast i razvoj pojedinih klijanaca u svakom od deset potomstava (obrojčani od I do X) registrirani su periodički tokom godine dana. Neke varijacije zapažene su među svim potomstvima, ali naročito izrazite razlike desile su se između potomstva IV i VI. Dok je u srpnju prosječna visina potomstva VI bila za 25%> manja od visine potomstva IV, prvospomenuto je preraslo drugo sredinom listopada. Koncem studenoga potomstvo IV je imalo za 15%> veću visinu, nego potomstvo VI; a sredinom veljače ta razlika se povećala na 25´/o. Najveći dio potomstva VI završio je vegetacijski period svoga visinskog rasta koncem kolovoza; 93°/o njegovih klijanaca razvilo je terminalne zimske pupove sredinom listopada koji su mirovali sve do konca veljače, dok je, naprotiv, 74°/o potomstva IV nastavilo rast kroz jesen i zimu. Svi klijanci kod potomstva VI bili su tipični za P. taeđa dok su tri četvrtine biljaka kod potomstva IV više sličili vrsti P. eehinata nego P. taeđa. Većina potomstva IV je čak imala krivinu na vratu korijena koja je karakteristična za P. eehinata. Autor je uvjeren da barem dio potomstva IV predstavljaju prirodni hibridi vrste P. taeđa i P. eehinata. Pokusi Instituta za šumarsku genetiku u Placervillu, Kalifornija, pokazali su da je sposobnost križanja između P. taeđa i P. eehinata bila 47"V tih dviju vrsta kroz cijeli njihov prirodni areal rasprostranjenja razlika u vremenu cvatnje Međutim autor je kroz nekoliko godina promatranja u okrugu Nacogdoches u istočnom Teksasu utvrdio da se cvatnja bora P. taeđa djelomične poklapa s raspršivanjem polena P. eehinata. Također se i u radu Dormana i Barbera, koji tretira vrijeme cvatnje i sazrijevanja sjemena kod južnih borova, spominje okrug Nacogdoches kao jedini od proučavanih lokaliteta gdje se razdoblja sazrijevanja polena borova P. taeđa i P. eehinata poklapaju kroz otprilike tjedan dana (Dorman i Barber, 1956). Prema tome postoje izvjesni podaci da su izgledi za prirodnu hibridizaciju između spomenutih vrsta veći na zapadnom rubu, nego li u drugim arealima južnog područja borova. Zaključuje se da je potrebno posvetiti naročitu pažnju pri testiranju potomstva iz sastojina koje rastu na rubovima prirodnih areala testiranih vrsta. Testovi potomstva vođeni pod raznolicnim temperaturnim režimima mogu dati protivurjecne rezultate, a neadekvatna zastupljenost testiranih populacija može dovesti do krivih zaključaka. LITERATURE CITED 1. Critchfield , W. B. 1962. Hybridization of the southern pines in California Proceedings of a Forest Genetics Workshop, Macon, Georgia, October 25—27. 2. D o r m a ii, K e i t h W. and John C. Barber, 1956. Time of flowering and seed ripening in southern pines. U. S. Forest Service Southeastern Experiments Sta. Station Paper No. 72, 15 pp. 3. Zobel, Bruce J. 1953. Are there natural loblolly-shortleaf pine hybrids? Jour. Forestry 51: 494—495, illus. |