The Austrian X Red Pine Hybrid

Home , Pinus nigra, Pinus resinosa, Rhyacionia buoliana

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ZEITSCHRIFT FDR FORSTGENETIK UND FORSTPFLANZENZDCHTUNG

JOURNAL OF FOREST GENETICS AND FOREST-TREE BREEDING

JOURNAL DE GENETIQUE ET D'AMELIORATION DES ARBRES FORESTIERS

The Austrianx Red Pine Hybrid

By W. B. Critchfield*)

D, Sauerlander's Verlag, Frankfurt a. M,

Silvae Genetica 12, Heft 6,181—212 (Nov.-Dez. 1963)

D 21809 F Silvae Genetica

continues the setzx die continue le Journal of Forest Genetics and Zeitschrift fur Forstgenetik und Journal de genStique et Forest-Tree Breeding Forstpflanzenzfichtung d'am€lioEation des arbres forestiers

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P. Bouvarel, Station de Recherches et Experiences W. Langner, Institut fttr Forstgenetik und Forstpflanzen- forestieres, 14, rue Girardet, Nancy, France. zttchtung, (24a) Schmalenbeck ttber Ahrensburg (Holstein), Siekerlandstrafie 2, R.Z. Call ah am, Institute of Forest Genetics, 1912 Carson Road, Bundesrepublik Deutschland. Placerville, California, USA. J.D.Matthews, Department of Forestry, University of Aber C. Heimburger, Southern Research Station, Maple, Ontario, deen, Old Aberdeen. Canada. K. Sato, Faculty of Agriculture, Kyushu University, H.Johnsson, Fdreningen Skogstrfidsfdrfidling, Fukuoka, Japan. Syd&stra Distriktet, Ekebo, Svaldv, Schweden. J. w. Wright, Department of Forestry, T. N. Khoshoo, Postgraduate Department of Botany, Michigan State University, Jammu and Kashmir University, E. Lansing, Michigan, USA. Naseem-Bagh, Sringar, India.

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INHALTSVERZEICHNIS

Geographic and Individual Tree Variation in Some A New Method of Dealing With Results of Provenance Wood Characters of Teak (Tectona grandis L f.). — Tests. By J. H. Wiersma 200 I. Fibre Length. By S. Kedharnath, V. J. Chacko, Berichte 206 5. K. Gupta and J. D. Matthews 181 The Austrian X Red Pine Hybrid. By W. B. Critchfield 187 Notlce 208

Acute Gamma Irradiation of Quercus Seed. — Its Effect on Germination and Seedling Growth. By G. R. Stairs 192

Ausgegeben im Januar 1964 The Austrian x Red Pine Hybrid

By W. B. Critchfield*)

(Received for publication May 22, 1963)

The genetic improvement of red pine (Pinus resinosa more than 300 female strobili in attempts to make this Ait.) presents tree breeders with one of their most difficult cross, using both species as female parents. Unsuccessful problems. Not only is this valuable species remarkably attempts at the Institute of Forest Genetics since 1940 total uniform, .but until 1955 it resisted all attempts to cross it more than 30 tree X tree combinations and 500 female with other pines. In that year red pine and Austrian pine strobili. (P. nigra var. austriaca [Hoess] Aschers. & Graebn.) were The developmental stage at which this cross fails has successfully crossed at the Institute of Forest Genetics, been described by MeWilliam (1959). Ovules of Austrian Placerville, California. The few hybrid trees from this pine pollinated by red pine collapse toward the end of the cross have been .mentioned and illustrated by Duffield first season after pollination and at the beginning of the and Snyder (1958) and Righter (1962). second season. Breakdown of the ovule is initiated in the This cross is the first successful hybridization between megaspore and later in the developing female gametophyte. hard pines of the Eastern and Western hemispheres. It is MeWilliam found red pine pollen growing normally in also one of the few interspecific crosses in Pinus that has about 30 percent of the ovules of Austrian pine. These been studied developmental^ (MeWilliam 1959), and we ovules are the ilast to break down, and some of them remain know at what point the reproductive processes usually intact until seed coats are formed at about the time of break down. The hybrids may prove to be of economic fertilization, early in the second season of development. value in increasing red pine's resistance to its most serious pest, the European pine shoot moth (Rhyacionia buoliana Production and Crossing of the Hybrids

[Schiff]). 'Finally, the hybrids are heterotic, greatly ex The only successful cross of these two species was made ceeding either parent species in early height growth at in May, 1955, between two trees growing in the Eddy Placerville. Arboretum at Placerville (table 1). The parents were a 30- Austrian and red pines are grouped together in all year-old Austrian pine of unknown origin and a 27-year- modern classifications of the pines. Shaw (1914) places old red pine from an 'unspecified Maine source. The cross them in the Lariciones, a well defined group that includes yielded 45 sound seed, 42 of which produced seedlings.

most of the hard pines of the Eastern Hemisphere. The only During their first growing season, the seedlings were not Western Hemisphere members of this group are red pine, readily distinguishable from their Austrian pine half-sibs a native of northeastern North America, and P. trppicalis growing in adjacent rows (products of the P. nigra X nigra Morelet, a Cuban species. cross listed in table 1). The following year F. I. Righter Austrian pine, in contrast to red pine, has been success singled out four seedlings as possible hybrids. His selection fully crossed with several other species in the Lariciones. was based on their marked superiority in height growth The first authentic pine hybrid, produced by A. F. Blakes- and on the lighter green of their foliage compared to the lee in 1914, was P. nigra X densiflora (Austin 1927). Aus Austrian pine controls. trian pine has since been crossed with P. sylvestris L. and These putative hybrids were outplanted the following several East Asian species. These crosses and unsuccessful spring (1959), together with their Austrian pine half-sibs attempts to cross Austrian pine are summarized by Wright and unrelated red pines of Wisconsin origin. The out- and Gabriel (1958). planted trees were watered only during their first season The cross between Austrian and red pines has been tried in the field. Most of the Austrian pines had to be replaced on a much larger scale than any other cross involving the following year, and nearly all of the red pines have either species (Johnson and Heimburger 1946; Duffield 1952; died since outplanting as a result of severe summer Holst and Heimburger 1955; Wright and Gabriel 1958). Be droughts. tween 1948 and 1955 Wright and his coworkers pollinated The majority of seedlings from this cross of P. nigra X

*) Geneticist, Pacific Southwest Forest and Range Experiment P. resinosa have proved to be nonhybrids. Of the eighteen Station, P. O. Box 245, Berkeley 1, California. 5-year-olds surviving in 1961, only six were probable hy-

187 Table 1. — Results of several controlled crosses involving P. nigra, Conelets and Cones P. resinosa, and their hybrid. The conelets of Austrian -and red pines are easy to dis Total No. Per tinguish (figure 1). The scales of the Austrian pine conelet Polli Per no. of cent Cross nation cent seeds stro— filled are transversely ridged and armed with a small prickle. year cones per bili seed cone Both features are pronounced in the Austrian pine parent. The smaller conelet of red pine is unarmed, and the ex nigra (N7) X resinosa (V29)1) 1955 25 60.0 12.3 24.32) posed face of the scale is slightly or not at all ridged. The hybrid conelet is intermediate in size, and has obscure nigra (N7) X nigra (2-tree mix) 1955 23 100.0 46.3 80.3 prickles and inconspicuous ridges. nigra (N7) X resinosa (V29) 1959 146 67.8 22.2 0 nigra (4 trees) X 1955 and resinosa (V29) 1959 66 43.9 3.7 0 nigra resinosa (11) X resinosa (V29) 1960 6 100.0 17.7 0

') Numbers in parentheses are Institute of Forest Genetics tree designations. 2) Includes both hybrids and non-hybrids. brids — the four trees selected by Righter and two trees remaining in the nursery. The others were indistinguish able from the Austrian pine checks. This mixture of hy brids and nonhybrids may be due to contamination at the time of pollination, or it may be the result of cone or seed Figure 1. — Conelets of Austrian pine parent (left), hybrid (center), and red pine parent. mixing. An attempt was made to repeat this cross in 1959, using The first hybrid to flower matured several cones in 1961. the same parent trees. Although the cross was made on a They could be compared only with cones of the Austrian much larger scale than the 1955 cross, no sound seed was pine parent, since the red pine parent rarely produces ma obtained (table 1). ture cones and the young Austrian pine controls had not In both 1955 and 1959 this tree X tree combination yet begun to flower. The color of the hybrid cones is much produced a much higher set of hollow seed than other Aus like the tawny yellow of Austrian pine cones and unlike trian X red pine combinations tried at Placerville. The the nut brown of red pine cones. In cone size, however, the high yield of hollow seed from this combination is a prop hybrid is like red pine, which has cones 4 to 6 cm. long. erty of the Austrian pine used as female parent, since cros The cones of the hybrid, with a mean length of only 5.1 cm., ses of the red pine parent with several other Austrian pine are significantly smaller than cones of the Austrian pine female parents yielded few hollow seed (table 1). According parent (mean length 7.0 cm.). to McWilliam (1959), the ovules of Austrian pine collapse before the seed coat is formed unless the development of Time of Flowering and Cone Opening red pine pollen tubes is normal and vigorous. Since this particular Austrian pine parent yields many hollow seeeds, Red pine flowers in late April at Placerville; Austrian its ovules must provide an unusually favorable environ pine, 2 to 4 weeks later. When past dates of pollen collec ment for the growth of red pine pollen up to the time of tion and maximum receptivity of female strobili are com seed coat formation. bined, the red pine parent averages 14 days earlier in The first attempt to backcross one of the hybrids to its flowering time than the Austrian pine parent. red pine parent was a failure. The backcross yielded no In 1960 the female strobili of the single flowering hybrid sound seed and a rather low number of hollow seed (ta reached maximum receptivity at the end of April, 12 days ble 1). The backcross was repeated when the same tree and after pollen shedding of its red pine parent and 9 days be one other flowered in 1961, with results not yet known. fore pollen shedding of the Austrian pine parent. The fol lowing year, the female strobili of the two flowering hy Characteristics of the Hybrids brids were at maximum receptivity 4 and 10 days after Austrian and red pines differ in many features, although pollen shedding of the red pine parent. Although these their general similarity caused some 19th centu.ry botanists dates are not fully comparable, they suggest that the hy to class red pine as a variety of P. nigra (Shaw 1914, p. 51). brids fall somewhere between the parents in flowering Not all of the differences between the two species could time. be used in establishing the identity of the hybrids. Some Red pine matures its cones several months before Aus gross morphological features such as bud shape and leaf trian pine at Placerville. Cones of red pine regularly orientation were too variable to be helpful. The conelet open in the last half of September. Austrian pine cones re and cone provide reliable distinctions, but only two hy main green throughout the fall, and do not ordinarily ripen brids had flowered by 1961. For this reason we have relied and begin to open until December or January. chiefly on the more stable features of needle structure in In 1961 the cones of the hybrid were intermediate but establishing the hybrid identity of the nonflowering trees. erratic in time of opening. By October 10, two of its six Many characteristics are influenced by tree age, and cones had turned brown and the cone scales had begun to comparisons of these features cannot usefully be made be separate. By November 1, when the cones were collected, tween the hybrids and their much older parents. Conse three cones had started to open. Not until two months later quently, we also compared the hybrids with related Aus did the cones of the Austrian pine parent tree begin to

trian pines and unrelated red pines of the same age. open. •- '

188 Height Growth crown. These trees have developed pronounced leans and had to be mechanically supported. Red pine does not grow nearly as well as Austrian pine at Placerville. The red pine parent tree, one of the most Leaves vigorous red pines in the Eddy Arboretum, was only 37 feet tall in 1961 at 34 years. The Austrian pines used in the in The needles of Austrian and red pines differ in dimen terspecific and check crosses were much taller: 52 to 54 feet sions, texture, and structure. Two anatomical charac at 35 to 37 years. teristics — the amount of hypoderm and the location of the The hybrids have grown faster from the start than either resin canals — have provided the most conclusive evidence parent species. By the end of their first growing season, of hybrid identity, but several other leaf characteristics they were nearly twice the height of their Austrian pine have also proved to be useful. half-sibs and three times the height of the red pine checks Austrian pine has shorter and wider leaves than red pine (table 2). They have maintained this superiority since out- (table 3). In both species these dimensions are highly vari planting. At 5 years the hybrids were more than two and able and affected by tree age, young trees having shorter one half times as tall as their Austrian pine relatives and and narrower leaves than older ones (table 3). The leaves almost five times as tall as the two surviving red pines of the hybrids are intermediate in length and width com (table 2). pared to Austrian and red pines of the same age. The dif The superiority of the hybrids in height at 5 years may ferences between the hybrids and their Austrian pine sib •be somewhat exaggerated. Four of the five outplanted lings, however, are not statistically significant (table 3). Austrian pines are replacements outplanted a year after The leaves of Austrian pine are straight and stiff, and do the hybrids. The trees they replaced had suffered severe not break off when they are bent double. Red pine leaves rabbit damage during their first winter in the field, while are flexible and break off cleanly when they are bent the taller hybrids in an adjacent row suffered only minor double. The leaves of the hybrids are intermediate in stiff damage to their lower branches. The extra year the re ness. They often break off when they are bent double, but placements spent in the nursery may have affected total the break is ragged compared to that of red pine. height at 5 years, but is unlikely to have had much in This difference in texture reflects the great difference fluence on fifth-year increment. During their fifth growing between the two species in the abundance of thick-walled season (1961), the height growth of the hybrids was more cells within the leaf. The fragile needles of red pine have than double that of the Austrian pine checks (table 2). one, or occasionally two, layers of relatively thin-walled The heterotic height growth of the hybrids may have hypodermal cells. They have no fibers in the transfusion produced structural unbalance in some of the trees. In tissue surrounding the vascular bundles, 'but the cells of these cases the rapid development of the crown appears to the endodermis have thickened outer walls (Harlow 1931). have outstripped the ability of the trunk to support the The tougher needles of Austrian pine have a thicker epi dermis, a much more extensive hypodermis, and a layer of Table 2. — Early height growth of hybrids and parent species. fibers in the transfusion tissue (figure 2; and Harlow 1931). The hypodermis is usually three cell layers thick (occa Number Mean ht. Mean 5th- Mean Species or hybrid of at year ht. ht.at sionally two or four), and the cells of the inner layers are trees 6 months increment 5 years very thick-walled (figure 3). The endodermis is uniformly Feet thin-walled. nigra (N7) X The leaves of the hybrids are intermediate in some of resinosa (V29) 6.41) 0.28 1.28 4.85 these anatomical features and resemble Austrian pine in 2) 2) 2) others. Both the epidermis and the hypodermis are inter nigra (N7) X nigra mediate, but the hybrids resemble Austrian pine in having (2-tree mix) 53) 0.15 0.51 1.77 a layer of fibers in the transfusion tissue (figure 2). The resinosa (Wisconsin) 2 0.11 0.43 1.01 hybrids and the young red pine controls lack the thickened ') Six-month height includes all six hybrids; later measurements outer endodermal walls of the red pine parent, suggesting include only the four outplanted trees. !) Highly significant difference. that this characteristic may be influenced by tree age. 3) Includes one survivor of first outplanting and four replace Of these anatomical characteristics, the hypodermis is ments. the most useful in establishing hybrid identity. In the hy-

Table 3. — Leaf characteristics of hybrids and parent species').

Location of resin canals No. No. resin Mean Mean Species or hybrid of Age canals Principal length width Accessory trees per leaf Med. Ext. Med. Ext.

Years Cm. Mm. Percent nigra (N7) 1 37 11.9 1.82 14.2 100 0 100 0 nigra (N7) X nigra (2-tree mix) 4 5 8.8 1.52 4.28 100 0 98 2 2) 2) 2) nigra (N7) X resinosa (V29) 5 5 10.1 1.40 3.78 83 17 57 43 resinosa (Wisconsin) 2 5 12.1 1.32 2.0 5 95 0 0 resinosa (V29) 1 34 12.7 1.39 5.3 5 95 73 27

•) Based on. 10-leaf samples from vigorous primary branches. Observations on midportion of leaves. *) No significant difference.

189 dermal layersN endodermis accessory resin^ .fibers canaL

principal resin'canal

principal^resin canal

Figure 2. — Leaves of parent species and hybrid in transection. (A) 5-year-old Austrian pine half-sib (Ni-50). (B) Austrian pine parent. (C) 5-year-old hybrid (NiRe-ll).(D) Red pine parent.

mesophyll

hypodermis

} epidermis cuticle

Figure 3. — Dermal layers of the leaf in parent species and hybrid. Portion shown lies be tween lines of stomata near the middle of the abaxial surface. (A) 5-year-old Austrian pine half-sib (Ni-50). (B) Austrian pine parent. (C) 5-year-old hybrid (NiRe-11). (D) Red pine parent.

brids it usually consists of only two layers of cells. The the Austrian pine parent all resin canals, both principal hybrid leaves lack the very thick-walled inner hypodermal and accessory, are medial (table 3). cells characteristic of the parent Austrian pine and the The hybrids are extremely variable in resin canal loca young Austrian pine controls (figure 3). tion. Three trees can be distinguished from both parent species solely iby the location of their principal canals, Austrian and red pines have two principal resin canals which may be either medial or external. Unlike the ex and a variable number of accessory canals in each leaf. ternal canals of red pine, however, those of the hybrids are The principal canals are often larger than the accessories always adjacent to the hypodermis of the convex abaxial and lie near the lateral margins of the needle (figure 2). The surface of the needle (figure 2). The external position is distinction between the two kinds of resin canals is a rare in one tree and common in the other two. critical one, since the principal canals are relatively stable Neither parent species ever has principal resin canals in in presence and position, whereas the accessory canals this location. They are never external in Austrian pine, often vary in number and position within a single leaf. while in red pine they are always adjacent to the flat inner The principal canals of red pine are nearly always ex face of the needle, never the rounded outer face. This re ternal. In this position the sheath of cells surrounding the markable feature, which sets off these hybrids from both resin canal is continuous with the hypodermis inside the parent species, is rather common elsewhere in the Laricio- flat adaxial face of the needle (figure 2). Occasionally the nes group. The principal resin canals of P. sylvestris, P. principal canals are medial (table 3). Accessory canals, montana, and several other species characteristically oc when they are present, may be either medial or external. cupy this position (Shaw 1914; Harlow 1931). The red pine parent has predominantly medial accessory Four of the hybrids, including the three above, can also canals (table 3). be distinguished from Austrian pine by the high proportion The principal resin canals of Austrian pine are always of external accessory canals. The highest incidence of ex medial, and so are almost all of the accessory canals (ta ternal accessories observed in an individual Austrian pine ble 3). In a total sample of 145 leaves from 12 trees of was 2 out of 43 in a 10-leaf sample. In the four hybrids, 50 varying ages, 97 percent of the accessory canals were me to 70 percent of the accessories are external, the rest me dial, 2 percent internal, and less than 1 percent external. In dial.

190 The remaining two hybrids are indistinguishable from the northeastern United States and eastern Canada (Holst Austrian pine in resin canal location. The identification of and Heimburger 1955; Wright and Gabriel 1958). these trees, neither of which has flowered, rests on their Austrian pine is less susceptible than red pine to shoot leaf dimensions and hypodermal characteristics. moth damage (Holst and Heimburger 1955; Miller and Heikkenen 1959). Backcrosses of the hybrid, or backcross derivatives, might reduce the susceptibility of red pine in Discussion two ways: (a) by introducing Austrian pine genes which The few hybrid trees described here are the sole product lessen susceptibility; and (b) by increasing the growth rate of many attempts to cross Austrian and red pines at Placer of red pine, since faster growing red pine is less suscep ville and elsewhere, making this perhaps the most difficult tible to tip moth damage (Heikkenen and Miller 1960). cross so far successfully attempted in Pinus. A further in These possibilities will be explored as the hybrids start to dication of the incompatibility barrier between the two flower more regularly and abundantly. species is the failure of our first attempt to backcross one

of the hybrids to red pine. This failure was unexpected, Summary since most pine hybrids backcross fairly readily with their In 1955 Pinus nigra (Austrian pine) and P. resinosa (red parent species even when the parents themselves are dif pine) were successfully crossed at the Institute of Forest ficult to cross. Genetics, Placerville, California. This cross is the first in This failure, and our inability to repeat the cross be volving Eastern and Western hemisphere hard pines and tween Austrian and red pines, focuses attention on the the first cross of red pine with any other species. An at circumstances of the original cross. Its most noteworthy tempt to repeat the cross was unsuccessful. Our isolated feature was the mixed progeny resulting from it, mostly success may have been due to contamination with mater Austrian pines with a minority of hybrids. We are inclined nal-species pollen, and we are now trying to reproduce it to attribute the mixed progeny to contamination with Aus by using mixtures of pollen of the two parent species. The trian pine pollen at the time of pollination, although the six hybrids are intermediate between their parents in most possibility of later mixing cannot be eliminated. characteristics, but they greatly exceed either parent in Deliberate contamination with maternal-parent pollen to early height growth. In one feature, the location of the improve the chances of success of a cross is a standard principal resin canals in the leaves, some of the hybrids technique of Michurinist tree breeding as practiced in the are unlike either parent species but resemble other pines U. S. S. R. (Forest Service 1961). The same technique has in the Lariciones group. The hybrids may prove useful in been tried with unknown sucess in an interspecific pine the transfer of genes between the two parent species, and cross in Sweden (Johnsson 1956). particularly in the introduction into red pine of genes af We think that an accidental admixture of Austrian pine fecting insect resistance. pollen may have been responsible for our isolated success in crossing these two species. The structure of the female Resume gametophyte of Pinus provides a mechanism by which ma Titre de l'article: L'hybride entre le Pin noir d'Autriche ternal-parent pollen contamination might help in effecting et Pinus resinosa. a difficult cross in this genus. Each gametophyte has sev En 1955, on a croise avec succes a l'lnstitut de Genetique eral eggs available for fertilization, .but usually only one Forestiere de Placerville (Californie) Pinus nigra (Pin noir of the resulting zygotes develops into a mature embryo d'Autriche) et Pinus resinosa (red pine). Ce croisement est (Foster and Gifford 1959, p. 409). Austrian pine pollen, if le premier qui concerne 2 pins du sous-genre Eupinus, it were mixed with red pine pollen in amounts so small Tun americain, Tautre eurasiatique, et egalement le pre that only a fraction of the available eggs could be ferti mier croisement de Pinus resinosa avec n'importe quelle lized, would prevent the collapse of the female gameto autre espece. Un essai de repeter ce croisement a abouti phyte observed by MeWilliam (1959). Under these circum a un echec. Notre succes isole a peut-etre ete du a une stances the red pine pollen tubes which develop normally contamination avec du pollen maternel et nous essayons in Austrian pine ovules might be able to continue their maintenant de la reproduire avec des melanges de pollen development to the point of fertilization. The postem- des 2 especes parentes. Les 6 hybrides sont intermediaires ■bryonic vigor of the hybrids makes it unlikely that em pour la plupart des caracteres entre les 2 parents, ma is ils bryonic selection following fertilization would discriminate depassent nettement Tun et l'autre en ce qui concerne la heavily against the hybrid embryos. croissance initiale en hauteur. Pour un caractere, la situa On the basis of this hypothesis we repeated the cross in tion des principaux canaux resiniferes dans les aiguilles, the spring of 1962. The red pine pollen was deliberately certains hybrides ne ressemblent a aucun des parents, mais contaminated with small amounts of live Austrian pine ressemblent a d'autres pins du groupe Lariciones. Les hy pollen. We also used red pine pollen diluted with large brides se reveleront peut-etre utiles pour transferer des amounts of dead or homogenized Austrian pine pollen, in genes d'un des 2 parents a l'autre et en particulier pour hopes that one of these combinations will enable us to re introduire dans le genome de Pinus resinosa des genes de produce this hybrid. resistance aux insectes.

These hybrids, if they can eventually be backcrossed to Zusammenfassung red pine, will provide the first opportunity to improve this species by introducing genes from other species. This Titel der Arbeit: Vber den Bastard Pinus nigra X Pinus source of genetic material is important to red pine because resinosa. of its apparent genetic uniformity (Buckman and Buchman 1955 wurden vom Institut fur Forstgenetik in Placer 1962; Fowler 1962) and its serious insect pests. One of these, ville (Californien) Pinus nigra (Schwarzkiefer) und Pinus the European pine tip moth (Rhyacionia buoliana [Schiff]), resinosa (Rotkiefer) erfolgreich gekreuzt. Diese Kreuzung is so damaging that it limits the use of red pine in parts of war die erste zwischen eurasischen und amerikanischen

191 Kiefern und die erste Artkreuzung mit Pinus resinosa (1958). — Forest Service: Forestry and forest industry in the U. S. S. R. Report of a technical study group. U. S. Dept. Agric. iiberhaupt. Eine Wiederholung der Herstellung des Bastar- 92 pp., illus. (1961). — Foster, A. S., and Gifford, E. M., Jr: Com ■des gelang nicht. Unser einmaliger Erfolg konnte durch parative morphology of vascular plants. San Francisco: W. H. Vermischung mit Pollen der Mutterart hervorgerufen wor- Freeman & Co. 555 pp., illus.- (1959).-— Fowler, D. P.: Initial studies den sein, weshalb wir jetzt seine Reproduktion mit einer indicate Pinus resinosa little affected by selfing. Proc. 9th North east. Forest Tree Improvement Conference: 3—8. illus. (1962). — Pollenmischung von beiden Elternarten versuchen. Die Harlow, W. M.: The identification of the pines of the United sechs Bastarde sind in ihren meisten Merkmalen interme- States, native and introduced, by needle structure. New York diar, sie iibertreffen aber jeden Elter wesentlich im frii- State College of Forestry Tech. Bull 32, 21 pp. illus. (1931). — hen Hohenwachstum. In einem Merkmal, ahnlich der Lage Heikkenen, H. J., and Miller, W. E.: European pine shoot moth der Hauptharzkanale in den Nadeln, unterscheiden sich damage as related to red pine growth. Lake States Forest Expt. Sta. Paper 83, 12 pp. illus. (1960). — Holst, M., and Heimburger, C: einige Bastarde von beiden Elternarten und ahneln ande- The breeding of hard pine types resistant to the European pine ren Kiefern aus der Gruppe der Lariciones. Diese Bastar shoot moth (Rhyacionia buolinna Schiff). Forestry Chron. 31: 162— de konnen sich als nutzlich erweisen bei der "Obertragung 169 (1955). — Johnson, L. P. V., and Heimburger, C: Preliminary von Genen zwischen den zwei Spezies, und besonders fur report on interspecific hybridization in forest trees. Canad. Jour. Res., Sect. C, 24: 308—312 (1946). — Johnsson, H.: (Annual report on die Einbringung von Genen fur Insektenresistenz in die the activities of the Association for Forest Tree Breeding during Pinus resinosa. 1955.) Arsberrat. Foren. Vaxtf. Skogstr. 1955: 3—18. (Swedish) (Plant Breed. Abstr. 26: 3792) (1956). — McWilliam, J. R.: Interspecific Literature Cited incompatibility in Pinus. Amer. Jour. Bot. 46: 425—433, illus. (1959).

Austin, L.: A new enterprise in forest tree breeding. Jour. For — Miller, W. E., and Heikkenen, H. J.: The relative susceptibility estry 25: 928—953 (1927). — Buckman, R. E., and Buchman, R. G.: Red of eight pine species to European pine shoot moth attack in Michi pine plantation with 48 sources of seed shows little variation in gan. Jour. Forestry 57: 912—914, illus. (1959). — Righter, F. I.: Evi height at 27 years of age. Lake States Forest Exp. Sta. Tech. dence of hybrid vigor in forest trees. In: Tree Growth, ed. T. T. Note 616, 2 pp. (1962). — Duffield, J. W.: Relationships and species Kozlowski, N. Y. Ronald Press, 345—355 pp., illus. (1962). — Shaw, hybridization in the genus Pinus. Z. Forstgenetik 1: 93—97 (1952). — G. R.: The genus Pinus. Pub. Arnold Arboretum 5, 96 pp.. illus. Duffield, J. W., and Snyder, E. B.: Benefits from hybridizing (1914). — Wright, J. W., and Gabriel, W. J.: Species hybridization American forest tree species. Jour. Forestry 56: 809—815, illus. in the hard pines, series Sylvestres. Silvae Genet. 7: 109—115 (1958). 9n 3. Jfuflage ersdiien: CARL HEINZ LANGNER

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