A Study of Genetic Control of Bud Bursting in Douglas-Fir Roy R. Sileo SEASONAL growth patterns influ­ ence a tree's adaptiveness to a par­ ticular site (1) and perhaps such important traits as snmmerwood ratio in the annual ring (.2, 9). Observations started in 1933 have shown that Douglas-fir, growth patterns in particularly the bud bursting trait are very consistent. While the date that bud bursting starts may be early or late, depend­ ing on spring weather, the order of A randomized block design w:is used for the experiment with three fluences. Occurrence of a random pattern in bud bursting of the scions would have indicated re­ replications sponse to environmental influences. Conversely, the original order of types, or 21 grafts assigned ran­ domly to 21 limbs in the upper half bursting of the scion types on all understocks would indicate strong genetic control of the trait. of the crown of each understock The experiment was established in 1955. Scions from six Douglas­ grafts. fir trees, known from years of ob­ servation to have widely differing of the seven scion tree. Since seven understock trees were used, this gave a total of 147 High mortality vras ex. pected among these limb grafts. The use of three grafts of each scion type on every understock tree was in the hope that at least one of bursting for a group of trees is dates of bud bursting, were grafted practically the same year after year .1 From provenance studies onto clonal Douglas-firs. Observa. tion of bud bursting dates in 1956 each type might survive. this order of bursting has been and 1957 indicated there was a March 5-6, 1955. proved to be under some degree of high degree of genetic control of taken from the upper third and genetic control, since the same races this trait. Information on some re­ lated questions was also obtained. south side of crowns of the parent burst in the same relative pattern in planting sites at both low and high elevations ( 6). A means of Materials and Methods This study was based on a 12-tree estimating the degree of this ge­ netic control was the objective of this study. The approach to studying the de­ gree of genetic control was to select clone of 17-year-old Douglas-fir (5) growing an a 1/5-acre area of the McDonald Forest near Corvallis, Ore.2 Seven trees of the clone, rang­ ing in height from 14 to 25 feet, trees displaying wide differences in date of bud bursting; it was hoped thereby to maximize genetic differences. Scions from these tree• were grafted onto clonal under­ stock grown in a very limited and uniform area. This eliminated ge­ netic variation in the understock and minimized environmental inTHE AUTHOR is a research forester, Pa­ cific Northwest Forest and Range Expt. Sta., Forest Service, U. 8. Dept. Agric., Portland, Ore. Be is stationed at Cor­ vallis in cooperation with the School of Forestry, Oregon SU..te University. The study was planned and established jointly by R. R. Silen and H. lrgens­ Moller, geneticist, School of Forestry, Oregon State University. Field measure­ ments and analysis were made under the author's direction. 1.W. G. Morris of the Pacific North­ west Forest and Range Expt. Sta. has kept continuous phenological records since 1933 on many Northwest speeies. The aix trees provided tor the study are among those on which he has long rec · ords. were used as understock for the study. · Scions of this understock, usually cut from the same limb, were graft­ ed as controls. Other scions were gathered from each of three trees from two locations : Locati01t and re1ati11e time of bud burstin-g Elevation of scion tree parenf (Feet) Corvallis clone: A (Control) Portland, Ore.: B (Early) 0 (Intermediate) D (Late) 8.W. Washington:• E (Early) F (Intermediate) G (Late) ·---·········-····-- ···-··-·······--···- ·--·- · ----·-·· ---····---- ··--·- ···············-··----- 300 800 800 750 500 400 500 his clone was established in 1939 by Dean W. F. McCulloch, Oregon State University, as rooted cuttings from 1· year-old wood from a single limb of a tree on the 0.8.U. campus. 8Elevation has been found to be a fac­ tor related to bud bursting of Donglas­ 472 Scion material was collected on Cuttings were trees, except in the case of tree E. This codominant tree was too slen­ der, due to competition, to allow climbing high in its crown, so scion material was collected from the cen­ tral branches. Three to six large limbs were cut from each tree. Cut­ tings were stored under wet burlap in continuous shade during cool weather until March 21-24 when understock trees were at the de­ sired stage of growth for grafting. The best scions from each limb, generally including terminal buds of the branchlets. were used for the grafts. Whip grafts were employed, using only first-year wood in 2- to 3-inch lengths as scion material. Understocks were often cut back to second-year wood. Grafts were coated with asphalt emulsion wax, and each scion was protected for about a month with a polyethylene bag enelosed by a ventilated kraft bag. Records were kept of bud burst­ (1, 6, and7). 'In the Douglas-:fir heredity plantation, Wind Ri'ter Experimental Forest, Carson, Wash., ele'tation 1,150 feet. E and G are from seed collected near Granite Falls and F from seed collected near Fortson, both in northwestern WaRhington. :fir 473 JULY1962 Results ing date, elongation, and survival of each graft as well as for three ungrafted limbs per understock There was regular and highly tree. Bud bursting was defined as significant progression in bud bursting of the grafted material in the date when the first green needle accord with relative time of bud could be seen through the ruptur­ ing, papery scales of the expanding bursting of trees from which scions viere collected (Fig. l). This held bud. Observations were made at true for both years of observation. least twice weekly during spring During the sum­ Genetic effects, as expressed by variation in bud bursting time of mer, when little growth was occur­ the several scion types, were sig­ 1956 and 1957. ring, observations were made at intervals of one week or longer, terminating each year in late Sep. tember. Analysis Analysis of variance "·as made nificant at the 1-percent after earliest bud bursting, April 22. Bud bursting for each scion type was recorded on the earliest burst­ ing bud of the best surviving graft on each understock tree. Because was used on each understock tree so that as many scion types as pos­ sible could be included in an ortho. gonal analysis. A similar analysio was made of the 1957 data, but April 19, the date of earliest bud and intermediate scions from south. west Washington reduced the num­ ber of understock trees having all seven scion types for this analysis to five in 1956 and four in 1957. Estimates of the genetic component of variation for each year's data were made OF CORVALLIS CLONE UNDER STOCK A CORVALLIS CLONE GRA TS B PORTLAND ( Early l c PORTLAND I lnfermedicrte ) D PORTLAND ( late) E WASHINGTON variance, using data on total elon­ (Early ) A regression was also com­ puted for the above bud-bursting dates, usng total elongation as the independent variable. r;Computed fron1 formulas: Mean square for scion types = a2 + Koo' and genetic component ao' = ---- in '"·bieh a' APRIL 20:2530 SCIONS { Bud bursting time of pcrent tree ) growth was made by analysis of tree. = er or mean square, OG2 = genetic variance, K Dumber of clonal trees. = 729.25 558.24 15.82 10.16 5.25 Error 9.15 A multiple range analysis of the 1956 data showed that average time of bud bursting of all the scion F WASHINGTON ( lntermediofe ) G WASHINGTON (Late l 1957 1956 SOURCE MAY " 20 25 "' 5 · · · : :J •JI ::F ,E . : JUN 4 9 ® : : r'[ '.f 5 10 0 MAY 15 20 25 30 JUNE 4 9 ' ' ------ ® [ ® 5E 2025 ® I .l Ji. APRIL w. t, Li_L_ ® > "' gation of the best surviving graft of each type on the understock Scion types Clonal understock 1957 group where differences averaged only 2.2 days (Fig. 1). (4) .• A test for differences in scion Mean squares 1956 squares from the analysis of vari­ ance sho,vs variability due to scion burst, was used as the beginning date. Death of many grafts of early Source of variability types differed from one another with exception of the Portland of high mortality of some scion types, only the best surviving graft times larger for 1957 than due to understock effects: ences within the plot, was not sig­ nificant. A comparison of the mean on 1956 bud-bursting data, using as the variable the number of days level. Variation attributed to understock, a measure of environmental differ. types more than seventy times larg­ er for 1956 and more than thirty I 11 . [ I I .. 1ll 1A.1 II I .. I •I• , ' ® II I ! [ II ' , I I ,.. ' F1a. 1.-Frequeney distribution of bud bursting dates for clonal understock and grafts of the clone, including three Portland, Ore., and three western Washington trees. Average date of bud bursting is shown by a trta.ngle below each distribution. Circled X marks date of bud bursting of parent trees in Portland and Corvallis. No bud bursting records were kept of the Washington trees. JOURNAL OF FORESTRY 474 Estimates of the genetic compo­ nent of the bud bursting time were Initial success of grafting, meas­ bursting time seen in the forest have a completely genetic basis. That ured by formation of definite un­ this is not so, but applies only to the narrow environmental range very high for the scion types-96­ percent for the 1956 observations and 94 percent for the 1957 obser­ vations. This means that practically ions between scion and understock, types. of this experiment, is shown by the Seventy-one percent of an grafts following observations from this an the variability was genetic in the sense that differences in time of bud were judged successful on July 13 of the first growing season. At this and other studies. Environment also plays a large part in the bud bursting pattern seen in the forest. For example, the showed far closer relationship to understock than to scion bursting of the seven scion types time, grafting success by various were consistent and little differ­ ence was shown from one under­ scion types _ showed relatively small stock tree to the next. percent. However, the range of range in average date of bud burst­ ing for scions of the three Portland nonsignificant variation-57 to 81 Growth rate of the grafts also success by understock trees was 43 trees was only 2 days in 1956 and differed widely and significantly by scion types. Greatest growth oc­ to 100 percent, a highly significant variation. Since the understock was 3 days in 1957. At Portland these same trees have burst their buds curred on the control grafts made by cutting off a scion and regrafting it to the same limb. Their seasonal without genetic variation, signif. icant variation in grafting success indicates that some physiological ing 11 years of observation. This growth averaged 7.4 inches on Au­ condition of the understock trees were small, but consistent environ­ over a period of 7 to 14 days dur­ suggests that genetic differences gust 9, 1957. Scions of the three such as vigor was different. There­ mental differences were appreciable trees from Portland averaged 3.8 fore, an analysis was made on the inches, whereas scions from Wash­ assumption that height was an ex­ between the three trees on tbe same hill at Portland. ington trees inches. pression of vigor. Grafting success Another example related to the was not found to be significantly natural stand surrounding the clone. Bud bursting of the mature averaged only 1.8 Bud bursting date was correlated related to heights of the seven with growth rate. In general, early clonal trees, although a trend to­ bursting scions of the clone grafts and Portland trees made the great. ward such a relationship was indi­ trees averaged nearly two weeks later than their seedling progeny, presumably beeause of the more shown by the late bursting Wash­ ington scions. About 65 percent of cated. By the beginning of the second year, death of additional grafts gave further evidence of the same small and large trees of similar the variation in seasonal elongation understock effect. However, in ad­ genetic material seems to apply also to the clonal understock which est growth. (r = Poorest growth was 0.80, d.f. = 37), a highly sig­ nificant amount, was related to bud dition to poor survival of grafts on certain understock trees, survival of favorable microclimate near the ground. This difference between has consistently burst its buds bursting in 1956. Considerable mor­ tality occurred the second year, so grafts of the three Portland trees about ten days earlier than the was mature parent tree on the Oregon only 32 scions were available for Washington trees. This effect of the the correlation in 1957. The rela­ scion types on second-year survival Most clear-cut data are from the tionship was highly significant, but was statistically significant at the only 38 percent of the variation in length (r = 0.61, d.f. = 30) was 1-percent level. Douglas-fir provenance study be­ gun in 1912 (6, 7) where 13 races related to date of bud bursting. nearly double that of the Discussion Elongation of natural branch terminals was compared with elon­ gation of clone scion grafted to The aim of the study, to deter­ mine the degree of genetic control clone understock (clone grafts A, bursting time in Douglas-fir, seems to have been accomplished. Under Fig. 1) to determine if grafting itself caused a reduction in growth. A definite reduction was noticed the first year but little reduction occurred during the second year. This is evident when growth of the single longest graft, A, is compared with growth of two ungrafted branches in the same relative posi­ tion on each of the five largest clone trees : Graft A Ungrafted branches (Inches) (Inches) 1956 6.7 8.3 1957 7.9 8.1 Growing season that can be shown for the bud conditions of the experiment, the several scion types burst buds at consistently different times over the 2 years of the study. Relatively small environmental differences heightened the ability of this study to show the genetic effect. Esti­ mates indicated that the genetic component of total variation in bud bursting time was very high -94 and 96 percent. Caution should be exercised in drawing inferences from these high figures for the genetic component. For example, one might infer that practically an variations in bud State University campus. follow about the same bursting or­ der in each plantation. In the 1912 study the same race began growth in April at the lowest plantation and in June at the highest, a two. month delay due to environmental differences. In this study, reduction in growth of the scions the first year after grafting was expected. This poorer growth, however, did not seem to influence the order of bud bursting. The relationship of increasing growth rate with earliness of bud bursting is at variance with other studies that show little relation of the two traits (1, 6, 7). However, this relationship could be acciden­ tal since the slowest growing scions were from the most northerly as well as the most suppressed trees. In addition, the clonal understock and all scion types completed elon­ JULY1962 475 gation at the same time in late June. Thus the late bursting scions had a shorter growth period. This apparent result of growth cessation influenced by the understock tree may not apply to ungrafted plants. Understock condition contributed far more than scion type to initial survival of grafts. Although this pattern seemed related to vigor of the individual clone tree, the rela­ tionship was not significant when height was used as an indication of vigor. In time, scion types also showed great differences in sur­ vival. Again this appeared to re­ late to vigor of the scion parent tree. Scions from open-grown trees survived better and grew larger than those from trees growing un­ ferent bud bursting dates onto limbs of each of seven trees of a much as two weeks. 17-year-old clone. The experiment included replications of seven scion rate only the first year. Relation­ types on each clone tree, the sev­ enth type being a control graft in which a limb of the clonal tree was cut, then regrafted. The genetic component of the bud bursting trait was estimated at 94 percent and 96 percent of total variation for the two years of .ob­ servation. Thus, practically all variation was genetic in the sense that differences in bud bursting of the seven scion t ypes were consist­ ent and little difference in this re­ gard was found between under­ stock trees. netically similar material for as Grafting depressed the growth ships 1. !RGENS·MOLLER, 2. 3. 4. tion. However, no valid statistical test was possible whereby tree vigor l ­ minimizing environmental infu ences on bud bursting insofar as 5. could be related to survival and growth after grafting. was possible. The study thus serves as an example of the need for cau­ tion in using such estimates except The degree of genetic control over bud bursting in Douglas-fir was investigated by grafting scions from trees with known widely dif­ the study indicate that local en­ vironmental differences may con­ sistently delay bud bursting of ge­ between Literature Cited These high estimates of the ge­ netic component were obtained by with natural or isolated cultured populations, since other data from investigated of both parent tree and understock. der crowded conditions in a planta.. Summary were survival of grafts and growth rate HELGE. 1957. Eco­ typie response to temperature and photoperiod in Douglas-fir. Forest Sci. 3: 79·83. Illus. KENNEDY, R. W. 1961. Variation and periodicity of summerwood in aome second-growth Douglas-fir, TAPP! 44:161-166. Illus. LARSON, P. R. 1960. A physiological consideration of the springwood-sum­ merwood transition in red pine. For­ est Sei. 6: 110-122. LusH, JAY L. 1948. The genetics of populations. Iowa State College. 381 pp. (Processed.) McCuLLOCH, W. F. 1943. Field snr­ vival of vegetatively propagated Douglas-fir. Jour. Forestry 41:211­ 212. 6. MORRIS, WILLIAM G., R. R. SILEN, 7. and H. WENS·MOLLER. 1957. Con· sistency of bud bursting in Douglas­ :fir. Jour. Forestry 55:208-210. IllU& MUNGER., THORNTON T., and WILLI,UI G. MORRIS. 1936. Growth of Douglas fir trees of known seed source. U. B. Dept. Agrie. Tech. Bui. 537. 40 pp. DJus. PRESENTATION OF SERVICE AwAJID.-John w. Smith, president, Seaboard Air Line Railroad Company, was honored May 8 during a Seaboard sponsored forestry field demonstration meeting by the U. 8. Forest Service when the company was cited for 25 years of outstanding service in the field of forestry development­ t-he first railroad to be so honored. Shown above, left to right: Congressman J. Vaughan Gary of Richmond, Va.; Edward P. Cli1f, chief forester. U.S. Forest Service, Washington, D. C.; Mr. Smith; and the principal speaker, Charles B. Stauffacher, executive vice president, Continental Can Company, Inc., New York City. More than 700 attended the forestry field meeting in Chesterfield County, Virginia, which in­ cluded the running of a special train from Washington, D. C., to the demonstration area jnsi south of Richmond. Aboard the special train were 33 Members of Congress representing 13 states, and 245 bwrl..ness, industrial and government leaders from the northeastern section of the nation. The over-all program was under the direction of the Seaboard's general forestry agent, Robert N. Hoskins.