Inheritance of rnegastrobili colors in Douglas fir (Pseudotsuga menziesii)

Forestry Sciences Laboratory, Pacific Northwest Forest and Range Experinlent Station, Forest Service, U.S. Department of Agriculture, Corvallis, Oregon

Received February 3, 1972

COPES, D. L. 1972. Inheritance of megastrobili colors in Douglas fir (Pse~rrlofsziga meilziesii). Can. J . Bot. 50: 2045-2048.

Megastrobili color was studied in 7- to 9-year-old progeny resulting from cross-pollinations of parents with green, light pink, light red, or dark red megastrobili. Crosses of green X green parents produced 49% green progeny, while crosses of light red X dark red parents produced only 7% green progeny. Two bract traits, color of margins and tips and color of the central areas, combined to produce whole megastrobili color. Both the central and margin-tip traits appear to be controlled by different multigenes. An epistatic relationship was suggested between genes for central and margin areas.

COPES, D. L. 1972. Inheritance of megastrobili colors in Douglas f?r (Pseudots~iga menziesii). Can. J. Bot. 50: 2045-2048.

La couleur des n~egastrobiles a it6 6tudiBe dans une progkniture de 7 ans a 9 ans, resultant de pollinisa- tions croisks entre parents ayant des megastrobiles verts, rose plle, rouge clair, ou rouge fonce. Les croisements vert X vert ont produit une progeniture de 49% d'individus ayant des mCgast~wbiles verts, tandis que les croisements entre parents rouge clair et parents rouge fonce ont produit seulement 7% de progeniture verte. Deux caracttres des bractees, la couleur de la marge et de l'extr6mite et la couleur de la region centrale, produisent ensemble la couleur du megastrobile. Ces deux caracteres semblent contrales par des multigknes differents. I1 semble y avoir une relation epistatique entre les genes pour la region centrale et les genes pour la region marginale. [Traduit par le journal]

Introduction strobili (4). One of the compounds, cyanidin-3-

Forest geneticists do not often have oppor- mOnOglucOside, was found only in dark red

tunities to study inheritance of traits with &king megastrobili- Megastrobili color frequency was

color differences, but megastrobili, or female examinedin a natural Scots pine population,

"flower", color in Douglas fir is an exception. and it appeared that flower color was controlled

Megastrobili range in color from bright red to by a single gene with two alleles (1). The fol-

light or dark green. Colors vary between trees lowing study examined megastrobili color in-

but are uniform within a tree from year to year heritance in 395 Progeny produced from crosses

(3). Exact color classification in the field is diffi- of Parents that had red, green, or intermediate-

cult because effects of environment, exDosure to colored megastrobili. - A

direct sun rays, and the number of days since the rnegastrobili scales and bracts emerged from Materials and Methods

the protective cover of the bud, all influence the Controlled pollinations were made in 1962 and 1964 anlong 30 Douglas-fir clones in a grafted seed orchard

exhibited the megastrobili, near Shelton, Washington. Geographic origin of parent but they do not cause major shifts from red trees for the grafted orchard was the Soleduck area of the green or green to red. Thus, some meaningful Olympic Peninsula. The clones were crossed with intent color determinations can be made in the field. to study inheritance of various growth traits, hence are

~ i ~ ~ l ~ is known of the inheritance of mega- probably a random selection for megastrobili color. By chance, crosses of most color combinations of parents strobili color in Douglas fir or in other conifers. were made. About 2400 progeny from 58

A study of megastrobili color variation and crosses were grown in cold frames and were field-planted frequency of occurrence in a small geographic in the seed orchard in 1966 and 1968. In 1971, 395 of the area in British Columbia was made for Douglas 2400 progeny matured nlegastrobili.

Whole megastrobili color was determined only in fir (3)' In Oregon, a On pigments flowers which were in an upright receptive position with lJting to megastrObili bracts and scales fully open. This development stage cor- 11 flavonoid compounds in Douglas-fir mega- responds to that labeled No. 2 by Griffith (3). Parent and

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2046 CANADIAN JOURNAL OF BOTANY. VOL. 50. 1972

progeny trees were classified on April 19 and 20 into one of four broad color groups: green (G), light pink (LP), light red (LR), and dark red (DR). The G, LP, LR, and DR color classes correspond closely to the five bract color classes previously illustrated by Griffith (3). His classes 1 and 2 corresponded closely to G, 3 to LP, 4 to LR, and 5 to DR. Although the G, LP, LR, and DR grouping was an artificial classification system for a trait with seemingly continuous variation, possibilities of biasing the groupings in allotting borderline trees were very low. The 30 parents separated into the four classes as follows: 12 G, 10 LP, 6 LR, and 2 R.

A close examination of whole megastrobili revealed that two bract traits combined to produce whole mega- strobili color. The two traits were color of margin and bract-tip areas and color of the central bract area. The margin-tip areas impart most of the red color to the rnegastrobili. In the field, it was not possible to evaluate quickly the degree or intensity of color found in such small areas of the bracts; to evade this problem, central and margin areas were not separated into four classes like whole megastrobili color but were simply classified as green (G) or red (R) (red being any shade of red or pink). Margin-tip and central areas were evaluated separately to determine whether they were controlled by different genes. The 30 parents were classified as 22 G and 8 R for central areas, and 4 G and 26 R for margin- tip areas.

Results

Whole megastrobili colors of the 395 progeny are presented in Table 1. Crosses of G X G produced 49y0 green and only 3y0 dark red (DR); crosses of LR X DR produced only 7y0 G but 30y0 D R trees. A gradation or dilution effect in percentage of G progeny (49y0, 25%, 22%, and 7% for G, LP, LR, and DRY respec- tively) was noted when G parents were crossed with parents having progressively more red pig-

TABLE 1 Whole megastrobili colors observed in progenies resulting from crosses of green (G), light pink (LP), light red (LR), and dark red (DR) parents. Results are expressed as percentage of trees within each parentage that exhibited

the indicated color

No. of Phenotypes of Phenotypes progeny progeny, %

of with mega- ~ a r e n t strobili. n G LP LR D R

G X G 39 49 31 18 3 G X LP 8 1 25 49 25 1 G X LR 45 22 31 29 18 G X D R 111 7 41 45 6 LP X DR 79 8 39 35 18 LR X DR 27 - 7 22 41 30

382=

-Sample size does not equal 395 because progeny from LP X LP. LP X LR, and DR X DR were excluded because of inadequate sample size.

ments. Conversely, red parents crossed with parents having progressively less red gave per- centages in descending order of red (i.e., 30y0, 18y0, 6y0). Multiple comparisons by the Scheffe test (degrees of freedom (d.f.) = 5, 376) indicated highly significant differences in the number of green progeny arising from G X G vs. LR X DR, and G X G vs. G X DR. Number of green progeny from LR X DR vs. G X DR were not significantly different.

Progeny results for bracts are presented in Table 2. The same inheritance trends exhibited for whole megastrobili color were shown in central areas of the bracts. In general, crossing G X G gave a majority of progeny with green central areas (79y0), while crossing R X R gave primarily pink red (64%). Multiple comparisons by the Scheffe test (d.f. = 3, 391) showed highly significant differences in number of green progeny from G X G vs. R X R, G X R, and R X G. No significance was found between G X R and R X G.

A slightly different trend was shown for margin-tip color (Table 2). Crosses of G X G gave a majority of the seedlings which had pink- red margins and bract tips (66%). Although the percentage of green progeny obtained from the G X G crosses was only 34%, Scheffe test com- parisons (d.f. = 3, 391) indicated highly signifi-

TABLE 2 Bract colors observed in (1) central area and in (2) margin and tip areas of progeny resulting from crosses of parents with green or pink-red pigments in areas 1 or 2. Results are expressed as percentage of trees with green or red

megastrobili within each parentage

Phenotypes of NO. of progeny, %b

Phenotypes progeny with of parenta*b megastrobili, n G R

(1) Central area G X G 103 79 21 G X R R X G R X R

(2) Margin and tip areas G X G 38 34 66

-Parent phenotypes were classified independently for both central and rnargin-tip traits.

bGreen. G ; red. R (red included all shades of pink and red).

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COPES: INHERITANCE IN DOUGLAS FIR 2047

cant differences when compared with G X R (6%), R X G (12%), and R X R (7%). Color differences between G X R vs. R X G and G X R vs. R X R were not significant.

An apparently epistatic relationship was in- dicated between central and margin-tip color genes. Green margins were never found where central areas were pink-red, but both green and pink-red margins were found in megastrobili with green centers ( ~ 2 = 70.96*:': for 1 d.f.). Progeny from crosses with one or two red parents had only 670 to 12y0 with green margins and bract tips (Table 2). These lower than ex- pected values resulted because about soy0 of the progeny from the crosses had pink-red central areas which masked gene expressions for green margins.

Seven percent of the 30 parent clones from northwest Washington were found to have dark red megastrobili. The frequency of Douglas-fir trees with dark or bright red megastrobili near Vancouver, British Columbia, was reported to be 7.87, (3) and near Corvallis, Oregon (2), 67'. It appears that, at least for these three areas, there is little variation in the gene frequencies for dark red megastrobili color ( ~ 2 = 0.23 for 2 d.f., not significant).

Discussion No true-breeding (homozygous) combinations

of parental genotypes were evident from study- ing megastrobili color of their offspring. Crosses between two red parents gave some green progeny and crosses between green parents gave some dark red progeny. For Douglas fir, it ap- pears that a simple one- or two-gene model will not adequately fit the observed data. The data suggest multigenic control for whole megastrobili color and for color of margin-tip and central bract areas. Whole megastrobili color crosses of G X G parents produced many more progeny with green megastrobili than crosses of LR X DR. Crosses made between green and red parents tend to give a majority of the progeny with intermediate-colored megastrobili.

A case of epistasis or variable penetrance was

margin-tip genes could be seen. It appeared that genes for green margin and tip were recessive and did not have visible effect in margin and tip areas when the central areas were red. The sym- metry of the data in Table 2 for central color supports this conjecture.

When one considers that 11 different flavonoid compounds have been identified in Douglas-fir megastrobili (4), it is not surprising that a num- ber of genes may be responsible for megastrobili color in Douglas-fir. Like flower color in clover, in which each flavonoid is controlled by one or more genes (5), megastrobili color in Douglas fir may depend quantitatively on the number of flavonoids present and upon their relative con- centrations. This situation would fit the con- tinuous range of color variation evident in the larger Douglas-fir families.

In a previous study (2), inherited differences in hypocotyl color were found in progeny pro- duced from crosses of parents with green and red megastrobili. Crosses between parents with green megastrobili gave progeny with the fol- lowing hypocotyl colors: 18yo red, 32% pink, and 50% green. This color array was amazingly close to megastrobili colors obtained in the present study from crosses of G X G parents (21y0 red, 31% pink, 49% green). Also, hypo- cotyl color of green X red crosses closely fit megastrobili results for G X D R of this study (48y0 vs. 51y0 red, 48y0 vs. 41y0 pink, and 5y0 vs. 7y0 green). Hypocotyl pigmentation of 2- week-old seedlings may be controlled by the same genes which control megastrobili color in 7- to 9-year-old trees. Further work is needed to verify this relationship.

Acknowledgments Gratitude is expressed to Tom Greathouse,

now with F A 0 in Turkey; Dr. Roy Silen, Pacific Northwest Forest and Range Experiment Station in Corvallis, Oregon; and to Virgil Allen of the U.S. Forest Service, Shelton Ranger Station, in Shelton, Washington. Each played a significant role in pollinating and growing the plant mate- rials examined in this study.

suggested for the genes controlling margin-tip coior. Genes contrilling the color of the central area of the bracts also caused pigmentation of cells in the margin area; thus, margin color genes had to dominate or suppress the central trait color in margin and tip areas before effects of

1. CARLISLE, A., and A. H. TEICH. 1970. The Hardy- Weinburg law used to study inheritance of male inflorescence color in a natural Scots pine population. Can. J. Bot. 48(5): 997-998.

2. CHING, K. K., H. AFT, and T. HIGHLEY. 1966. Color variation in strobili of Douglas-fir. Proc. West. For. Genet. Assoc. pp. 37-43.

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2048 CANADIAN JOURNAL OF BOTANY. VOL. 50, 1972

3. GRIFFITH, B. 1968. Phenology, growth, and flower 4. HIGHLEY, T. L. 1964. The flavonoid con~pounds of and cone production of 154 Douglas-fir trees on the three floral phenotypes of Douglas-fir. M.S. Thesis, University Research Forest as influenced by climate Oregon State University, Corvallis, Ore. and fertilizer, 1957-1967. Univ. B.C. Fac. For. Bull. 5. TAYLOR, N. L., C. J. KELLER, M. K. ANDERSON, and No. 6. W. A. KENDALL. 1971. Anthocyanidin floral pigmen-

tation in red clover. J. Hered. 62(1): 13-15.

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