Notes 127 numbers 102, :30, 54, and 7) is 3.45, and less than 7 percent of similar twin samples would yield proportional differences as great or greater than that observed were tongue rolling ability not in fact influenced by hereditary factors. The data are inconsistent, therefore, with the hypothesis of chance fluctuations, and we conclude that hereditary factors strongly influence tongue rolling ability (P < 0.07). The fact that only 88.:) percent of monozygous twin pairs are concordant would indicate .5. 7 5 percent (half of 11.5 percent) lack of penetrance. This frequency might be due to either hereditary factors or environmental factors such as the learning component previously mentioned. An even stronger case for genetic influence is exhibited when the twins in the third group- parenthesized in Table I -are eliminated from the analysis. The numbers in Table I then become 96, 24, .51, and :3 with a chi-square of .5.97. Now P < 0.025, and 94.4 percent of the monozygous twin pairs are concordant, with 2.8 percent of these subjects exhibiting a lack of penetrance. "White Seedling": A Pigment Mutation That Affects Seed Dormancy in Douglas-fir FnANK C. SoRENSEN T HIS note describes a chlorophyll-less mutant of Douglas-fir and its association with speed of germination. Hecessive chlorophyll mutants have been frequently observed in plant species (e.g., Gustafsson 5 with regard to forest trees). In maize, it has been observed that the lack of pigmentation often has been aecompanied by premature germina- tion or absence of dormancy 14 • There appear to have been no observations linking lack of chlorophyll or carotenoids with germination characteristics in other species, however. This may be because the traits are not assoeiated in most other speeies, or because it is diffieult, at least in many plants, to distinguish the albino from the normal seedling at the onset of germination, and the association has The author is principal plant geneticist, Forestry Sciences I,aboratory, Pacific Northwest Forest and Range Experiment Station, Forest Service, U. S. Department of Agriculture, Corvallis, 97330. Summary Data were collected from 193 pairs of twins on their tongue rolling ability. This sample population included 61 pairs of monozygous twins. The data were then analyzed for concordance and discordance among monozygous and dizygous twin pairs by the chi-square method. It was found that the data were inconsistent with the hypothesis of chance fluctuation and that the ability to roll the tongue is strongly influenced by hereditary factors. The data further indicated a lack of penetrance of 5.75 percent using the entire population sample, and 2.8 percent if the doubtful group (19 individuals exhibiting intermediate expression) was eliminated. This lack of penetrance may be due to either heredi- tary factors or to environmental factors such as a learning component. Literature Cited 1. MATLOCK, PHILIP. Identical twins discordant in tongue- rolling. J. Hered. 43:24. 1952. 2. STURTEVANT, A. H. A new inherited character in man. Proc. Nat. Acad. Sci. 26:10Q-102. 1940. 3. . A History of Genetics. Harper and Row, New York. p. 127. 1965. been missed. In the present case, germinating white seedlings could be distinguished from their normal siblings at the time the radicle was first visible, which made the relationship between albinism and speed of germination readily apparent. Materials and Methods Two trees, designated in our laboratory as Lac-2 and XWC-8, growing about 30 miles apart in the Willamette Valley of western Oregon and which previously had been identified as carriers of the same recessive white seedling gene, were self- and reciprocally cross-pollinated in the spring of 1968. Seeds were collected in the fall, and germination tests were made in the next winter and spring. Test seeds were those containing white seedling embryos. Control seeds were from the same progeny and contained normal embryos. Initially, germination tests were made under our standard conditions for Douglas-fir of 16- to 20-hour water soak at room temperature, 2-week stratifi- cation at .5° C, and germination at 30° C day and 20° C night temperatures with 12-hour photo- and thermoperiods. ::iubsequently, some samples of seeds were germinated without stratification and with stratification at 0.5° C and 7.5° C. The purpose of 0.5° C temperature was to provide stratification at a temperature at which little or no embryo elongation would be likely to occur. Purpose of the 7.5° C temperature \vas to stratify at a temperature Downloaded from http://jhered.oxfordjournals.org/ at DigiTop USDA's Digital Desktop Library on January 26, 2015
Transcript
Notes 127
numbers 102, :30, 54, and 7) is 3.45, and less than 7 percent of similar twin samples would yield proportional differences as great or greater than that observed were tongue rolling ability not in fact influenced by hereditary factors. The data are inconsistent, therefore, with the hypothesis of chance fluctuations, and we conclude that hereditary factors strongly influence tongue rolling ability (P < 0.07).
The fact that only 88.:) percent of monozygous twin pairs are concordant would indicate .5. 7 5 percent (half of 11.5 percent) lack of penetrance. This frequency might be due to either hereditary factors or environmental factors such as the learning component previously mentioned.
An even stronger case for genetic influence is exhibited when the twins in the third groupparenthesized in Table I -are eliminated from the analysis. The numbers in Table I then become 96, 24, .51, and :3 with a chi-square of .5.97. Now P < 0.025, and 94.4 percent of the monozygous twin pairs are concordant, with 2.8 percent of these subjects exhibiting a lack of penetrance.
"White Seedling": A Pigment Mutation That Affects Seed Dormancy in Douglas-fir
FnANK C. SoRENSEN
T HIS note describes a chlorophyll-less mutantof Douglas-fir and its association with speed
of germination. Hecessive chlorophyll mutantshave been frequently observed in plant species (e.g., Gustafsson5 with regard to forest trees). In maize, it has been observed that the lack of pigmentationoften has been aecompanied by premature germination or absence of dormancy14 • There appear to have been no observations linking lack of chlorophyll or carotenoids with germination characteristics in other species, however. This may be because thetraits are not assoeiated in most other speeies, or because it is diffieult, at least in many plants, todistinguish the albino from the normal seedling atthe onset of germination, and the association has
The author is principal plant geneticist, Forestry Sciences I,aboratory, Pacific Northwest Forest and Range Experiment Station, Forest Service, U. S. Department of Agriculture, Corvallis, Ore~on 97330.
Summary
Data were collected from 193 pairs of twins on their tongue rolling ability. This sample population included 61 pairs of monozygous twins. The data were then analyzed for concordance and discordance among monozygous and dizygous twin pairs by the chi-square method. It was found that the data were inconsistent with the hypothesis of chance fluctuation and that the ability to roll the tongue is strongly influenced by hereditary factors. The data further indicated a lack of penetrance of 5.75 percent using the entire population sample, and 2.8 percent if the doubtful group (19 individuals exhibiting intermediate expression) was eliminated. This lack of penetrance may be due to either hereditary factors or to environmental factors such as a learning component.
Literature Cited 1. MATLOCK, PHILIP. Identical twins discordant in tongue
rolling. J. Hered. 43:24. 1952. 2. STURTEVANT, A. H. A new inherited character in man.
Proc. Nat. Acad. Sci. 26:10Q-102. 1940. 3. . A History of Genetics. Harper and Row,
New York. p. 127. 1965.
been missed. In the present case, germinating white seedlings could be distinguished from their normal siblings at the time the radicle was first visible, which made the relationship between albinism and speed of germination readily apparent.
Materials and Methods
Two trees, designated in our laboratory as Lac-2 and XWC-8, growing about 30 miles apart in the Willamette Valley of western Oregon and which previously had been identified as carriers of the same recessive white seedling gene, were self- and reciprocally cross-pollinated in the spring of 1968. Seeds were collected in the fall, and germination tests were made in the next winter and spring. Test seeds were those containing white seedling embryos. Control seeds were from the same progeny and contained normal embryos.
Initially, germination tests were made under our standard conditions for Douglas-fir of 16- to 20-hour water soak at room temperature, 2-week stratification at .5° C, and germination at 30° C day and 20° C night temperatures with 12-hour photo- and thermoperiods. ::iubsequently, some samples of seeds were germinated without stratification and with stratification at 0.5° C and 7.5° C. The purpose of 0.5° C temperature was to provide stratification at a temperature at which little or no embryo elongation would be likely to occur. Purpose of the 7.5° C temperature \vas to stratify at a temperature
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that was known to be above optimal for Douglas-fir. Seeds were checked each day for new germination.
A seed was tallied as germinated when any of the radicle could be seen. White seedlings could be distinguished at this time, but all germinated seeds were still held for a few days to make sure of correct identification. Germination proceeded rapidly for these lots and a germination test was considered complete when two days passed without any seeds germinating. Germination was, in most cases, 9.5 to 100 percent complete at this time.
Rate of germination is expressed by simply determining the average number of days from the time a sample of seeds enters the germinator until germination is completed. For example, if one seed germinated in 8 days, a second seed in 9 days, and a third in 11 days, the average number of days to germination for the three seeds would be 9.3.
Results Description of mutant
The white seedlings, when allowed to develop in the light, had neither green nor yellow pigmentation. However, if the seedcoat was removed prematurely, the freshly exposed portions of the cotyledons of many seedlings showed varying intensities of green, from pale to quite dark . (.3ome germinant seedlings were without green pigmentation even in freshly exposed portions of the cotyledons. Proportion of seedlings showing green coloration under the seedcoat was not determined.) Green color faded after a few hours exposure to light. Yellow pigment was not noticeable in either the portion that had been exposed to light or the portion that had been protected from the light. The white seedlings developed until seedcoat was shed or nearly shed. At this point the cotyledons started to wither, and the entire seedling withered within a to 7 days.
Germination tests
Table I, which gives results of germination tests, shows that seeds yielding white seedlings germinate much more rapidly than normal siblings. Rapid germination of white seedlings occurred with or without stratification; in fact, it even occurred in stratification when the stratification temperature was a little higher than normal. In addition to more -rapid germination regardless of pretreatment, the results also indicate that the seeds containing "white embryos" lack the response to moist chilling that most Douglas-fir seeds seem to show.
The more rapid germination characteristic can be seen in all the tests, but is perhaps best illustrated by the Lac-2 and XWC-8 seeds that were stratified at 0 . .5° C. At this temperature, little or no embryo elongation can be expected during stratification. The fact that the mutants germinated more rapidly under these conditions shows that the white embryo grew faster at the germination temperature.
The lack of response to moist chilling (i.e., Jack of dormancy) by the mutant embryos is best seen by comparing seed lots for Lac-2 X XWC-8, which were unstratified, with those that were stratified at
0.5° C. Normal seedlings responded to stratification by germinating more rapidly with stratification than without. \Vhite seedlings, on the other hand, germinated at about the same rate with or without stratification. A similar comparison can be made between Lac-2 X XWC-8 seed lots that were stratified the same length of time (14 days) but at .5° C and 7 . .5° C. Normal seedlings responded to lower stratification by germinating more rapidly after stratification at .5° C than after stratification at 7 .. 5° C. Seeds containing mutant embryos "responded" to the higher stratification temperature by germinating in stratification. That these seeds germinated more rapidly when stratified at 7 . .5° C than at 5° C, and normal seeds did not, indicates that the former lacked a chilling requirement and, instead, simply responded to higher temperature with more rapid elongation of the embryo.
Discussion Occun·ence of the mutant
Although lack of pigment and lack of dormancy would seem to be a peculiar combination of ehamcters, the combination may be quite frequent. The phenotype was apparently first reported in maize where the absence of seed dormancy aspect was stressed under such names as "germinating seeds"10
and "viviparous"4• Hecently, the combination of traits also has been observed in western white pine (personal communication, R. T. Bingham, Forestry Sciences Laboratory, Forest Service, U. S. Department of Agriculture, Moscow, Idaho 83843) and in ponderosa pine (Sorensen, unpublished) .
Lack of pigment and lack of dormancy requirements are not always associated. :i\[any albino mutants have been reported in maizc2 • '-~; however, it is only those that are also associated with white or pale yellow endosperm that show vivipary 15 •
But even among these, not all are viviparous.
Table I. Germination of white and nonnal green seedlings from se,·eral segregating Douglas-fir families
Stratification
Temper-Family Length ature
Days oc XWC-8 X self 14 5 Lac-2 X self 14 5 X WC-8 X Lac-2 14 5 Lac-2 X X WC-8 14 5 Lac-2 X XWC-8 14 7.5 Lac-2 X XWC-8 0 Lac-2 X XWC-8 15 .5 Lac-2 X X WC-8 29 .5
Days to germination•
White Normal seedlings seedlings
2.6- 5.4 3.5 8.3 1.4 4.6 1.5 9.2 .2t 11.4
4.4 16.5 4.5 9.0 3.7 8.0
• Average number of days to germination of all seeds which germinated. Test was considered complete when 2 days passed with no new germination. Day on which seeds went into germination was called 0.
t Of 29 white seedlings, 27 germinated while seeds were in stratification, but on the day called o-hence, days to germination less than one.
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Robertson15 found that 7 of 13 such mutants never conditions are right, especially in the absence of exhibited premature germination. Also, Eyster', dormancy-breaking treatments. They are similar l\1angelsdorf11 and Robertson14 , have described only in that in both cases an aspect of dormancy is viviparous mutants that are not albino. involved and control is in the embryo.
Comparative description of mutant One gene or two
Among albino-viviparous or albino-rapid germi The first impression in maize was that there was a nating mutants in maize and conifers, the pigment physiological connection between premature germiphenotypes are remarkably similar. In general, nation and formation of chlorophyll11 • It appeared the mutant seedlings are white, lacking both chloro _that single genes with pleiotropic effects were phylls and carotenoids. iVIany of the Douglas-fir responsible for the two traits appearing together. white seedlings have some green color until the Recombination has been observed\ but this could colored tissue is exposed to light, but it then bleaches be the result of heterofertilization rather than out. Similarly, maize viviparous-albino mutants recombination14 • Also, there are some "viviparous" are green or tinged with green when germinated loci not associated with albinism, and vice versa12 14
• •
in the dark or in dim lighV 7 but bleach in the light. In Douglas-fir data presented above, the white Western white pine mutants are described as pink seedlings have averaged more rapid germin~tion albino (personal communication, R. T. Bingham); than have the seeds yielding normal seedlmgs. ponderosa pine mutants are pink albino or white. However, there is some overlap in the two classes. Pink albino seedlings are known in corn, and they A small percentage of green seedlings in almost are viviparous (personal communication, D. S. every germination test appears before the appearance Robertson, Iowa State University, Ames 50012). of the last white seedling. This is probably chance
In maize, vivipary is also associated with white or distribution of the classes, but it could indicate pale yellow rather than yellow endosperm. However, that some of the green seedlings are carrying the there is no comparable pigmented tissue in the allele for rapid germination and some of the white conifers. seedlings are not-that there has been some recombi
Examination of several albino maize mutants nation between the two classes. reveals that they produce protochlorophyllide and Several white pine carrying the same gene for protochlorophyll during germination and growth white seedlings have been identified (personal comin the dark and convert these pigments into chloro munication, R. T. Bingham). In the majority of phyll and chlorophyllide in the lighV 7• Chlorophyll the progenies from these trees, seeds containing production is normal or nearly so; but carotenoids normal and white embryos germinated contempoare reduced or absent, and all mutants bleach with raneously. But in the selfed progeny of one tree, continued illumination1 16
• • Levels of chlorophyll and perhaps another, seed with white embryos and carotenoid production are not known for germinated more rapidly or with less stratification Douglas-fir, except that some chlorophyll is fre than did seeds with green embryos. This could be quently formed, that it is rapidly bleached in the interpreted as evidence for separate genes. However, light, and that yellow carotenoid pigmentation is subtle environmental differences in cone and seed not apparent. handling, or in germination conditions, could pro
It is more difficult to compare the dormancy duce the same result, particularly if the albinophenotypes because of differences between conifers rapid germinating mutants were exceptionally sensiand maize, both in the expression of the mutant tive to drying and wetting conditions (personal and in reproductive behavior. Two points in particu communication, D. S. Hobertson). lar should be mentioned.
In maize, seeds are produced from double fertili Conclusion zation. Therefore, both the embryo and the nutritive endosperm tissue contain sets of paternal The genetic association between pigment prochromosomes. Dormancy control could be in the duction and a dormancy control mechanism may be endosperm or in the embryo. However, Hobertson13 rather widespread in the plant world. There is produced single maize seeds with different genetic evidence that the association may sometimes be constitutions in the embryo and endosperm and due to linkage. Usually, however, it appears to be showed that the viviparous allele affected dormancy due to a single gene, or to linkage that must be through the embryo only. In conifers, the nutrient very tight. In either case, the fact that the effects tissue for the embryo is the female gametophyte, have been located together in Douglas-fir, pine, and which is maternal. Since green and white full at several points in the maize genome indicates that siblings germinate at different times, dormancy some basic relationship between the dormancy control here also must be in the embryo. mechanism and pigment formation exists.
A second possible point of difference is that vivi Eyster4 remarked that continuous development parous maize and other grains18 19 • are characterized of white sporophytes was strongly influenced by by continuous development of the sporophyte environmental factors, especially moisture. In that concludes with sprouting in the ear. In Douglas fact, he was able to induce dormancy or delay fir, the development of the mutant embryos is not germination by prematurely drying the ear. Varis continuous but only more rapid when germination and Manneri18 also reported that sprouting in the
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ear by green kernels of VIVIparous races of winter wheat was related to water retention. We have observed only that white Douglas-fir seedlings areextremely turgid, the cotyledons being almost hardin the presence of very little structural tissue. Ifphysiological work is done on the action of thismutant in the dormancy process, perhaps a goodplace to start would be with the water relations ofthe germinating seed.
Summary
A white seedling mutant in Douglas-fir and itsassociation with speed of germination are described. Mutant seedlings appeared to lack all carotenoidpigment; green pigment, though initially present in some germinant seedlings, bleached rapidly in thelight. Comparisons of seed lots after exposure toseveral combinations of stratification temperaturesand periods showed that seeds containing mutantembryos apparently lacked any stratification (moistchilling) requirement and germinated more rapidlythan their nonmutant siblings. Union of whitealbino or pink albino seedling trait and vivipary, orrapid germination, also has been reported several times in maize and in western white and ponderosapines.
Literature Cited I. ANDEHSON, I. C. and D. S. RoBEHTSON. Role of caro
tenoid~ in protecting chlorophyll from photodestruction. Plant Physio/. 35:531-534. 1960.
2. DEMEREC, M. Inheritance of white seedlings in maize. Gene/i(S 8:561-593. 1923.
3. EYSTER, W. H. A primitive sporophyte in maize. Am. J. Botany 11:7-14. 1924.
4. ----. Vivipary in maize. Genetics 16:574-590. 1931.
Inheritance Of a Dwarf Character in Sericea Lespedeza
.J. D. ~fiLLER AND E. D. DoNNELLY
SEIUCEA, Lespedeza cuneata (Dumont) G. Don, has been used for many years as a forage and
soil-conserving crop. This study reports the inheritance of a dwarf internode character that was discovered in selfed progeny of an irradiationinduced sericea mutant.
Hanson and Cope2 reported inheritance of a
The authors are research associate (now research geneticist, Crops Research Division, ARS, USDA, Canal Point, Florida 33438), and professor, Department of Agronomy and Soils, Auburn University Agricultural Experiment Station, Auburn, Alabama 36830. Contribution from the Department of Agronomy and Soils, Auburn University Agricultural Experiment Station. Data were taken from a thesi~ submitted by the senior author to Auburn Universitv in partial fulfillment of the requirements for the Ph.D. degree.
5. GusTAFSSON, A. Polyploidy and mutagenesis in foresttree breeding. Proc. Fifth World Forest. Congr. 1960, Seattle. vol. 2, pp. 793-805. 1962.
6. LINDSTROM, E. W. Chlorophyll inheritance in maize. Cornell Univ. A gr. Exp. Sta. Memoir 13. 68 pp. 1918.
7. . Concerning the inheritance of green and yellow pigments in maize seedlings. Genetics 6:91-110. 1921.
8. . Complementary genes for chlorophyll develop-ment in maize and their linkage relations. Genetics 9:305-326. 1924.
9. ----. Genetic factors for yellow pigment in maize and their linkage relations. Genetics 10:442-455. 1925.
10. MANGELSDORF, P. C. The inheritance of defective seeds in maize.J. Hered. 14:119-125. 1923.
11. . The genetics and morphology of some endosperm characters in maize. Conn. Exp. Sta. Bull. 279: 513-614. 1926. ''
12. NEUFER, M. G., L. JoNES, and M. S. ZunEH. The Mutants of Maize. Crop Sci. Soc. Amer., Madison, Wis. 1968.
13. ROBERTSON, D. S. The genotype of the endosperm and embryo as it influences vivipary in maize. Proc. Nat. Acad. Sci. 38:580-583. 1952.
14. . The genetics of vivipary in maize. Genetics 40:745-760. 1955.
15. . Linkage studies on mutants in maize with pigment deficiencies in endosperm and seedling. Genetics 46:649-662. 1961.
16. , M. D. BACH~LINN, and I. C. ANDERSON. Role of carotenoids in protecting chlorophyll from photodestruction. II. Studies on the effect of four modifiers of the albino c/1 mutant of maize. Photochem. Photobiol. 5:797-805. 1966.
17. SMITH, J. H. C., L. J. DunHAM, and C. F. \VuRSTEH. Formation and bleaching of chlorophyll in albino corn seedlings. Plant Physio/. 34:340-345. 1959.
18. VAms, E. and M. MANNEHI. The effect of the morphological properties of the ear on the susceptibility of wmter wheat to sprouting in the ear. M aataloust A ikakausk. 35: 27-35. 1963. (Plant Breed. Abstr. 35: #4021. 1965).
19. YAMAMOTO, K. Investigations on" viviparous" germination of seed in barley varieties in Japan. Rep. Ins/. A yr. lles. 1'ohoku Um"v. 3:13-27. 1951.
dwarf mutation in serieea that was characterized by shortened internodes, small leaves, and light green color. This trait was conditioned by a single recessive gene. A second dwarf mutation in sericea was reported1 that had longer and fewer internodes but attained a height of not more than 1.5 em. It
-----<'lO·-------_.'lO·---
FIGURE 1-Dwarf plant (left) and normal stature plant (right) within selfed progeny of X, 18-4.
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