Amaranthus retroflexus, A. hybridus and A. powellii were grown in a uniform garden at Ames from seed collected over a wide geographic area. Intraspecific variability in flowering response to photoperiod was studied. There was a significant correlation between date of flowering and the collection site

Landers, R. Q.

Mahlstede, J. P.

McWilliams, E. L.

Name not available

Ecotypic Differentiation in Response to Photoperiodism in Several Species of Amaranthus

University of Northern Iowa

Proceedings of the Iowa Academy of Science Volume 73 Annual Issue Article 10 1966 Ecotypic Differentiation in Response to Photoperiodism in Several Species of Amaranthus E. L. McWilliams Iowa State University R. Q. Landers Iowa State University J. P. Mahlstede Iowa State University Let us know how access to this document benefits you Copyright ©1966 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation McWilliams, E. L.; Landers, R. Q.; and Mahlstede, J. P. (1966) "Ecotypic Differentiation in Response to Photoperiodism in Several Species of Amaranthus," Proceedings of the Iowa Academy of Science, 73(1), 44-51. Available at: https://scholarworks.uni.edu/pias/vol73/iss1/10 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu. Ecotypic Differentiation in Response to Photoperiodism in Several Species of Amaranthus1 E. L. McWILLIAMs2, R. Q. LANDERS'\ J.P. MAHLSTEDE4 Abstmct. Amaranthus retroflexus, A. hybridus and A. powellii were grown in a uniform garden at Ames from seed collected over a wide geographic area. Intraspecific variabili-ty in flowering response to photoperiod was studied. There was a significant correlation between date of flowering and the collection site. Arnaranthus retrofiexus L., A. hybridus L. and Amaranthus powellii Wats., commonly called pigweeds, are wide ranging weedy species. They are often difficult to identify. Examination of these species for variability has been made by growing plants in a uniform garden at Ames, Iowa, from seed collected over a wide geographic area. This report considers the responses of collections to photoperiod. It may be accepted as fact that wide ranging plant species, in general, show genetically based ecological differentiation in morphological as well as physiological characteristics (Heslop-Harrison, 1965). Hiesey and Milner ( 1965) have stated recently that many ecological races and species of diverse plant groups differ in photoperiodic responses. This phenomenon was first demonstrated by the work of Olmsted ( 1944) on races of Boute-loua curtipendula distributed over 17 degrees of latitude. Larsen ( 1947), and more recently McMillan ( 1965), have demonstrated regional differentiation in photoperiodic responses of other wide-spread perennial grasses. Photoperiodic responses of Chenopodium quinoa and Amaran-thus caudatus, two annual species, have been studied by F'uller ( 1949), and reexainined by Zabka ( 1961). In a similar study to ours, Davidson ( 1965) observed that flower initiation in popula-tions from Iowa and Texas of Froelichia fioridana, an annual species in Amaranthaceae, is promoted by short-day photoper-iods and retarded by long-day photoperiods. However, the degree of long-day retardation was less for northern than for southern plants. Davidson considered that these photoperiodic differences were adaptive. Allard and Garner ( 1940) reported that photo-periodic responses in Amaranthus species were indeterminate, although no attempt was made to compare responses in ecologi-cal races. METHODS Seeds of Amaranthus retroflexus L. were requested from 40 1 Journal Paper No. J-5S99 of the Iowa Agricultural and Home Economics Ex-periment Station, Ames, Iowa. Project No. 1519. • Graduate Assistant, Dept. of Horticulture; 3 Assistant Professor, Dept. Botany & Plant Pathology; • Professor, Dept. of Horticulture. 44 1McWilliams et al.: Ecotypic Differentiation in Response to Photoperiodism in SeveralPublished by UNI ScholarWorks, 19661966] PHOTOPERIODISM IN" AMARANTHUS 45 state and Canadian seed laboratories and many foreign botani-cal gardens and herbaria. Many seed analysts pointed out that Amaranthus species are practically indistinguishable on the ba-sis of seed morphology; as a result many species were received in these seed samples. The seeds were planted in steam-treated soil on April 15, 1965, in 27i inch "Jiffy Pots" in a greenhouse under a 16-hour photoperiod. The seedlings were maintained under a 16-hour photoperiod until June 5, 1965, at which time they were planted ( 4-6 leaf stage) at the Iowa State University Horticulture Farm. The rows were spaced 6 feet apart, and the plants were spaced 2 feet apart within each row. The planting was a completely randomized design, and replications for each geographical loca-tion varied from 1 to 10 plants depending upon the number of seeds available. Most locations were represented by three plants. Because the soil contained indigenous Amaranthus seeds, pre-cautions had to be taken to maintain the identity of the planted seedling. Each plant was carefully labeled, and each pot was surrounded by a two inch layer of "perlite" extending 3-4 inches from the pot. The area was hand-weeded weekly. AMARANTHUS RE.TROE! EXlJS Fig. 1. Flowering date.. and isotherms of the average length of the frost free season for U. S. and Canadian collections of AmManthus •etroflexus grown at Ames ( inG!icated hy triangle) Iowa, during 1965. Subscript letters indicate the number of plants obse1-ved for each location a=l .... d:=4. OBSERVATIONS As growth of seedlings progressed, it became obvious that considerable variation existed. This variation could be attributed to the fact that several Amaranthus species were received, to 2Proceedings of the Iowa Academy of Science, Vol. 73 [1966], No. 1, Art. 10https://scholarworks.uni.edu/pias/vol73/iss1/1046 IOWA ACADEMY OF SCIENCE [Vol. 73 140 1e~ 150 140 ~;!>lQ-~· Hie ~-..'.::l~-\.l--....J~;;t::::::::'.:,_l_~L:::::..--l~-l-~-:~:::::::t-:::::t:::::::::~71-,&0 AMARANTHUS RETROFLEXUS Fig,. 2. Flowering dates and isotherms of the average length of the frost free season for Iowa collections of Amaranthus retroflexus grown at Ames, Iowa during 1965. Subscript letters indicate the number of plants observed for each location a=l .... d=:4. intraspecific differences between geographical collections, and to random variation. Intraspecific differences were most obvious at the onset of flowering. The date was recorded when the :floral primordia were macroscopically visible on each plant The range of variation in the date of flowering for a collection usually was less than + 5 days. Dates of flowering and average length of the frost free season are compared for some of the U.S. and Canadian collections of Amaranthus retrofl,exus in figure I, for Iowa in figure 2, and for Illinois in figure 3. Dates of flowering are compared with frost free season for some of the United States collections of A. hy-bridus in figure 4, and for Iowa and Illinois collections, respec-tively, in figures 5 and 6. Climatic data were obtained from "Climates of the States" ( 1959). A weather station near each collection site provided us with data on mean date of first fall frost, mean date of the frost free season, and the mean summer temperature. A multiple regression was determined for date of flowering, latitude, first fall frost, frost free season and aver:age summer temperature for A. hybridus and A. retroff,exus. For A. hybridus, the correlation between date of flowering and latitude was sig-nificant at the 1 per cent level. All collections of A. hybridus are from the mid-continental area of the United States except for two collections from Virgina. For A. retrofiexus, the cor-3McWilliams et al.: Ecotypic Differentiation in Response to Photoperiodism in SeveralPublished by UNI ScholarWorks, 19661966] PHOTOPERIODISM IN AMARANTHUS 180·· ....... ---,....~-""r'/I AMABANTHUS RETROFLEXUS 47 Fig. 3. Flowering dates and isotherms of the average length of the frost free season for Illinoi,s collections of AmaTanthus retroflexus grown at Ames, Iowa, during 1965. Subscript letters indicate the number of plants ob•erved for each location a=l ..... d=4. relation between date of flowering and latitudes approaches sig-nificance at the 5. per cent level. When the collections from the 4Proceedings of the Iowa Academy of Science, Vol. 73 [1966], No. 1, Art. 10https://scholarworks.uni.edu/pias/vol73/iss1/1048 IOWA ACADEMY OF SCIENCE [Vol. 73 AMARANTHUS HYBRIOUS Fig. 4. Flowering dates and isotherms of the average loogth of the frost free season for collections of Amaranthus hybridus grown at Ames (indicated by triangle) Iowa during 1965. Subscript letters indicate the number of plants observed for each location a=l , . . . . d=4. Rocky Mountain states are removed from the regression, the correlation between date of flowering is significant at the 1 per cent level. In mountainous areas flowering is more a function of altitude than latitude. For both A. hybridus and A. retrofiexus the correlation be-tween date of flowering and first fall frost gave the second best measure of fitness although it was not statistically significant. DISCUSSION AND CONCLUSIONS McMillan ( 1965) noted early flowering in prairie community transplants of northern origin and late flowering in those of 5McWilliams et al.: Ecotypic Differentiation in Response to Photoperiodism in SeveralPublished by UNI ScholarWorks, 19661966] PHOTOPERIODISM IN AMARANTHUS 49 1311 140 1411 1110 11111 150 140 AMARANTHUS HYBRIDUS Fig. 5. Flowering dates and isotherms of the average length of the frost free season for Iowa collectioru of Amaranthus hybridus grown at Ames, Iowa, duxing 1965. Subscript letters indicate the number of plants observed for each location a:=l ..•. d=4. sohthem origin when grown in a uniform garden. He noted fur-ther that the ecological variation resulting from natural selec-tion included early maturity within northern and monrl:ane pop-ulations. We observed similar effects of the climate on the date of flowering of the Amaranthus collections of the montane re~ gions, the coastal regions, and the Lake Michigan region as shown in figures 1 and 4. Collections from coastal regions and the Lake Michigan region exhibited a later maturity date than did mid-continent collections from the same latitude. A flowering gradient or cline extending from Canada to Kan-sas was observed for collections of A. retrofiexus, from Iowa to Louisiana for A. hybridus, and from Canada to Iowa for A. powellii. On the basis of these observations it is hypothesized that the first fall frost is an important factor of the environ-ment acting upon the genetic variability controlling the photo-period response mechanism. A population is maintained which is a compromise between large, late flowering plants capable of producing many seeds and smaller plants which aJmost al-ways produce some seeds before frost. In those regions where the growing season is longer because of large bodies of water the compromise allows a later date of floral induction. Within any given location where all three species are pre-sent, the order of flowering is usually as follows: A. powellii, A. retroflexus and A. hybridus. Nougarede et al. (1965) consid-ered A. retrocflexus to be a quantitative short-day plant rather 6Proceedings of the Iowa Academy of Science, Vol. 73 [1966], No. 1, Art. 10https://scholarworks.uni.edu/pias/vol73/iss1/1050 IOWA ACADEMY OF SCIENCE AMARANTHUS HYBRIDUS [Vol. 73 Fig. 6. Flowering dates and isotherms of the average length of the frost free season for Illinois collections of Amammthus hybridus grown at Ames, Iowa, during 1965. Subscript letters indicate the number of plants observed for each location a=l .... d=4. than an indeterminate plant as described by Allard and Garner ( 1940) . Our study indicates that the northern collections of A. retroflexus and A. hybridus arn quantitative short-day plants, although plants grown from seeds collected in Louisiana were unable to flower before frost in Iowa. Therefore, the type of photoperiodic response of a wide ranging species may depend to a large extent on the collection site. Davidson ( 1965) stated that one may suspect that to the north of the present distribution of Froelichia fioridanus the selective pressure associated with photoperiod and length of growing sea-son is too demanding to have been overcome by the narrow limits of the current gene pool. This would appear to apply to 7McWilliams et al.: Ecotypic Differentiation in Response to Photoperiodism in SeveralPublished by UNI ScholarWorks, 19661966] PHOTOPERIODISM IN AMARANTHUS 51 our information on the northern range of A. hybridus which appears to be presently limited in the midwest at the latitude of northern Iowa. Despite the continual mixing of genotypes of these weed popu-lations by agricultural practices and seed introductions, it ap-pears that these three species have evolved genetically adapted populations in response to different environments throughout their ranges. ACKNOWLEDGMENTS We wish to thank Dr. Jonathan Sauer, Department of Botany, University of Wisconsin, for verifying the identification of many of the collections of Amaranthus. Literature Cited Allard, H. A., and W. W. Gamer. 1940. Further observatiODS of the re-sponse of various species of plants to length of day. U.S. Dept. Agric. Bull. 727. 64 p. Davidson, Robert A. 1965. Ecol. 46: 520-523. Fuller, H. J. 1949. L. Amer. J. Bot. 36: 175-180. Heslop-Harrison, J. 1965. Adv. in Ecol. 2: 159-247. Hiesey, William M. and Harold W. Milner. 1965 Ann. Plant Physicol. 16:203-216. Larsen, E. C. 1947. Bot. Gaz. 109: 132-150. McMillan, Calvin. 1965. Amer. J. Bot. 52(1): 55-65. Olmsted, C. E. 1944. Bot. Gaz. 106: 46-74. Nougarede, Arlette, Ernest M. Gifford, Jr., and Pierre Roodet. 1965 Bot. Gaz. 126: 281-298. U.S. Dept. of Commerce Weather Bureau. 1959-1961. Climates of the. States. U.S. Govt. Printing Office. Washington, D.C. Zabka, G. G. 1961. Amer. J. Bot. 48:21-28. Notes on Prairie Species in Iowa. I. Germination and Establishment of Several Species PAUL A. CHRISTIANSEN1 AND ROGER Q. LANDERS2 Abstract. Information is given concerning the germination and early establishment of 30 _prairie species. A stratification treatment was included for all seeds, and scarification was also used for the legumes. Germination percentage in green-house flats was generally higher than in field plots with var-iation in germination :r!anging from 96% in compassplant, Silphium laciniatum, to zero in some such as Rosa suffulta and Gentiana puberula. Seedlings in field plots were subjected to five levels of competition throughout the growing season. Establishment, measured by numbers of seedlings and vigor in September, was most successful on weed free treatments, least successful on cover crop treatments. -----1 Assistant Professor, Cornell College, Mt. Vernon. • Associate Professor, Iowa State University, Ames. 8Proceedings of the Iowa Academy of Science, Vol. 73 [1966], No. 1, Art. 10https://scholarworks.uni.edu/pias/vol73/iss1/10

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Ecotypic Differentiation in Response to Photoperiodism in Several Species of Amaranthus

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