GROWTH AND DEVELOPMENT. Larry Teuber. Judy Jernstedt and Karl Foord

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ALFALFA GRWTH AND DEVELPMENT Larry Teuber. Judy Jernstedt and Karl Frd Department f Agrnmy and Range Science University f Califrnia Davis, Calfrnia 95616 ABSTRACT The alfalfa (Medicaq sativa L.

The initial fur stems are the primary stem, tw stems differentiating f:t'm the axils f the ctyledns and a stem frm the axil f the uniflilate leaf.

Allf these prcesses are influenced by sil temperature, and t a lesser -!xtent, by phtperid.

1 ALFALFA GRWTH AND DEVELPMENT Larry Teuber. Judy Jernstedt and Karl Frd Department f Agrnmy and Range Science University f Califrnia Davis, Calfrnia ABSTRACT The alfalfa (Medicaq sativa L.} seedling develps int a mature plant by differentiatin f several stems which frm the primary crwn. The initial fur stems are the primary stem, tw stems differentiating f:t'm the axils f the ctyledns and a stem frm the axil f the uniflilate leaf. Establishment f the primary crwn is dependent n the develpment f these initial stems and the degree t which cntractile grwth ccurs. Allf these prcesses are influenced by sil temperature, and t a lesser -!xtent, by phtperid. We have determined ptimum temperatures fr alfalfa seedling develpment t be in the range f 68 t 72 degrees fahrenheit depending n the drmancy classificatin f the cultivar. Using thi!; infrmatin and climatic infrmatin fr a given area in Califrnia :it may be pssible t predict the mst desirable time t plant alfalfa in that area. NDEX WRDS Medicag sativa L., Lucerne, seedling grwth, crwn develpment, planting date, envirnmental physilgy. NTRDUCTN ne f the mst critical peratins in the prductin f alfalfa is stand establishment. n the alfalfa research prgram at Davis we are cmmitted t the applicatin f fundamental bilgy t the imprveme1lt f bth the alfalfa plant and the cultural methds used t grw the crp. n the present paper we will discuss the general pattern f alfalfa seedling grwth, the influence f sil temperature and phtperid (day lengt11l) n seedling develpment, and the use f this infrmatin t make farming decisins that take int accunt bth bilgical and ecnmic cnsideratins. ( SEEDLNG DEVELPMENT Shrtly after planting and watering, the seed begins t germinate. This is first detected by the penetratin f the primary rt int the sil t prduce an unbranched tap rt. Cntained within the mature seed are seed leaves r ctyledns. As the area belw the ctyledns (hypctyl) straightens and elngates, the ctyledns are pushed abve the sil surface (Figure 1).The first true fliage leaf t be prduced is the uniflilate (having a single leaflet) leaf. The seedling stem (primary sht) cntinues t develp, prducing spirally arranged triflilate (having three leaflets) leaves (Figure 2).Subsequently prduced stems are referred t as secndary stems. The first secndary stem develps frm an axillary bud at the uniflilate nde. This is fllwed by the secnd and third secndary stems which develp frm axillary buds at the ctylednary ndes (Figure 3,4). These fur stems (primary plus 3 secndary) cnstitute the primary crwn. Cncurrent with the grwth f the primary and secndary shts, the hypctyl shrtens thrugh a prcess knwn as cntractile grwth. Specific internal cells (parenchyma) f the hypctyl are respnsible fr cntractile grwth, since they simultaneusly expand laterally and shrten lngitudinally. This results in a lengthwise tensin which shrtens the hypctyl verall. uter tissues f the hypctyl, which d -145-

nt actively cntract, are lifted in flds and wrinkles ver the surfa<:e, prducing the characteristic appearance f cntracted rts and stems.

As a cnsequence f this cntrac1:ile grwth bth the ctylednary ndes and the uniflilate nde may be pujlled beneath the sil surface (Figure 3,5).

n rder t insure that a new planting is established it is imprtant t allw this grwth t take pjlace prir t intrducing farming practices that are disruptive t this prc:ess.

2 nt actively cntract, are lifted in flds and wrinkles ver the surfa<:e, prducing the characteristic appearance f cntracted rts and stems. Hypctyl cntractin in alfalfa seedlings begins at abut the time the cambium (layer frm which new cells are prduced) becmes activated t prduce wdy stem and rt tissues. As a cnsequence f this cntrac1:ile grwth bth the ctylednary ndes and the uniflilate nde may be pujlled beneath the sil surface (Figure 3,5). The adaptive value f cntractjlle grwth is cnsidered t be in prtectin f grwing pints frm dessicatin, cld r mechanical damage. n rder t insure that a new planting is established it is imprtant t allw this grwth t take pjlace prir t intrducing farming practices that are disruptive t this prc:ess. NFLUENCE F PHTPERD AND SL TEMPERATURE Bth phtperid and sil temperature have an influence n alfalfcl seedling develpment. These envirnmental cnditins influence grwth rate, stem initiatin, and the allcatin f phtsynthetic prducts t the develpment f rts and stems. Hwever. nt all cultivars respnd t the same degree t these envirnmental cnditins. With multiple regressin, the relative imprtance f phtperid and sil temperature can be determined by cmparisn f their standardized partial regressin cefficients (Table 1). Seedling develpment f drmant cultivars is influenced by bth phtperid and sil temperature, with phtperid having abut 75% as great an impact as sil temperature. n semidrmant cultivars such as Lahntan, during the first mnth f grwth sil temperature has the same imprtance as in drmant cultivars but phtperid. while still significant, has abut ne-half the imprtance! it des in drmant cultivars. n semidrmant cultivars phtperid has less effect after the first mnth f grwth. Seedling develpment in nndrmant cultivars like Mapa 69 is nt influenced by phtperid but is strngj.y influenced by sil temperature. Table 1. Standardized partial regressin cefficients fr the relative imprtance f phtperid and sil temperature n the grwth f alfalfa seedlings frm three cultivars. Time frm plantinq Cultivar lst mnth 2nd mnth Pht- Temp- Rati# Pht- Temp- Rati# perid erature perid erature Nrseman Lahntan.21 * NS -.55 Mapa 69 NS -.6 NS -.57 The mre imprtant factr influencing seedling develpment is si.1. temperature. During the first 4 weeks fllwing germinatin the ptidlum temperature fr rt grwth is between 69 F and 76 F, depending n the cultivar. n general, drmant cultivars have lwer ptimum temperature!s during this initial grwth phase than nndrmant cultivars. During the secnd 4 weeks f seedling develpment the ptimum temperature fr rt: develpment is abut 72 F (Table 2).ptimum stem grwth temperatures during this initial 8 week perid f time are between 72 F and 76 F (Talble 2).Under cler sil temperatures (less than 68 F) a greater prprtj.n f the ttal bimass prduced is allcated t rt develpment (Figure 6)

Table 2. ptimum sil temperature fr rt and stem develpment during the first tw mnths f grwth f three alfalfa cultivars.

temperature in cultivars grwn thrughut mst f Califrnia, there are tw majr grwth characteristics influenced by phtperid that must be cnsidered in understanding seedling develpment.

Secndly, under shrt phtperids a higher prprtin f the phtsynthate (dry matter) prduced is allcated t the develpment f rts.

3 Table 2. ptimum sil temperature fr rt and stem develpment during the first tw mnths f grwth f three alfalfa cultivars. -Time frm plantinq r Cultivar st nd 1 mnth 2 mnth Rt Stem Rt Stem degrees Fahrenheit Nrseman Lahntan Mapa While the effect f phtperid is less than that f temperature in cultivars grwn thrughut mst f Califrnia, there are tw majr grwth characteristics influenced by phtperid that must be cnsidered in understanding seedling develpment. Firstly, a phtperid in the neighbrhd f 12 hurs stimulates the initiatin f crwn buds and stems. Secndly, under shrt phtperids a higher prprtin f the phtsynthate (dry matter) prduced is allcated t the develpment f rts. Therefre, seedlings develping under shrt phtperids might be expected t develp mre crwn buds and large rt systems than seedlings develping under lng days. MPLCATNS FR ALFALFA ESTABLSHMENT t fllws that there is a greater chance f success in stand establishment if the alfalfa plant is given as near ptimum cnditins fr develpment as pssible. This can be accmplished by matching planting dates t prevailing climatic cnditins. We have btained lng term ean mnthly sil temperature and phtperid infrmatin fr three representative lcatins in Califrnia (Figure 7-9).By matching the ptimum temperature and phtperid fr a cultivar with the crrespruding seasnal cnditins fr a lcatin, it may be pssible t predict the mst desirable time t plant. When this prcedure is fllwed, the predictin is that alfalfa planting shuld be accmplished during either mid March t mid April r early t mid ctber in the lw deserts, during either liate April t mid Mayr mid September in Davis, and during mid June t th,e beginning f August in the Tulelake area. t Althugh specific field experiments t verify the abve predicti,:)ns have nt been cnducted, we have tw types f infrmatin which suggegt that these predictins are valid: 1) The predictin clsely matches tjtle recmmended dates f planting in these areas, and 2) bth Schner et.al. and Marble and Petersn have cnducted planting date experiments with results which supprt the fall planting date predictin. Results frln these trials demnstrate that significantly higher yields are btained frm fall plantings than frm spring plantings. This advantage f the fal;l planting ver the spring planting is manifested beynd the first prdlj.ctin seasn. A pssible explanatin fr the apparent lack f agreement be1tween the predicted time f planting in the spring and the results frm the studies cnducted by the wrkers cited abve is that 1) fall planting is fllwed by a perid f cl temperature and reduced phtperid which prmtes crwn bud and rt frmatin and 2) spring planting ccurs wlder lnger phtperids than fall planting and is fllwed by much warmer sil temperatures which are nt cnducive t rt and crwn develpment. ( -147-

4 Clearly the grwer wants t receive maximum ptential returns frm a crp. The true benefit f precisely timing planting date t crrespnd with near ptimum envirnmental cnditins fr seedling develpment is the imprvement f farm prductivity and incme. f the cst f planting t early r t late is a significant lss in the ptential yield f that crp ver the life, f the stand, then ecnmically it is t the grwers advantage t plant an alternative crp. The develpment f such infrmatin n the relative ptential yield frm different planting dat:es wuld cntribute significantly t making this type f farm management decisin. LST F FGURES F1gure 1. Sequence f seed germinat1n and 1nitial seedling develpment in alfalfa, depicting cntractile grwth and develpment f secndary stems frm axils f the uniflilate leaf and ctyledns. Figure 2. Diagramatic representatin f primary stem grwth f an alfalfa seedling. Figure 3. Digramatic representatin f secndary stem and cntractile grwth f an alfalfa seedling. Figure 4. Lngitudinal sectin f alfalfa seedling, shwing ctyledn buds (8) which will frm the secnd and third secndary stems. The primary sht (PS) and ctyledns (C) are als visible in this micrscpic view. Figure 5. Lngitudinal sectin thrugh a prtin f a cntracted hypctyl. nternal cells have shrtened in length cmpared t th,e same cells in uncntracted hypctyls. uter tissues are wrinkled and flded, indicating a decrease in verall hypctyl length. Figure 6. Prprtin f ttal phtsynthate allcated t the rt and 'tp in 8 week ld alfalfa seedlings frm three cultivars grwn at several sil temperatures. Figure 7. Predicted ptimum dates f plantjng fr ndi, CA based n average mnthly phtperid and sil temperature. Figure 8. Predicted ptimum dates f planting fr Davis. CA based n average mnthly phtperid and sil temperature. Figure 9. Predicted ptimum dates f planting fr Tulelake, CA based n average mnthly phtperid and sil temperature. REFERENCES Frd, K. E Genetic, physilgical, and envirnmental determ1ncmts f seedling crwn develpment in Medicag sativa L. Ph.D. Diss. University f Califrnia, Davis (Diss. Abstr. 85:2123). Hesterman.. B Effect f phtperid and irradiance n fall drmancy respnse f alfalfa (Medicag sativa L.) M. S. Thesis. University f Califrnia. Davis. Marble, V. L. and G. Petersn Planting dates and seeding rates fr central Califrnia. Eleventh Califrnia Alfalfa Sympsium, Fresn, CA. December 9-1. Cperative Extensin University f Califrnia. Schner, C., W. Knipe, and F. Auti Alfalfa, time f planting Ninth Califrnia Alfalfa Sympsium, Fresn, CA. December Cperative Extensin University f Califrnia. p

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5 .. G),,,..,, :) c ;.3 u! c E.2 ";: la U; ( 'U Nrseman Lahntan a Ma u. ' Q) :5: 6 "tg. E (fj ;: Q) f 9 = u. g..,. D :; 6 " D. E Sl Temperature. (F) \ c 3 -; t: Q) Q "K) -u..c a. Q) 9 :; 68 Q. E 5. U) 3 Jn Ftb Mr AW My -W Mc T1.1 l.ake. Aut Sap ct tcjv ec c. 9.. JM Fell Apr M8Y Jll.A A9 Sell ct «v Dee Mnth J8 Fe...AW lly AugS8lltt..8C -149-

Teuber. L. R. and M. A. Brick. 1988. Chapter..Mrphlgy and Anat,my. p. 125-162.!B A. A. Kansn, R. R. Kill, and D. K. Barnes (eds.) Alfalfa and Alfalfa mprvement. American Sciety t Agrnmy, Madisn W. (n.

6 Teuber. L. R. and M. A. Brick Chapter..Mrphlgy and Anat,my. p !B A. A. Kansn, R. R. Kill, and D. K. Barnes (eds.) Alfalfa and Alfalfa mprvement. American Sciety t Agrnmy, Madisn W. (n. Press) Williams. W. A The emergence frce f trage legume seedlings and their respnse t temperature. Crp Science 3: Acknwledgements. acknwledged. The technical assistance f R. C. Shahrk is gratefully -15-

Plant Science Course Outcome Summary Chippewa Valley Technical College

Plant Science Course Outcome Summary Chippewa Valley Technical College Curse Number 006-160 Credits 3 Cntact Hurs 64 Develpers Flint Thmpsn Plant Science Curse Outcme Summary Chippewa Valley Technical Cllege Infrmatin Types f Instructin Type f Instructin Cntact Hurs Outside