Natural Cross-Pollination in Cotton - AgEcon Search


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Acknowledgments ,

This bulletin summarizes the results of a study of natural crossing in cotton conducted under the sponsorship of the Cotton Impl'o"ement Oonference. Research personnel participating in the study included: Alabama Agricultural Experimellt Btation-A. L. Smith. Arkansas Agricultural Experiment Station-.r. O. ,lare, R. L. Thurman, J. F .•Tacks, R. H. Ramey, Jr., and Oharles Hughes. Coker Pedigreed Seed 00., Hartsyillc, S. 0.-0. H. Rogers. Georgia Agricultural Experiment Station-H. D. Loden, R. L. Miller, T. J. Stafford, B. S. Ha:wkins, and J. H. Turner. Louisia,na Agricultural Experiment Station-F. 1V. Self and Jack E. Jones. North Oarolina Agricultural Experiment Statioll-S. G. Stephens and M. D. Finlmel'. Oklahoma Agricultural Expel'illlent Stntion-J. M. Green and Mack G. Keathley. Texas Agricultural Experi))lt'llt Station-To R. Richl1l0n(~ and C. F. Lewis. • U. S. Cotton Field Station, Sacaton, Ariz.-It H. Peebles. U. S. Ootton Field Station. Stoneville. Miss.-J. B. Dick and E. O. Ewing.. ' , U. S. CottOl! Field Statioll, Stnte College, N. Mex.-A. R. Leding. U. S. Cotton Field Station, Knoxville, Tenn.-E. N. DlUlcan . F. S. Cotton Field Station, GreeIlYil1e, Tex.-D. R. }T.ooton and D. D. Porter.

Contents Review of literature __________ _ Regional natural-crossiltg tesL__ Plan of experiment- ________ _ Results and discussion ______ _ Population counts necessary for accuracy Of data. _____ . ____ _ Rowand plant variation ______ _ Varietal response to natural crossing _______ ,. ___________ _

·Wasbingtoll, D. C.



1 Insect activity ill cotton flower::;.

3 Heterozygosity in Btl c ccs::: i v e hybrid gcnerations __________ _ 3 4 Hole of natural cro:;:;ing ill current breeding ______________ ,.

!J Summary ___________________ _

10 Literatur(' cited ______________ ..

13 14.

15 Hi 17



August 11)54

For Sllle by the SupC)rintendent of Documenls, U. S. Goyernment Printing

Office, 'V!lshington 25, D. C. l'riec 10 cents.

NATURAL CROSS.POLLINATION IN COTTONl B.I· D. ~r. SUlPSlIN, (lgrollomist, Piehl Orop8 Reseal'('/I

Brancll, .,lgriclIltll1"al Research Serpice

Xatural cross-pollination has imFtli.tant implications ill cotton breeding and cottonseed production. Control of the genetic complex that determines the potential wlue of a cotton plant for economic use is impOl:tnnt, regardless of the breeding methods employed. In the past, natural crossing in cotton has received attention mainly as the Ct,\Use of lll1cleRil'ahle hybridization and 1l10ngrelization of seed 5tock5. Breeders have adopted artificial means of maintaining the genetic purity of their stocks, and allowable limits of segregation from other yarieties have been set up for organizations engaged in the multiplication and distribution of cotton-planting seed. :More re­ cently, natural crossing in rotton has l'eceiyed increased attention because the phenomenon has possiblt, use as 11 meanS of uti11zing hybrid vigor und also for producing hybrid seed in commerc1al quantities. Formerly, studies were directed almost exdusively to reducing ont­ crossing; now, means of increasing natural rl"ossing in cotton are of widespread interest. .

REVIEW OF LITERATURE Katural cros£ing in cotton has been investigated by numerous incli­ yiduals durillg the past 50 years. The studies have served to elll­ phasize the ,\'ide difrerences in amount of natural crossing in diU'erent localities and in different years. However, the materialR used and the methods employed in these sepamte investigations "ere so >':tried and the results so contrn.dictory that they furnlshecllittle ill the\~'ay of uniform information. Loden and Richmond (3),2 in their excellent review of hybrid vigor i;.1 cotton, have sununarized the pertinent data on lHltnml cross­ ing available up to 1950. The information in table 1 is taken from their article. There is no geneI'nJ pattern of behavior detectable from the dn.ta in table 1, but, in the discussions of their elata, the i11\7esti­ gators are in O"eneral agreement concerni11g the following factors that influence t~le amount of natural rrossing: (1) Cotton pollen is relatively heavy, and wind is not an agent in pollen dispersal; (2) therefore, the amount of na{:UY'nl crossing in cotton is determined by the number 0'£ insect pollinators preS('Ilt in relation to the number of cotton flowers; fmc] (3) inte1'C!rossing may be affec't~(? by the flower­ 1 1

Submitted for publicfttion Murch 15, 11)G4.

Italic numbers in par('atheses refer' to IJitemtut:l' ('itcel. p. 17.



ing habits of the varieties grown, by the abundance of unlike pollen, by location of the fields in relation to insect habitats, by flowering periods of other plants attractive to insect pollinators, by distance between unlike varieties, by topography n,nd barrier crops, and by other environmental, climatic, and biotic factors. TABLE

1.-Pe1'oentages of natuml Grossing repo1'ted in the lite1'atu1'e,

1903-50 1




Percent natural crossing

Experimental design

Max- Mini­ imum mum

----South Carolina________ 'VebbeL _________ Alternate rows ____ I· 10 5

North Georgia_________ {Allard _____________ .. ___ do __________ _ 220 ----_ .... MeLendoIl _____________ do _________ _ 22

Tft Ga {Turner________________ dO ___________ 1 34 -----11

1 .on, ------------ ____ do ___________ Male 90 percenL__ 34 26

Alabama______ .. ____________ c1o ___________ Male 90 percent+_ 43 40

KnoxviJ1e, Tellu _______ {P.ope et aL _______ A1tl'ruate rows ___ _ 227 -----Slmpsoll__________ Male 90 pcrcent.__ 53 44

BrOWn ___________ Male 90 percent+_ 81 57

MississippL ___________ Ricks and Brown__ AIt~rnate rows ___ _ 5

{ Brown ________ • __ AdJacent Plants- __ 2 11 19 -----Fayetteville, Ark ______ Ware ____________ Alternate rows ___ _ 241 -----Scott, Ark _______________.__ clo________________ clo__________ _ 2 1 RIChmond et aL ________ do__________ _j 29 ------

1-----College Station, Tex_ __ { Stroman and Ma- Acljacent plants __ .I

3 2

honey. . Waco, Tex ____________ Shoema~er----.-- Excess of ~a:e ____ 1 211 II 5

Sacaton, Ariz __________ {Kearnc) ---------- Alternate 10\\ s____, ____clo___________ Male 90 percent+_ 35 : 14





--------....,--------,-_.------;------,._Kottur_______ - ___ Alternate rOwl' ___ _

Afzal and Khan ________ do __________ _

____ do________________ do __________ _

1 d' n



1 2

2 1-----2

{ ====3~=:====:=::= _~\_C~j~~~~~~~~~~:::1

Cammie__________ Alternate rows ___ _ China______ - _________ Yu unci Hsieh_____ do __________ _ U.S.S.R.• _______ ___ __ Anonymous ____________ do__________ _ .{Balls______ - - __ - - -,1- ____ do_ - - - - - - - --Egy )t



2 ')


-- -(10 -----------1----- clo •.----------



o2 ___ . __

28 1_____ _

9 i


15 5


3.3 I



After Loden anel IUchmond (3), tables 2 and 3.

Average figures.

Sevemll'eliable methods of artificial self-pollination are available t.o cotton breeders, and the gelletic purity of smull stocks may be readily maintained by such methods. However, the use of barrier crops (preferably cotton) and of adequate isolal'ion from unlike geno­



types are the only practical methods suggested for reducing inter­ varietal crossing in field-size plantings (2, 5). .A.s natural crossing in cotton heretofore hus generally been considered a lumdicap in breed­ ing programs and a hazard to be llVoicled, it is not surprising that the literature c:untuins little data on methods or means of increasing the amount of crossing. From consideration of the factors that have been suggosted as influenclng the amount of natural crossi ng, it is apparent t\ut lllterstrain crossing can be increased by intermingling the unlike genotypes [md by increasing the population of insect polli­ nators. Meade (4-) reported that honey bees (Apis meZlije'i'Ct L.) are dfeetiyc cottOll pollinators and sngge::lted bCPke£'ping as an aid to cotton growing. Bumble bees (Bombu8 spp.) arc most frequently mentioned as pollen carri£'rs. From other f'uggestiolls, we It. ty infer t~lat insect activity lllig~lt be highest in 811101"t('(1. 1101' hayp I'll(' mo<'phologiellI and physiological bases for such int'eeactions bpC'l1 thoroughly explored. "l'se of a male-sterile or semi-lllaip-stprile stock as the female' parl:!nt (3) has been suggested as a ll1CllllS of obtaining lllaxiltlUlll crossing. A number o-f \\-orkers 1mVt' stllllipd this problem, but as yet ther£' ha \'e beell llO practical results hom this line of approach. REGIONAL NATURA.L-CROSSING TEST Phm of Experiment

Tplltatin' plalls for n rpgionaillatul'al-("l'ossinp: tpst were formulated at the First ('olton IIll]lI'OYl'UH'llt ('onfpl'PIJ('P hphl at Baton Rouge, La., ill Felll'nary ID"Hl. rucler tIl(' l1irpf'tion of n ('oJ1nuiftep appointed at that ('011 1'(' 1'('1[('P, a uniform planting plan was ]H'pp:trecl and seed slocks \\"('re ohtained for distribution to all eooperntors. The gPlieral pIau oJ th£' pxpprilllent pro\-ided for planting a small bloe!\: (20 rows wide by 100 fppt long) of upland reel-leaf ('ottO!) in a ]oeatioll st'llli-isoJated from other sorts. .A sm,tll proportion of U1'­ hmcl grN~Il-leaf cottou (apPJ'oxilll:lit'ly 10 percent or the toUtl plant popuitltion) was interplallted :>ystelllatieall.\· nt lO-foot intplTals, :-;tag­ gered in altemate rows. in thh: rl'd-lea'r block. 'fhp ~('Pcl cotton from the gJ'(ll'n-leaf plants was retained sppal'atpl\': awl (lIp :-;('('<1 was slIb­ seqllPntly plantNI for cletl'nninatioll of 't'll(' pl'l'<:('ntngp of red ( 1;) X gl'PPl1 ( ~ ) hyhl'icls in ! lIP populatioll. The clel£'l'millatioll:> of tllt' olllt'I'ossin,!I pel'Celltagps were made by each cooperator for his O\\"1l lo(·:tt iOIl. Yarions lI1l'lhods of !.'.Towillg out the plants \\"pre l1Sl'




Since the test plots were seeded ,yith the ratio of \) reds to 1 green, the estimates obtained were actually 90 percent of the toUt 1 outcrossing. assuming the sU:l11e frequency 0 t ontel'ossinp' l)l'h'N~n gl'el'll plants as that between red and green. The red-lenf Y:l.riety used ,Yn~ DeRidch~r. and the grecu-lea:f Ylll'ict~, "llS Bmpire. 1'\::; of this c]'o<,:-; are ensily • recognized by the intermediate-reel piglllentatioll in the sl'edlillg"s 01' in the mature plants. The results obtninecl by the method us('d 11('1'(' in lt1e;tslll'ill!! naturul croS8inp: are strictly n.pI;1ic~lbk only to tll(' two YH l'il'liei' {:mployt'd. As pointed out by SteplH.'l1s and Fillkner (8). nIP I'(,Sl111" cOllld be biaf:ed hy marked differences in flower Pl'OdlH'il011. llol\('oilh'id('IlCe of fio,Yering period, 01' other ph~'siolo:zi('al OJ' ll101'pholop:i(~al differ­ ences in the vllrietie8. Admdlv. initialllo,\'('l'in!! Wlt~ SO!1w,ylmt lat~'l' in DeRidder than in Empirc, ~o that ill ":01\;[' (';\:-;1''': n fpl\' nIT cady Empire flowers Jllay have hall DO OPPOl'tlll,;ly fol' (,l'Oss-pollination with DeRi(lclt,l'. .A Yaib,ble illfol'malioll imli('ate:" that in otht'r 1'e­ Sl)ects .the two vltl:ieties arc near a ~'el'H!!t' aH1011~ uplan~l ('(Ml)ns for potentIal ontel'OSsIng anel that l"l'('lpl'ocal natlll'al ('l'o~,;il1p: b('t\WCll them is tlbout equal Tlw results. tlwl'cfol'l'. I' \"(l {'on~idvl"Pcl fa il'1v ~'r:prr:sentative :/'01' the locations under the ~pet'ifk ell\"il'OllllH'l1tal cml­ clitions in the sea.SOll of test. Pla.ntings of this test w'ere at 1:2 loeatiolls in 1(H0, 15 in HliiO. 15 in 1031, a.uel G in 1932. All cooperators weTe requested to ('OH­ IOI'm as nearly as possible to the general plan of the experiment so that data from the dil\:el'r:ut al"Plts would he ('omparnble. This ,\'I):". done in most easps. A clifrprent Pl'oc(,([l1l'P, howcwr, was llsed at Sacaton, Ariz.~ in an :~ yea1'f: of tests. HOlllozygous 1'C'c1-1enf plants of Acala 'Wl'f' randomly spaced in a plot (rr greell-leld cotton, and the percentage of gref'n ( &) X reel ( Q) hybrids was detC'l'lHined frolU a plant population g"rown from the fcmaJe (reel) paI'ent. At lhlei:zh, N. C., ill 19;)(\ the ratio of rcd-leaf plants to other tYPf'f: in the cross­ ing block wru:; 9: 11 insteac1 of f) : 1 ns ill thE' gellf'ral plan. The 10:l() data for Raleigh were correctecl :for thc diITe1'C'nt proportion oj! reel stocks llsN1. .Results and Discussion The Coitoll-13elt-,,'ide scope of the experiment is illustrated in the ma.p (fig. 1) which shows Ole :zC'ographie locations of the tC'sts. _'tt least OJ1(' t:C'st: was (,OlHllldecl in ewry ('otton-gl'owing State C'x('C'pt Califol'uia. The cltlta :for the .1: years of test an' SlllllllHtl"izecl (tablp :!). For the pm])oses of this experiment. the data. ba\'c been cliyic1ccl into regional groups. This p:roupillg il1Yol\'es certain oYel'Japping" of an(l di"Pl'g('ll('e from tIl(' W'IlC'rally aee('p!<'<1 gpographie Rllbcliyisiol)s of thE' Cotton 13('It. This was 1ll'eessitatpc1 b)' ecological l'elaLioll;.;hips of these snhcljyisions, as cli~()ussecl OIl ('l1s11ing pnges of this bulletill. The percentages oJ nlltlll'al cl'ossill~ showll wi t 11 ill illP regioHnl [.!TOllpS jl1clicn.te 11 d8(-inite pattcrn of behavior drpPllclent on the climatic and biotic rUyil'Olll1lPnt W!lPl'ttlly itnpos('cl by g('().gmphic locution. T1](' wiele elifrercnce in IWl'eentnge of (Jutel'ossing between and wHhi n re­ gions shows clearly why this has hecl! a. highly ('ontJ'o\'crsial subject in the past. The southeastern region of the Cotton Belt (not includinp: the Mississippi Vnlley) c()nbtins more tluw one-third the total acrcnge





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MAP NO A50' 019


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FIOUlIE 1.-The distribution of ('otton uerenge in the Ul1i lcd State~, ] ().IO. The circles indicate the locations ut whirh one 01' more of {he Ilatural-('ro>ising tests wE're '·OIHlucted.



2.-Sullnmary of results of 1'egional natu1'CJ)-crossing tests with cott(Jn, 194J)-5fJ Total plants examined (in thousands)



Standard deviation of the mean

Location 19·19









1 Southeastern (except

R~fli~k N .




C____________________ 12 25 ________________ Perce5~ Perc~i _~~:~e~: __ ~~:~e_n!_ Knoxville, Tenn__________________ 25 8 1'1 14 40 42 42 52 Loretto. TemL___________________ ________ ________ 8 5 ________ ________ 29 39 Experiment, Ga___________________ 4 ________ 6 ________ 25 ________ 42 _______ _ Athens, Ga________________________ ._____ 19 27 3 ________ 27 '18 50 TUton, Ga_______________________ 3 3 ________ • __ .____ 27 33 __ • ____________ _ Auburn, Ala______________________ 2 3 5 ________ 29 24 ,15 _______ _ Hartsville, S. C___________________ .2 t-------- ________ ________ 12 ________ -------- --------

49 46 3,1 34 42 30

-1--------1--------1-------- -------- ----------------1----.--­ 1 = 30 ------j--------I------\;- 191 '1 /------?- --------1 84 _______ 26 _ 11 31 18

l\fean_ - - - - - - - - - - - - - - - - - -. ,. - -- - --- - - - -


Mississippi Yaller: l\1unfo:d, TC'~l1_. ___________ Stonevllle,1\[lss_________________ ._]O Baton llouge, La _________________ • 1 l\1ealJ ________________________




___ .____

2 ________ 1





30 _

SOn~~s~~lJgt;,:, La___________________ ._~___ J_______ _______ -' j

Tipton, Okla______


--------1-------- --------

Meau_ - - - - -.-- - - - - - - - - - - - - - - - -1- -~----- - -- --- -- - -- - - -

24 -------- --------

--1--------1-- - -- - --r- -- - - ___ L _____ -1---- ----I I


6 7




14 _________ _ 20 11


34 _________ _ 20


24 ---------22






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10 ________ ________ ________ 14 ________1 18 14 15 ________ 10 9 42 7 ________ ________ ________ 34 ___________ .____ 4 (j 1________ -----.-26 15 ________ 1 7



-'=_-=-=I________ -------- -------- -------- ________1________ --------1

Fayetteville, Ark_________________ Stillwater, Okla___________________ ________ Chickasha,Okla__________________ l________



5 8 7 3



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15 ~

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• N OD

Central Texas: Greenville, Tex-------------------1 College Station, Tex____ • - __ ._ ..• _.


w"'::.·;;;:i~:;~;)-,---------- ---------------

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19 15


Sacaton, Ariz______ c ______________ State College, N. nL______________ l\Iean _______________ 1



• I

13 1 (j

"1__ ·__ .1--I 2

-r--- - - -


----- -------~ ;,;,- -

1.07 25 a

aR I


________ 1

a ________

19 1.0


17, _______ _ 1L a

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29 12

25 12 I


46 5 ________.




3 2





6 3

22 1


~=:~-_--_--_-~_ -_-_- : ~~~-~-J~-~~~-~=£=_ -~~~~I--:-_-___~J=--~_ J_ _ ~===.__I-_-_~-=~~j--.~..:.......___

less than 1,000 plants; not included in regional menno

-~ 8



'0 ~




~ 0

~ ~

~ ~ 0





planted to cotton in the United States and produces more than one­ third the total cotton yield. This estimate is based on the lO-year ayerage for the period 1939-'18, as given in Agricultural Statistics, 1951. The region is characterized by rolling to hilly topography, J'elatively small fields of cotton, and reln.tiyel,r large areas of wood­ land, pasture, and wasteland. With abundant natural cOYer in proximity, insect pollinators OCCllr in great numbers in the cotton­ fields. Natural crossing in this region approximated 39 percent lUlder the conditions of this expel'iment. This re1n.ti,'el,r high per­ cenLage of natural c]'ossing undoubtedly reflects the general physio­ • gra.phic ecology of the region. The cotton region borc1ering the :M:ississippi Rh'el' is a ,,'ell-defined geographic area, but it is less ,yell-defined in terms of ecological rela­ tionships. On the allm'ial soils in the flood plain 0:1' the Mississippi RiTer, a high proportion of the land is planted in cotton, ttnd this region is one of the most produC'tive cotton areas in the United Sttttes. .tU0l1g the margins of the flood plain and in places whel'e the plains nl'e narrow, the riYer bottoms arc adjacent to considerable areas of rolling, eroded loess soils, much of which is wasteland. In such areas, the insect-phmt association is much ]ike that in the southeastern region. :i\1:1Ulford, Tenn., and Baton Ronge, La., with natural­ crossing percentages of 30 and 37, respectively, are l'epresenbttiYe of such locri,tions. However, , flood plains widen, as in parts of eastern Arkansas, northwest :i\Iississippi, and northeast Louisiana, the topography is flat or lUldulating, and the land is intensely eul­ tiyated, predominantl~' in cotton; and there are few areas of waste or uncultiyated land suitable as a natural Imbibtt for insect pollina­ tors. Stoneville, Miss., is situated in an area of this type and natural crossing (18 percent) was generally lower there than at Munford, Tenn., and Baton Rouge, La. There is a ·wide area ,,,est of the :Mississippi Delta, including pltrts of Arkansas, Louisiana, east Texas, and Oklahoma, thnJ, Jies within the Inunid region. In soil type and topography, it is not lmlike the Ooastal Plain that extends through the South Atlantic and Gulf coast areas of the Ootton Belt. No data on natural crossing are available from this general area, but it may be assumed that the })er­ centage of crossing ,vould be somewhat intermediate to that obtamed in the southeastern fmd south central regions. The great cotton-producing region of the Blackllwd Prail'ies and contigllolls areaS of eentral Texas. and possibly simila]' climatic n,reas of Oklahoma ltnd '''est Texas. are rrgions of l' 1o-w natural ('rossing (tables 1 tmd 2). A htrge proportion o:f the In,11d in this region is under cultiyation. with Itu'ge aC'l'eages in eotton and few bOl'(lering areas o



favorable biotic conditions, us at Sacaton, Ariz., a high pereentage of natural crossing is not unexpected. It is increasingly apparent from the data, on t.hiG subject that nn.tuml crossing is lo,,'est in areas of intensiye cotton ('uUh·ation 'where fields are large and contiguous to other (iE'lch; of eotton 01' other cultiyated lands. -cllcler such- conditions insE'ct popuhltions are smull in rela­ tion to the total cotton acreage, and visitations to flowers al"~ too in­ frequent or too long dE'lnFcl to be greatly efl'E'ctiYe in cross-fertilizfl­ tion. The distribution of cotton acreafre in the Cuited StatE's (fig. 1) mclieates roufrhly thE' IU'E'US of hifrh and 1m,· natural ('l'ossings, but thE'8E' areas emmot: be ('learly dpfined on ill(' basis of dl'lbt cUlTE'ntly antilable. POPULATION COUNTS NECESSARY FOR ACCURACY OF DATA At the beginning of this study, no information was avuiln,ble as to thE' size of samplE' necessary to deterlllillt, ,dtll aeeUl'acy the PE'l'CE'ut­ age of natul'al cfossing. Populntion counts ill Hl49 at the'various locations ranged from approximately 200 plants at Hartsville, S. C., to :25J)OO at KnoxYille. TE'lln.. nnc1 at- StatE' College, N. Mex. At Raleigh, N. C.. KlloxviJle, Tenn., and StatE' CollE'ge, N. Mex., popula­ tions counts ,\·el'E' made by units of planting that made it possible to caleulate the pereE'ntage of hybrids on one 01' more units and judge the aecunte)" of resuUs from populations of differpnt sizes (table 3). It is apparE'ut that reasonably :tccumte determinations of the per­ centage of hybrid plants cnll be obtnillE'd by E'xllmining II population of 1,000 plants. Counts o:r larger populations reduced the standard deviation of the mean but did not materially ehunge the mean. The natural-crossing percenta!!es shown in table 2, with one exception, are based on counts of 1,()()O or more plants. The data are therefore ('ol1siderecl highly reliable. The arithmetie ayerages of table 2 are justified since thl> perl:elltage data from all locations furnish approxi­ mately equal information. TAllT,E

3.-17ariation in natu.]'ul-(,l'o88ing percentages at three locations when based on ~'ariously sized 7)Op1llations, J9J,f) ['l'he populations used are cumulative] Hybridd at the locations shown

Approximate total population :



x. c.

}(nox\"ille, Tenn.



500_________________ ________ 5~ 0 1,000 __________________ .____ 52. ,1·±2. 9 ' 1,500 _______________________ i 52: 2± I. 7 2,500_______________________ 57. 0±3. 1 '1,500 ___ .. __ _ _ _ _ __ _ _ __ __ _ _ _ ! 5a. 5 :t: 2. 7 0,500 ____________________ .. __ ' 5a. 7± l. 9 9,500 _____________ ._________ 54. 2±1. 5 . 12,500 _________ .. __ .. _______ .... 5'1. 9 ± 1. 2 25,000 ___________ .. _______ .. __ ;____ .. ________ _


! :

State College, N. i:v[cx.

.__ i_~_~_. ____.. _

41. 2 4.5. a:f.: 4. 48. n±2. ,14. 1 ± l. 44. 5 ± 1. 4<1. \l±0. M. 8±0. 44. 5±0.

·15. 5±O.

Percent 1

- ... ----- ...

1 5 , 0 .

8 (j



....... -"'"

9.5 9. a±o. 2 10. O±O. 7 10. 2±0. 9

10. 10. 10. 11.

1±0. 7 5±0. 0 8±0. 4 :i±0. a



The dd.a (tu.ble 3) from Klloxvi1le, Tenn" and from State College,

N, Mex" show tendency of the mean pel'centage of 11ybl'ids to increase l)l'ogl'essiYely with the larger population COllnts, At Knoxville the counts by lUlits consumed considerable time and the work was spread over a period of about 2 weeks, It was obser\'ed that thl' hybrid plants ill the populat.ion werE' npP(lrently less susceptible to seedlin~ diseases than the plants of the llHttE'l'llal green-leaf variety, On June 2, a re­ check of the COllllts ()I'i§,!iUlllly s('ored on :niay 16 on 10-l'OW nnits indi­ cated thRt (i percent of the ol'igi nal stand lutd been losl from seedling diseases 01' other causes, The loss, 11owe\'er, was 8 percent among green-leaf plants and only 3 percent n,mon~ the intel'medin.te reds, The percentage of hybrid plants in the original count ,YUS 44..~, whet'eas the perCE'lltage from the eounts made on .Tune 2 on the sante, row units was 45,'L T~lus, undel' sllch conditions, the 10nger the cOllnt ,\'as de­ ]a:n~c11 the higbee the apparent pen'ettUtge of natu!'a 1 ('rossing, SeY€'l'nl of tlll:' coopel'lttors in the l'E'~ionnl natllral-l'l'oBsing test haye raised thE' point that hybrid plants al'e mOl'e "igOt'OllS and thnJ possibly a lal'gl'l' pel'('entnge of the h)Tbl'id seeds procluc-c sertllings than do seH-pollinated sE'edsin Ihe same lot. The vigorous growth of the DeRidde).' X Empi]'1:' 11),l)1'[(18 \YilS noted during the ('ourse oJ HlP re­ e:ional t('sts, AJ Knoxdl1(' in lD;iO, Jlyhl'ic1 seE'dlin~s WE're 1'1- percent llE'tlYi('l', basre! on gl'('en w~dght. than those of the grcE'n-leaf plll'ent ,ariety, TllE's(' observai iOllS indicate the possibility that the §,!1'eaI:N' vigor of the hybrids may result in a higlH'l' percentage of ernel'gence Hnd sUlTivaI of seeclHngs from hybrid seed thnn iTom seJfed seed,

ROW' AND PLANT VARIATION The general p1nn :fOl' the l'('gioua 1 llahll'lll-crossillg (('sts sped fiecl a TIE'ld plnntin§,! 0:1' nbout 20 ]'o\\'~ appl'oxil1ltttejy 100 :fe('(' lonp: in l\ loea­ iion at least sE'llli-iRolated :frollJ ot-lH'1' cotton, This W'llE'ral plan was adh€'l'ccl to 1111110:':.1" of the tE'sis, SE'\'E'ntl crt' th(' (,OOp('l'n 1m'!') lna intained thE' iclE'ntity of thE' 13('('(1 :f1'0111 thE'ir C'l'oBsillP: plots hy row and plant lHllllh('l' until (he llE'l'C'cntngE' of fwJul'Hl (,l'ossin[! was dE't'Cl'll1inE'

OJ' tE'St. Thr row 1'al'ia(jons (hlbk ~.) ::;hown lJ~' the chta :ft'oll1 Ral('igh, N, C ..

and Alhens, Ga" nppE'lU' to be a random c1i'iitl'ibntion of vn111(,o' Hl'ol1ml thE' lH('an p('r(,Pllhlg(' of natural ct'm;sing ohf:ainc(l Jor (11p l'E'speC"tivt:) loC'lttions, Xatul'aJ crossing in nH'~1(, tE'sts 1' (>Jl\'il'Olllnental factors, aHhough no in'I'Ol'JlUttioll 1S IlYailuhll' as 1'0 t)w naim'p of such possible cliJr(,l'(,llces, The percentages of h~'l}j'id:, in (h~ FayC'1.! C'"ine samplC's W(,1'P detC'rlll i11('tl 1']'0111 seeel spronfpel jn gE'I'Jlllllatol's. and the results could not have been clue to difl'C'T(,l1tiul S('("(llil1~ mortality tlS dE'scribec1 :for clelayec1 counts at Knoxville (see table 3),



'l'ABLE 4.- Variation in percentage of nat1bral c1'ossing as affected by row position ---------~-----------,,------~----------------

Hybrid plants by rows atRow No.

L_ .• _

. =- =~ ==: ==: =~

2. ______ _ 3 ____ . __ . __

- - -.-

4 ____ . __ " __

Raleigh, 1949 Percent 53.9 43. 2 =.- =: \ 54.1 52.0 64. T

___ . __ .


Athens, 1951

Fayette­ ville, 1950

Percent 37.9 42.2 '1'1. 4 41. 9 46.0

Percent 8. 7

7. 2 9.1

8. 7 6. 4

53.6 27.3 42.5 8.0 1=======1=======1=======1=======


__ 1

Average, rows 6-10_---------1

Percent 20.5 25. 0 26.7 33. 3 30.9

-- . ---- _. ---,

Average, rows 1-5 ____ .. ~_____

10 __ _

Athens, 1950

iii Ii! in III I









ik::=: == ====== == ==:= ==::::== =:==O=~~=:=i=i===~2=1:=~=I===~=.~=:=~=11=-===1=1~=:=~ 13 ____________________________ , 14 ____ • ___ . __ • _______________ . 15 ______ ... _. _________________ ,

61. 7 52. 1 55.2

24.0 23. '1 27.6

'17.1 47. 6 45.1

9.5 11. 9 12.5

AYcrage, rows 11-15 ____ .. ____ .'1






16. ___ . _____________ •. ______ ! 17 __ . _________________________ i

18___ ,. ______________________ . .! 19 __________________________ . .1 20 ____________________________ 1



J.. ocation lDean 1


16-20,.• ________ ,

54.0 63. 2 59.8 51. 6 55.8 56.9

1 __________ • ___ • '



29.8 34. 0 24.0 26.7 2'1. '1

',15.8 '19. 2 47.8 45.5 '12.1

17.1 17. 4 11.7 10.6 15.2

1'_===2=7=.=8=:=====46=.=1=1~=====14=.=4 27. ~L ~~~.8_,____~O. 3


total count.

Data on natmaJ crossing b.y individual plants were obtained at Raleigh, N. C., Athens, Ga., and Fayetteville, Ark. The class fre­ quenCles derh-ed from these data (t!tble 3) are from relatively small populations and therefore show mtmy irregularities, but they appear to be llear-llormal clistributions arolmd the location means. This is an expected result, as both parental varieties are fairly homozygous line-bred types.

VARIETAL RESPONSE TO NATURAL CROSSING In general, DeRjclder and Empire have been used as parent'lLl varieties for the regionalll!1,tural-crossing tests, with EmJ>ire as the female parent. Some different result might have been obtained if



other varieties had been used. It is possible, even highly probable, that the extent of outcrossing is affected by varietal differences in mechanical and physiological characters, such as time of flower open­ ing, time of anther delriscense, style length, ablUldance of pollen, and rate of 'pollen-tube growth. Varietal response to natural crossing. has receIved some attention, and preliminary evidence indicates that varietal differences may be quite large. Turner (9) reported 30 percent crossed seed from an Acala strain as compared with 13 per­ cent from Florida Greenseed when similarly exposed to cross-pollina­ tion. At Raleigh, N. C., 79 perf'Allt natlU'al crossing was recorded ·\yhen a virescent yellow stock was used as a female parent as com­ pared with 42 percent from Empire (green-leaf) and 45 percent from DeRidder (red-leaf). TABLE

5.-Frequency distrib·ution of natural crossing by

individual plants

Number of plants in respective class intervals at-

Class interval (percent,


Raleigh, N. C. 1949 1


Location mean (percent hybrids) _I



0.0-5.0 _____________________ _ 5.1-10.0 ____________________ _ 10.1-15.0 ____________________ _ 15.1-20.0 __________ - __________ I 20.1-25.0_ - - - - - - - - - - - - __ - - - ___ j 25.1-30.0 _____________________ ! 30.1-35.0_____________________ , 35.1-40.0_- ___________________ i 40.1-45.0 ____________________ _ 45.1-50.0 ____________________ _ 50.1-55.0____________________ _ 55.1-60.0_- __________________ _ 60.1-65.0 ____________________ _ 65.1-70.0 ____________________ _ 70.1-75.0 _______________ - ____ _ 75.1-80.0 ____________________ _ 80.1-85.0_- __________________ _ 85.1-90.0____________________ _ 90.1-95.0 ____________________ _ 95.1-100.0 ___________________ _

Total Plants___________________


Athens, Ga. 1950 1

01 0 1 1 0 :3 6 12 34 51 21 11 4 1 0 0 0 0 0 0

0 0 1 0 2 3 6 10 16 22 24 21 20 21 II 5 2 1 1 0

5 18 19 41 41 33 31 19 20 14






5'1. 9



11 4

0 2 2 2 0



Fayetteville, Ark. 1952

Athens, Ga. 1951 1


0 0 0 3 3 5 .20 34 39 33 21 13


5 0 0 0 0 0 0 180 42.2




Plants with 10 or Jess seeds omitted.

At Knoxville, Tennessee, :in 1951, 2 replications of 79 varieties strains of green-leaf cotton were planted in alternate rows with DeRidder red-leaf, to study response to Eatural crossing (6). '.1'he average natural crossing between red-leaf and green-leaf was 41 percent. The range among the 79 strains ,,-as from a Jow of 29 percent to a lrigh of 60 percent. A statistical analysis of the data indicated that a 01'

• .



differ0nce of 13 percent between strains was highly significant. Fur­ ther tests will be necessary to determine whether genetic differences that can be used to increase or decrl3ase the normal percentl1ge of nahlral crossing exist jn these strains.

INSECT ACTIVITY IN COTTON FLOWERS Gross-pllllinntion is not l'eadily detected ill ('.otton unless distinctive marker characters are present jJl the parental lines. .For this reason, the extent of natural crossing in open-pollinated fields has been con­ sistently underestimated by some cotton breeders. Some idea o'f the potential for crossing may be gained from a study of insect activity and visitations to cotton flowers. Ecl,:ert (1) found that when colonies of honey bees were separated from a given nectar-producing area by badlands, with no other source of food intervening, they would fly a distance of at least 8.5 miles. Experiments on the distribution of bees from apiaries located within a nectar-pl'oduciDg area showed that bees would fly for 2.75 to 4.6 nules in one direction and confine their efforts to working in that direction rather than in nearer fields of seemingly eqlUtl attractiveness. '.rhe results indicate that bees establish feeding lutbits and tend to 1'e­ tum to the same portion of a field, or to the same small field, on suc­ cessive days for nectar orpollen, even though other areas of the same forage plant are nearer. Bee experts state that when bees are brought into Helds to improve pollination and increaEe seed-set, best results are obtained if the colonies are moved in a/tel' the particuhr plants are in flower, so that flight lanes to some other food source will not be estab lished. A unique method for studying insect activity has been used by S. G. Stephens at Raleigh, N. C. The method and results as described by Stephens are as follows: 3 If you grind fairly finely a dye like methylene blue and dry it thoroughly before use it wOl'ks as a good marker of the 1J)0yements of the uees. 'Vc put a light sprinkling of the methylene ulne powcler over the anther column early in the morning when the anthers burst. The next clay we open the stale flowers from the prm'ious clay ancl examine for blue stain. It works very well. There is enough moisture accumulated when the flower fades and closes to spread even one tiny grain of the dye and make an easily recognizable blue spot. Further­ more you can see whether the bee has been collecting pollen or visiting nectaries or both by the position of the stain. In our vlots wc placed the dye in foul' flowcrs at one eud of the field. Next day we found blue stained flowcrs for a distance of 30 yards as far as a broad alleyway. Apparently the bees did not cross the alleyway or if they dic1 the blue stain had become exhausted by the timc they reached it.. In the vicinity of the "dye-clnstecl" flowers uU flowers examinecl were blue pigmcnted. Appa~'ently very few flowers arc missed by uees under our conditions which accords with the high percent of outcrossing observed [in Kime's experimeut). The methylene blue apparently dOes not dcter the bees from \'isit­ ing flowers, neither does it cause the flowers to drop without setting. So it appears to be quite a useful technique in finding out how much visitation goes on, how far the bees range and also one could probably cletermine what effect a neighboring fielcl of, say, alfalfa woulcl have on the activity of the bees in the cOttOIl. I think one couIn improve the technique hy grinding the dye i:cally finc am1 possibly diluting with talc.

This method appears useful in studying insect visitations, including how far the bees rlLl1ge, and the percentage coverage of flowers in a 3

Letter dll ted July 28, 1050.



given area. It should be of particular interest to breeders who have hesitated to conduct conventional natural-crossing studies for fear of introducing red-leaf or other distinctive marker characters into their seed stocks. HETEROZYGOSITY IN SUCCESSIVE HYBRID GENERATIONS

Hybrid vi~or is associated with heterozygosity, and the maximum expression 01 heterosis is obtained in the Fl generation. Cotton is a partially cross-pollinated plant; thus, some degree of heterozygosity is maintained indefinitely when open-pollinated seed from an original Fl pOPlihttion is continued on through F 2 , F s, and subsequent genera­ tions. The relative proportions of selfing and outcrossing determine the amount of hybrid vigor retained in later generations. Stephens (7) has given the following formula for calculating the proportion of heterozygotes in the current generation when the proportion of hetcrozygotes in the preceding generation and the proportion of out­ crossing is kno'yn: h=¥2 [(l-lc)h'+l.:] in which h is the proportion of heterozygotes in the current generation, h' is the proportIon of heterozygotes in the preceding generation, and k is the proportion of outcrossing. The formula provides an estimate of the lwerage heterozygosity of any number of gene pairs expressed as a percentage of the Fl heterozygosity. A practical test of heterozygosity, as measured by the frequency of 1 gene pair in successive hybrid generations, has been conducted at Knoxville, Tenn. In 1948, mass crosses were made between pilose­ leaf (T-Gll) and a smooth-leaf cotton. The pilose character in 1'-611 is controlled by a single gene. All Fl plants of this cross were inter­ mediate with incomplete dominance of pilosity. The F2 generation showed :3 leaf-cln!Os phenotypes readily recognizable by field examina­ tion of mature phtnts. The Fl generation was grown, open-pollinated, in an isolated plot on the station in IU-Hl. The seed cotton was hanested in bulk from this planting and ginned; the seed was thoroughly mixed, and part of it was used for a similaL' planting in 1950. The same procedurc was followed in obtaining seed for IDuI andI052 plantings. 1\. count was made each )!eal' (ID".!:!") /0 19u2, inclnsive) of the nwnber of plants in each leaf-class phenotype in the total population. The amount of natul'a1 crossing at Knoxyille dtleing this period averaged about '.1:5 percent. The aetnal proportions of plants heterozygou~ for the pilose charactcL' is compared with the expected proportions cal­ culated on the basis of L.l:i) pCl'crnt l1tltnml (,l'os~i Ilg (table ()).



6.-Freguency Of pilose, intermediate, and smooth-leaf plants in F1 and late?' open-pollinated ge'nel'ations of the hybrid, and P?'O­ p01,ti0118 of plants hetm'ozygoll.s for pilosity, at Knowville, Tenn.


Plant.s in leaf-class phenotypes Year

Generation Intermediate Smooth


1949 ________ 1950________ 195L _______ 1952 ________

1 1




Proportion of plants heterozy­ gous for pilosity Actual

Number Number Number Percent F _____ Number (2) 0 0 -------100 F 1 _____ 151 384 144 57 679 F 2 _____ 257 361 250 42 868 3 F t _____ 319 i 675 47 150 I 206




Ex­ pected


Percent 100 50 36 32


Based on 45 percent natural crossing. All plants.

The theoretical proportion of heterozygotes su~gested by Stephen's formula is based on equal viability and equal proauctivity of all types in the mixture. 'With types which show heterosis, the formula is likely to underestimate the proportion of heterozygotes actually obtained. For instance, if the more heterozygous plants in a given population had higher than average yield, the succeeding generation would contain a larger proportion of seed from such plants than would be indicated by the actual number of plants of that class in the cm:rent ,generation. Disproportionate frequencies could occur if clifferences III seedling vigor, dIsease and insect resistance, or other factors caused a larger proportion of one c1uss of plants than another to be left in the stand of mature plants. It is likely in this material that natural selective processes have operated to favor the heter­ ozygous phenotype, although the alternative possibility that the amount of natural crossing 'was greater than 45 percent cannot at present be disregarded. ROLE OF NATURAL CROSSING IN CURREl'I'T BREEDING

The fundamental but perhaps unsuspected role of natural crossing in current breecling techniques has been pointed out by Stephens and Finkner (8) : In developing new vnrieties of cotton the breeder attempts to extract superior lines from his breeding stocl{s. Following systematic testing the hest lines are commonly bulked and multiplied for two or three years in increai


r. S.


Since medium to high pereC'lltngp~ of aOf;::-p<,1lination occur in extensiw, areas of thC' Cotton Belt, iJlelucling highly important seed­ producin cr areas, the phC'llommon mllst lIa no' eOllsiderable practicill effect on tite genetic l'omplex of Yllriptie~ produced in ~u('h ilreas under open-pollinated conditions. If hybrid yigor, retained through natul"ll crossing ilmOllg COlllpollC'nt ::traillt:'. is a contributing factor to the productivity, quality, and adapiability or SOllle of our i)l'esent­ day connnel'cial cotton variC'ties, recog11ition of this fact may suggest modification:: of present breeding techniques. In rC'gions of moderate to high nilturnl crossing. the COlllllOllPllt strains might better bp selected on the basis of their rom~)inillg ability rather than extrellH' uniformity as represented by clof'ely related hOlllOZY!!OUS lines. On the contrary, in regions of low natl11'al cro~sing, the (,(llubining ability of the COlll­ ponent stmins would haye liltlp pfreet on the eOlllpo~ition of a "ariety. Yilrieties grown in such rC'gi()Jl~ would tplul to bpcome or re111ain mechnnica.l mixtures of relntiyp]y homozygolls hiotypes.

SUMMARY The amount of natural erossin~ in cotton, dpternLined fr0111 48 !:epartlte tests in 12 States OWl" n. period of ·1 years, ranged :from less than 10 percent in parts of central TC'xas to approxill1atE:ly 50 per­ cent in parts of the southeastern regioll of the Cotton Belt. The pxtent of lHlturtu crossin~ apparently is cloSPl)' related to the fre­ quency and timeliness of the yisits of inseet pollinators to the cotton Ho"wers. The dahl from thp sev("ml :U("tlS sup:gest a regional paUun for Datural crossing f'ol1ll'what coincidpnt "with the cotton-acreage dis­ tribution. In areas of intpllsi,'e cotton cultivation, the mtio of insect pollinators to cotton flowers is low and cross-fertilization is infrequent. In areas 'If sman fields mul ;;patch" cotton, as in most oJ the south­ pastern region, the ratio oJ insect polli11ators to cotton flowers is high, and cross-fertilization is corrl'sponclingly high. Thus, tbe phenome­ non reflects the general phYf'iographic 1'(~ology of the region. ReHfionably HCCHrt'ltt' ('Ul'S \\"h(,11 thl'Y [lr(' similarly ex­ posed to IOl'pign POllP1l. Thb fact mlly he of ('ollsi('cling IIlethod.., lltilizing hybrid ,,](ro1'. I-jumble bees and hOlH'Y lll'C's urt' lII()~t hp<[ll(,l1t 1,\" lllPntiOJH'cl a~ insect carriers of cottOl1 pollpIl. The actiYit), of (he~(' iul'Pcts in thp cot­ ton flO\\'(,1'S is a go()(l indpx of the po{pntinl fo)' c-ro::sing. The sprpacl ofmethylplH' 11'111(' from tl ,{"(>W ;·dvp·<1ustp(l" (lO\\'(')'s to nf}w]' Jlowprs in the ylcinit\· has bpC'Il used to stllcly suell flcti,·ih'. A stlldy 0 f heterozygosity in ad,;anced generations of an original 1i\ population llla([p at J(lH)x,·i11e. '1'pl1l1., illdie:ttpd n hi~hel' percentage of heterozygous plants ill the F2l F" and F, ~{,lH'ratiolls tlmll the



theoretical expectation. The disparity may hn YC beell l'ltused by natural selectIve processes operating to ftlvor the heterozygous .phenotype. Katuntl crossings mH,), playa fmtdtlluentll,l Lut perhaps unsuspected role in cnrrent breeding techniques. Recognition of this role may suggest modifications of breeding methods to employ natural crossing as n. useful tool for cotton improvlllnent. LITERATURE CITED J. K 1033. '.rUE FLIGHT

(1) ECKEItT,


)lA:\UE OF 'flll~ 1l0:\BYlllm. ,Jour. Res. illus. GHEEN, .T. ~:L, und.•JoNES,)I. D. U)(j3. ISOLA'l'lOX OE' co']"rON l!Olt SB1W ISCHE:ASE:. Agroll.•Tour.

47: :!37-283, 4;): 3GG-3GS,

illus. (3) LODE:N, II. D., and llIOll~[Q:\D, 2,'.R, 1l)f!1. ll,nmD YIGOH IN COTrO::>-CY'l:OGE::\WrIC 1,Sl'ECTS AND l'llAO'nCAL .\Pl'LI­ CA.'rIONS. Beoll. Bot. (j: a~'-I0l). (4) )[EAIJE,R.:U. B1,I" Krml'IXG ~\r.\Y IXCHEASE '11I~~ COT'1'OX cnop.


21)5, ilIus. (;}) POl'J~, O. A., ~DU'SOS, D. )1., and Dusc.\s, K X. H)·H. En'Ee'I' Ok' COHN B.\ltltlEHS ()~: NNl'CllAL cnOSSlNG Hes. Gb: 347-301, illus.


.Tour. lIered. IN C01"ION.



.Tour. Agr.



tc'I'ILIZA'rIO:-I 01:' UYlIlUD "WOR 1:-1 COT'1'ON-r1'S l'IlOBLE~[S AND PllOSPECTS.

Cottoulmllr. ('ouf. ProC. \3,:!\) 1111. [Processed.] (I) ST1!:l'llENS, S. G.


I:'ACTOHS AFFECnXG 'l'UJi; GENE'rIC CO~u'LEXl'rY m' A PAU1'IAU;, ou'r­ CROSSEI> POPULATION. Cotton Impr. ConL Prot!. 2, 10 pp., mus. [Proe~Si"cd.]

(l::) - - - und FI1:'.'1'>:NEll, ill. D.

1!Ji33. XA'runA!. cnOSSIXG 1:\ COTTO:\'. Eeon. Bot. 7: 2;)7 ~2GO, illus. (9) TUlI:\EII, .T.H. 19;;0. NATlJIIAI> Cl108SING IN corrol'<. Cotton Impl'. ConE. PI·OC. 2, ;) pp.

[ P roecssed. 1

II, $, (iO\"ERKMEHT Pftl,NTltlG OFFICE: 195.4


Natural Cross-Pollination in Cotton - AgEcon Search

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