the value of hybrids and synthetics in sunflower seed production

13
THE VALUE OF IIYBRIDS AND SYNTIIETICS IN SUNFLOWER- SEED PRODUCTION c a n a d d D e p a rt tn e nt !;2?; rii#r r, M o r d. e n, M an i t o b a lReceived for publication December 19, 196ll ABSTRACT Highly .significanr. correlatio,ns. in exce-ss of +,7, occurred between rhe per- c€ntage of hybrids in the seed for planting and thc yielding ability of iwo srngle-c-ross sunflowers, -{d'ance arrd Adrenr. The percentage of hybrids app. roac.hed or reached 100 l hcn the hybrids l ere produ&d by 'hand_ polli'ation without emasculatio' and r-aried dorvn ro "dty tr p"i ce'nt when produced commercia.lly by narural pollination in 2 X'2 ciossine blocks. Seed from a 50-50 mixrur'e of the tir o parenrs of Aiilance conta.=ned less fybrids than seed of the female from cr6ssing brocks "uJ*", 1"-.i l"tJ- ing. Quantity of polle' transferrcd to the f"emale ;;;;. "*;rl;-afiected percentage of. hybrids. .Yields of four synrhetics, each cofrrposed of foui rnDred rrnes. rndrcated that sl nthetics arc a better means of using inbred lines in sunflowers than hybrids such as Advance. Double.tort.u p-roduced ,1I.1","t" polli^ation were not superior to synthetics made from'the same INTRODUCTION The value of double-cross hybrids in corn production is well known. Synthetics (2, 4) also show promise as a means of usinq inbred lines in corn. In oilseed sunflorvers, the hybrid Advance has been ifrporrant in Manitoba. Its pedigree is 5-37-388 X-sunrise. The male p"t.ni originated from an inbred line and.is quite uniform; Advance couri thus be"termed a single cross. The seed for planring is pr.oduced by narural crossins in fields cJm_ posed of two_rows of s-lz-;ss alternating -ith t*o ro*, oT Sunrise, com- monly termed 2 X 2 crossing blocks, and-because the percentage of narural crossing is greater on s-37-388 than on sunrise it is used'as the f6male parent. Even so, a low proportion of cross-pollination occurs to result in fe#actual hybrids i1' ,.\"'rhybrid" seed. A sLortage of hybrids is arso a serious fault of. the.hybrid.Advenr, r,vhich is a rust-reiisranr iounrerparr of Advance, and wjth the hybrid.Admiral. This paper reporrs the effecf of different methods of seed production on the percentage of iybrids in the seed for planting and the effect of per cenr hybrids on the yield bf the s.tc.eeding crop'. Seco"ndly, th_e results of a study of synrhetics ind double crosses as"alternate methods of using inbred lines of sunflowers are given. MATERIALS AND METHODS , The,ped.igrees of the three hybrids used for the study of methods of seed production are as follows: Advance - 5-37-388 X Sunrise Adaent - S-37-388RR X Sunrise Adrnirol - S-37-388RR (CM5 x.CMz7). Seed of Advance and Advent was produced by commerciar growers in 2 X 2 crossing blocks and at the Experimental Farm, Morden, in sriall narural ,- lContrib-ution No. 25 from the Experimental Fam, Rmerch Brmch, Cauad.a Department of Agri- culfure, MGden, Man. 488 Can. J. Plant Sci. Downloaded from pubs.aic.ca by 90.16.202.142 on 04/06/13 For personal use only.

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Page 1: the value of hybrids and synthetics in sunflower seed production

THE VALUE OF IIYBRIDS AND SYNTIIETICS INSUNFLOWER- SEED PRODUCTION

c a n a d d D e p a rt tn e nt !;2?; rii#r r, M o r d. e n, M an i t o b a

lReceived for publication December 19, 196ll

ABSTRACTHighly .significanr. correlatio,ns. in exce-ss of +,7, occurred between rhe per-

c€ntage of hybrids in the seed for planting and thc yielding ability of iwosrngle-c-ross sunflowers, -{d'ance arrd Adrenr. The percentage of hybridsapp. roac.hed or reached 100 l hcn the hybrids l ere produ&d by 'hand_polli'ation without emasculatio' and r-aried dorvn ro

"dty tr p"i ce'nt when

produced commercia.lly by narural pollination in 2 X'2 ciossine blocks.Seed from a 50-50 mixrur'e of the tir o parenrs of Aiilance conta.=ned lessfybrids than seed of the female from cr6ssing brocks "uJ*", 1"-.i l"tJ-ing. Quantity of polle' transferrcd to the f"emale ;;;;.

"*;rl;-afiectedpercentage of. hybrids. .Yields of four synrhetics, each cofrrposed of fouirnDred rrnes. rndrcated that sl nthetics arc a better means of using inbredlines in sunflowers than hybrids such as Advance. Double.tort.u p-roduced

,1I.1","t" polli^ation were not superior to synthetics made from'the same

INTRODUCTIONThe value of double-cross hybrids in corn production is well known.

Synthetics (2, 4) also show promise as a means of usinq inbred lines in corn.In oilseed sunflorvers, the hybrid Advance has been ifrporrant in Manitoba.Its pedigree is 5-37-388 X-sunrise. The male p"t.ni originated from aninbred line and.is quite uniform; Advance couri thus be"termed a singlecross. The seed for planring is pr.oduced by narural crossins in fields cJm_posed of two_rows of s-lz-;ss alternating -ith t*o ro*, oT Sunrise, com-monly termed 2 X 2 crossing blocks, and-because the percentage of naruralcrossing is greater on s-37-388 than on sunrise it is used'as the f6male parent.Even so, a low proportion of cross-pollination occurs to result in fe#actualhybrids i1' ,.\"'rhybrid" seed. A sLortage of hybrids is arso a serious faultof. the.hybrid.Advenr, r,vhich is a rust-reiisranr iounrerparr of Advance, andwjth the hybrid.Admiral. This paper reporrs the effecf of different methodsof seed production on the percentage of iybrids in the seed for planting andthe effect of per cenr hybrids on the yield bf the s.tc.eeding crop'. Seco"ndly,th_e results of a study of synrhetics ind double crosses as"alternate methodsof using inbred lines of sunflowers are given.

MATERIALS AND METHODS

, The,ped.igrees of the three hybrids used for the study of methods of

seed production are as follows:

Advance - 5-37-388 X SunriseAdaent - S-37-388RR X SunriseAdrnirol - S-37-388RR (CM5 x.CMz7).

Seed of Advance and Advent was produced by commerciar growers in2 X 2 crossing blocks and at the Experimental Farm, Morden, in sriall narural

,- lContrib-ution No. 25 from the Experimental Fam, Rmerch Brmch, Cauad.a Department of Agri-culfure, MGden, Man.

488

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Jdy, 19621 PUTT-SUNFLOWER SEED +89

crossing plots or by hand-pollination. In the small natural crossing plots,sinsle rows of the female parent of the two hybrids were planted in a I X 2

arr-a.rgement with the malb parent. In the hand-pollination, liberal amountsof pollen were applied every second day during flowering. The femaleparent was not emasculated. Additional lots of seed were obtained byplanting a 50-50 mixture of the two parents of Advance and harvesting themtogether. Some samples from the two parents in the mixture also wereharvested separately. Samples of Admiral were produced by hand-pollina-tion and in 2 X 4 crossing blocks of experimental and commercial size.

The percentage of hybrids in Advance and Advent was determined inthe field by vigor and by size and shape of the seed, or in the greenhouseby the method described by Stefansson (9) using seedling markers. Thedeterminations in Admiral were made in the field.

The second study reported here was with four groups of inbred lines,consisting of four unrelated or distantly related lines in each group. Thelines were similar in flowering data within the groups and had good com-bining ability with either the male or female parent of Advance.

The four groups of inbred lines were used to prepare Synthetics 10 to13 inclusive. One hundred viable seeds of each line within the groups weremixed,.planted in isolation and allowed to interpollinate freely. Duringsuccessive seasons, second and third generations were produced in smallisolated plots containing 100 to 200 plants.

The lines of each group also .were crossed in all combinations by handand without emasqulation. In making these crosses, lines known to crosswell under natural pollination were irsed as the female parent wheneverpossible. The following season the three possible double crosses within each

group were made by hand and by natural crossing in isolation. The isolatedplots for the natural crossing lvere of four rows 2O feet long rvith the twosingle crosses placed in an r y ,c y anangement. Seed from one of the innerrows was used in the subseouent vield trials. In most instances the coin-cidence of flowering -"t good. Where differences occurred, 5 to 10 plantsjudged to have the best opportunity for cross-pollination were marked whenin bloom and their seed used for the yield tests.

In1957, the first and second generation of each synthetic, the single anddouble crosses of their component lines, a sample of Advance produced bynatural crossing and a second generation sample of Advance were tested foryield. Advance produced by hand-pollination 'lvas included in some tests.The following season the third generation of each synthetic was added tothe tests and the double crosses were deleted.

The designs of the yield tests varied with the number of entries. Sixreplicates .were used except for one test in which there were eight. Theplots were one row 20 feet long and were spaced 3 feet apart. Sixty toseventy seeds per plot were planted and the stand thinned at random afteremergence to 6 to 8 inches between plants. One rod was harvested foryield estimates.

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490 CANADIAN JOURNAL OF PLANT SCIENCE

%hybrids

lVol. 42

Yield

137 2

1125153 1

RESULTS

Methods of Producing Hybrid Seed

Most lots of seed from the commercial 2 X 2 crossing blocks containedless than 50 per cent hybrids. Thus 52 samples of Advance ranged from16 to 54, with a mean of 39 per cent; 19 samples of Advent had a range of36 to 54, with a mean of 45 per cent; and 19 samples of Admiral showed a

range of 32 to 50 and a mean of 39 per cent.

Tesro l.-PrR cENT HyBRIDs AND yrELD pER ACRE IN pouNDs or AoveNce eNoAovnNr suNFLowERS GRowN FRoM sEED pRoDUcED By ITAND-cRossrNG AND BlrNATURAL cRossrNc rx 1 X 2 pl.ors AND rx 2 X 2 coMMERcTAL cRossrNc BLocKS

lX2naturalcross 2X2naturalcrossYear

oftest

56

JI/1

-l

i

l

I

%hl'brids

8077848792921a

/o73

Yield

195319.541 9551 9561 9591 959195919601960

929189969393797984

1 800227 4

ziz204622051299217 8

19 75

21611+231 869

AdvancelAdvancelAdvanceAdvanceAdvance2AdvancelAdventlAdvancelAdventl

i

I Hand crossI

Yariel v'l(aL , o., Yieldi nvt)rlos

lMean of two yield tests2Mean of three yield tests

Tenlp 2.-PrR cENT oF HyBRIDS AND yIELDS oBTATNED FRoMsEED oF THE FEMALE pARENT fS-37-388) AND MALEpARENT (SuNnrsn) or Aovll,rcp pRoDUcED rN 2 X 2cRossING RLocKS AND rN FTELDS or' 50-50 MrxruRE

Seed Sourcel No. ofsamples

Yield per acre (pounds)

s-37-388Sunrises-s7-388SunriseMixture

s-37-388Mixture

apCB

50-5050-5050-50

CB50-50

54 6431 4062-7238 4947 58

40-5 1

2+ 38

1110917

1099t0261008

t8771698

J355.)

5936674454

1052-t17 3875 996958-1201976-1150958-1059

17 59 197 51463,18i2

1954

l

++30

lCB : 2 X 2 crossingblock,.5o 50 : mi.\ture

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July, 19621 PUTT-SUNFLOWER SEED 49r

The percentage of hybrids in Advance and Advent produced by hand-pollinatioir and b"y natJral crossing in 1 X 2 plots 'was much'greater(Table 1). There was a highly significant correlation of *.716 betweenyield and percentage of hybrids for the 16 paired values in Table 1.

Weighted ai'erages ihow thit the yields from the I X 2 natural cross andthe 2 x 2 commercial natural cross were 94 and 72 per cent' resPectively,of the hand-crossed seed. In 1960, commercial samPles, containing 47 and51 per cent hybrids, yielded only 78 per cent of the seed from I X 2 naturalcross. Hand-crossed seed of Admiril, not reported in Table 1, and of itsrust-susceptible counterpart, has shown 88 per cent hybrids or more.

Two experimental three-way crosses were produced in a 2 X 4 atrange-ment, using'two different inbred lines as the iemales and Advance as ihemale. BotL these inbreds had given 82 per cent hybrids in 1 X 2 crossingplots with Sunrise. In the 2 X 4 crossing blocks one produced 81 per centhybrids and the other 7+ per cent.

In 1953, seed from five fields planted to a 50-50 mixture of the twoparents of Advance and from three 2 X 2 crossing blocks was tested(Table 2). The mean percentage of hybrids in the rwo parents harvestedseparately from the fields of the mixture was higher than in the correspond-ing parents from the crossing blocks. However, the mean percentage ofhybrids in the five samples of the mixture of the two parents was lower thanin the 5-37-388 or female parent from the crossing blocks (i.e., Advance).Likewise, average yields, is well as maximum and minimum yields, werelower from the mixture than from 5-37-388 or Advance out of the crossingblocks.

The tests in 1954 (Table 2) show that seven samples of the mixture gavea mean yield of 1698 pounds per acre compared with 1877 for seven samplesof S-37-388 or Advante fromthe crossing blocks. The mean percentage ofhybrids was 44 in the 5-37-388 from the crossing blocks and only 30 in theseed from rhe mixture. The mean differences iriyield and in peicentage ofhybrids were highly significant. ,Co-variance analysis also showed a highlysignificant correlation of +.703 between yield and percentage of hybrids.In the two seasons a total of 10 entries of 5-37-388 from the crossing blocksgave a mean yield of 1647 pounds per acre and had 49 per cent-hybridswhile 12 entries of the 50-50 mixture gave l4l1pounds per acre and had 40per cent hybrids.

Synthetics

The results of the rests of Synthetics 10 to 13 and the single and doublecrosses of their comDonent lines are shown in Tables 3 to 6 inclusive. Inthese tables any two means followed by the same leffer were not significantlydifferent, on the basis of the Duncan multiple range test.

In every test the highest yield was obtained from a single cross. Exceptfor the cross CM2l X CM31 (Table 5), and some crosses of the lines inSynthetic 13 (Table 6), notably CM35 and CM79 in which cross-compati-bility was indicated by only 4 and 6 per cent hybrids in the two seasons,most of the single crosses had a high percentage of hybrids.

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Page 5: the value of hybrids and synthetics in sunflower seed production

lVol. 42CANADTAN JOURNAL OF PLANT SCIENCE

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493PUTT_SUNFLOWER SEEDIrly, 19621

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cANADIAN JOUR\AL OF PLANT SCTENCE [YoL 42

. Though the synthetics usually were lower-yielding than Advance pro-duced by natural crossing, in most tests the differences were not significant.The two most promineniexceptions were the second generation of Synthetic12 and of Synthetic 13 in1951 (Tables 5 and 6). No re"ron was ipparentfor the pooi performance of Synthetic 12 in this season. Two of thi: linesin S1-nthetic i3 are susceptible'to asrer yellows while the Advance hybridis resistant. This disease was severe in iSSZ. In the following year, whenaster yellows was not serious, the third generation of this syrithetic washigher--y-ielding than the sample of Advanie produced by narural crossing,even falling into the same gioup of means al the hand-crossed sample ofAdvance which had 9l per cent hybrids. In 1959, its fourth geneiation,and the third generation, \\,'ere tesred against hand-crossed Advance and didnot differ significantly from the latter in yield. Note that in each testreported in Tables 3 to 6 the second generarion of Advance was substantiallylower-yielding than the first generaiion, the difierence being significant ihsix of the eight tests. In contrast, the advancing generarions of the syn-thetics either showed an increase in yield, or at leisino significant decrease.

When the mean yields of the three single crosses involving each lineare calculated they reveal marked differencesln the combining ablliry of thelines within the synrhetics. As examples , in 1957, in Syntheti-c 10, iMl had

l mean yield of 1072 pounds per acre compared with 1402 for CMZT; inSynthetic 12, CMl3 had a mean of 1351 against 2227 for CM32 and in Syn-thetic 13 the mean for CM35 was 904 versus 1844 for CM33. In the laiterinstance, the poor performance of CM15 may be caused by incompatibilityshown in the cross CM35 X CM79.

T!. yields of the double crosses produced by hand were higher thanthose from natural crossing, with the exception of the (CM13 X CUZI;(CMl2 X CM31) cross (Table 6) which performed poorly in the hand-cross.Aside from this one exception the double crosses prbd.tced by hand did notdiffer significantly in yield, indicating that these tests did not disclose differ-ences in performance of the double crosses due to arrangement of lineswithin them. The double crosses produced by natural pollination, againwith the exception noted, did not differ significantly from either one orboth generations of the respective synthetic. For Synthetic 10 the threedouble crosses produced by natural pollination were all lower-yielding thanthe second generation of the synthetic.

DISCUSSION

The performance of the single crosses reported here sholvs that highyields can be obtained from many of them if the seed contains a high per-centage of hybrids. Thus single crosses in which a high percentage ofhybrids can be obtained under narural pollination may be the ultimate inthe utilization of heterosis in sunflorvers. However. the percentage ofhybrids in the seed of Advance and Advent. when produced^co--.i"i"llyin 2 X 2, or Admiralin2 X 4 crossing blocks is much too low for their fullvalue to be realized.

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From the data in Table 1 it is evident that quantity of male pollen has

an important bearing on the percentage of hybrids in Advance and Advent.Thusi when liberal"quantitiei of polTen weie provided by hand, the per-centage of hybrids rvas always high, ranging from 79 to g6. These vafuesalso indicate that cross-incompuiibilitv -is -not a factor in these crosses.

When the pollen was transferr.a by i.t"".ts, presumably in lesser quantitie-s,in 1 X 2 iataral,crossing plots, ttie percent;ge of hybrids was.I6wer. Itwas much lower in seed'pioduced commercia-lly in i X 2 crossing.blo-cks,a fact which may be attributed to the lower ritio of male parent-in these

fields. The sam-e positive efiect of quantiry of male pollen is seen in thehigh percentag"s of hybrids obtained ivhen Admiral wai produced by hand-pollination and when the two experimental three-way crosses were__Pro-

duced in the 2 X 4 crossing blocks using Advance as a male Parent. How-evet, when Admiral was produced in 2 X 4 crossing blocks the percentageof hybrids was similar to Advent and Advance from 2 X 2 crossing blocks.Oboiensky (7) has noted differences in the amount of pollen produced_byinbred lines. Perhaps the male parent of Admiral does not produce pollenas profusely as the male parent bf the other rwo named hybrids or as Ad-vance did in the two experimental three-way crosses.

The percentage of hybrids in the seed of each of the parents of Advancewas higher r,vhen-they were grown in the 50-50 mixture than when theywere grown in 2 X 2 crossing blocks. Thus, by bringing the parents intocloseiproximity in the mixtuie, a condition which wo-uldfaciliiate transferof pollen, the percentage of cross-fertilization was increased' However,even though an-increase occutred, the percentage of hybrids in the mixturewas inferior to the percentage in seed bf S-lZ-lss from the 2 X 2 crossingblocks or Advance produced by the common means. This inferiority wasexoressed in lor'ver vields of the mixture and shows that this method is notsatiisfactory for producing hybrid seed of Advance. The same may beexpected for Advent.

The superior yield of the double crosses, made by hand, compared withthe same crosses made by natural pollination, indicates that a greater amountof crossing occurred with haird--pollination wherein great;r amounts ofpollen would have been transferred to the female parent than in naturalirossing plots.

Furgala (l) reported a higher percentage of hybrids in seed from cross-ing blocks populated with honeybees than in seed from crossing_ blockswithout horiefbees. His result is in agreement with those given here inthat greater amounts of pollen would have been transferred in the oopulatedfields. Obolensky (7),-on the other hand, obtained results differing fromthose in the present study.

_ He. found that.variation of th3 _proportion.

offemale (5-37-3S8) to male (Sunrise) parents berween 1:1 and 3:1 in crossingplots had no effect on the percentage of hybrids obtained from seed of theIemale. Also, seed from the parents grown in mixtures containing 10 to50 per cent male showed little difference in percentage of hybrids betweenthe two parents or between them and the female fr6m the'crossing plots.His data ivere, horvever, gathered from a very limited study in one season.

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White the percentage of hybrids occurring in the mixture of the Ad-vance pal-ents reporred here and the resulting yields were inferior to thoseof seed^ from the'crossing blocks, this may be"a siruation specific ro the twoParents under study. Obolensky (7) found no significant correlation be-tween self-compatibility and amount of pollen produced, and Russell (8)reported a significant negative correlation between self-compatibility andthe amount of crossing under open pollination. Thus it may be possible toselect lines that are relatively self-incompatible and are good pollen producersand to obtain a high percentage of hybrids by planting thern in mixtures.An inference that this is possible is seen in the results of Kugler et al. (5).Two hybrids, produced bi hand-pollination. gave yields of ti5 and 189 percent of the Klein check variety. The same hybrids, produced by mixingthe parents, both gave yields of 182 per cent of Klein. While no data onpercentage of hybrids are given, the yields of the mixtures indicate that theycontained as many hybrid plants as the seed from pollination by hand.Therefore, the uliimaie of i single cross in which i ttign perceritage ofhybrids can be obtained under natural pollination may be attainable.

Until this ultimate is achieved, the performance of the synthetics re-pgrted here shows that they have prospect of being a better means of using

!1br9d lines than hybrids, such as Advance, producEd by natural pollination-.While, in general,'they did not outyield samples of Aivance coirtaining 6lto 100 per cent hybrids, they likely would have yielded much better thanmost commercid samples of Advance, because the latter had an average ofonly 39 per cent hyblids in 52 lots examined. AIso, their performance inrelation to the double crosses produced by natural pollination shows thatheterosis can be exploited as effectively wich synthetics made of four linesas with double crosses made from the same lines.

Besides promising better yield than the present hybrids thar are pro-duced by natural poiiination,'seed of synthedics would cost less. BecauseoJ the special care required in planting and harvesting crossing-blocks andthe low yield of the inbred parents the cost of hybrid seed has ranged from25 to +0 cents per pound. Seed of synthetics might be produced for 10

cents per pound or less.

One practical disadvantage of the synthetics would be less uniformitythan in a single-cross hybrid. Also, the lines entering a synthetic all shouldcarry resistance to the prevalent diseases. Otherwise situations will occursuch as the poor performance of Synthetic 1l in the aster yellows epidemicof 1957. This requirement is more difficult to fulfil than for a single-crosshybrid, composed of just two lines. Also, only one line of the single cross,preferably the female, need carry resistance if the character is dominant.

Tysd"l et al. (10) hrrr. pr.r.nted theoretical values showing that yieldsof synthetics can approach F' hybrids, pafticularly if the amount of sibbingin the component lines is low. They also showed that the yields of syn-thetics increase as the number of lines in them increases from two to eis'ht.A slight further increase is possible with l6 lines. Kinman and Spraguel+)in a study of ten inbred lines of corn in their 45 possible single crosses,

predicted that the best synthetic could be composed of the five or six lines

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of best combining ability. Furthermore, synthetics in com have showngood performance"in field tests. Hayes et al. 121 reported on one composedof tne eight best combining lines out of a group of twenty. Its yield wassimilar tJ a recommended f,ybrid for the aiea.

^Lonnquisf and M-ccill (6)used S, lines from a second'cycle of recuffent selection to form four_ syn-thetics which averaged 96 per cent of the yield of the hybrid U.S. 13.

Kiesselbach (3) found thatlhe yield of double crosses in F,, or in otherwords synthetics composed of four lines, was 85 per cent of the F'. If.o-p"tJbl" performance can be obtained from synthetics in sunflowers theywill'be valuable in sunflower oroduction. Eveh the best samples of com-mercially produced Advance'and Advent, containing +7 t9

^56--per cent

hybrids, only yielded 72 per cent of the samples from hand-pollination as

#as shown 6y'the data of'Table 1. Commeriial Iots in general, which fre-quently have less than 40 per cent hybrids, would be even Poorer.

Improved synthetics should be attainable in sunflowers' Those reportedhere contained four lines instead of the Iarger numbers which aPPear moredesirable on the basis of theoretical considerations. Several of the lines usedin the present synthetics are known to be relatively self-fertile. Choice oflines with lower self-feftility or less prone to sibbing should give furtherimprovement. The selection of groups of lines known to combine well witheaih other in all combinations rvould be equally or more important. Thiscondition did not exist in the groups of lines used in these synthetics. Whenthese studies were commenied the choice of unrelated lines of similarflowering date was limited. Since then several promising new inbred lineshave bedn developed. The objective now is to identify a grouP.of linesthat are cross-compatible and have superior combining quality with each

other. Such a group should form a high-yielding synthetic.

ACKNOWLEDGEMENT

The author gratefully recognizes the assistance of the firms Co^-op'Vegetable Oils L]mited, hltonai Manitoba, and Western Canadian See-d

Prdcessors Limited, Lethbridge, Alberta, who have provided many of thesamples of seed used in these studies.

REFERENCES1. Furgala, B. 1954. The effect of the honeybee, Apis mellifera,(L.) on the seed'set, yield and hybridization of the cultivated sunflower, Helianthus annuus L'

M.Sc. thesis, Dept. of Entomology, Univ. of Manitoba.2. Flayes, H. K., E. H. Rinke, and Y. S. Tsiang. 1944. The developrnent of a syn-

thetic variety of corn from inbred lines. J. Amer. Soc. Agron. 36:998-1000.

3. I(iesselbach, T. A. 1960. Performance of advanced generatitrn corn hybrids.Agron. J. 52:29-32.

4. Kinman, M. L., and G. F. Sprague. 1945. Relation between nurnber of parentallines and theoretical performance of synthetic varieties of corn. J. Arner. Soc.AEron. J7:J47-351,

5, Kugle;, W. F., A. Luciano, y. M. Davrzux. 1958. Meloramiento del girasol e,n

Pergamino. Comunicacion presentada a la IV Reunion Latino-americana deFitotecnia (Santiago de Chile) noviembre.

6. Lonnquist, J. H., and D. P. McGiIl. 19t6.advanced generations of synthesis afterAgron. J. 48:249-253.

Performance of corn synthetics intwo cycles of recurrent selection.

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8.

9.

7. Obolensl,1,', G. 1958. Production of pollen in different lines of sunflowers and itsrelation to the production of crossed seed. Qualitas Plantarum et MateriaeVegetabiles 5:64-84.

Russell, W. A. 1953. A srudy of the inter-relationships of seed yield, oil-content,and other agronomic chiracters with sunflower inbred lines and their topcrosses. Can. J. Agr. Sci.33:291-314.

Stefansson, B. R. 1959, A rnethod for estimating the percentage of.hybrids inseedlois of first generation Advance sunflowers by means of a seedling charac-teristic. Can. T. Plant Sci.39:71-74.

10. Tysdal, H. M., T. A. Kiesselbach, and H. L. .Westover. 1942. Llfalfa' breeding.

Nebraska Agr. Expt. Sta. Research Bull. 124.

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