genetics of sesame

8/8/2019 Genetics of Sesame

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GENETICS OF SESAMED. G. LANGHAM

V. Some Morphological Differences of the Sesame Flower (S. mdicum L.)IN a previous paper8 in which colordifferences in sesame flowers werediscussed it was pointed out thatmany structural differences also existed.These are too numerous to describe indetail, but their principal characteristicswill be the subject of the present paper.Material for this study consists of 35varieties of sesame with numerous hy-brids between many of them. The off-spring of crosses of varieties from wide-ly separated geographical regions haveexpressed many characters not .found ineither parental phenotype. The expres-sion of some other characters waschanged by transferring the genes re-sponsible for them to other genotypes.The study of this wealth of material hasbeen extremely useful in preparing alinkage map for sesame and also in ex-plaining certain cases of sterility andsemi-sterility among varieties.

Descript ion of CharactersThe extreme variation in the sesameflower revealed by an intensive tudy ofdifferent varieties makes the selection ofa typical flower difficult. T h e mo st fre-quently appearing type is shown in Fig- 'u re \A A and is described in Bailey'sCyclopedia1.Some of the variations of this typicalflower as seen in our breeding plots aredescribed below:1. Foveola vs. absence of foveola.The typical sesarne flower has a smallV-shaped pit in the petal, which formsthe base of the floral tube. N eithe r the

origin nor the purpose of this small in-dentation is known at this time, but itis useful in a genetical study of the flow-er because of its relation to color distri-bution and to certain morphologicalcharacters. A few plants without thisfoveola occurred and have been selec-tively bred to give pure lines.

2. Internal pubescence vs. its ab-sence. Near the foveola of some varie-ties is found a small brush of plant hairs;these are absent in other varieties. Th enumber of hairs varies from one to ap-proximately 50 per flower, but the num-ber for any given variety is relativelyco ns tan t. T h e ease of classification ofthis character in segregating populationsmade possible the determination of sevendifferent qualitative factors for the pres-ence or absence of hair. Second ge nera -tion ratios of 3: 1 , 9:7 , 1 3:3 , 15 :1, 1:3,7:9 and 1:15 have been confirmed byF 3 and F 4 populations.

3. Tubular flower vs. split flower.In contrast to the usual tubular flower,a type with five petals completely sepa-rated has been isolated. It is structu ral-ly sterile because the absence of the tubepermits the style to curve upwards there-by separating the stigma from the an-thers. Application of pollen, however,resu lts in seed set. In the F2 prog eniesstudied, recessive duplicate genes havebeen found responsible for "star" flower.Other types of split flower occur in

which the tube may be opened by divi-sion of the two dorsal petals, or alongone side, or near the base. All of thesetypes have been isolated in pure lines.Segregations of normal to split flowerrecorded in different F 2 generations are3 :1 , 9:7, 1:3.4. Open flower vs. closed flower.Ordinarily about seven o'clock in themorning, the lip of the lower petal ofthe flower bends downwards, leaving an

open ing in the floral tube. Som e lineshave been isolated in which the tube re-mains closed. Th ere are three differenttypes of closed flowers:A. Lip normal, but remains closed.B. One half of flower tube, including lip,remains green instead of becoming violetin color.

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FLOWER MORPHOLOGYFigure 14

A "Norm al" sesame flowers on day of opening. The curva ture in the center of the verticalportion of the flower tube is the U-shaped foveolar indentation. BPortion of flower with thedorsal part of corolla removed, showing tuft of flat hair near foveola as compared with ab-sence of this hair. C"Star" flower, with petals separated. D Extra enations on ext erio r ofthe corolla, a characteristic associated with non-shattering seed capsules. EFlower with fusedstamens, as compared with normal flower (Z 7), and flower with extra tissue on inside of corollaCO.


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Langham: Genetics of Sesame 349C. Tip s of petals become necrotic the daythe flower should normally open.A and C are recessive and B are domi-nant in Fi hybrids with normal floweredtypes. The F 2 generations have not yetbeen studied.5. Extra citations on the exterior ofthe corolla tube vs. wild type.Flowerswith these extra growths have been iso-lated three times and in each case theplant differed from the others in that theseed capsules were indehiscent in con-

trast to ordinary sesame. This valuablemutant form behaves as a simple reces-sive.66. Extra tissues on the inside of thesesame flower vs. wild type.Ordinarilythe five petals are smoothly joined toform the corolla tube; the borders ofadjacen t p etals unite edge to edge. Anew type of flower in which adjacentpetals, particularly the lower ones, dou-ble inward and unite with extra tissues

on the inside of the tube, has been iso-lated in a pure line.7. Fused filamen ts vs. separate fila-ments. Usually the filaments are com -pletely separated one from another, butnew lines have been obtained by selec-tion among hybrids in which several orall of the filaments ar e fused. T hi s typeis recessive to the normal.8. Flattened vs. curled lip.A type

of flower in which the lip curls down-wards instead of remaining straight, oc-curre d in a variety from Bra zil. It isrecessive in F i ge ner atio ns and difficultto classify in F2.9. "Rough" foveola vs "smooth".By looking in profile at the foveola ofsome varieties, the elongated cells in thepit of the foveola have a brush-like ap-pearance, while in others the surface issmooth. In crosses between the two

types smooth is dominant and segre-gates as a simple Mendelian factor.10. Defective foveola vs. normalfoveola.In some segregating popula-tions individual flowers occurred inwhich the foveola does not form a com-plete U, but rather a portion of it, or asplit U . Seeds from these plants give

progeny with similar type flowers. Incrosses between this and ordinary flow-ers the complete U dominates in Fi gen-eration and classification is difficult inthe second generation, although the de-fective types occur in approximately 25per cent of the progeny.

11. Single vs. double lip.Selectionsin which the majority of the flowershave an extra petal in the base, givingtwo lips and usually two foveoli, havebeen made in segregating populations ofcertain hybrids.12. Single vs. multiple flowers.Se-lections have been made in which dou-ble flowers occur frequently. T h e flow-ers may be nearly separated, or fusedat different angles. Triple and othermultiple forms occur in these samelines.

13 . Large, normal, and small flow-ers. Th e average flower is app rox i-mately two and one-half centimeterslong and one centimeter in diameter.But flowers three and one-half centi-meters and others one centimeter longwith a corresponding variation in diam-eter have been isolated. T he size of the.flower segregates as a multiple factorcharacter in hybrids.14. Thick, normal, and thin petals.The flowers of some varieties are so thin-walled that they become soaked by a

heavy dew, while others are so thickthey are quite firm to the touch. Th emost common flower type is betweenthese two extremes.15. Wide, normal, and narrow fove-ola.In the study of color distributionin the sesame flower, a wide foveola isdesired because the limits of the differ-ent pattern factors are more easily deter-mined than in narro w types. Individu alplants in which flowers with a broad

foveola were obtained in a variety fromChina. Th e narrow type occurs in a va-riety from Nicaragua.16. Reduced lip of the petal vs. nor-mal lips.In a variety from Brazil cer-tain types were isolated in which the tipsof petals were shortened and the liphardly existed. In this type natu ral

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350 The Journal of Hereditycrosses are reduced because the bees can-not find a resting place to enter the flow-er. Reduc ed petal segregates as a simplerecessive in F2 generation.

DiscussionThe morphological differences in thesesame flower described in this articleoccurred in breeding plots in whichmany varieties, hybrids and selectionswere under study for commercial use.The importance of flower type in thepercentage of natural cross-pollination,

dehiscence of seed pod, relative fertilityand other factors demonstrate the need

of a detailed study of genetics of flowertype in order to facilitate plant breedingwith this crop. The results presentedwere obtained from a study of approxi-mately fifteen thousand segregating pop-ulations.S u m m a r y

1. Brief desc ription of some morph-ological differences occurring in thesesame flower are given.2 . The relation of the differences to

the sesame breeding program are dis-cussed.

V I. Some Genetic Variations in Plant Color in SesameTH I S is a preliminary report of astudy on inheritance of color dif-ferences in the sesame plant. Someof these plant characters are related toflower color and to seed color. The com-plete relationship between foliage, flow-er, and seed will be discussed in a fu-ture article.

Seedling Colors1. Albino seedlings. For the pastsix years a few albino seedlings havebeen observed in commercial plantings,but it was impossible to isolate this char-acter without testing thousands of plantsin an effort to find the heterozygous

form. This year, however, one line froman individual plant selection segregatedgreen and white seedlings in the ratio of3 : 1 , and a heterozygous strain is nowavailable.2. Virescent seedlings.In spite ofthe fact that sesame is approximately96 per cent self pollinated 2 '8 , virescentseedlings are found frequently. T ho seobserved in our breeding plots are sim-ple recessives and three have been dem-onstrated to be genetically distinct.3. Pale yellow. There is extremevariation in the degree of color in sesameplants, ranging from pale yellow to darkgreen. One of the yellow types segre-gates as a simple recessive but the oth-ers are difficult to classify in segregatingpopulations due to intermediate grades.

4. Purple, green, and yellow leaf tips. W h e n the tips of the first pair of t rueleaves are barely visible between thecotyledons, they may be purple, green,or yellow. Both the purple and the yel-low change within a day or so to greenand the classification must be made atthe proper time. In all cases studied todate, purple dominates green or yellow.Two types of purple have been ob-served : one which is independent ofwhether the plant germinates in the sunor in the shade and another which ge rmi-nates green in the shade and purple inthe sunlight. The se are complementarydominant genes and one is linked with avirescent. Classification is simple.Among many F2 progenies from nu-merous crosses, green leaf tip dominatesyellow in some cases, and yellow is domi-nant in others. Two complementarydominants have been isolated for greenleaf tip (yellow leaf tip being recessivein these cases). Yellow leaf tip segre-gates as a simple dominant in certainother crosses.5. Purple stem.The color of theseedling stalk immediately below thecotyledons may be purple or green. Pur-ple stem is dominant to green and segre-gates sharply in the F2 generation. Seed-lings with the combination of purple leaftip and purple stems, green leaf tips andgreen stems, purple tip and green stems,have been found, but the combination of

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Langham: Genetics of Sesame 351

Cp X Gpop

Op Gp OpCOLORED LEAF TIPSFigur. 13

The tips of the first pair of true leaves may be purple, green, or yellow as they emergebetween the cotyledons. La ter the purple and yellow va rieties turn green, so that the ch aracte rcan only be recognized during a brief period.

green tips and purple stems has not yetbeen recorded.Plant Colors

6. Purple stems and leaf petioles.Two types of purple have been encoun-tered :a. Develops in the shade or in the sunlight.Determined by a simple dominant gene.b. Develops only in the sunlig ht Dom inantcomplementary genes differentiate thispurple from green.All of these genes for purple are es-sential for the expression of the flowercolor known as flake.87. Bronze stem and leaf petioles.This color is usually faint and is visibleonly in the young leaves and stems ofthe nearly mature plants. It is deter-mined by a simple dominant.8. Dotted stem and leaf petioles.

This type in which the color is localizedin dots, occurred in a variety from Bra-zil and in our Selection N o. 5. It is re-cessive to green stem and also to purpleand bronze.9. Green stem and leaf petiole. Ascan be seen from the above discussiongreen acts as a recessive to purple andbronze, and as a dominant to dottedstem . Th e com bination of the flowercolor known as flake and green stem hasnot yet been found; but the flower colorsmear occurs in combination with greenstem and bronze stem, but not in purpleor dotted.10. Mottled leaf. This characterwas described in a previous paper4 andconsists of yellow blotches in the greenleaves of nearly m atu re plants. It is asimple recessive.



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352 The Journal of Heredity

GREEN AND YELLOW COTYLEDONSFigure 16

Green and virescent cotyledons represent an allelic pair, with green dominant.' In F, a3:1 segregation of green and yellow is observed.

DiscussionMost of the seedling and plant colorsdescribed in this paper can be easilyclassified in segregating populations, ifcare is taken to make the observation atthe proper stage of growth and underfavorable conditions of light. Purple

leaf tips, for example, are visible just asthey emerge between the two cotyledons,but a day or so later they cannot be dis-tinguished from green. Bronze stemsmay be confused with green stems un-less classification is made in the laterdevelopment of the plant. If proper

care is exercised in classification, allthese characters are useful in a geneticalstudy of sesame. They are particularlyvaluable in reference to flower and seedcolor. A complete discussion of the re-lations of the three will be made at afuture date. S u m m a r y1. Brief descriptions of seven seed-ling colors and five plant colors are given.2. The mode of inheritance of mostof these is discussed.3. The importance of the time factorin making classification is emphasized.

Literature Cited1. BAILEY. L. H. The Standard Cyclopediaof Horticulture. Vol. Ill, pp. 3157.2. LANCHAM, D. G. Circular Xo. 4, Insti-tuto Experimental de Agricultura y Zoolecnia(Depto. de Genetica), Venezuela. 1943.

-Science 103:2670. p. 280.(abst ract ) . Genetics.

-Circular No. 18, Minis-3.256. 1944.4.152. 1946.

Jour, of Hcrei. 35:254-Jour. of Hcrcd. 37:149-

1946.6.1946.7.

terio de Agricultura y Cria (Depto. de Ge-netica), Venezuela. 1947.8.224. 1947. Jour, of Hered. 38:221-



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378 The Journal of HeredityNone of these investigators recordednausea caused by P . T . C . in the amountsused for testing, although some of theirsubjects must have had far greater dosesthan the two concerned in this note.( F r o m the unused portion returned, itwas calculated that those tested in thisfamily each had used about one-third ofa square inch of the tes t paper. Th iscontained whatever amount of P . T . C .was absorbed during immersion in a 0.5per cent solution in ace tone) . Two per-sons tested by Blakeslee and Fox didbecome nauseated, but both had takenby mistake many times the proper dos-age of the actual crystals. Dr. L. H.Snyder (private comm unicat ion) wri testhat he has known people to complainthat P.T.C. almost nauseated them, butnever to the point of actually vomiting.It is easy to say that nausea is notunusual and that the occurrence of thesetwo cases inone family is merely a coin-cidence, but it would be difficult to con-vince the family concerned with thatargument . Obviously, the experimentshould be repeated, but, while it is allvery well for Haldane to drink dilutehydrochloric acid, or for the writer togorge himself on chicken said tobe load-ed with estrogenic hormones, there arelimits to the experimentation that onemay ask of a six-year-old child and hergrandfather.

It isworth noting that neither of thesepersons became sick at the time of chew-ing the paper, but that both did so whileasleep two or three hours later. It isdoubtful if many adult persons testedwith P.T.C. have been asleep within ashort time thereafter, as most such testsare made during working hou rs . Couldsensitivity be heightened merely by in-activity, by sleeping, or by recumbentpos ture? Althou gh this last suggestionseems far-fetched, it may be recalled thatone genetic character in man is mani-fested more readily in patients flat ontheir backs than otherwise (asthma)and that another is suppressed simplyby lying down (urobi l inuria) .As far as they go, these two cases inone family only suggest that there maybe an extreme sensitivity to phenylthio-carbamide and that it may be genetic.They are noted here merely so that otherinvestigators will be encouraged to re-port similar instances if they occur.

Literature Gted1. BLAKESLEE, A. F. and A. L. Fox. / .Hered. 23:96-107. 1932.2. Editor. /. Hered. 23:107-110. 1932.3. FALCONEB, D. S. Ann. Eugen. 13:211-222. 1947.4 . HARTMAN, G. Ann. Eugen. 9:123-135.1939.5. SALMON, T. N. and A. F. BLAKESLEE.Proc. Nat. Acad. U.S.A. 21:78-83. 1935.6. SNYDER, L. H. Ohio J. Sci. 32:436-440. 1932.

Postscript on the Diabetes-Non-Tast ing Corre lat ionO E V E R A L in te rest ing quest ions were rai sed by the correlation between diabetesO melitus and inability to t a s te PTC, as reported by T e r r y and Segall in theMay 1947 issue of this JOURNAL. The authors suggested the possibili ty that non-tasting diabetics may be genotypic tasters. Can it be that non-tasting in diabetesis non-specific for P T C ? Have any tests been made to determine whether a lessen-ing of taste acuity in general accompanies diabetes ? Has the possibility been ex-plored that there may be a correlation between non-tasting and insulin ? Thefollowing reply was received from the senior author.TO THE EDITOR:

The data from which our paper waswritten contain no answers , I am sure ,to these questions. I am no wiser as tothose particulars than I was severalyears ago when, after testing 36 persons,diabetic and non-diabetic, I saw what I

saw, viz., 46 per cent of non-tastersamong thediabetics. All I have got, forsure, from the present much larger num-ber of observations is assurance that theundertaking was worth while .I have not inquired how far out ofbounds the following ideas may be with



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DiabetesPTC Postscript 379respect to genotype and phenotype; butI have thought that an experiment withalloxan and rabbits, white rats, or dogs,might turn up something new. W hiterats would be best because of rapid re-production (and because they wereavailable to me in the Department ofAnatomy), dogs best for a better reason,viz., their known susceptibility to dia-betes.I tested a few dogs (and even a fewbirds!) and found that, with one excep-tion, the dogs showed a strong dislikefor P T C . Th e one exception was a veryfat, very old, Cocker Spaniel bitch whois much of the time under a veterin-aria n's car e. She does not object to thetaste of any medicine he gives her. Sh emay be diabetic for all I know.Blakeslee et al (at Smith) made astudy on threshold recognition of thetaste of P T C ; but, of course, withou tany thought of diabetes.Alloxan diabetes, they say, may becon trolled indefinitely by insulin. If so,experiments could be devised.There are exogenous factors in theincidence of human diabetes. The Met-ropolitan Life Insurance Company men-tions some of these in their pamphlet ondiabetes and undertakes to give advice.In a 1945 number of the Nezv EnglandMedical Journal, (233[13] :376-78),Dr. H. C. Miller presents some evi-dence for a "prediabetic state" operative,in his cases, well before the appearanceof the disease but not discovered un-til long thereafter. Pe rha ps PT C mighthelp to identify such "prediabetics." Dr.Miller's data consist in the followingmortality rates for "prediabetic" andnon-diabetic mothers at childbirth.

N u m b e r N u m b e r N u m b e rS t a t u s of of of of infa nt M or ta li tym o t h e r m o t h e r s b i r t h s d e a t h s r a te %Xon-d iabe t i c" P r e d i a b e t i c " 5957 253264 522 2.08.3

T h e difference is highly significantstatistically. All of the 57 "pre diab etic"mothers were non-diabetic at the time ofdelivery. All 57, it was discovered, de-veloped diabetes later, but none before40 years old.Dr. Best, of Toronto, has a chapterin a new book entitled, Currents in Bio-chemical Research, in which he says(page 431) in speaking of the possibleprophylactic use of insulin: "applica-tion will not be easy until the potentialhuman diabetic can be recognized much

earlier tha n is possible at pre sen t." Itis barely possible that PTC or the likemight be of some service here.There is a diabetic woman here whosays she can tell by a bitter taste in hermouth when she must take her shot ofinsulin. N eithe r jus t before taking theinsulin nor at any time before or afterdoes she detect the taste of PTC.It looks as if the Negroes may con-stitute a special case.

M. C. TERKY, M.D .P.P.S. As to the possibility that insulintherapy (or diabetes itself) may change a tast-er to a non-taster, we may have to wait untilthe youngest diabetic known to be a taster isold enough to have the trophic ulcers of thedisease. I have but one case to the pointapatient who was a tasterand so remains.The following was contributed by a physi-ologist who knows some of them: "There arediabetics who do not take insulin; if they weretested they would show a low I.Q ." Pro jec-

tion: Insulin is taken now by all diabeticssmart enough to get it W ider use would tendto preserve an unwanted mutant gene for sus-ceptibility to diabetes, to lower I.Q. and tomore diabetes 1It isn't insulin that makes smart diabeticssma rt, it keeps them sm art longer. If any con-trollable exogenous factor in the causation ofdiabetes is found,* the use of insulin may beexpected to raise the I.Q. and decrease dia-betes ! Therefore: On with surveys, experi-ment, and theory. M . G T .See the control chart for poliomyelitis in California (Rich and Te rr y: Public HealthReports Vol. 61, No . 42. 1946). Also the rep ort on diabetes in a New England town, J.A.M.A.Sept 27, 1947. There are two other recent articles of some relevancy: 1) C. W. Jungablut:Annals of Internal Medicine 26:1, 1947, and 2) M. B. Frank: Proc. Soc. Exp. Bio/, and Med.62:1, p. 17, 1947. The first correlate s blood grou p A 3 with paralytic poliomyelitis, and thesecond correlates it with filariasis.

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