: ) - t N O T E S O N T H E P P , , O G E N I E S O F V A ] , , I O U S

:POTATO H Y B I ~ I D S .

By WILLIAM BLACK, B.So.

(Scottish Pla'nt-Breeding Station, Corstor chine, Midlothian. )

(With One Text-figm'e.)

CONTENTS.

In t, roducgiou Flowm, colom, . Tuber colom' Tuber flesh colom' Tuber shape Eye depth Summary Litera,tnrc cited

]~A(I]']

27 28 gI 20 ,-37 4:0 4:2 4:g

INTI%ODUOTION.

IN experiments a,t the Plant-Breeding Station, Corsto]:phine, to obtain new and improved varieties of potato, plants of many varieties have been hybridised. In the course of this work data have been collected with reference to the modes of inheritance of several characters in various progenies, and an endeavonr has been made to discover which w~rieties, when hybridised, give the best results as judged by economic standards.

To obtain satisfactory comparisons of hybrid progenies it is necessary to have some asstu'anee that the seedlings are all hybrid plants of known parentage. Therefore in all cases where the variety used as female parent produces viable pollen, the flowers were emasculated before opening and thereafter protected by pergamine bags. When they became fully open and receptive, pollen was taken from the anthers of the male parent and applied to the stigma of the female. The pergamine bag was then replaced and[ allowed[ to remain in position until the berries had set. Where the female parent was fotmd to be devoid of viable pollen emasculation was omitted, but ~he flowers were protected as before. Every precaution was taken to prevent the introduction of foreign pollen, and the progenies which, wi]l be enumerated can be regarded as true hybl~ds of the parentage stated.

That all modern commercial varieties of the potato are more or less

28 Potato Hybr ids

genetically impm'e has been suggested by l~obb(s) and others, and this view appears to be generally accepted. In the following notes attention will be confined to a few ougstanding characters.

A list of the parent varieties of hybrids described in this paper, together with a brief description of. each parent, with regard to five characters, viz. flower colour, tuber colom:, flesh colour, tuber shape and eye depth is ]?resented in Table I. The first eight varieties in the list are well-know:u commercial varieties, and further information concerning them can be obtained from Miscellcmeous Publications, No. 3, of. the Board of AgricNtm'e for Scotland(% from Potato Varieties by 1r N. Salaman(9), or from. The .Potato by T. P. NcIntosh(7).

TABLE I.

List of parent vaq'ieties. Flower T~tbor Tuber Tuber :Eye

Variety colonr skin colom' flesh eolonr shape depth :British Queen White White White Oval Shallow + ]gpicnre White White reddish White I~onnd Deep

purple Flom'b~ll White, tinted P~Io reddish White l%onnd i~ledinm

pml)le pro'pie Glassel 7geo, nty White Pale reddish White I/,ound Shallow

purple Golden Wonder Purple, tipped :R,nsset (white) Whlte+ Kidney Shallow

wlfite Great Scot Wlfi~e White White + I~onnd Medium - Km'r's Pink White Pink White l~ound h'[edium + U1)-to-date Gighb reddish White White Oval Shallow

purple :Bell White White Pale yellow ~omtd M.edima 39 (15) P~eddish purple, White Pale yellow Kghmy ShMlow

tipped white 800 (2) White White White I/,onnd Medium + 993 (a) (4) White White Pale yellow Oval - Shallow +

White+ =white inclining to be pale yellow Oval - =oval inelhahtg to be round Shallow + =shallow inclinhtg to be medium ~iedimn- = medium inclining to be shallow ~'Iedinm-b =medium inelitting to be dee r

~- LOWEI~ CJOLOUI~.

Salaman(9) has distinguished two types of flowers which arc com- monly known as white, viz. "pm'e white" and '"tinted white." The latter possesses a small ammmt of pigment, more i'cadily fonnd in the bud, and is usually COllfilled to the under sm'facc of the petal. It is claimed by the above author that the two types referred to arc distinct, and that their rmion by hybridisation would result; in the prod.u.ction of a certain number of offspring bearing hdiotrope-coloured flowers.

W. BLacI,: 29

Pm'ple i~ ~hc :flowers, a, ccording ~o East (5), is dominant to i~s a,bsence, a~ld Sa]a,man 0o) suggests that he]iotrope colom' is due to two factors and purl?le to a third.

[Fertility in the poga,to :is controlled by genetic factors (Salaman(l:t)) which include a dominant factor inhibi:bing the formation of pollen. That there :Ls a difference between the degree of sterility conveyed through the egg ~md that eo~lveyed through the pollen to the next generation is saggested by Sal~ml~m and Lestey 02). Clark (3) distinguished fern' difl!erent types of sterility in the tnber-bearing Sohmmns.

TABLE II.

Class~ification of the hybrid progenies ,with ~'eqard to flower col, our.

Flowering seedlings

Total No. No. no. o[. Term No. reddish bluish

Paren tage seedlings no. white imrple purple IV/~,~;te x l lZ /dte

Eplenre x l?lottrball 71 21 21 0 0 ]3ri~ish Qneen x l?lom'bMl 51 19 19 0 0 ]s P ink x li'lom%Ml 75 28 28 0 0 Gt'e~t Scot x 993 (a) (4) 62 28 28 0 0 ] (er r ' s P ink x Boll 311 31 25 2 4: Gre~t ,Scot x [Bell 288 25 16 9 0 ]~'lom:ball x Glassel BeanLy 28 4 2 2 0

Coloured x W h i l e Golden Wondm' x 800 (2) 9 5 5 0 0 l-[p-~o-d~te x l~lom'bM[ 57 18 15 3 0 Golde~t Wonder x G.lassel Beattty 56 28 15 11 2

l,Vh, itc x 6'olou,red K e r f s P ink x 39 (15) 52 25 14' 11 0

The majority of the parents of the hybrid progenies shown in Table II possess white flowers but apparently they are not all alike in genetic constitution. Four progenies containing no coIom'ed-flowered seedlings were derived from the white-flowered parents Fl.om%all, Epicm:e, British Qtteen, KerFs Pink, Great Soot, and 993 (a) (4). Two of these varieties, viz. KerFs Pink and Great Scot, mated with another white- flowered variety Belt, produced both colom'ed- and white-flowered seedlings, but in significantly different proportions. This indicates that Bell is a heterozygous white; and also that KerFs Pink and Great Scot possess different genetic constitutions signifying that both cannot be pure whil]es.

Flora'ball, commonly known as a white-flowered variety, is really a "tinted white" since it possesses a small amount of pigment on the nnder-sm'face of the petal, tb should, therefore, according to Salaman's hypothesis, produce, on crossing with a pm'e white, a oerbMn number of

30 .Potc, to Hybr id ,

offspring bearing heliotrope-colonred flowers. No colortred flowers, however, appeared in these experiments, t~esults of five hybrid pro- genies may be mentioned, derived t!rom Flonrba]l as @ parent :in each case, and Epicure A, Epienre ]3, ]3ritish Queen, K e r f s Pink and Ally as ? parents respectively. Out of a total of 449 seedlings, 119 iprodnccd flowers, all of which were similar to one or other of the pa.rents ill respect of flower colom:. A few " t in ted white" flo~vcrs appeared but no hclio- trepe ones.

lr however, when mated with Glassel ]3earthy (white-flowered) gave equM ]?:ropor~ions of whi~c and eolonred flowers in the offspring. Gtassel ]3tangy is therefore probably a heLerozygoas white.

I t appears then tha t " t in ted white" • "pure white" gives t inted white and pure white, and tha t " t in ted white" • "heterozygons white" gives eolom'ed and white, the latter probably including pare whites, t inted whites and heterozygoas whites.

Of the two families derived from Groat Soot x Bell altd Great Scot • 993 (a) (~t) (all white-flowered) the former contained both eolom'ed and white flowers in the proportion of 9 : 16 respectively, while the latter prodneed nothing but white flowers. The ? parents being the ~same in both cases, the difference in results mltst be due to differences in the hereditary factors of ~;]le pollen parellts. The variety ]Bell is, therefore, apparently hcterozygons for flower eolom', while seedling 993 (a) (4:) ~t least shows no signs of hetcrozygosity in tha t respect.

None of the progenies derived from a eolom'ed variety crossed with a white-flowered one, or vice versa, co,trained a majori ty of eolom'ed- flowered seedlings. From the evidence, this oeenrre~me seems to be due t6 the parents possessing heterozygons constitutions for flower eolom'.

In potato hybridisation it is invariably fonnd tha t a fair proportion of the seedlings either do not produce flowers which reach maturi ty, or do so only sparingly. The proportion may vary considerably as, for example, in the two related t!amilies derived from Great Scot • ]3ell and Great Scot • 993 (a) (~t) (see Table III). The former produced 8.68 per

TABLE iII.

Comparisons of flower colour, etc., Of three hybrid progenies. �9 % o~ % of % of % of

No. of flower- white- coIoured- self-fertile l?lang.~ boa.ri~lg flowered flowered seedlings

:P~rentage (a,ll white-flowered) in progeny seedlings seedlings seedlings (nal~ural) A. Clreat Scot xlBell 288 8.6 64 36 0 iB. (~h'eat)Scot x 993 (a) (4) 62 ~t5-1 100 0 75 C. lierr's Pink xlBell 311 9-96 80.64 19.36 0

W. ]~LAC~ 31

cent. flower-bearing seedlings, all self-st;erile, and the latter 4:5.16 ]?el: cclit, of which 75 per cent. were sclf-fcrgile (nataral).

These plants were tested over two years since first-year seedlings can.no~ be relied upon to exhibit their full flowering propens2gies. Bell has apparently a tendency go produce few flowering otlspring, and those wlhi& did flower were in this instance self-st, crile. A fm'ther example of the effec~ of Bell is seen in the family derived from Kerfs Pink and Bell where 31 plan~s out of 311, or less than 10 per cent., succeeded in pro- dueiug flowers in a ~es~ lasting '~wo years. Here, again, all were self- sterile. The two varieties, Golden Wonder and Glassel Beauty, when crossed produced 50 per een.t, of flowering seedlings of which only a few were naturally self-fertile.

The c2 parents, Bell and 993 (a) (4=) (Table III) exhibit wide differences in constitution although both are naturally self-:fertile. A suggested difference be~wecn the degree of c? sterility conveyed through the egg and that through, the pollen, to the next gcncra,t~ion (Salaman and Lesley(:t2)), and. the distinguishing of more than one type of stcrilit~y by C31ark(3~, point towards a complex inhcrit~ancc of that character which consequently cannot readily be explained in terms of single factors.

The abscission of flowers is considerably influenced by environ- merit, but appears to be controlled go some extent by genegic factors also. There are different varieties which, although apparently pos- sessing equal free-flowering capacities in themselves, are widely different in constitution for flower production. Scarcity of flowers may be due to a dominant factor inhibiting their production. -Were this factor eliminated by inbreeding there would be no di~culty arising through lack of flowers in proceeding through an. indefinite number of generations. This in itself, however, is insufficient since there is practically no corre- lation between flower production and self-fergility. Both free-flowering sterile plants and scanty flowering self-fertile plants are common. On the ol~her hand, once a free-flowering self-fertile line is established it should remain so ghrough an indefinite number of selied gcncr~tions.

TuBEI~ OOLOUI~.

A wide range of tuber eolom' exists in the potato. Pr~mtically all the shades of reddish pm.ple and bluish purple h~ve been :found, ranging fi'om jusg a slight t~racc of rcdd!sh pigment at the one extreme to a deep bluish, purple at the other, tn addition to these sclf-colourcd types there are others showing colour on a part of the tuber only, the remainder bcitlg uncolourcd. Further, there are tubers showing individually more

32 Pots, to Hybrid8

than one shade of colom'. The ground colottr may be pale but splashed wibh darker pabchcs, or the ground colonr may be reddish pm'ple with bluish pm'ple markings on it. There is also another type which does not produce colom' in the absence of light bn~ which, on exposure to light, prod.nets an appreciable amount of pigmenb. The in:bensity of ]?igmen- tabion may increase with prolonged cxposm:e.

In. the case of va,riei~ies with :faintly coloured tubers, Kelly(0) suggesl~s. the existence o~ a factor restricting the production of colour as fotmd in "Red NeOormiclc." Uniform distribution of colom' over the tuber surface is introduced by a factor S (SalamanO)). Col]ins(<l), working with t~ihe King Edward variety, says that parti-eolour in that variety depends upon a definite factor for which it is heterozygous. I:fe suggests that it behaves as a dominant to recessive white and as recessive to fN1 colour. Production of colom' in the eye of the tuber, according to Salaman (,a) and AsscycvaO), is dependent upon. sgill another factor.

Distribution of colors' in the tuber will be disregarded in this dis- cnssion. In classifying tubers a~cording to colom' three groups will be used, viz. white, reddish purple and bluish pm'ple.

Salaman considers that reddish colom' in potato tubers is controlled by two factors, D and R, which independently produce no colour. D is a basic factor necessary for colour production and t l is a reddening factor. A further factor P modifies l:l, producing a purple colom'. Stuart03), on l~he other hand, from a s tudy of the hybrid progenies of

TABLE IV.

Classification of hybrid progenies with regard to tuber colour. Tnbm: colom'

Toi~al c ~ no. of No. reddish No. bhfish

Pm'oni~go seedlings 51o. whi~e ptu'ple lmrplo White x White

G.reaI~ ScoI~ x :Bell 288 284 ~l 0 Golden Wottdor • 800 (2) 53 51. 2 0 C4t'eal~ ScoI~ • 993 (a) (4:) 62 50 12 0

]'Vldle x Redcl'ish Purple J3rils Qneml x Iqonrba.ll 51 26 25 0 Up-go-da, box ]flonrb~dl 57 29 28 0 Golden Wonder x Gla, sso]. I~c~mby 136 62 39 35

Red, dish I~'~n'l)le x W l d t e I(err 's Pitfl~ x te l l 311 202 109 0 ](err 's ]?ink x 39 (].5) 52 26 26 0

Reddish Pu~'ple x Reddish 1J'urple I{.m'r's ]?ink x ;t~lourball 75 30 d:5 0 ]~'lourb~l] x Glassd ]3e~ufl~y 28 11 17 0 E1)icm:e • lVlourb~dl 71 24 47 0

Not< Goldml Wondm' is lmrdn considm'ed as a white-imbm'ed varioI~y since I~lm rns.seI~ skin a,1)pavmai~ly does noI~ t~ffeol~ I~h.e gmmI~io oonsi~iiafl~ion.

W. B~ae:rr 33

white and colom'edl parents, wherein he obtains a consistent majority of white-tubered seedlings, coucludes tha t "wh i t e " :is not a recessive character in the.seedlings of the crosses he dealt~ with.

According to Salaman both F]om'ba]l and ~l].assel Beauty are hetero- zygous for the factors D and R and give, on selfing, a progeny in tile proportion of 9 seedlings bearing coloured tubers to 7 bearing white. A simi]ar proportion was obtained by the writer in the case of ]?lourball. (selfed), and also in a cross between the two varieties Flourba,ll and[ Glassel Beauty. The colom'ed tubers posgessed the red pigment but not the pm']?le, and the range extended fl:om a, medium red to a flush of pfilk, The family consisted of 28 seedlings, of which 1.7 ware coloured alld I1 white.

In the family of. 51 seedlings derived from British Queen and[ Flourball, 25 })ore coloured tubers and 26 white. Various shades of red were noted bnl; ~tone of the tubers possessed purple. Since British Queen is a white- tubered variety it must be heterozygous, possessing at least oHe of the factors necessary for colour. A variety witlh the constitution dd.RR would give with Flora'ball equal mmlbers of coloured- arid white,tubered off?spring. One-half of the coloured tubers would be darker than the other half, and the whole family would be heterozygons for tuber colour. As these proportions were obtained in the above cross, British Queen may be consiclered to have the constitution ddRR.

Similar results were obtained from tlhe cross Up-to-data and Flora'ball, and[ the constitution of Up-to-de,re is therefore considered to be the same as tha t of British Quean., viz. ddRR.

In the cross between l(err's Pink and Flora'ball the numbers of coloured- and white-tubered offspring obtained ware 4-5 and 30 re- spectively. The tubers of l(err's Pink are pale pink in colom', and since it must contain the factors D and R, there are indications tha t an inhi- bi.tiHg factor is also present. If such a factor, called It , is introduced wh.ieh inhibits the action of D, but is incompletely domiHant to it ill plants homozygous for R or P, then. a possible explanation may be rea.ched. Thus a plant, either homozygous or heterozygous for both D and H bug homozygous for I~ or P, would produce a trace of colour, herein termed a flush. On this basis Kerr's PiHk may be DDRrHh, a~d when this variety is crossed with Flora'ball, Dd Rr h h , coloured seedlings and white seedlings in the proportion of 4-0 to 24, respec- tively should be produced.

Epicure, which develops a red fl.ush on exposm:e to light; may be described as possessing the colour factors DdRRHh. SiHce the results

J o u r n . of Gen. xxn: 3

3~1- Po~a, to Hybrids

obtained by m,%ting it~ with l~'lonrball are eompa:r`%ble with those o:[ Kerr 's Pink and Flourba]l, and since Epiem'e possesses much less colour th,%n Kerr's Pink, it must be heterozygous for D and homo- zygotts for I~ to give the necessary proportion on the ,%ssumed b,%sis of :l!ac{~or rel~tionship. The factorial constitution D d t l R H h stands for a, flush el'. red, and on ma.ting a, pla.nI~ of I~,his type wis one ot! the D d R r h h type (e. 9, Flora'ball) a, proportion of 40 ]?lant~s colonred to 2~s plants white should be obta, ined. In the cross bet;ween El?ie~Lre and Flourball the proportion of 47 colom'ed to 2t whitc-ttlbered seedlings was obtained, and. is a dose approxima,tion to the theoretical expectation. In breeding work, therefore, Epicure should be considered as a colonred variety.

K e r f s Pink crossed witlh Bell g`%ve a family of. 311 seedlings, of which 109 bore eoloured and 202 white tubers. This proportion be,%rs a, close resembla.nee to ,% 2~L: 40 ratio. The trtber eolom' ranged from nl.edinm red to a ]?ink flush. It'. it is assumed that Bell can be represented :faetorially by Ddr rhh , it shortld give, on mating with K e r f s Pink, DDRrHh, 2~ eolonred to ~1:0 white.

The seedling 39 (15) gave a higher proportion of eolom'ed-tubered ot~!s]?ring than Bell when mated to Kerr's Pink, viz. 26 eolom'ed to 26 white. The factorial constitution ot! 39 (15) may therefore be described as DDrrhh.

In the family of 288 seedlings derived from Great Scot and Bell, four showed a trace of eolour in the eyes o:~ the tubers, l~'rom other breeding results it would appear tha t @.teat Scot when ma,ted with Bell should give nothing but white-tu.bered o~spring. The reason for the occurrence of fern' plants displaying slight eolotu' in the eyes of the tuber is obsem'e, but it is possible they may have arisen th.rough the interaction of factors :for eye eolour. If such is the case there is this and other evidence in favom' of-the fa, etorial constitution, as regards the tuber eolom', of Great Soot being described as DDrrhh .

Great Sect mated with seedling 993 (ce) (4) produced 62 pla,nts, o:1! which 12 were eolom:ed and 50 white. This is an a,]?l?roximation to a 1 : 3 ratio. The eolom'ed tubers were all flushed pink. The results were simila, r to those obtained from a !amily derived from British Queen and 993 (a) (~l:). With Great Sect bearing the taetors DDr rhh , British Queen d d t l t l h h and 993 (c~) (~) Ddlqr I IH the above results would be obt,%ined.

Before considering the hybrids from Golden Wonder it may be of interest go quote the results obtained when that vari.e/~y was self- fertilised. The family of ].9g seedlings showed a great variety of eolour,

W. BLACK 35

ranging t!rom deep purple through various shades of red to white. Cla,ssifi.eation was rendered difl3eult owing 4o the dit~!ereng eolours merging into one another, but, an a,ggelnl)g was made 4o classify ~he plants int;o three groups. In this classification 4:7 were "reddish," !7 "purplish" and 99 white. The other t'a,egor, P, apparently comes in.go pla,y ]1ere. It a,ppea,rs ghag this factor nob only modifies t l bug is capable of producing ,.t purple eo]oltr in eombinat~ion with D.

J?rol11 ~hese results ii; is assumed gha,i; for tuber eolour t;he genetic constitution of @olden Wonder is DdtlrPpI-Ih, that is, ig is hegerozygous for a,]l i;he fa,cgors concerned. This variety on selfing should, on this hypothesis, give a family of seedlings in the ratio of 110 eoloured t;o 1.4:6 whige-tubered plants. Of the eoloured seedlings, 40 should contain more " red" than "purple," ~1:0 more "purple" ~han "red," and 30 equal proportions of " red" and "purl)le" t!aetors, and would be represented in 3~1 difl!erent genotypes. There would be 47 different, genogypes among t;he whJt;e-tad)ered oil!spring , and only 1 in 256 would be homozygous for' all t~he recessive fae~gors.

Golden Wondd' crossed, with Glassel Beauty produced a family of 136 plants, of which 7,t bore eolom'ed tubers and 62 white. 39 of the eolonred progeny were reddish and the remaining 35 purplish. The eoloured types ranged from pale red go deep purple. If t;he genetic constitutions of Golden Wonder and Glassel Beauty arc DdRrPpI-Ih and Dd t l rpphh respectively, a 128 : 128 ratio of eoloured and white tubers should be obtained. The actual ratio obtained-agrees fairly well with exl?eetathon. Salaman(lO) and .Kelly(0) suggest the possibility of a dis- 1)ropori;ionai;e mortality of "creams" in certain families, and the slightly smaller proportion of white-tubered seedlings in this ease may be similarly accounted for. Theoretically, of the 128 eoloured seedlings, 56 should be red, 56 red with purple and 16 purple only. There should be 1.7 different geuotyl?es among the eolom'ed offspring and 19 among the white. One plant in. 64 should be recessive for all the factors concerned.

Golden Wonder crossed with 800 (2) produced 51 white-gubered and 2 pink-flushed offspring. This result points go the absence of eolour- producing factors and the presence of an inhibiting factor in gh.e seedling 800 (2), and its genetic eonst;igugion may be described as ddttrppI-II-I. It should give, on crossing with a variety represented faegorially by DdRrPpI-Ih, 8 red flushed and 8 reddish pm'l?le flushed individuals to 240 white, i.e. a ratio of 1 :flushed ~o 15 white.

3-2

36 Potato Hybr ids

TUIBElg FLESIt CJOLOUI~.

Comparatively little is known of the inheritance of :flesh. eolour fit potato tnbers. A disturbing element is occasionally found[ in the presence of aarthocyaniu pigment in the flesh where it may affect the whole or only part of tlhe internal eolour of the tuber. The presence of such pigment is often, associated wit]l skin eolour, and is found in snob varieties a.s Flonrball and Congo, but pigmentation has been observed by Wilson(l.4). in white-skinned seedlings of a hybrid progeny, and also by the writer in immatm'e white-skinned seedlings of an inbred family. A small proportion of the seedlings derived from Kerfs Pink x Flourball and ]~ritish Queen x Flonrball possessed, tubers with pigmented flesh, ]nrt iu every case the skin of the tuber was colonred. In m.aking comparisons of flesh colonr, the shade of white or yellow is considered, apart from the infusion of any anthocyanin pigment.

In the ordinary comm.ereial varieties the eolour ranges :from white to yellow. SalamanO) considers that flesh oolour is controlled by a single pair of factors represen.ging deep yellow and white, ~hat deep yell.ow is dominant and white recessive, that both breed true, and that the hetero- zygous form is a variable but pale shade of yellow. In ordinary com- mercial varieties deep yellows and pm'e whites are seldom fonnd. Pale yellows vary from one extreme to the other, and[ diflloulty is experien.oed in classification since no definite line of demarcation can be readily fixed.

TABLE V.

Ulassi, fication of hybrid progenies iv'ith reyar3 to,flesh colour. To~al no. No. pale

Parentage of seedlings No. white yellow No. yellow I'Vl, v~te x J'Irhile

9 { K e r f s ~ ink x Flourbal l 75 66 9 0 U1)-~o-dato x ~'lom'ball 57 44 13 0 Golden Wonder x 800 (2) 9 5 4 0 E1)icuro x Flourball 71 32 38 1 Golden Wonder x dlassol ]3oaul~y 43 11 27 5 Flourbal l x Glassel [Beauty 28 5 23 0 [British Queen x Flourba!l 51 3 47 1

White x .Pale Yel low K e r f s P ink x ]Boll 311. 173 133 5 Great Soot x 993 (a) (4) 62 19 43 0 Groat Sool; x Bell. 288 71 187 30 I~2orr's P ink x 39 (15) 47 Id: I2 2I

I~esnlts of the hybrid progenies with regard to flash co]our are shown in Table Y. It appears that the majority, if not all, of tt['e varieties used in the matings are heterozygous for flash, eolour. Whites when inter-

W. :BLACK 37

crossed should, if pure, t)hrow not)hing bug whites; but~ apparentfly from varieties commercially known an whit)cs, t)herc i~s a great~er likelihood of obt}aining a majorit)y of pale yellows o1: hybrid intermedial~es t~han a majoril~y of whites. The eommereiM description of varieiies cannot~ be l~aken as indieal~ivc of their gcnotypie nalmre. Pure whil~es, being recessive, a.re probably scarce, and the parent variet~ics used in t~he experi- ments were probably hybrids; but m a n y were so very pale in flesh eolour as to appear whit;e. The mat;ings of so-called white-fleshed varie- ties l?rodaeed widely diffe:rent; resnlt;s and t;hree families exhibil;ed a sma}l pro]?ort;ion of the detain.ant yellow type.

In. every ease gl]e families were the offspring eit;her of two wNt, e- fleslmd varieties or of a white-fleshed and a pale yellow-:fleshed variety, and consequently yellow-fleshed seedlings were seldom fmmd. 8aecl~ing 39 (15) appears t;o be genetically the deepest yellow in t;he series, s'ine'e ig prodaeed the highest~ proportion of yellow-fleshed plants when crossed with the white-fleshed variety Kerr's Pink.

The various di~stinet ratios obt~ained and t;hc wide range of hybrid forms suggest t~h.e ]?rcscnee of more than on.e pair of factors controlling the inherita.nee of flesh eolom:.

TUBE~ 8~APE.

An. exptanat~ion of the heredity Of tuber shape is given by Sataman (9,1% who says that shape, in t;he main, i~s controlled by one ]?air of fact;ors, "long" and "shori~." Long is dominant go short bug sometimes not completely. Bot)h types breed true. The hybrid form i~s kidney. This gives three well-defined sh.apes and the numerous remaining shapes are modifications due, in some eases, to fmCher quMifying hereditary reciters, and in others to environment;el influences. A modN.catory factor convcrt~s "ronnds" to "pebbles." These "pebbles" 5vhen crossed witch the hybrid form, kidney, give a high percent)age of kidneys as well as 25 per cent. pure rounds. The variety, Ftourball, :is not a l~rue round, since on selling it gives longs and rounds in gh.e proportion. 0f 3 : 1 respectively. Another form of long is t~he cylindrical, of which Congo i~s a l?ure llype, iBrit)i~sh Queen is a short form of cylindrical.

A classifieal)ion of tuber shapes is given by McInt~osh(7) wherein all shapes are eit)ber rounds or longs, the latter inc]n.ding ovals (short; and long), pear-shaped and pointed-oval types. The dominant long referred 1~o by SMaman is in t)his classificat~ion termed "long oval."

Foi' simplieit)y tuber shapes are herein grouped under fortr headings, viz. l%onnd, OvM, Kidney and Long, and lfllesc d.escript~ions refer more

38 P o t a t o H y b r i d s

�9 ~o the relation of length and b read th t h a n to any individual pecul iar i ty of shape.

In Table VI ig is seen t h a t nnmm'ons sha]?cs eail be obtained f rom intercrossing r o u n d - t n b e r e d varieties. Ill m a n y respects t h e result;s obta ined are compal 'able. Thel.e are present; in each progeny, round, oval and k idney-shaped seedlings, and in every ease the figm'es show t h a t ovals were in the major i ty and ]ddneys in the minor i ty . Flora:ball is eonlmon ill the paren tage of tllree families showing similar proport ions, eonseqnent ly the obher paren~s concerned, viz. C41assel Beauty , Ker r ' s P ink and Epicure can be emlsidered aPl?roxima,tely similar genotypes.

TABLE VI.

6'lass,ification of hybrid progenies 'with regard to t~&er shape.

To~rd no. Prbrml~go of seedlings No. round No. ov~l No. kidney No. long

Round x l~ound .I~m'r's l~ink x Bell 311 147 ~. bib 1.4 2 lqom'ha.ll x Glassel Berm~y 28 9 17 2 0 I~m'r's Pink x Flom:b~fll 75 18 51 6 0 Gro~ Sco~ x Boll .288 65 201 22 0 :Epicure x Flourbrdl 71 12 56 3 0

7~ound x Oval G r o ~ Sco~ x 993 (a) (4) 62 4 53 5 0

Oval x l~ou~d Up-t~o<lMm x Flom'b~ll 57 23 34: 0 0 Brli~ish Queen x l?lourbM1 51 6 33 10 2

Round x J~:dney Km'r's Phfl~ x 39 (15) 52 5 35 12 0

J(idney x Round Golden Wondm' x Gla,ssol Boaul;y 136 16 66 33 21 Golden Wonder x 800 (2) 53 0 27 21 5

Different propor t ions were obtained f rom Kerr ' s P ink • Flora'ball and KerFs P ink x Bell. The former cross exhibited a large propor t ion of seedlings bearing oval-shaped tubers, a lmost three times as m a n y ovals a,s rounds, while the lat ter gave pract ical ly equal numbers of rounds and ovals. I n bo th cases a small pro]?ortion of kidneys was ~ound, bu t only in. the progeny of Ker r ' s P ink x Bell did longs appear. I t is probable t h a t longs would also ap]?ear in the ,p rogeny of Ker r ' s P i n k • Flora'ball if a comparab ly large n u m b e r were grown, since the average tuber shape in this family possesses a relat ively longer axis t h a n t h a t of the family derived f rom Kerr ' s P ink • Bell. Bell a]?pears to be less heterozygous for the factors t:o1' rormd- tuber shape than.Flourbal l , and a l though bo th are po]mlar ly t e rmed l 'ound-tubered varieties, the lat ter breeds more as a,n oval t han as a round.

Kerr ' s P ink and Gl.eat Scot, as 9 parents, wm:e crossed with Bell.

W. BLACK 39

From the fignres it is obvions that KerFs Pink breeds trner to round than Great Sect. I t throws a higher percentage of ronnds and a ]owes percentage of ova]s and kidneys than Great Sect.

In the class formed by mating an oval with a ronnd there are two progenies slhowing diverse resnlts, a]thortgh the parents, Up-to-date x Flora'ball, and British Qaee:n • Flora'ball, are comparable: Th.e eou- stit atJo:aal difference lies in the ? ]?arm:rts, since the c~ ]?areut is the same :in both eases. Up-to-date x Flora.ball has a tendency to produce ova]s and ronnds, and British Qneeu x Flourba]l ovals and[ kidneys. The f, nbers of both. Upq;o-date and British Queen are classed as oval, but within that class British Queen tnbers possess a slightly longer axis than those of Up-to-date. This difference is emphasised by the resnlts obtained front the progenies of these two varieties when crossed with Flonrball, and it indicates that B~tish Qneen is genotypieally allied to the ldd.ney rather than to the ovM-tnbered type.

Two progenies derived from Golden Wonder x Glassel Beauty and Golden Wonder x 800 (2) respectively are in each ease hybrid plants of a kidney variety crossed with a rom~.d. The results snggest that Glassel Beauty, Mthongh rather fiat, is genetically a less heterozygons ronnd than 800 (2) since the latter variety prodneed no ronnd tnbers in the mathlg. The appearance of long-tnbered plants which transgress the range of the parental, type may be attributed to the heterozygons nature of the parents and pat~ienlarly to that of the -9- parent.

In the 11 re.stings given in Table VI there was obtained in each. ease a majority of ovals. Five families, derived t:.rom ronnd-tnbered parents and inelnding altogether 773 plants, gave over 61 per cent. of oval- tubered offspring. In each of the families a small proportion of Ndn.ey- shaped. tnbers appeared, attaining on an average just over 6 l?er cent. With the exception of two long-tnbered seedlings which appeared in a family of 311 derived from Kerr's Pink • Bell, the remainder, about 32.4 per cent. were ronnd. Obviously the majority, if not all, of these ronnd-tnbered parents are heterozygons for tuber shape, and varions kinds are involved. Two different kinds of ovals ha,ve been demonstrated in Up-to-date attd British Qneen.

"The inheritance of tuber shape is genetically complex, and in. most modern varieties this character probably exists in a heterozygons con- dition. The Shapes are so nnmerons and the differences so slight that it is hardly possible to make an aeenrate general classification. The classi- fiesrich nsed ill the foregoing notes is pnrely arbitrary and it is admitted that it is sometimes ditllenlt to decide to wMeh of two classes a plant

40 Potato Hybrids

actually belongs. Between the two extremes "long" and. "round" there exists a contim]ous series of intermediate shapes, i.nel.uding a range of flat and eylindrieal and irregnlarly pointed tnber types. The range of types as %and in o]le progeny is shown i]1 Fig. 1, a,nd shape is represented by ratio of lengtl~ to breadth.

The graph wan obtained by plotting the ratio, maximum length/ ]naximum breadth, against the frequency, and illustrates the range of types together with. their freqnency in a, fami]y o:f 136 F 1 seedlings derived from Golden Wonder and Glasse] Beauty. The ratio with the maxiln.mn frequency lies between the ratios of the parents, but closer to

40

80

2(}

0.8

B!

/ 1~0

A

i

1'2 1-4 1"6 1"8 2"0 9.9 9.4 9-6 9.8 B'O 3"2 8"4

~ig. 1.

that of q-lassel Beauty (]3) than to that of Golden Wonder (A). Trans- gression oeenrs in both direetim~s bnt it is more prononneed h~ the higher ratios.

Tnber shape, from the point of view of the relation between length and breadth alone, appears to be controlled by more tl~an one pair of factors. Peculiarities of shape, such ~s the pear-shaped type, hH;rodnee other factors which ma,y fnnetion as modifiers. Sneh modifying factors apl?ear to be mnnerons, and i.t seems probable t:h at the number of :l!~mtors eontrolling tnber shape may vary h~ di:fferent varieties.

]~YE DEI?TIL

The depth of eyes, except in the two extremes, is di.mol]lt to esthnate aecm'ately on account of its variable nature. It is affected to a great ext;ent by envh'onmental conditions. [Eyes tend to be deeper hi tubers grown on wet clayey soil, a,nd shallower in tlmse grown i n dry sandy soils.

W. ]~LACI( ~il

Again, the e:ffeet of second growth is often suffmient to make normally deep eyes appear shallow o1' even snperfic:ial. Apar t t'.rom these con- ditions dassifiea,tion according to depth of eyes is, at the best, merely the expression o:1:. an opinion whiell cannot readily be arrived at by actual measm'eme:nts.

9 Eye character according to Salaman(. ) is inherited on a single factor basis. ])eel? eyes breed trne, bnt only in some eases do fleet eyes breed true. The lat ter character :is incompletely dominant and the hybrid between dee]? and fleet is more fleet than deep.

TABLE VII.

Classification of hybrid ~)rogenies ,with regard to eye depth.

Total no. ]?~rentage o1! seedlings No. shMlow. No. medimn No. deep

,S'hallow x Shallow Golden Wondm' x Glassel Beauty 1.36 77 53 6

Shallow x Medium British Qneen x Flonrball 51 39 12 0 Golden Wonder x 800 (2) 53 39 16 0 Up-to-date x :~lom'b,~ll 57 15 38 4

Mediu~n x Shallow Flora'ball x Gl~ssel Bounty 28 21 7 0 Gre~t Scot x 993 (a) (4) 62 39 21 2 K e r f s :Pink x 39 (15) 52 31 20 1

Medium x Jlledium Great Scot x :Boll 288 20'1. 75 9 Kerr's :Pink x li'10m,ball 75 39 36 0 I(err's Pink x Boll 311 87 199 25

Deep x Mediu~n Epicm'e x l~'lom'ball 71 38 32 1

The eross:ing of two shallow-eyed parents, Golden Wonder and Glassel :Beauty, gave an unexl?ectedly high proportion of medium- and deep-eyed seedlings. Only 56.6 per cent. of shallow-eyed types were found, which indicates a heterozygons constitution i~z at ].east one of the paa.'ents. Golden Wonder has in other experiments proved itself to be hcterozygous for eye depth. The progeny of Golden W o n d e r • 800 (2) contained a higher percentage of s]lal]ow-eyed pla~sts than tha t of Golden Wonder • Glassel Beauty, al though the eyes of 800 (2) are of reed.iron depth. Glassel Beau ty m a y therefore be regarded as heterozygons :t!or eye depth.

"Of the two families derived f rom British Queen x Flora'ball an/[ Up- to-date • Flourball, the former gave a, comparat ive ly high ]?or- oralrage el:. shallow-eyed plants, while in the latter the percentage was compara t ive ly low. The difference lies in the female parents and indicates tha,t Ul?-to-date breeds deeper-eyed types than British Queen.

With the eXCel?lion of one instance the mating of medium- grid

~2 Potato Hybr ids

shallow-eyed parents or vice versa gave, in each case, a majority ok seedlings with shallow-eyed tubers.

Comparisons between the hybrid families of medium-eyed parents demonstrate that C4reat Scot tends to give more shallow-eyed seedlings than. Kerr's Pink, a,nd Flourball more tha,n Bell.

The hybrids of medium- and deep-eyed varieties as derived fl'om Epicure and Flom:bM1 coral?rise comparatively large nmubers of shn,llow- eyed. seedlings. The smn,ll percentage of really deep-eyed pJa.nts obtMned is eousistent with the view that deep eyes are recessive.

From. the evidence obtMned from the progeny ok Gotdet~ Wonder x Gtassel Beauty shallow eyes sometimes do not breed true. Various families in the Fa generation have been found to breed true for shallow eyes. This :is in agreement with Salaman's views (9) on. shallow-eyed tuber types.

It seems higMy probable that eye depth is controlled by genetic factors which represent the extremes of types, and that all intermediates between true deep-eyed and true shallow-eyed, are heterozygous. The. majority of the parents i.n the hybrid progenies just described are un- doubtedly heterozygous. There is a distinct tendency for hybrid progenies to give a large proportion ok forms intermediate between the parent types, and transgression frequently occurs to a limited extent.

Various hybrid progenies are described, and compared with reference to several characters, vim flowers (flower eolour alld flowering cal?aeity), tuber eolom:, tuber flesh eolour, tuber shape and eye depth.

Various genetically different white-flowered varieties are ~loted, and eolom'ed flowers doubtless represent numerous different genetic ty]?es. The inheritance of flower eolour appears to be controlled by several factors.

Oon.siderable hereditary differences in flowering capacity and in fertility are noted in varieties which ap]?ea~' to be similar for these characters.

It is suggested, that the inheritance of tuber eolom' apart from pattern in the potato is in several varieties con.trolled by fern: factors, vim I), a basic factor necessary for the production, of eolom' alone; R, a factor which in con.junction with 13 produces a red eolour; P, a factor which in conjunction with D produces a purple eolom', and in conjunction with D trod R an intermediate reddish purple eolour; and H, a~l inhibiting

W , B:~Ac:x 4-3

fact~o:r h~com]?le~ely dominani) to ~he J!ac~or D ] n ~he ]?resence of ho:mo- zygous fac tors t t or P .

Tube r flesh colour is controlled b y genetic factors and l?roba, b ly b y more l~b~n one pair . So-c,r whil)e-fleshed varieties axe, in m a n y cases, hybr id h~termedia~es.

T u b e r sha,pes h]clude pracgically all the ini, ermedia~es begween round and long considered from. the poing of view of the ragio leng@/bread~h. Many so-called rmmd-tu.bered var ie t ies appear to be hel~erozygous. In hybr id progenies , t ransgress ion f .requently occurs. u l!actors are iuvo lved and the n u m b e r ]?robably var ies in. di:ffereut varieties.

The de]?gh of eyes in ghe tube r a.ppears to be control led b y genetic Gc tors , p r o b a b l y represent ing ~he ext remes , viz. deep-eyed and fl.eet- eyed, The pa ren t s discussed are p r o b a b l y all h)q~rids. Tra,nsgression is found 6o occur iu cergain hybr id ])rogeni:es.

LITE]~ATU~E CITED.

(1) Ass~u T. (]927). ":Bnd mnt~a~ions in t~he ]?el;aide m~d t~heir chimerical Natm.e." Jour~. Gen. xIx, No. ].

(2) ]30~1~5D O1~ ACmIOUL~r'U~]~ ]~Or~ SOO'I:L~ND (1927). "MMal~enance of l?nre m~d vigormr~ stocks of varieties of ~he ]?o~ato." Misc. Pub. No. 3.

(3) CL,k~K, C. F. (1927). "Types of s~erili~y in wild and mrlbiva~ed ]?obatoes." Mere. Heft. ,S'oc. New York, rCL

(4) Cosm~S, E. J. (]924). "Itdmrit;ance of t~he colom. ])a~geru of King Edward ]?ogato." Jou'r)~. Gen. xIv, No. 2.

(5) EAS'.t', E. h~. (]9]0). ":[nherLgmlee in ]?ot;agoes." Amer. Nat. New ~ork, xLrg. (6) K~Lr~u J. P. (]924). "Seed ]?rogeny of a ]?ol~a~o witch fMnt~ly coloured t~ubers."

Journ. Gen. xlv, No. 2. (7) McI~q'ros~, T. P. (]927). f['he Potato : Its History, Culture and Diseases. Oliver

and ~oyd, Edinburgh. (8) ]~o~B, W. (192]). "]~reedir~g, select~ion and dcve]opment~ work in :Bri~Mn."

Paper, In~ernat~iona.l ]?ot;at~o Co~fference. (9) SAT~k~'XA~, ]:~. N. (]926). Potato Va~'ieties. Camb. Univ. Press.

(10) - - ( 1 9 1 0 ) . "Inheritance of colonr and o~]ter characters in the ]?o~ato." Jo~,~.n. Gen. I.

(11) ' (]910). "]KMe s~eril[~y in ]?o~a~oes." Journ. Linn. Soc. Bot. xxxx. (12) S~tLA~a~, I~,. N. and LtCSL~Y, J. W. (1922). "Gene[ic s~udies in ]?ota~oes:

S~eri]ity." Jou~"n. Agri~. S'ci. x~ . (13) Sa'vA~a', W. (]915). "Potato breeding and selecgion." U.S. Department of

Agric. Bull. 195. (14) Wr~.so~, J. H. (]916). "Ex~2erimen~s in crossing pota~oe,~." ~l',rans. High.

Ayric. Soc. S'cotland, 1916.