THE GENETICS OF TROPAEOLUM MAJUS

B~ A. A. MOFFETT John Innes Horticultu,ral Institute;on, Me,'ton, London

CONTENTS :PAGE Introduction 151 Morphologica,l thetors . ].51 Factors aft'coting leaf eolour 153 Flower colours 154 (1) Plasgid eolours 1.5~I (2) Anghoeyanin colours 157 Two-factor r~ios . 159 Discussion 160 Summ~ry 161 Aelmowledgement 161 I~eferenees 161

INTI%ODUOTION TgE investigations on T~'ol)aeolum reported upon in this paper were begun in 1929 and continued to 1935. The work is incomplete in many respects, especially as regards the inheritance of anthoeyanin flower colours, but the present author is unable to continue the investigations and the results obtained seem of sufticient interest ~o warrant publication. So far, very little has bee11 published upon the genetics of T,ropaeolum. Rasmuson (1918, 1920) reported upm~ the inheritan.ee of plastid colour in flowers and leaf colours, but his data are meagre. Correns in 1920 investigated the genetics of variegation and light green leaves. During the years 11.91.1-18 a considerable amount of work, principally on the inheritance of sex and doubleness, was carried on by the late Mr Bateson at this Institution. The results of this investigation were never published, and the material ha.s since been lost. Some of Bateson's data on the inheritance of i~y leaf and variegation have been included in the present paper.

I~{OP~PHOLOG IOAL FACTORS Three factors affecting fihe external morphology have been isolated, as follows : b produces dwarf bushy habit. 152 The Genetics of Tropaeolum majus i produces Smaller leaves with deeper lobes; petals narrow with coarsely serrated edge. d gives dm~ble flowers, the pe~als, stamens and carpels all being more nun]erorls. The./hctor B The bush or dwarf habit is characterized by short compact growth wi~h an absence of long trailing shoots. Dwarf habit is completely re- cessive to the tall straggling type. The factors B and b gave the following segregation : TABLE I Bb sdfed Family Origin B b 3/31 2't/30 selfed ]3 4 13/31. 15~*/30 ,, 13 8 16/31 16~/30 ,, 38 15 6/34 61/33 ,, 26 12 9/34 97/33 ,, 5 3 10/34: 9s/33 ,, 10 ~ 61/34 26n/33 ,, 141 43 Total 251 89 Calcnlated 255.25 84.75 Bb x bb 1/31 P/30 x 2~/30 17 8 2/31 P"/30 × 2'1/30 7 8 11/31 13~/30 x 16~/30 4 4: 12/31 13n/30 x 15~/30 18 17 Total 46 37 Calculated 40.5 60.5

The factor I The ivy-leaved type is completely recessive to normal leaf. In i plants the leaves are more lobed, while the petals are narrow with a coarsely serrated, distal edge. Ivy leaf is frequ.ently accompanied by a con- siderable amount of male sterility, this being especially the ease when it is combined with other recessive factors. I and i gave' tlte following segregation : TABLE II Ii selfed Family Origin I i 3[31 2't/30 15 7 14/31 16"730 46 7 1/32 2~/31 4 1 10 families from ]3ateson's records 162 51 To~l 227 66 Calculated 219.25 73.25 One :[h,lnily from Ba~eson's records, Ii x ii 21 19 Calculated 20 20 A. A. 1V[OFI~'ETT 153

The.factor D The factor d produces doubles of the now welt-known "Golden Gleam" ~y]?e. The flowers tend to be double throughout, having more numm:ous pebMs, stamens and frequently carpels than in the normal. These dout)les produce plenty of good pollen and are quite fertile, d is eoml?letely recessive and segregates in a normal single-factor ratio, as follows : TABLE III Dd sclfc.d li'amity Origin D cl 61/34 ea**/aa 1.48 45 26 12 Total 17:1: 57 Calculated 173.75 57-25

]FACTORS AFFEOTING. LEAF COLOUI% Three factors for leaf colour are known, two of' these, X and Y, l)eing complementary, as follows: vv plants have variegated leaves. xxyy plants have yellow-green leaves. Xxyy, XXyy, xxYy or xxYY have medium green leaves. XxYy, XXYy, XxYY or XXYY have dark green ]eaves.

The factor V The data for the inheritance of this factor are taken entirely from Bateson's work. Variegation varies considerably in amount, the leaves sometimes showing a fine mottling of white, sometimes large white patches occupying a considerable portion of the leaf surface. Variegated leaf is a simple recessive to whole colom:ed leaf.

TABLE IV Vv selfed V v Total of 30 tlmfilies 847 273 Calculated 840 280

The two factors X a,nd Y Three shades of leaf colour occur which are easily distinguishable in scoring--yellow-green, medium green and dark green. As previously shown by Rasmuson (1920), two complementary factors are concerned 15_4 The Genetics of.Tropaeolum majus with the inheritance of these shades. When both recessivcs are present, the leaves are light yellow green. (xxyy). When one or other dominant is present the leaves are medimn green, and when. both dominan.ts are present the leaves are dark green. Medium green, of the four different possible genotypes cannot be distinguished phenotypical]y. It should, however, be possible to obtain dark greens from crossing the two types of medium green together. In. family 1.]./33, in which all tyl?cs should occur, several medinna green plants were crossed by pollen from a single medium green. Of these one cross, 11a~/33 x 11"~/33, gave dark greens in the next generation, showing thaC the two types of medium green, due to different t3,ctors, actually do occur. The data, in Table 5 from crosses between different leaf colours give a close agreement with. expectation. The Nct tha,g the two types of medimn green can.not be distinguish.ed gives modifications of.the expected ratio. On selfing a, plant of the con- stitution. XxYy the unusual ratio 9 : 6 : 1 occurs in the next generation (see tables).

~LOWEI~ COLOUP~S The flower colours may be divided into two types: (1) Plastid colours, i.e. yellow and primrose; (2) Anthocyanin sap colours, i.e. pink, scarier, etc. The plasCid colours are inherited independently from the mlthocyanin colours.

(1) Plas~id colou~'s Rasmuson (1918) reported a single-factor difference between dark yellow and light yellow (yellow and primrose), but his data are very meagre. In the present investigations some of the earlier families gaye 3 : 1 ratios as if a single factor difference was involved, bug later families gave ratios which diverged widely and made it necessary to consider some other scheme to account for the facts. Two complementary factors, P and Q, appear to be involved, as in the case of the leaf colottrs. When both one or other of the factors are recessive the flowers are primrose. When both are dominant the flowers are yellow. Thus pq, Pg, and pQ are all primrose, while PQ flowers are yellow. The segregation of yellow and primrose depends upon the constitu- tion of the primrose plant used in Cite original cross, i.e. whether recessive for both factors or for one only. The F 2 :families 3, 6, 7/31 and 29/34: gave a close approximation Co 3 : 1 yellow to primrose, the primrose used in these cases being presumably ppQQ or PPqcI. Three other A. A. MOFFETT 155

TABLE V F~ from (medium green × light green) se!fed (Xxyy or xxYy selfed) Family Origin Medium green Light green 8/31 911/30 selfed 35 21 23/31 l~I~u/30 ,, 6 6 23/32 331/31 ,, 27 10 29/34: ] 9'~/33 ,, 49 21 40/34 25~/33 ,, 50 16 To~l 167 74 Calculated 180.75 60.25 .F2 f~'om (da~']c green × qncd'ium green) selfed (XxYY or XXYy selfed) 3/31 24/30 selfed 16 6 6/31 5~/30 ,, 40 ll 13/33 10"-~/32 ,, 54 21 14/3o 151'~/32 ,, 23 4 31/34 22~8/33 ,, 73 20 34/34 23"'/33 ,, 51 20 41/3~1 26~/33 ,, 150 50 Tot~[ 407 132 Calculated 4:04.25 134:.75 F2fl'o~n (daq']c green × light green) selfed (XxYy selfed) Dark Medium Light Family Origin green green green 10/31 12~/30 setfed 17 17 2 13/31 15')/30 ,, 12 8 1 14/31 16'~/30 ,, 37 13 3 11/33 10a/32 ,, 36 2~1: 6 Total 102 62 12 Calculated 99 66 11 Heterozygous dar]~ g~'een × ~nedgum green (XxYY × XXyy or xxYY) Family Origin Dark green h'[edium green 1/31 11/30 × 2'1/30 13 12 2/31 12/30 × 2'1/30 6 9 21/31 23~/30 × 12~/30 24 29 2/32 2~'/31 × 2:1/31 3 3 23/33 161!~/32 × 21~/32 19 22 28/34 171°/33 × 23'~/33 16 10 32/34 22"~/33 × 162~/33 27 19 Total 108 104 C~%lcula~ed 106 106 Heterozygous dar]c green × light green (XxYy × xxyy) Dark Medimn Light Family Origin green green green 9/31 12"/30 × 1017/30 9 15 6 11/31 13~/30 × 16~/30 1 6 1 12/31 1.311/30 × 15"/30 10 18 7 Total 20 39 14 Calculated 18.25 36.50 18.25 Hctcrozygous g~'een, type A × heterozygous g~'een, type B (Xxyy × xxYy) 15/34 1 ]~/33 × ] 1~1/33 8 23 6 Calculated 9.25 18.50 9.25 156 The Genetics of Tropaeolum majus .F., families, 6/31 and 31 and 4.0/34., gave f~ ratios which do not differ significantly from 9:7, the primrose being presumably ppqq. Two families, i[0/3], and 23/31., have 23 to 12 and. 24. to ].3 yellows and[ prim- roses respectively. These figures might represent either a 3 : 1 or 9 : 7, ratio, as they do not diff.er significantly from either; they have therefore been omitted from the data,. [['he following are the data, for F~ segregations:

TABL:E VI PPQq or PpQQ selfed Family Origin Yellow Primrose 3/31 2'1/30 selfed 1.9 3 6/31 5'~/30 ,, 39 12 7/31 71~/30 ,, 19 6 29/34 19:'/33 ,, 54: 14 Total 131. 35 Calculated 124.5 41.5 PpQq selfed 18/32 21'~2/31 7 6 6/34 6~/33 16 22 31/34: 221s/33 49 40 4:0/34 25"~s/33 34 26 Total 106 94 Calculated 112-5 87.5

The t~milies resulting fl'om back-crosses give widely different ratios, all of which are, however, explicable in the two-factor basis. The following are the data for back-crosses:

TABLE VII Family Cross Yellow Primrose 21/31 235/30 x 12~/30 (PpOq xppOO) 26 27 Calculated on 1 : 1 ratio 26.50 26.50 32/34 22~a/33 x 16"-°/33 (PPQq x ppOq) 34 11 Calculated on 3 : 1 ratio 33.75 11.25 39/34 25~/33 x 17°/33 (PpQq x ppqq) 1.9 58 Calculated on 1 : 3 ratio 19,25 57,75

The back-cross in. family 32/34- gives resnl.ts consistent with selfing plants from th.e same F 1 family. Family 4.0/34., F2 from yellow x primrose, gave a. 9 : 7 ratio, showing the primrose to have beenrecessive for both factors. The back-cross of th.e same F 1 which was selfed to obtain 4-0/34. resulted in a ratio of 1 : 3, which was to be expected on back-crossing a plant heterozygous for two factors. These results therefore support the two- factor hypothesis. A.A. MOFFETT 157

(2) Anthocyanin colours The presence or absence of anthocyanin colortr in the petals is deter- mined by a single factor, the presence of anthoeyanin being dominant to its absence. The factor A gave the segregation: TABLE VIII Cross A a Aa selfed (20 families) 64=2 213 Calculated 64=1..25 213 /ka x aa (9 f~milies) 14=2 14:2 Crdculated 14=2 i~2 Th.e inherRance of anthoeya, nin colours is complicated by the inter- action of other genes, giving a wide range of colou.rs which has not yet been fully analysed. Chemical tests made by Miss Scott-Mon.erieff of this Institution have shown that two types of anthocyanin occur, a glycoside of pelargonin and one of eyanidin. The main colours found are pink, deep red., chocolate and scarle~. Pink and the scarlets contain pe]argonidin derivatives, while deep red and. clhoeola,te contain eyanidin derivatives. These colours differ in appearance on primrose or yellow plastid grounds, and with other factors such as that for dark green leaves. A recessive factor (or factors) produces anthoeyanin in the styles, reduces petal size and intensifies anthocyanin eolours. This factor is sometimes di~cult to score, and has not yet been fully analysed. It gave the following segregation:

TABLE IX F~mily Origin S s 3/31 2'1/30 selfed 18 2 6/31 5~/30 ,, 31 3 10/31 15~/30 ,, 22 2 14=/31 16s/30 ,, 37 8 11/33 10a/32 ,, 38 8 13/33 10~'~/32 ,, ~14= 11 14=/33 16~/32 ,, 21 4= 30/34= 20:~/32 ,, 35 5 31/34 22~s/32 ,, 70 20 34=/34= 232/33 ,, 56 9 • 4=1/34= 26n/33 ,, 128 34= Togal, observed 500 106 Calcula,ted on 3 : 1 454.5 151.5 It is possible that the smaller nmnber of reeessives is due to mistakes in scoring, since the tingeing on. the style is sometimes very slight, and might be overlooked. There is considera,ble evidence to show that deep red is the expression, on plants wRh medimn green ].eaves, of the factor which produces choeo- 158 The Genetics of Trop~eolum m~jus late flowers on plants with dark green ]eaves. Both types of flower contain cyanidin derivatives. Chocolate flowers never occur ia combina- tion with medium green leaves. In fa.mily ]3/33, the result of se]fing a chocolate plant ]:0~/32 segregating :for dark green and medimn green leaves, the medium green leaved plants had in every case dec]? red flowers, the ratio being: TABLE X Deep red flower, Chocolate flower, medium green :Family Origin d~rk lea~ves leaves 13/33 10"-'~/32 selfed 41 14 So :far, the following factors which a.ffec~ flower colour have been isolated : a, absence of anthocyanin co]our in the petals. r, pink, opposed to deep red or chocolate. c, pink or chocolate, opposed to scarlet. s, tinged sbyle, intensifies colour. l, whole colour as opposed to blotch (localized colour). The fa, cto~'s C a~,d tl G and It may be carried by plants having no anthoeyanin in the petals, and do not show their effect until a is present. In every case i~ was found that the primroses or yellows used at :first carried either G, 1:1 or both. Three types of primrose have since been isolated: (1.) Primrose ccrr, on. crossing with pink gives a piuk F 1. (2) ,, cctlR, ,, ,, deep red F 1. (3) ,, GGRR ..... scarlet F1. The primrose of type 1 on crossing to pink gave ill the F2: Table XI F~mily Origin Phlk Primrose 37[34 2~tl/33 selfed 25 4 38/34:. 24:'~/33 ,, 53 25 Total 78 29 C~leul,~ed 80.25 26.75 The pinks in this family were redder than the normal pinks, probably owing to the action of a minor modifier. Pink x primrose carrying R gave in the f 1 deep red, and in the F2 and back-cross:

TABLE XII ti'amily Origin ]R r 5/31 4'~/30 selfed 19 3 Caleuh~ted 16.5 5.5 20/31 23~a/30 x 12~/30 12 5 Calculated 8'5 8.5 A. A. MOFFETT 159 Pink × scarlet or yellow carrying G and R gave a scarlet F 1 which on selfing and back-crossing gave:

TABLE XIII F,%mily Origin Scarlet Deep red ]?ink 40/34 25-~a/33, CcRr, selfed ~13 7 2 C~lcub~ed on 12 : 3 : I 39 9.25 3.25 39/34: 25~5/33, CcRr × 176/33, ccrr '1.3 15 20 Calculated on 2 : 1 : 1 39 19.5 19'5

These ratios give a very close approximation to expec~a@on on the assumption that C acts independently of R and can itself change pink to scarlet. [['he scarlets of the constitution CR and Cr are indistinguishable, giving the observed modifications of the two-factor self- and back-crossed ratios. Dee 2) ,red and sca,rlet The following ratios were observe([ in crosses between scarlet, GR and deep red, cR. R was in some cases carrie([ by primrose and also by chocolate. Only plants carrying R are included in the data.

TABLE XIV

:Family Origin Pheno~ype of F~ p~u'en~s CR clR 3/31 24/30 selfed Sc~rle~ x primrose 17 3 6/31 5'V30 ...... 24 8 7/31 ~ 71"/30 ,, Searle~ × chocolate 15 10 10/31 12~/30 ,, Yellow (M:N) x chocolate 19 7 To~al 75 28 C~leula~ed 77.25 25.75 Baclc-c~'osses Family Origin CR cla 1/31 ll/3O × 2'~/30 7 11 17/31 22~/30 x 712/30 17 28 18/31 22"/30 × 125/30 21 18 21/31 235/30 x 1.25/30 22 30 14/3~ 1Pa/33 x 1 lal/33 14 17 To~al 81 104

TWO-FACTOR BATIOS TABLE XV (BBii × bbII) selfed ]~a,mily Origin BI Bi bI bi 3/31 2~/30 selfed 11 7 4 0 4/31 165/30 ,, 33 5 13 2 1/32 2a/31 ,, 3 0 1 1 ToLal 47 12 18 3 C~leul~ted ~5 15 15 '5 160 The Genetica of T,~opaeolum majus Table XV (cont.) (BBAA × bbaa) selfec~ 2Fa.mily Origin BA Ba t~A ba 3/31 2'1/30 seli~d 16 2 ,1: 0 14/31 165/30 ,, 32 6 ]3 1 To~al 48 8 17 1 Calculated 41.6 13.9 13.9 4:.6 (bBAA x BBaa) so!red 41/34 2611/33 115 38 37 6 C~lcul~ged 110.25 36.75 36.75 12.25 (AADD x aadd) selfed, t~mily Origin AD Arl aD a4 4:1/34 26n/33 118 34 33 11 Catcuh~Sed 110.25 36.75 34.75 12.25 Bushy x Double, BBdd × bbDD Family 0rigfll BD Bd bD bd 41]34 2611/33 115 37 36 8 C~lculated 110.25 , 34.75 34.75 12.25

DISCUSSION The factors B, I, D, V and A segregate in close agreement with the expected monofactorial ratios. Data for B, I and A were obtained from back-crossing as well as selfing Fl's, while the numbers from D and V were from selfing only. l~atios for S give too few recessives for a normal monofactorial segregation, but this may be due to the difficulty of detecting colour in the recessives. The two pairs of complementary factors, X, Y and P, Q differ slightly in their relations. In the former case, each of the dominant genes con- cerned has some ettect in the absence of the other, giving medium green leaves instead of light green; and both factors together intensify this effect by giving dark green leaves. With the plastid genes, neither dominant has any effect alone. The ratios for both pairs of genes agree closely with expectation. In the absence of modifiers the anthocyanin factor A produces pink flower colom'. R turns pink into deep red, and it appears that X and Y also interact with R, both leaf-eolour genes being necessary to convert deep red to chocolate. C is probably quite independent of R in its action. It modifies deep red to scarlet, and probably gives scarlet flowers also in the absence of R, though it remains to obtain scarlet flowers fl'om crossing pink (ccrr) with a plant carrying the scarlet but not the red i~ctor (CCrr), to prove this independence. A. A. MOF:FET~r 161 It has been tentatively suggested by ~{iss Seo~t-Monerieff that R is a factor for the production of cyanidin (deep red and chocolate) instead of the pelargonidin of the rr plants ; and that C inhibits tl and intensifies pelargonidin coloration. G is epis~atic to It. 0gher minor modifiers of petal eolour apparently occur, e.g. an in- tensifier of piuk anthocyan.in colour. From the double factor :ratios given, there is no evidence of linkage between the pairs of genes B and I, B and D, A and D; but B and A may be linked. ~ UM~'IAI~Y 1. The inheritance of 13 genes in Tropaeolum majus has been studied. 2. These genes include: Three controlling morphological characters (B, I, D). Three cmxtrolling leaf eolour (V, X, Y). Seven controlling flower colour, (1) plastids (P, O), (2) antho- cyanin (A, C, R, S, L). 3. There are ~wo pairs of complementary genes, X, Y and P, Q. 4. The presence of A is necessary for the expression of the other genes for anthocyanin colour in the petals; G is epistatie to R; and minor modifiers of eolour occur. 5. No certain linkage has been found between any of the genes.

AOKNOWLEDC'I~ENT Miss E. Sutton of the John Innes Institugion has completed the preparation of this paper for the press.

I{EFERENCES Com~s, C. (1920). "Vererbungsversuehe mit buntbl~tggrigen Sipl]en. IV." B'.B. preus,s. A]cad. Wias. 6, 212. gsssIvso~, H. (1918). "Zur Genegik der Bltil~enfarbenyon Troj)aeoht.m .mujus." Bet. Notiser, i918, 25;3. -- (1920). ~'I)ie Kaupgergebnisse yon einigen genegisehen Versuehen mig ver- schiodenon Formen yon fl'ropaeoh~m, Cla#~ia mid Iml)aticns." Hereditas, t, 270.