THE CYTOLOGICAL P~ELATIONSHIPS OF GOSN Y P I U M ARE Y S I A N UM DEFLEI~S

BY Ii. DOUWES

Em~)i~'e Cotton d~'owing Cor~)oration and Sudan Government

(With Eight. Text-figm'es)

Received 22 June 1952

CONTENTS

Int~roduction M~tcrial and megllmd .

Hybr id iza t ion wi6h other species of Gossypium . (1) 1-Iybrid Gossyldum somalensc x (4. areysian~on (2) I-Iybrid Nossyplum stocbsii x G. areysianum (3) :Hybrid Gossyl)i~o~ anomalum x a. arey~ianum (4) Hybrid Gossypium anomahtm x G. triphyllum

Discussion . Summ~ry References .

2AGE 611 611 6]2 614 615 618 619 621 622 624 62~

INTRODUCTION

I-Iutehinson (1947) grouped Gossypiu~ a~'eysianum with G. anoma~um and G. t~'i~hyltum in the section Anomala of the genus Gossyl)ium. This classification was based on a descrip- tion by Deflers of a specimen of G. a~'eysianum that he collected in southern Arabia in 1893. Deflers's specimen is kept at the Paris herbarium.

Since 19~9, G. a~'eysia~zum has been grown in culture and crossed with other Gossypium species at Shambat, in order to obtain more evidence concerning its relationships.

In this paper a full botanical description of G. a~'eysianum is given, and its hybrids with other species are analysed cytologically.

~/IATErClAL AND h{ETtIOD

Seed of G. a~'eysianum was received in 19~19 through the courtesy of B. J. Hartley, Director of ~ Agriculture, Aden Protectorate. The plants were found in non-grazed areas of the mountains of el 'Areys, on the slopes of valleys fooded by seasonal rivers, between 3000 and 5000 ft. above sea4evel in south Arabia. Deflers collected his specimen in the same area. The Beduins know the plant under the name 'Atiib ',

Lately, R. R. Anson, Consultant in Cotton Breeding, Empire Cotton Growing Corpora- tion, found g. a~'eysianum up in the hills at Ghael, some 40 miles from Khanfar, Abyan, in the Aden Protectorate.

The seed from the mountains of el 'Areys was sown in onr collection of wild species at Shambat in the same year. This is the first time this species has ever been grown in ctflgure.

612 The cytological ~'elationships of G o s s y p i u m a r e y s i a n u m Deifiers

The following species were used in hybridization:

G. stocksii: this occurs in Sind (Pakistan), in south-east Arabia and in British Somali- land. A Pakistan accession WE 1-I was used in the crosses recorded here.

G. somalense, the nearest relative of G. stoclcsii, occurs in British and Italian Somali- land, in Kenya, and all through the semi-arid region south of the Sahara. The Sudan WE 2-2 race of this species was used in the work described in this paper.

G. anomalum: this species is found in semi-arid areas all through Africa. Its nearest relative, G. t~'@hyIlum, is only known from South-West Africa and Angola. A Sudan accession of G. anomalum, W:B 1-2, and an Angola line of G. t~'il)hyllum, WB 2-2, were used as parents in the hybridization described in this paper.

G. a~'eysianum was taken as male parent throughout, because at that time only a few flowers of this species were available, whereas the other species were flowering freely.

The meiosis in the pollen m obher cells of the hybrids was examined with the help of the aceto-iron-earmine method in the same way as described by Douwes (1951).

]~OTAN'[CAL :OESOI~IPTION OF ~O,S'SYPIU,M ARE.KSIANUIll

Shrub, perennial, pyramidal, up to 1�89 m. high, branches from near the base upwards at an angle of ,15 ~ /

Stem and branches brown at the base; towards the top green, with short hairs. Leaves, ill a spiral ; stipnles linear, caduceus, up to 7 ram. long; petioles up to 60 ram.

long, cylindrical with short hairs and dark green dots; leaf blades up to 60 ram. long by 80 ram. broad, cordate, very shallowly palmately lobed, mostly with three lobes and covered with short stellate hairs.

Fruiting branches (sympodia) in the axils of the upper leaves of branches and twigs, up to 90 ram. long, cylindrical, hairy, with black dots. Each fruiting branch has as a rule one to fern: stalked flowers, mostly two, the lowest one in the axil os a small, of~en asymmetrical leaf, the following ones in the axil of small linear stipule-like bracts. With luxurious growth, the fruiting branches bear more than Zour flowers with a leaf at the lower three or four nodes, thus reducing only very gradually into bracts towards the higher nodes. Sometimes even adventitious buds, developing into small fruiting branches, occur in the axils of the lower leaves at the nodes os those frtdtin.g branches. Also on thriving plants two fruiting branches may occur in the ax~l of one leaf on a twig. The two stipnles at the base of each pedicel resemble the ones at the base of the petioles, but are smaller. Pedicels up to 10 mm. long, cylindrical, hairy, with black dots.

Flower complete, regular. Epicalyx (=bracteoles) consisting of three free, narrow, oblong-cuneate bracts, up to 20 ram. long by ~f mm. broad, very shallowly and irregularly dentated along the margin, hairy, with small dark dots. Calyx gamosepalous, campanu- late, 5-dentate, ~} deep; 10 mln. long and 7 ram. broad, light green, hairy, dotted. Corolla regular, choripetalous inNndibnliform, the five petals up to 80 ram. long by 20 ram. broad, asymmetrical, yellow, with a dark red basal spot, hairy. Stamens many, united into a conical colmnn up to 15 ram. long, lower half bare, reddish; upper half with anthers; filaments 1 ram. long, slightly shorter towards the top. Ovary superior, 5 ram. long, 3 ram. broad, eo~ical towards the top, glabrous, black-dotted, commonly three- locular with two ovules per locn]us. Style, 16 ram. long, protruding about 7 mm. from the s~aminal eolmnn, towards the top with black dots. Stigma three-united.

H

_~_.

~ .tx

~ ~

, ~ ~

.~

~~

,~

~~~

!~

t:

�9

614 Tlae cytological relationsh@s of G o s s y p i u m a r e y s i a n u m Deifiers

Capsule ovoid, about ] 5 ram. long and 10 ram. broad, distinctly gland-dotted, sparsely with pubescent hairs, top obtuse; opening from the top along the sutures; falling off together with epicalyx and pedicel. The sutm'es bear a ~hin line of hairs on the inside.

Seeds fnsiform, about 6 ram. tong, densety covered with firmly attached grey-brownish hMrs, about 9 ram. long.

Chromosome number n = 13. Our materiM shows great similarity in morphological characters with the specimen

collected by Doffers in 1893 and observed by the author at the Paris herbarium. Te~- fig. 1 shows our ma4~erial.

A botanical description of G. ano,mah~m, G. somalense, G. stocksii and a. tri~hyllu~ can be found elsewhere (Hutchinson, 19~7; Knight, 19~t9). A detailed description of G. areysianu'm, however, apart from the Latin description of Deflers's specimen, did not exist as far as the writer is aware.

HYBBI])IZATION WITH OTgER SPECIES 01~ GOSSyPIuM

As mentioned in the introduction, up to now G. areysianum has been associated with G. ano~alu~'r~ and G. triphyllu~n.

As it grew, however, it soon became clear that in habit, leaf shape and flower colour (s a~'e~ysianu~ resembled ~. so,m~d~nse rather than G. a~zomalum.

Hutchinson (19t7) brought G. somalensc and G. stodcsii together in the section Stoclcsiana, on morphologieM grounds. This relationship was confirmed by Douwes (1951) with cytological evidence. Geographically the nearest neighbour to G. areysianu~ is G. stocksii, and from G. somalense it is only separated by the Gt~lf of Aden.

However, as G. somale'nse and G. anomalum occupy the same habitats over large areas in Africa (Ktfight, 1949), without being near relatives (Doawes, I95I), the location of O. areysianu~n is not conclusive as to its relationships. Hence, in order to decide on its classification with the additional help of its cytological behaviour, the following crosses were made:

[Female parm~t 3lMe paren t

r Species Origin Type no. Species Origin T,gl~e no, a G. anomaZum Sudan W B 1-2 x G. areysiam~n Ar,~bia W E 3-1 G. somalense Sudan W E 2-2 x G. areysianuv~ Arabia W E 3 - I G. stoclcsii Pakis tan W E 1-I x (l. areysianu~t Arabia WE 3-1 G. a n o m a l ~ Sudan W B 1-2 x G. tr@hyllu~ Angola WB 2-2

G. t'riphylh*'m is the latest accession to our collection of wild species. Its chromosome number has been determi~led as n = i 3 (Douwes & Cushy, lgSl). ~[t has not yet been crossed snceessfnlly with G. areysianum, and it is tufty given here to establish its con- nexion wRh G. anomalu~'*u The hybrid G. ano,rnalu,m x G. t~'ilJhylb, t~'~ is easy to make. It shows Mmost complete chromosome pairing, and is fully fertile, conl~rming the close relationship between these two species previously assumed on morphological grounds.

t t Js strewn later in this paper that G. ano'mcdum and U. a~'eysic~n,~'~ do not associate cytologically, and it is a reasonable assmnption that G. t'riphyttum will not differ from (s anomalu~n in this respect. As t'r@hyltum is the only other species in the section Anomcda, the analysis of elle hybrids designed here, will complete the picture as to the place of G. a,reysia~,um.

H. D o v w n s 615

In the descriptions of hybrids which follow, only those morphological characters are mentioned, in which the parents differed distinctly. For many characters the hybrids will be found intermediate between the two parents.

(1) Hybrid Gossypium somalense x G. areysianum

Morphological cha,ra, cters. I-Iairiness intermediate between the shorter pubescent stel- late hairs of G. a~'eysianum and the longer ones of (4. somalense. All three have a hoary appearance.

Leaves intermediate in shape between the very shallowly cut lobes of G. areysianum and the deeper, about one-quarter cut leaves of G. somalense.

Epicalyx intermediate between the narrow lignliform bracts of G. a~'eysianum and the large ovate, cordate ones of G. somalense, in both parents and in the hybrid the cpicalyx is not caduceus, but drops together with the ripe boll and pedicel.

Calyx intermediate between the very distinctly dentated and gland-dogged one of G. m'eysia~zum and the vaguely dotted and shallowly dentated one of G. somalense.

Capsule more oblong and pointed towards the top than either parent, gland dots in clearness intermediate between the very pronounced ones of G. a~'eysianum and the weak, only just visible ones of G. somalense.

The hairs on the seed are greyish, nearest to those of G. a,reysianum. Cytological eha~'acters. From many crosses made, mnety-four seeds were obtained,

giving rise to ten hybrid plants. These were planted out in the middle of November 1950. They grew up very uniform and more vigorous than both parents. The G. a~'eysianum parent was sown and planted at the same time as the hybrids. The first flower buds on the hybrids already appeared in the middle of the following February, while the first ones on G. a~'eysianum did not appear until about 4 months lager. Unfortunately, --G. somalense, being available already, was not sown at the same time.

Five of the hybrids were examined cytologically. Table 1 summarizes the observations on chromosome pairing in these hybrids.

Table 1. Ch~'omosome co,njugation i~ two hun&'ed and twcnty-Jbu,r pollen motlier cells of the hyb'rid Gossypium somalense x @. areysianum

Combinat ion No. of pollen mother cells (percentages hi brackets i f ~ r

UnivMcn~ss ]3ivMents P lan t 1 P lan t 2 P lan t 3 P lan t 4 P lan t 5 Term 0 13 71 (86.6) 37 (88.l) 35 (89.7) 3l (93.9) 28 (100.0) 202 (90.2) 2 12 1[ (13.4) 5 (11.9) ~t (10.3) 2 (6.1) 0 (0.0) 22 (9.8)

Total 82 42 39 33 28 224

Total : UnivMents 22 10 8 4 0 44 ]3ivalents 1055 541 503 427 364 2890

IvIean: Univalents 0.3 0.2 0.2 0.1 0.0 0.2 Bivalents 12.9 [2.9 ] 2.9 I2'9 13-0 12.9

The great majority of the 224 pollen mother cells observed were in first metaphase stage, while some were still in diakinesis. All the first anaphase stages examined con- sisted of two groups of 13 chromosomes and no sign of 'bridge' fornlation was observed, indicating that the two parental chromosome sets are sufficiently homologous to allow normal disjunction.

One of the pollen mother cells in the first mebaphase stage had eleven bivalents still closely conjugated. The two remaining bivalents were already in the process of dis-

616 :The cytological rclationsh@s of G o s s y p i u m a r e y s i a n u m Deflers

junction, the two partners in each being wetl on the way towards the poles of the spindle. Their position and shape, however, indicated that they had been conjugated. Within each ])air, the two partners were lying exactly opposite each other ab an equal distance from the equatorial ])late in side view. In shape the partners were still pointed towards each other. This pollen mother cell was therefore counted as belonging to the 13 bivalent group. Thus disjunction within one pollen mother cell is nob always simultaneous. This presumably resnlts from the hybrid nature of the plants, and the reduced number of chiasmata, compared with the parents.

Among the twenty-two pollen mother cells put down as containing two univMents and twelve bivalents, three had their two univalents also arranged conspicuously opposite each other at an equal distance on both sides from the equatorial plate and at about one-third of the distance towards the poles. Although here the shape of the uuivalenfls did not indicate a broken connexion, it cannot be ruled out. The remaining nineteen pollen mother cells had their two nnivMents scattered over the spindle; sometimes both on the same side of the equatorial plate, in others on both sides of the plate but not opposite each other, and at different distances from the poles.

0

i I %

1o/, lOt,

Text-fig. 2 Tex~-fig. 3

Tox~-fig. 2. First me~aphase of the hybrid, G. somalense x G. areysia~um, showing twelve bivMen~s and two univMonl,s.

Text-fig. 3. ~h'st met~l)h~se of ~ho hybrid G. somalense x G. areysianum, showing thh'Leon bivMent~s.

All these metaphase plates were seen in side view, but the effect of the squashing on the relative position of tlie chromosomes is diffimdt to judge. A symmetrical position, however, is not likely to have been caused by squashing. It follows that in some of the pollen mother cells the two univalents might well have been paired during part of the prophase stage.

Text-fig. 2 gives a side view of a pollen mother cell, in the hybrid &. somcdens~ x G. a,reysianun~, with twelve bivatents and with two nnivMents lying opposite each other at equal distances from the equatorial plate.

Text-fig." 3 gives an example of pollen mother cells with thirteen bivMents in the same hybrid.

Two hundred counts were made of the number of microspores per tetrad. All were regular, contMning lbur microspores, as was to be expected from the almost normal chromosome pairing. The size and viability of mierospores is, of course, very closely correlated with the chromosome pairing. In a species with normal complete clu'omo- some.pairing all microspores contain the same number of chromosomes and consequently havc more or less the same size. Given homozygosity, their viability should also be equal.

~n

G.

anom

alum

(B

1)

G.

tri2

hyll

um (

B2)

G

. an

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tm (

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. t~

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G.

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(E

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1) •

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i (E

i)

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(B~

_) x

G.

som

alen

se (

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G. a

nom

alum

(Bz) •

G.

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sian

um (Es)

Tab

le 2

. Po

llen-

grai

n di

amet

ers o

f ~vi

ld G

ossy

pium

spe

cies

and

the

ir h

ybri

ds (

geno

m sy

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b~'ac

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)

No.

of

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iece

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eter

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atio

ns

(t0

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du

atio

ns=

32

-5tt

) 2~

f

\

8 9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37 T

ota

t

..

..

..

..

..

.

7 35

60

61

33

~

..

..

..

.

200

..

..

..

..

..

8

37

68

59

25

3 .

..

..

..

..

..

20

0 .

..

..

..

..

.

3 6

24

70

66

24

7 .

..

..

..

..

..

20

0 .

..

..

..

..

..

3

22

32

88

39

ii

4 1

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20

0

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..

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2

16

33

79

45

16

9 .

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200

..

..

..

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..

.

7 19

36

72

44

16

6

..

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2 6

7 8

7 16

28

36

51

21

13

3

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.

200

..

..

.

2 9

i0

12

ii

12

I0

9 IS

40

38

17

7

4 1

..

..

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200

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5

8 I0

12

12

12

18

27

36

26

23

9

2 .

..

..

..

20

0

3 4

4 8

14

18

19

23

22

18

19

15

13

7 2

1 1

2 2

2 1

1 1

200

1 3

7 13

15

23

29

27

18

12

12

i0

5

4 4

~ "4

2 3

2 I

I .

..

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.

200

2 5

5 8

7 8

i0

I0

II

13

16

17

II

8 9

II

I0

8 5

2 3

5 3

3 3

3 2

1 1

200

* Fo

r ch

romo

some

pa

irin

g se

e Do

uwes

(1

951)

.

618 The cylological ~'elationsh@s of G o s s y p i m n a r e y s i a n u m Deflers

k common reason why interspecific hybrids have a lower fertility titan their parents is because of the formation of gametes with an abnormal number of chromosomes, due to incomplete pahqng, which will make them differ in size and in viability. The degree of variMJility in size and in viability of microsl?orcs is therefore a measure for the degree of irregularity in chromosome pairing.

The hybrid G. somalense x G. a~'eysia~u~ gave plenty of naturM and selfed seed, and backeross seed to either parent was easily obtained. Chromosome pairing being almost complete gives reason for the expectation that the size of the microspores will not differ greatly from that of both parents. Table 2, in which the pollell-grain diameters of all the parents and hybrids dealt with in this paper are given, and also of ~he ones examined cytologically by Douwes (1951), shows this expectation to be justified. From the fore- going account it may be concluded that G. a~'eysianum is closely related to G. somalense.

(2) Hybrid Gossypium stocksii x G. areysianum

MorI)hological cha~'ctcters. Branches spread horizontally, thus showing the proeumbent character of G. stodcsii.

Leaves one-third to one-hMf cut into three to five lobes, thus very near to those of G. stoclcsii.

EpieMyx intermediate in size and in number and length of teeth. Cytological chct~'acte~'s. From many crosses forty-three seeds were obtained, most of

which were empty. Two germinated successfully and grew to maturity. They were planted out in late September 1951 and the first flower buds were collected and examined in the middle of January 1952.

Table 3 gives a summary of chromosome pairing in these two hybrids.

Table 3. Ch~'omosome eo~@~gatiog~ i~z o~ze hund~'ec~ crag t~oo pollen mother' eel~s of the hyb~'id Gossypium stocksii x G. areysianum

Combination No. of pollen mother cells (percentages in brackets) f

Ul~-ivMents 0 2 4 6 8

I0

A A

]~ivMents rPlanr 1 Pl~nt 2 Total 13 15 (62.5) 38 (48-7) 53 (51,9) 12 7 (29.2) 25 (32.0) 32 (31,4) ii - - (o-o) s (10-3) s (7.s) 10 2 (8.3) ~l (5.1) 6 (5.9)

9 - - (o.o) 1 (z.3) i (1.o) s - - (o.o) 2 (2.6) s (2.0)

Total 24 78 102

Total: UnivMents 26 134 160 t~iva.lents 299 947 1246

3{ean: UnlvMcn~s l-1 1.7 1,6 ]3ivMents I2-5 12.1 12.2

In the .hybrid G. stodcsii x G. c~'eysia~um pairing is not as complete as in the hybrid G. somale~se x G. a~'eysianum. This is in agreement with the morphological similarities of the parents concerned.

Most of the 102 pollen mother cells of the hybrid G. stoclcsii x G. a,reysianum were in first metaphase stage, a few in diakinesis. As in the hybrid g. somcdense x g. a~'eysian~tm, the bivalents did not show attenuation during disjunction, but lagging chromosomes were observed during first anaphase. Gamete formation therefore showed some irregulari- ties, due to the occurrence of up to ten univMents per pollen mother cell. Among 200 ' tetrads' counted, two were diads, one contained five microspores, six had six, and

H. D o v w E s 619

one contained seven. The extra microspores wore all small. This irregularity is reflected in the pollen grain diameters (Table 2). However, as natural seed forms freely, the plants are likely to be quite fertile.

Text-fig. ~l gives an example of pollen mother cells with ~hirteen bivalents in ~he hybrid G. stock, sii x G. a,~wsianum.

Text-fig. 5 shows the maximum mtmber of univalents observed. Thus the conclusion may be drawn that G. stoclcsii and G. areysianum are fairly closely

related. A close cytological relationship between G. arsysianu'm and G. somalense was recorded in the foregoing paragraph, and in a previous paper (Douwes, 195t), G. stocksii and G. somalense were found to be closely related.

In addition to their morphological similarities, this supplies enough evidence for placing these three species in one group.

0 % $ t

I

' : I d lO/x lo/x Tex%fig. 4 Tex~-fig. 5

Text-fig. 4. :Fh'st metaphase of ~he hybrid G. stocksii x G. areyslanum, showing thh'geen bivMents.

Text-fig. 5. First meg~phase of the hybrid G. stocksli x G. areysianum, sho~6Jag eight biv~lents and ten univalents.

(3) Hybrid Gossypium anomalum x G. areysianum

Morphological characters. Hairiness much nearer go the short, dense pubescent hairs of G. m'eysianum than to the long, soft hairs of G. anomcdum. To the naked eye the leaves and even more so the bwigs and pedicels look ahnost glabrous, although with a hoary appearance.

Leaves about two-thirds cut, slightly constricted, thus nearer to the three-quarters cut, constricted leaves of G. anomalum than to the scarcely cut leaves of G. areysianum.

Epicalyx bract-width intermediate, but mostly with three very conspicuous teeth, even more so than those of G. anoma~um.

Corolla shape and size nearer to G. anomalum; eolour of spot intermediate. CapsNes do not develop. Cytological characters. From many crosses 266 seeds were obtained, most of which

were empty. Twenty-five germinated and grew suceessNlly. They were planted out together with the ten hybrids G. somalense x G. areysianu'm in the middle of November 1950. However, they were much less vigorously growing and rather variable in their vitality. As three of them died soon after planting, it was feared that none of them would reach the flowering stage. Therefore two were grafted on to a perennial G. a~'boreum stock (Type ATe a) in the hope of increasing their vigour.

40-2

620 T he cytological relat ionsh@s oJ' G o s s y p i u m a r e y s i a n u m Deflers

On 1 January 1951 twenty-two hybrids (including the two grafted ones) were still alive, but had scarcely grown and by 1 July 1951 only six had survived, including the two grafted plants. One hybrid was more vigorous than the rest, right from the be- ginning. It was the first to flower early in Juty 1951 and was soon followed by the two grafted ones and by one more growing on its own roots.

Of these four hybrids three have been examined cytologically, of which one grafted. A less extensive examination of the other grafted hybrid showed similar results and will therefore not be recorded here.

On 1 November 195i the remaining two hybrids were still alive but not yet flowering. Thus although morphologically uniform (and also cytologically, as witl be seen), the

individual vigour of this interspecific hybrid is rather variable. As a rule interspecifie hybrids in Gossypium are uniform.

Valentine (1949) reports a similar variability in the F 1 of a cross between P,rimula vulga,ris and P. datior.

Table 4 gives the chromosome pairing in the three hybrid plants G. anomcdumx G. areysianum.

Table 4-. Chromosome conjugatio,~ in t~vo hund~'ed a, nd eighty-seven polle~'~ 'mot/wr cells of the hybrid Gossypium anomalum x G. areysianum

(

Univalents

26 2~ 22 20 18 16 ]~

Combination No. of pollen mother cells (percentages in brackets)

Bivalents Plant 1 Plant 2 Plant 3 (graft)

o 11 (26.1) 28 (35.~0 44 (26.5) [ 10 (23.8) 29 (36.7) 42 (25.3) 2 8 0.9.5) 16 (20.3) 40 (2~d) 3 7 (16'7) 5 (6"3) 22 (13-3) 4 5 (11.9) i (1.3) ~5 (9.0) 5 -- (o.o) -- (o.o) 2 (1.2) 6 I (2.~) -- (o.o) 1 (0-6)

Total 42 79 160

Total: Uniw~lents 946 [894 3788 ]3ivalents 73 80 264

~'Iean : Univalents 22'5 23.9 22.8 Bivalents l '7 1.0 ] '6

Total

83 (28.9) 81 (28.2) 64 (22.3) 3~ C1.8) 21 (7.7) 2 (0.7) 2 (0-7)

287

6628 417

23.1 1.5

Most of the 287 pollen mother cells observed were in first anaphase, judged by the presence of 'bridges', found during the disjunctive movements of the bivalent partners towards the opposite poles of the spindle. All the bivalents observed at this stage showed this attenuated appearance. The univatents at this stage are also spreading out towards the poles along the oblong shape of the spindle (Text-fig. 6).

The pietm'e is very similar to that of the first anaphase in the hybrids G. anomalum x G. somalense and G. anomahtmx G. stoc/csii, as described elsewhere (Douwes, 1951). Chromosome fl'agments in connexion with this 'bridge' formation were not seen in any of these hybrids.

Text-fig. 7 gives a first metaphase stage of the hybrid G. anomalum x G. areysianum. Here, as compared with Text-fig. 6, the bivalent partners are still closely conjugated, and the univalents still scattered more or less at random over the spindle, differ slightly in shape from. those at first anaphase.

Of the three hybrid plants examined in Table ~, plant no. 3 is the grafted one. A com- parison of the figures makes it clear that grafting does not effect the chromosome pairing. The mean values of the number of bivalents and univalents of the grafted hybrid lie

H. I ) o u w E s 62I

between those of the two ungrafted hybrids. A few counts of the chromosome pairing in the pollen mother ceils of ~he other grafted hybrid showed the same range. Both grafted hybrids grew well, but as one of the four surviving ungra['ted hybrids reached about the same height and vigom; no noticeable physiological influence of grafting could be inferred.

In consequence of ~he low chromosome paMng in the hybrid G. a'nomatum x G. a, rey- sianum, the gamete formation can be expected to be rather irregular. Table 5 shows the nmnber of mierospores found in one hundred 'tetrads'.

mm

Textdig. 6 Text-fig, 7

O

6

Text-fig. 6. First anaphase of the hybrid G. anomalum x G. areysianum, showhlg two bivalents a.nd twen~y-t~wo m~ivalen~s.

t Text-fig. 7. First metaphase of ~lle hybrid G. anomcd't*m x G. areysianum, showing three biva.lents and twenty univa.len~s.

Table 5. Number of mic,rospores in the ' tetrads' of the hybrid Gossyl~inm anom~lum x G. areysianum

No. of microspores 2 3 4 5 6 7 8 9 No. of 'tetrads' 13 8 45 21 9 3 0 1

Tot~l

I00

Although ~5 % of the ' tctrads' contain four microspores, these are often of unequal size, as is common wi~h an abnormal number of mierospores.

Thus it is not surprising that the hybrid G. anomatum x G. areysianum was found to be completely sterile. The great variability in pollen size as shown in Table 2, with a high proportion of small and inviable grains, is additional evidence for this.

(4) Hybrid Gossypium anomalum x G. triphyllum

Mo,rphologicat cha,racte~'s. Hairiness nearer to the denser and shorter tomentum of G. t,r@hyllu,m,.

Leaves divided to the base as with G. triphytlu,m, shape of lobes intermediate. Fruiting branches more like those of G. anomah~,m, mostly with two or more flowers. Cytologiccd characters. Out of many crosses, twenty-two seeds were obtained of which

thirteen germinated a,nd grew to maturi ty. Five of these were examined cytologically, as summarized in [['able 6.

Most of the sixty-six pollen mother calls observed were in first metaphase (Text-fig. 8), though some were in diakinesis. 0f the two congaimng twelve bivalents and two uni- valents, one was in diakinesis and bhe other in first metaphase. In diakiuesis the two

622 T h e cytologicid re lat ionsh@a of G o s s y p i u m a r e y s i a n u m De tiers

Table 6. Chr conjwation in sixty-six .pollen mother cells o/' the hybrid Gossypium anomalum • G. tr iphyllum

Combination No. of pollen mogber coils (percenLagcs in brackets)

Univa.lenLs J3ivalcnLs :Plant ] Plant 2 Planb 3 Planb 4 Plan~ 5 Total 0 13 17 13 13 l0 II 64 ( 9 6 . 9 )

2 3 2 - - 2 - - - - - - - 2 ( 3 . 1 )

Tot~l 17 15 13 10 11 66

Tol~al: Univalen~s - - 4 - - - - - -

]3ivMengs 221 ] 93 169 ] 30 143 856 h'~e~n : UnivalcnLs -- 0.3 - - - - - - 0' l

]3iva.len~as 13'0 12'9 13'0 13'0 ] 3'0 12.9

univalents lie close together but clearly free from each other. In the metal?hase they were seen opposite each other at an equal distance on both sides of the equatorial ]?late. Their shape, however, did not indicate a disjunction dm'ing early metaphase.

All first anaphase stages observed consisted of two groups of thir teen bivalents and looked normal.

Two hundred tetrads were examined, all contained four mierospores of equal size. In fact, the diameter of the pollen grains formed was not shifted noticeably from tha t of the two parents (Table 2). Consequently, the hybrid G. anomalum x G. triphyllum has a high degree of fertility. I t forms natural seeds freely, and selfing and backerossing could easily be achieved.

1o/~

TexL-fig. 8. First meL~phase of the hybrid G. anomalum x G. trilgtyllum, sho~4ng ~hh'teen bivMents.

Thus G. anomalum and G. triphyllum are not only morphologically but also cytologically very closely related.

DISCUSSION

I t has been shown tha t the chromosome set of G. areysictnum has great homology with that of G. somalense and a little less with tha t of G. stocksii. I t has ve ry little homology with the chromosome set o f G. anomalum. Judged by the close relationship between G. anomalum and G. triphylhtm, the same low homology can be expected between G. m'eysianum and G. triphyllu'm.

Beasley (19~2) gave the symbol E 1 to the chromosome set of G. stoc/csii. This was followed by E 2 for G. somalense (Douwes, 1951). Now E a is proposed for G. areysianum.

Thus sufficient evidmIce is given here, both morphological and cytological, to group G. areysia, num with G. stocksii and G. somalense into the section Ntoelcsianc~ of Hutchinson's (19~7) classification. Morphologically G. areysianum resembles G. somcdense more than G. stocksii, the lat ter being distinctly different from both in its procumbent habit. The cytological relationships between the three species is in accordance with theft" morpho- logical difference. The percentage of pollen mother cells (I,.M.c.) examined, showing complete pairing, illustrates this as follows:

To~al no. No. r.~Lo, with r.~Lo. 13 bivalcnts %

kIybrid G. somalensc x G. areysia~um 224 202 90.2 l~Iybrid G. somalense x G. slocksii (Douwcs, 1951) 41 27 65.9 IcIybrid G. slocksii x a. arcysictnum 102 53 51"9

H. D o u w E s 623

As to the real relative position of the three species concerned, the average pairing ill the hybrid G. somcdense x G. stocl~sii is the least accurate, based on the smallest number of pollen mother cells examined.

Geographically, as at present known, G. ct~'eysict~'~ttm occurs in the centre of the area of distribution of the Ntoc/csia'~w~, with G. somalense on its western, and G. stodcsii mainly on its eastern flank.

That Hutchinson (19~7) classified G. a,reysic~num wrongly as belonging to the section Anomalc~, together with G. a, no~nalum and G. t,r@hyllum, was caused by the fact that at that time the only material available was the description of one herbarmm specimen, collected in 1893. Further evidence was completely lacking, as the plant had never been collected again.

Thus the section _/hzomalcb shoNd now consist of G. anomalum and G. t~'i2)hylh~m oNy. G. t~'@hyllum, a recent accession like G. areysia~um, is only dealt with here in its direct relation to G. a'~zomalum. A cross between G. t~'@hyll~m and G. a~'eysian~m has not yet been successful, t~[owever, its very close cytological relationship with G. anomalum, together with their morphological similarities and with their geographical distribution leaves no doubt as to its position.

The fertility of the hybrid G. ano~nahtm x G. t,riphyllum, judged by its abundant seed production, in connexion with an almost normal chromosome pairing and pollen size, seems to be the highest found among the wild Gossy2i~tm species of the Old World. I t might well be comparable with the relationship between G. ha~'l'cnessii and G. a~'~zoto'ianum, the hybrid of which is Nlly fertile.

As the G. c~nomalum genom also shows a high degree of homology with that of G. a~'bo~'eum (Silow, 19~1) an investigation of the relationship between G. a~'bo~'eum and G. t'ri2)hylhe,m will be important.

The symbol B 1 has been given to the genom of G. anomalum by Beasley (1942). B s is therefore suggested for that of G. t~'@hyIlum.

In conclusion it can be said that all hybrids considered here show that the cytological amnity of the parents is in harmony with their morphological similarities. This in con- junction with t, heir geographical distribution, as known at present, gives the following picture:

The section JStoclcsiana, with its three E-genom species, has its centre of distribution in the area around the Gulf of Aden. G. stodcsii and G. a~'eysia~z~tm both occur in southern Arabia, while G. stoclcsii and G. somalvnsv have both been found in British Somaliland.

From this centre, G. stoclcsii extends towards the east (Sind), while G. somalense has been found in Kenya, in many places in the Sudan, and in French Equatorial Africa.

The centre of distribution of the section Anomala is in South-West Africa, where both its B-genom Sl~ecies occur. G. t,ri2)hyll~/m has not been found elsewhere, but G. a~zomalum has a widespread distribution all through the semi-arid areas of Africa.

South of the Sahara, the distribution of G. a, nomal~n overlaps extensively with that of G. somalc'~zsv. As they do not intereross (Douwcs, 1951), although often occupying the same habitats, it may be assumed that both species were already differentiated in different directions under different environmental conditions, before intermixing.

Assuming th a~ the presen~ centres of distribution of the two sections in dieate the areas from which they have arisen, it would mean thab G. som~densv has spread from the eas~ and G. c~nomal'ttm [u the south-west, thus converging in north Central Africa.

62~= ~V~e cytological re la t ionsh@s of G o s s y p i u m a r e y s i a n u m Deflers

S U ~ A R u

Gossy2ium a~'eysianum is shown to have the chromosome nmuber n = 13, as have all other wild species of Gossypiu~n.

A morphological description of it, together with a drawing, have been given. Three hybrids of G. a,reysianum were examined, mainly cytologically, in order to obtain

additional evidence for its classification. The hybrid G. somalense x G. a,reysianum shows a very high homology between the

two parental chromosome sets. The average chromosome pairing at first metaphase is 12.9 bivalents and 0.2 nnlvalent.

Although slightly less, a high homology was also found between the chromosome sets of G. stoclcsii and G. a~'eysianu'm, the hybr id having an average of 12.2 bivalents and 1.6 univalents at first metaphase.

A completely different picture, however, is shown by the hybr id 64. anomcdum x 64. areysia~zum. Here the average chromosome pairing at metaphase only amounts to 1.5 bivalents and 23.1 nnivalents. Thus there is very little homology between these parental chronmsome sets.

The hybrid 64. anomalum x 64. t,riphyllu~n, with an average metaphase chromosome pairing of 12.9 bivalents and 0.1 univalent, again shows a very high degree of homology between the parental chromosome sets. F rom this it may be concluded tha t the chromo- some pairing of the hybrid G. triphyllum • 64. a~'eysianu~n might be expected to be of the same low order as tha t of the hybrid G. anomalum x 64. areysianum.

Based on these conditions, the symbol E 3 has been given to the genom of 64. areysianum, thus linking it with its nearest relatives, 64. stoc/csii (El) and 64. somalense (E2).

The symbol B~ has been given to 64. triphyllum, as 64. anomalum (B1) proved to be its nearest relative.

The classification of these species on morphological grounds is found to be in harmony with their cytological at~inities, and so is their geographical distribution.

The author wishes to express his thanks to h{rs G. Andrew for making the drawing of G. areysianum and to Dr g . L. Knight, O.B.E., for his help in the writing of this paper.

1TEFERENCES [B~sLI~Y, J. O. (1942). l~{eiotic chromosome behaviom' in species, species hybrids, haploids, and induced

pol~q~loids of Gossy~ium. Genetics, 27, 25. Douwl~s, H. (1951). The cytological relationships of Gossypium somal~nse Gfirke. J. Genet. 50, 179-91. Do~w~s, H. & CuA~u P,,. L. (1951). Progr. 12cp. Exl~. Sla. 1949-50, Emp. Cott. Gr. Corp. pp. 3640. IIv'~cm~so~, J. B. (194~7). In The Evolution of Gossyl)ium, by J. ]3. Hutchinson, 1~. A. Silow and S, O.

Stephens. Oxford University Press.. ]~[c-H'~,, R,. L. (1949). The distribution of wild species of Gossypium fl~ the Sudan. Era1). Colt. Gr. ~e~.

26, 278-85. Smow, g. A. (1941). The compar'~tive genetics of Goss//l~iu'm, somalense and the cultivated Asiatic

cottons. J. Goner. 42, 259-358. VAI~]~NTI~E, D. H. (19'[9). Interspecific hybridization hi Primula. Here(lily, 3, 128.