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Day length and flowering inthe Solanum aviculare groupG.T.S. Baylis aa Botany Department , University of OtagoPublished online: 08 May 2012.

To cite this article: G.T.S. Baylis (1968) Day length and flowering in theSolanum aviculare group, New Zealand Journal of Botany, 6:2, 221-225, DOI:10.1080/0028825X.1968.10429059

To link to this article: http://dx.doi.org/10.1080/0028825X.1968.10429059

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\968] BAYLIS - FLOWERI NG I N SOLAN lJ M

DAY LENGTH AND FLOWERING IN THE

SOLANUM AVICULARE GROUP

G. T. S. BAYLIS

Botany Department. University of Otago

(Received for publicatioll 15 December 1967)

SUMMARY

221

Most members of the Solallum aviculare group flowered only in long days. but there were day-neutral races in S. simile and S. capsiciforme. S. aviclllare consisted of ecotypes in which photoperiod was adapted to latitude and temperature. A race from 6 0 S could flower normally in 8-hour days, and more !loutherly races required increasing photoperiods; but day lengths sufficing to produce flowers in warmer months produced abortive inflorescences in cooler ones. In S. l(lcilliatllm no latitudinal change in critical photoperiod was apparent.

1 NTRODUC'TION

Solanum aviL,,/are and its six allied species (Baylis. 1963; Herasimenko. 1965) are sel' . -woody shrubs which differ from the rest of the genus (x= 12) in chromosome number (n=23 or 46). Their area extends from the uplands of New Guinea through Australia and New Zealand. but only S. aviculare covers it at all completely: it extends from 60 S to 44°S. The other species are all confined to the warm-temperate and subtropical latitudes of Australia. except S. laciniatum. which is found from 35°S to 46° 30'S.

Seedlings produce a rosette of about six leaves close above the cotyle­dons. The axis then extends. bearing more distant alternate leaves and ending in an inflorescence. In the small species (S. capsiciforme, S. simile) there are fewer than 10 of these leaves; otherwise there are usually between 12 and 30. One or more axillary shoots arising close below the flowers end in turn in an inflorescence. but they bear fewer leaves. often fewer than five. even in the tallest species. Inflorescence primordia are thus an essential part of the branch system. but they do not always develop their flowers. The buds may fall. and the peduncle then withers. This may OCCur when the peduncle is anything between one and 60 mm in length. with buds in proportion.

N.Z. JI Bot. 6: 221-5

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222 Nl·W Zl AI AND JOURNAl. OJ< BOTANY [JUNE

PUlT TRIAl.

Seed from SO provenances. principally S. lacillialllnt (25 provenance~) and S. uviclllure (IS). wa.., u..,et! at Dunedin (Lal. 4fJoS) in a plot te~t of solasodinc yields. Seedling.., were rai..,ed under glass between May and Auoust and planted out by November. For each race th~re were 20 pla~ts. By the end of February almo..,t the entire planting. which included every species. was flowering and setting fruit. The exceptions were all in S. av.culure. Races of this 'ipecics from New Guinea (6

n

S). Brisbane (2X-S). and Auckland 07"5) produced nUl11erou'i flowers and (ruits; those from Mo\s Vale (35·5). Wilsons Promontory (39°S). and six localities in New Zealand sOllth of 3HoS bore only an occasional flower and no fruit-usually the seedling axis had branched. but the inflorescence had aborted. By the middle of April. though flowers were often still plentiful. younger inflorescence., were u..,ually aborting in most of the planting. But again there were exceptions--the fruiting plants of S. uviclI­lure. all four races of S .. Hmollii. one race of S .. \imi/C'. and the single race of S. cU{H-ici/orme still carried bud ... at all stages of development. and did so until winter injury began. From these observations. it seemed that long days were generally necessary for complete development of the inl1ore)'cence. For S. lacini­utum. S. ve\cum. and S. Iilleuri/olium this need Wa), met well into autumn. Southern races of S. uviculure appeared to have a longer critical day length. which had passed by the time they were ready to respond to it. while northern races. and the three other species that continued in flower until winter. seemed to need only a relatively short day. or to be day­length neutral.

A large number of leaves. exceeding 30. between the ro~ette and first branch in southern provenances of S. uviclllare suggested that day length might also affect inflorescence initiation.

GLA~SW)(JSI: EXPH{JMI'NT" Under glass (min. 5°c) all species grew through the winter. but only two races flowered continuously-S. cU{)\'ici/orme from Eyre Pen. and S .. \·imile from We~tern Australia. These also flowered and fruited when raised from seed in the spring in a cabinet receiving X hours only of natural daylight. Even in a warmer house (min. 15°(,) inflorescences of S. aviculare from Mt Wilhelm. New Guinea (60 S). began aborting late in April. and the plants did not flower again until mid August. In the cooler house the flowerless period for all races extended into October Or even November.

To confirm that basically these were reactions to day length. cuttings and seedlings of S. aviculare were grown under glass (min. 5°c): (a) under natural daylight followed by artificial light through the night. (b) under natural daylight alone. (C) in a light-tight box unlidded for 8 hours daily and lit artificially for one hour at midnight. (d) as (c) but without the light break at night. There were usually four replications (Table I).

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1968] BAYI.I<; - FLOWERI N(; IN SOLANUM 223

TAmE 1- -Onset of anthesis in So/allllnt aviclI/arc at Dunedin (Iat. 46°s) under glass (min. 5'c)

Treat- (a) (b) X hours daylight

"iource La!. ment Stock Continu- Natural ( 's) begun ous light days (c) + break

t'Mt Wilhelm 6 20/ S/67 Cuttings 9t10,'67 30/10/67 t*8risbane 27 19· X66 Cuttings 3111/66 24'10/66 14/10/66

Brisbane 20: 5/67 Cuttlllgs 15/10/67 9/10/67 Brisbane 20'1266 Seeds 1S/10167

'Coromandel "7 I'>' X/66 Cuttings 10/10/66 14/10/66 27/ 9/66 Moss Vale ,,5 19, X/66 Cuttings 24110/66 14/10/66 ( 14/10/(6) Moss Vale 20 1 5167 Cuttings 9/10/67 15110/67 Moss Vale 20112,66 Seeds ( 16/10/67) Farewell Spit 40 19' X,66 Cuttings 29/11/66 3/11/66 ( ,,'11/66) Kaikoura 42 20/ 51n7 Cuttings 25110/67 A

t var. hr;shallclIsc Herasimenko * provenances which flowered in their first summer in Dunedin

A all buds abortive () a few flowers on one of four replicates only. most buds abortive

- treatment omitted

(d) alone

16/10/67 A

( 17/10/67) (30/10/67) (231 9/66)

A A A A A

The treatments begun in August 1966 were followed by an attempt to reverse flowering behaviour by interchanging plants between boxes. The results were complicated by the pruning and fertilizing needed to maintain suflicient growth in a small space. However, all Brisbane and Coromandel cuttings transferred to the cabinet with the light break flowered within one to three months, while the Moss Vale and Farewell Spit cuttings continued to produce abortive buds. The oppm.ite transfer always termin­ated flowering within one month.

DISCUSSION

The flowering behaviour recorded in Table I establishes that Solanum aviculare is a long-day plant. since it was rarely able to flower in short (8-hour) days alone. but usually flowered when the accompanying 16-hour dark period was broken by a period of artificial light; and it also flowered normally in continuous light. It was also apparent that the day length required for full development of the flower buds increases with latitude. Eight hours of daylight produced normal flowering in the subequatorial Mt Wilhelm race. and sometimes sufficed to mature a few flowers on a plant from a subtropical environment. Conversely. the lioht break during the 16-hour night commonly failed to develop many of the buds on plants from the higher latitudes. For the most southerly proven­~nce. not only was this failure complete in all four plants, but the mflorescences were nearly all less than I cm in length when their last buds abscissed.

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224 NI \\ ZI AI ·\NI> .Iot·RNAI 01· ROIANY [.I 1I Ni"

The~e experiment~ al ... o ~howed that readion to day length i~ modified by other fador~. Four of the ... eedling~ that flowered in day-length boxes did !>o at their ~econd branching. in October. after the bud ... had all fallen from an inflore~cence formed between April and June. Similarly. the cutting~ that hore flower, under fixed day length in Odoher 1967 preceded the!>e with ahortive inflore~cem:c!> during Augu!o.t and September. Finally. ~tock from the relatively continental climate of Mo!o.s Vale flowered le~~ in the day-length hoxe ... than that from oceanic Coromandel. two degrees further ,outh.

The~e reaction~ involved the initiation a ... well a!o. the per~istence of flower huds. The ~eedling~ rai~ed in the day-length hoxe~ formed an exceptionally large number of leaves hetween the ro ... ette and the !irst inflore~cence~in the Bri~hane race 34 45. in the Mm~ Vale race ahout 10 more. For hoth. the higher numher ... were in treatment (d).

As growth in the So/unllm lIVicII/lIre group i, not inhihited by short day' or hy temperature'> falling nightly to 5°( (perhap~ le~~). the specie ... would all tend to nower continuou ... ly. at least in part of their range. if development of the innore~cence did not need long days. The ~elective advantage of thi ... need prohahly lie ... in the failure of pollination in cool weather (Baylis. 19(3) and the preference hird~ ~how for well ripened fruit. In the widely ranging S. llvicu/are there i~ a latitudinal pattern of adaptation to day length such a!o. ha!o. heen e ... tahli!>hcd for Northern Hemi~phcre "'pecie!. (Hie~ey and Milner. 1965). The principle that low temperature may ~uh~titute in part for darkne ... ~. and high temperature for light (Searle. 19(5) abo applie~. '0 that a photoperiod ineffective in a cool ~ea~on or climate. may ... ullice in a warmer one. and conversely_ The New Zealand gra~ ... Chio"oclr/pa rigicJa abo ~eem~ to con~ist of ec()type~ needing different comhination... of long day and temperature to flower- -temperature being the critical variahle when the series studied i~ altitudinal rather than latitudinal (Mark. 19(5). S. /acinilltlll1l. however. mu~t vary little in it~ day length and temperature re4uirements. ~ince all races. including three from 33 35°S. hehaved ~imilarly in the plot trial.

To maintain their integrity a~ !>pccie~ S. lIvim/lIre and S. Illcillilltum must occa!o.ionally crO!>~ the Tasman Sea. which is J'Ol-sihle without changing latitude. hut. if the vector~ follow the prevailing wind~. there will be a change from continental to in~ular temperature~. The di~similar behaviour at Dunedin of Mos~ Vale and Coromandel race~ of S. Clvicu/are sugge~ts that this would su h ... tantially alter the day length re~pon~e. and that an immigrant race might fail to flower in its tlr,t ~eason in New Zealand. Similarly. the South bland races ~eem unlikely to extend their range to Dunedin. though they can overwinter there in a sheltered place. Their spring growth begin~ late. and in the relatively cool summer their photoperiod i!> never sati~fied in their fir ... t year. and not always in suh"equent summer~. There are thu~ grounds for suggC!.ting that day­length adaptation i!> proving a harrier to !'outherly ~pread and to gene flow in S. avicillare. accounting for ih failure to enter the \Oltlhern half of the South 1"land. and. in ,orne mea'ure. for it ... varietie .... Neverthelc\s.

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1968] BAYUS - Fl.OWERING IN SoLANUM 225

races of the type variety from New South Wales and from the North Island are similar morphologically and are fully interfertile.

ACK NOWLI-.DG M E NTS

The provenance trial was financed by a grant from Ciba Ltd. received through Dr H. Hiirlimann. I am also indebted to Dr M. Holdsworth for the use of apparatus and for advice. and to numerous colle'agues for collections of ~eed.

REFERENn.S

BAYLIS. G. T. S. 1963: A cytogenetical study of the So/anllm tlviclI/l/re species complex. Allsl. J. BOI. II: 16H-77.

HERASIMENKO. I. I. 1965: Noviye fonni Solanum L. podroda Archaeosolanum Ritter. BYlIll. gll/vn. bOI. Sadu, Leningr. 59: 71-)

HIESEY. W. M. and MILNER. H. M. 1965: Physiology of ecological races and species. A. Rev. PI. Physiol. 16: 203-16.

MARK. A. F. 1965: Flowering. seeding. and seedling establishment in the narrow­leaved snow tussock, Chionochloa rigida. N.Z. J/ Bot. 3: IHO-9).

SEARLE, N. E. 1965: Physiology of flowering. A. Rev. PI. Physiol. 16: 97-118.

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