Effect of light conditions on the development of the inflorescence in tomato

Scientia Itorticulturae, 6 (1977) 15--26

15

Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

EFFECT OF LIGHT CONDITIONS ON THE DEVELOPMENT OF THE INFLORESCENCE IN TOMATO

J.M. KINET

Centre de Physiologie V$g$tale Appliqu$e (I.R.S.I.A.), D~partement de Botanique, Universit~ de Liege, Sart Tilman, B-4000 LiSge (Belgium) (Received 15 June 1976)

ABSTRACT Kinet, J.M., 1977. Effect of light conditions on the development of the inflorescence in tomato. Scientia Hort., 6: 15--26. By growing tomato plants (Lycopersicon esculentum Mill. ) in 4 different light regimes (2 photoperiods -- 8 and 16 h -- combined with 2 light intensities -- 9,000 and 18,000 ergs cm -2 s-' ), it was shown that increasing light integrals hastened flower initiation, greatly promoted the development of the inflorescence and increased the rates o f leaf production and the growth of the stem. In similar light integrals, flower initiation was earlier and inflorescence development far better in short photoperiods than in long ones; the rates of leaf production were almost the same and stem growth was greater in long days. Transfer experiments from favourable to insufficient light conditions and inverse transfers at different times during the life of the plant indicated that light conditions were critical at the time of, and after, the macroscopic appearance of the inflorescence. At that stage, a transfer to low light conditions for 10 days induced complete abortion of the truss in our growth conditions. The effect of a transfer from insufficient to favourable light conditions was slower since at least 15 days in these latter conditions were required in order to achieve the development of the inflorescence. INTRODUCTION

Several studies have stressed the difficulty in obtaining satisfactory development of the first inflorescence in early tomato growing in temperate countries such as the United Kingdom (Cooper, 1964; Cooper and Hurd, 1968; Calvert, 1969). As Calvert (1969) has pointed out, the problem concerns the postinitiation stage of development of the flower buds since plants which fail to produce a normal inflorescence always reveal a small immature truss which invariably aborts. Although there is much evidence on the importance of light conditions and temperature in the control of the development of the tomato inflorescence (Lewis, 1953; Calvert, 1959, 1964; Kristoffersen, 1963; Lake, 1967; Hurd and Cooper, 1967, 1970), there is little information available on the critical levels of these environmental factors inducing abortion, and on the stage of development during which the plant is most sensitive to adverse con-

16 ditions. It appears however, that the sensitivity is maximal during the late stages of development of the inflorescence since abortion occurs when high temperature and low light are applied at this time (Calvert, 1969). Abortion is a c o m m o n and critical problem in winter-grown tomatoes in Belgium and it is essential to try to avoid it. Because increasing light intensity in glasshouses with artificial light would be t o o expensive, it is necessary to find other means to prevent abortion. This is the objective of the present research. A better knowledge of the conditions giving rise to abortion is, however, required and is a prerequisite for further studies. That is why in this first paper, our aim is to gain accurate information on light conditions leading to abortion. What is the effect of light intensity and photoperiod? At what stage in the life of the plant do unfavourable light conditions mainly affect the development of the truss? In order to avoid temperature effects, all the present experiments were performed at the same constant temperature. The cultivar 'King Plus', c o m m o n l y grown in Belgium, was used in this study. MATERIAL AND METHODS G r o w t h c o n d i t i o n s . -- All the experiments were carried out in the growth rooms of the p h y t o t r o n of the Botanical Department at Liege. Seeds o f the cultivar 'King Plus' {Etabl. Pannevis, Duffel, Belgium) were germinated at 26°C in a peat c o m p o s t (TKS1 from Floratorf, Oldenburg, Germany). After 2 weeks, plants were pricked o u t in 7 cm pots filled with TKS: peat compost (Floratorf) and at an appropriate time into 14 cm pots. During growth, the day and night temperature was maintained at a constant 20 ° C. We chose this high temperature as it is known that a higher temperature is less favourable to inflorescence development. Light was provided exclusively b y white fluorescent tubes (ACEC LF-40W/2 4 3 0 0 ° K or P h y t o r C.R.H.Lg.). The light intensities used were low, which was also in order to obtain high percentages of abortion. There were 12 plants per treatment and at least one replication. In most treatments, the data were recorded in respect of the first and second inflorescences. R e c o r d i n g m e t h o d s . - - Flower-initiation, development of the inflorescence and

plant growth were considered. For practical reasons the observations had to be stopped after flower formation, so that no data on the fruits are available. These will be collected in the near future. For flower-initiation, the data presented refer to (a) the n u m b e r of days from sowing to the macroscopic appearance of the truss, recorded when the sepals of the first flower could be visualized individually; (b) the number of leaves formed before inflorescence initiation. For the development of the inflorescence, the data refer to (a) the n u m b e r of days from the appearance of the truss to the first anthesis; (b) the per-

17

centage of plants flowering at the considered truss using the anthesis of at least 1 flower as the criterion; the complete failure of the truss to develop any flower bud to the stage o f anthesis indicates the abortion of the inflorescence. Data regarding plant growth refer to (a) the stem length measured from the cotyledonary node to the shoot tip; (b) the rate of leaf production determined b y recording periodically all the leaves having a blade more than 1 cm long. RESULTS

Effects o f photoperiod and light intensity on flower-initiation, development o f the inflorescence and plant growth. -- After pricking-out, plants were grown in 4 light regimes. There were 2 photoperiods -- 8 and 16 h -- and 2 light intensities -- 9,000 ergs cm -2 s'' and 18,000 ergs cm -2 s" at the top of the plants. In these different conditions, the flowering-responses for the first 2 inflorescences are shown in Table 1. The appearance of the inflorescences is earlier and occurs after the formation of fewer leaves, in days with higher light flux integrals. However, in days with similar light flux integrals, flowering initiation is hastened in short days. TABLE 1 E f f e c t o f p h o t o p e r i o d a n d light i n t e n s i t y o n f l o w e r - i n i t i a t i o n , i n f l o r e s c e n c e d e v e l o p m e n t and g r o w t h . LI : L o w light i n t e n s i t y ; HI : High light i n t e n s i t y . Means a n d p e r c e n t a g e s w i t h 95% c o n f i d e n c e limits. F o r p e r c e n t a g e s , c o n f i d e n c e limits in square b r a c k e t s are read directly f r o m P e a r s o n and H a r t l e y (1969, see Table 41 ). Light regime 8h-LI

8h-HI

16h-LI

16h-HI

1st truss 2nd truss

78.1 +- 5.69 > 92

48.5 +- 1.00 61.1 +- 1.58

52.1 ± 1.37 66.5 +- 2.18

40.6 +-0.94 51.3 +- 1.09

N u m b e r o f leaves formed before 1st truss initiation o f t h e 2nd truss

12.2+_0.65 > 17

9.2_+0.27 13.2 +-0.48

9.8+-0.25 14.1 -+0.30

9.3+-0.34 12.7 +-0.57

1st truss

0 [0--14]

62.5 [ 4 1 - - 8 1 ]

0 [0--14]

100 [ 8 6 - - 1 0 0 ]

2nd truss

0 [0--14]

100 [ 8 6 - - 1 0 0 ]

18.2 [ 6 - - 3 9 ]

100 [ 8 6 - - 1 0 0 ]

N u m b e r o f days f r o m sowing t o m a c r o s c o p i c appearance of the

P e r c e n t o f flowering plants at the

N u m b e r o f days 1st truss from macroscopic a p p e a r a n c e to firSton d truss anthesis at t h e S t e m length ( m m ) at t h e

51st day

--

18.0 +- 1.51

--

15.8 +- 0.66

16.0 ± 3.90

13.0 +-0.48

114 ± 12.4

156 ± 17.6

173 ± 7.8

56 ± 12.0

--

13.1 +-0.56

18 Regarding t h e d e v e l o p m e n t o f the i n f l o r e s c e n c e , it is clear t h a t it is mark e d l y a f f e c t e d b y the daily light e n e r g y received. All plants f l o w e r e d at the first 2 inflorescences in days with t h e higher light integral; all a b o r t e d in days with the l o w e r light supply. O f the 2 t r e a t m e n t s with the same light integral, i n f l o r e s c e n c e d e v e l o p m e n t is far b e t t e r in s h o r t days with high light i n t e n s i t y t h a n in l o n g p h o t o p e r i o d s with l o w light intensity. L o o k i n g at t h e t i m e interval f r o m t h e m a c r o s c o p i c a p p e a r a n c e o f t h e i n f l o r e s c e n c e t o t h e first anthesis, it appears t h a t it is s h o r t e r w h e n the daily light s u p p l y is higher and, as s h o w n at the s e c o n d i n f l o r e s c e n c e , it is identical in b o t h t r e a t m e n t s with t h e same light flux integral. S t e m g r o w t h is also a f f e c t e d b y t h e light t r e a t m e n t s . T h e higher the light flux integrals, t h e taller t h e plants; w h e n t h e daily light s u p p l y is t h e same, t h e stem g r o w t h is faster in long p h o t o p e r i o d s . Figure 1 shows regression e q u a t i o n s f o r leaf n u m b e r o n days f r o m sowing

/

14,

12-

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•

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8h-LI

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3'1

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Days from sowing

Fig.1. E f f e c t o f l i g h t o n r a t e o f l e a f p r o d u c t i o n . H I : H i g h I n t e n s i t y - - LI : L o w I n t e n s i t y .

16 h -16 h -8 h -8 h --

high intensity : y = 0.34 x--4.42, r = 0.999; low intensity : y = 0.29 x --4.04, r = 0.998; high intensity : y = 0.31 x --4.91, r = 0.999; low intensity : y = 0.17 x--1.65, r = 0.999.

19 and the respective regression lines. The rate at which new leaves are produced is constant with time when the environmental factors remain constant; it increases when the total a m o u n t of light energy supplied daily to the plants increases and it is almost similar for plants grown in days with similar light integrals.

Effects o f transfers from favourable to adverse conditions on the developm e n t o f the inflorescence. Time o f effectiveness. -- Plants were grown from sowing in light conditions allowing the development of the inflorescences in a high percentage of plants. These so-called "favourable conditions" were daylength 12 h and light intensity 20,000 ergs cm -2 s-~ . In order to determine at what time during the life of these plants insufficient light conditions are most effective in inducing the abortion of the inflorescence, plants were transferred at different time intervals, for 10 days, to adverse conditions: daylength 8 h; light intensity 12,000 ergs cm -2 s-~ . All the inflorescences from plants continuously kept in these adverse conditions aborted. The effect of these transfers on the development of the inflorescences is shown in Figs 2 and 3. Giving the adverse light conditions before the 46th day does n o t reduce the flowering-response at the first truss. From the 46th Macroscopic appearance of the truss

70-

~

60-

Control in favourabie conditions

= ~"

50-

°itl,-

40-

I:: k. 0

30"

o ~"

20-

C 0.

1O-

N

Control in adverse conditions

- ~e

4~

3~

Transfer

to

(days

s~

adverse from

~6

7~

conditions

sowing)

Effect of a transfer from favourable to adverse light c o n d i t i o n s , at different times after sowing, on flowering of the first truss. The duration of the transfer was 10 days. Fig.2.

20 Macroscopic appearance

~of the truss

I!

90,

Control in favourable conditions

80-

70-

~*

60-

¢ 0 ¢) 50o

40. P i. 0

30.

¢ ~ 0.

20.

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C o n t r o l in adverse conditions

l_ o 2'6 Transfer

3'~

to adverse

,~ conditions

s~ (days

6'6 from

7~ sowing)

Fig.3. E f f e c t o f a t r a n s f e r f r o m f a v o u r a b l e t o adverse l i g h t c o n d i t i o n s at d i f f e r e n t t i m e s a f t e r sowing, o n f l o w e r i n g o f t h e s e c o n d truss. T h e d u r a t i o n o f t h e t r a n s f e r was 10 days.

day, i.e. the time of macroscopic appearance of the first truss, to the 56th day adverse light conditions completely prevent inflorescence development. Later, their effect is less and less marked with time (Fig.2). For the second truss, similar results were obtained. However, the time of greatest effectiveness is 10 days later than for the first truss; it corresponds with the time of macroscopic appearance of the second truss (Fig.3). D u r a t i o n o f t h e transfer. - - Plants grown until macroscopic appearance of the first truss in favourable conditions were transferred for 2, 4, 6, 8 or 10 days to adverse conditions and then returned to favourable conditions. Results are summarized in Fig.4. They show that the n u m b e r of plants flowering at the first truss decreases as the duration of the stay in adverse light conditions increases. The effect of these adverse conditions is already detectable after 2 days and the abortion is almost complete after 10 days.

21

80¸

60.

40e0 .?

20-

\

C D.

Control ir, adverse conditions ~ •

o -

g

~

~

;

~

ib

D u r a t i o n of thb s t a y in a d v e r s e conditions (days)

Fig.4. Effect of the duration of the transfer from favourable to adverse light conditions on flowering of the first truss. The transfer begins at the time of the macroscopic appearance of the truss.

Effect o f transfers from adverse to favourable conditions on the development of the inflorescence. Time o f effectiveness. -- Plants grown since sowing in adverse light conditions were transferred at different time intervals to favourable conditions. The duration o f the transfer was 15 days. As shown in Fig.5, favourable conditions c a n n o t prevent inflorescence abortion when given before the 56th or after the 71st day. When the plants were transferred at the time o f the macroscopic appearance o f the inflorescence, i.e. at the 56th day, the favourable light conditions p r o m o t e flowering. Later experiments have shown t hat t he prom ot i ve effect of the transfer to favourable conditions was greater when it began a few days before the macroscopic appearance o f the inflorescence. Similar results were obtained at the second truss (Fig.6). Duration o f the transfer. -- Plants grown in adverse light conditions were transferred to favourable conditions just a few days (2--4) before t he macroscopic appearance of the first truss. The duration of t he transfer varied from 5 t o 20 days. The results in Fig.7 show t hat a stay of at least 15 days is required in o r d er to achieve the d e v e l o p m e n t o f the inflorescence in a n u m b e r o f plants as high as in the controls c o n t i n u o u s l y kept in favourable light

22 Control in favourable conditions 70'

Macroscopic appearance of the truss

60"

.,i

50"

40'

0') ¢: i. ¢P

30"

i=

0 q.

20-

e. I:.

10-

Control in ~caodnV~irtSens i

L_ o

4~

5~

~

Transfer to favourable

~6

i~1

conditions

(days from sowing)

Fig.5. Effect of a transfer from adverse to favourable light conditions, at different times after sowing, on flowering of the first truss. The duration of the transfer was 15 days. conditions; abortion is almost complete when the transfer is only for 10 days or less. DISCUSSION The effect of environmental factors on the flowering of tomato have been intensively studied. From the work already published, it appears that the effect of the daylength is small and hardly demonstrable because several other factors influence the flowering-response of this species. For instance, it is known that light intensity, temperature and nitrogen content in the soil (cf. Wittwer and Aung, 1969) greatly affect flower-initiation. This complicated situation can account for the different photoperiodic responses which were successively attributed to tomato. From our experiments, using different daylengths with a constant daily light energy supply, we can conclude, in agreement with Wittwer (1963), Binchy and Morgan (1970), and Hurd (1973), that tomato is a quantitative short-day plant: its flowering is earlier and occurs after fewer leaves in short photoperiods than in long ones. In other respects, our results clearly show that light intensity has a large effect on the initiation of flowering in tomato, so that, irrespective of photoperiod, days with higher light flux integrals are more suitable.

23

90"

Control in favourable conditions

81:1,

70' Macroscopic appearance of the truss

~

60

"0 e" 0

o

J:

C

':"

50-

40-

30-

2 ~ C

20-

~

10Control in

~ caodnV~irt::ns O-

L o

4~

56

Transfer

7'1

to favourable

(days from

86

101

conditions

sowing)

Fig.6. Effect of a transfer from adverse to favourable light conditions, at different times after sowing, on flowering of the second truss. The duration of the transfer was 15 days. Inflorescence development in tomato is affected in the same way as the initiation of flowering by light conditions. As in a number of other species (cf. Nitsch, 1965) these two developmental processes thus have similar light requirements. Inflorescence development is nevertheless more dependent on short photoperiods and high light intensities than flower-initiation; in days with similar light flux integrals anthesis occurs in almost all plants grown in short days with a high intensity when abortion is almost complete in long days with a low intensity. Several studies demonstrated a flowering-inhibition by young leaves in tomato (De Zeeuw, 1954; Leopold and Lam, 1960; Hussey, 1963} and it was suggested that flower abortion is due to competition for available assimilates between vegetative growth and inflorescence development in insufficient light conditions (Hussey, 1963; Calvert, 1965, 1969; Cooper and Hurd, 1968; Hand and Postlethwaite, 1971}. Postulating a priority of vegetative over generative growth in the use of

24

80-

~

60'

~

40'

Control in favourable conditions

f~)

¢ L. 41 Q ~e.

~

20"

o. 1__ D u r a t i o n of t h e s t a y in f a v o u r a b l e conditions (days)

Fig.7. Effect of the duration of the transfer from adverse to favourable light conditions on flowering of the first truss. The transfer begins 2--4 days before the macroscopic appearance of the truss. photosynthetic products under conditions of limited photosynthesis (Cooper, 1971) could explain why the effectiveness of a transfer from favourable to adverse light conditions is greater than an inverse transfer (in our experiments, complete abortion occurred after 10 days in insufficient light when at least 15 days in favourable conditions were required in order to achieve the development of the inflorescence). It might be, indeed, that during a transfer to adverse conditions, the depletion in photosynthates first affects the inflorescence; on the other hand, the increase in photosynthates after a transfer to favourable conditions first favours vegetative growth (probably the growth of y o u n g leaves). This hypothesis could also explain why a transfer from adverse to favourable conditions is more effective in the prevention of truss abortion when it begins some days before the macroscopic appearance of the truss, these days being devoted to the p r o m o t i o n of vegetative growth. Our experiments show that adequate light conditions are required particularly at the time of, and just after, the macroscopic appearance of the truss, i.e. during the late stage of the development of the inflorescence including the lengthening of the peduncle and the growth of the floral organs. Calvert (1969) came to the same conclusion. In his study, he showed that in contrast with the first inflorescence, the second truss was not affected by adverse light conditions. In our experiments, both inflorescences reacted similarly,

25

suggesting that our observations are of general occurrence whichever the truss studied. However, it must be pointed o u t that after a transfer to adverse light conditions, flowering-inhibition at the second truss is of shorter duration than at the first truss, while an inverse situation exists for floweringp r o m o t i o n after a transfer to favourable conditions. This p h e n o m e n o n could be due to the fact that there are a greater n u m b e r of mature leaves supporting the supply of photosynthates during the development of the second inflorescence than during the development of the first one. As a result, the effect of adverse conditions would be more injurious to the first truss than to the second one and favourable conditions would favour the second rather than the first inflorescence. This fact, connected with the weak flowering-inhibition that Calvert obtained at the first truss could explain w h~ this author did n o t observe any effect of adverse conditions on the development of the second truss. So the discrepancy between the results o f the British worker and our observations would be greater in semblance than in reality. The fact that a transfer from adverse to favourable light conditions can prevent abortion when given at a critical time during the life of the plant b u t n o t later, suggests that there is a point of no return in the progress o f the inflorescence to abortion. A similar conclusion can be drawn from experiments using transfers from favourable to adverse light conditions: during the normal development of the inflorescence to flower anthesis a point of no return is likewise reached. A precise knowledge of the time after which abortion is no longer possible could have value in practical applications. REFERENCES Binchy, A. and Morgan, J.V., 1970. Influence of light intensity and photoperiod on inflorescence initiation in tomatoes. Irish J. Agric. Res., 9: 261--269. Calvert, A., 1959. Effect of the early environment on the development of flowering in tomato. II. Light and temperature interactions. J. Hort. Sci., 34: 154--162. Calvert, A., 1964. Growth and flowering of the tomato in relation to natural light conditions. J. Hort. Sci., 39: 182--193. Calvert, A., 1965. Flower initiation and development in the tomato. N.A.A.S. Quarterly Review, 70: 79--88. Calvert, A., 1969. Studies on the post-initiation development of flower buds of tomato (Lycopersicon esculentum). J. Hort. Sci., 44: 117--126. Cooper, A.J., 1964. A study of the development of the first inflorescence of glasshouse tomatoes. J. Hort. Sci., 39: 92--97. Cooper, A.J., 1971. The effect of root pruning on the growth of tomato plants. J. Hort. Sci., 46: 111--114. Cooper, A.J. and Hurd, R.G., 1968. The influence of cultural factors on arrested development of the first inflorescence of glasshouse tomatoes. J. Hort. Sci., 43: 243--248. De Zeeuw, D., 1954. De invloed van het blad op de bloei. Meded. Landbouwhogesch., Wageningen, 54: 1--44. Hand, D.W. and Postlethwaite, J.D., 1971. The response to CO 2 enrichment of capillarywatered single-truss tomatoes at different plant densities and seasons. J. Hort. Sci., 46: 461--470. Hurd, R.G., 1973. Long-day effects on growth and flower initiation of tomato plants in low light. Ann. Appl. Biol., 73: 221--228.

26 Hurd, R.G. and Cooper, A.J., 1967. Increasing flower number in single-truss tomatoes. J. Hort. Sci., 42: 181--188. Hurd, R.G. and Cooper, A.J., 1970. The effect of early low temperature treatment on the yield of single-inflorescence tomatoes. J. Hort. Sci., 45: 19--27. Hussey, G., 1963. Growth and development in the young tomato. II. The effect of de~ foliation on the development of the shoot apex. J. Exp. Bot., 14; 326--333. Kristoffersen, T., 1963. Interactions of photoperiod and temperature in growth and development of young t o m a t o plants (Lycopersicon esculentum Mill.). Physiol. Plant., Suppl. 1: 1--98. Lake, J.V., 1967. The temperature response of single-truss tomatoes. J. Hort. Sci., 42: 1--12. Leopold, A.C. and Lam, S.L., 1960. A leaf factor influencing t o m a t o earliness. Proc. Am. Soc. Hort. Sci., 76: 543--547. Lewis, D., 1953. Some factors affecting flower production in the tomato. J. Hort. Sci., 28: 207--220. Nitsch, J.P., 1965. Physiology of flower and fruit development. Encyclopaedia of Plant Physiology, XV (1), Springer-Verlag, pp. 1537--1647. Pearson, E.S. and Hartley, H.O., 1969. BiometrikaTables for Statisticians, Vol. I, 3rd edition, Cambridge University Press. Wittwer, S.H., 1963. Photoperiod and flowering in the t o m a t o (Lycopersicon esculentum Mill.). Proc. Am. Soc. Hort. Sci., 83: 688--694. Wittwer, S.H. and Aung, L.H., 1969. Lycopersicon esculentum Mill. In: L.T. Evans (Editor), The Induction of Flowering. Some Case Histories. Macmillan, Melbourne, pp. 409--423.