THE INFLUENCE OF TEMPERATURE AND LIGHT ON THE VEGETATIVE DEVELOPMENT OF CITRUS TREES

By K. Mendel

The 'I olcani Institu te of Agricultural Research (N.U .LA,.), Bet Dagan, Israel. 1968 Series, No 1315 - E.

If the influences of temperature and light on the vegetative developmt;)nt of Citrus trees are to be assessed, they have to be considered under conditions of soil and nutrition which do not hamper this development. Any comparison which does not take this into account is bound to render erroneous results.

With these premises in mind, it can he stated that In all climatiC zones, whether subtropical or tropical, where citrus trees are grown, they ultimately reach more or less the same size. The exceptions are areas on the fringe of the citrus belt between 40° Nand 30° S, and at several high elevations in tropical areas.

Numerous investigations have been carried out on the influences of climatic factors on fruit development, but much less is known about such influence on the trees during their development to ultimate size, it has generally been found that the rate of vegetative development is more accelerated in warmer climates than in cooler ones.

TEMPERATURE

The main temperature ranges for growth are: minimum, 12.S-l3°C; optimum, 23-34°C; and maximum (limiting growth), 37-39°C (1,8, 18).

Heat units are calculated from temperatures above 12.S

oC (55°F) for a given area, and Bain - on the strength

of his comparison between California and Trinidad ­postulated a close correlation between the sum of heat units and the growth rate of the trees in a given area (1).

Table 1 shows the sum of heat units for various areas. Citrus trees are found in all areas listed in the table, but for comparison purposes the behavior of the trees in tropical regions will be of special interest.

In addition to the sum of heat units, the length of the growing season also has to be taken into account. Table 1 shows that other than several regions in California and the Mediterranean area, the various localities !Jsted have no months with an average temperature below 12.SoC. How­ever, if we note the number of months with an average less than 17.S

oC (up to 5°C over the minimum), the pattern is

qUite different. Especially at the higher elevations in tropical regions we arrive at an appreciable number of months with presumably reduced growth activity.

Only the average July temperatures at Indio, California, ,'-- reach the maximum temperature range. Whereas the daily

maxima in many places reCl,ch these temperatures dUrIng th~

hottest months of the year, especially in the northern subtropical regions,::he hours of restricted giowth ar~

limited,

LIGHT

It has long been recognized that light ha~ an aHreciabl~

influence on the rate of growth. Light intensity is a grmvth retarding factor, with tht;;

growth rate decreasing with increasing light intensity (12), ~herefore, in areas with "bright" S;Jmmers, like California and the Mediterranean basin, the high light intensities tend to restrict tree growth.

On the other hand, citrus trees rflact strong"y to increased day length. Under conditions of illumination for 16 hours, citrus trees produced more and longer shoots than with short-day (8 hours) illumination (4,14,17,19).

The quality of the light received by the plants also has an influence on the growth rate. It has been shown (14) that in the red range of the spectirum, "far-red" light promotes the elongation of .internodes of lemon shoots whereas "fed" light has the opposite effect. A recent observation by Gael!* showed that fluorescent light - emitting largely far-red light - (14-16-hour illumination) results in an almost uninterrupted growth activity in PalestIne Sweet Lime seedlings.

The effects ofU.V. radiation on growth are well known, as is the fact that at higher elevations (above l200m), it has an overall influence on plant growth.

GROWTH FLUSHES

Citrus shoots grow in cycles, with the numbers of growth flushes during the growing season varying from two to five (l, 8, 9, 15, 18), according to area. It is generally stated that in tropical regions no clearly defined growth flushes occur, and the trees remain more or less in a state of continuous growth, unless interrupted by drought.

Drought results in the same reactions of the citrus tre~s

as does cold: cessation of growth and inductIOn to flower, ing. The well known production of summer lemons ('1er delli) in Italy is based on this phenomenon. In tropical

* A. Goell, personal communication (1967).

~ [Tfl.BlE 1.

Data on Temperature ana Annual Heat Units {above 12.5°C} ( for Various Citrus Growing Areas * ..

I

Area and Latitude Elevation Annual No of months with I Location (m) heat average temp.

Units (:less than less than

°c 12.5°C 17.5°C ( ik (

a: Sub t r 0 pic a I Regions ~:

("Spain (\hlencial 39°30' N 30 1600 3 6 ~~

" sCal ifo;"nia (Riverside) 34° 0' N 260 1700 3 6 r~. CCalifornia (Indic) 33°40' N -10 3900 1 4 israel (Deganial 32:40' N -200 3600 0 4 I C

:srae! (Rehovot) 31 50' N 50 2600 1 4 ..;

( I~

Is!=!orida (Orlando) 28°40' N 30 3700 0 2 CTexas (Weslaco) 26°05' N 40 3900 0 2 ('

I, ~, FBrail {Umeind 22°30' S 700 3000 0 1

s b; T r 0 pic a I Regions T

ii"inidad (:'iaico A'rp.) 10°40' N 10 5000 0 0 -Coiombia {Aracataca~ 10°30' N 30 5600 0 0 • Colombia (Girardot) 4°20' N 400 5700 0 0 Colombia (Palmira) 3°30' N 1000 3500 0 0 Colombia (LaFloridai 4°40' N 1800 1700 0 10 ECuador (Sta. RossI 3°30' S 10 4400 0 0 Ecuador (Conocoto) 0°15' S 2200 1000 0 11 te Kenya (Mombassal 4° 0' S 20 5200 0 0 st Kenya (Nairobi! 1°20' S 1600 2500 0 1 of Uganda (Jinja) 0°30' N 1100 3330 0 0 su Ceylon (Mannar) 9° 0' N 30 5700 0 0 Ceylon (Nuwara Elyia) 7° 0' N 1900 1000 0 12

• According to various sources

regions, drought plays the same role as cold does in the subtropical regions, leading to renewal of growth and flowering with the onset of the rainy period (1). In an irrigation experiment in the arid Negev area of Israel, the long-interval treatments resulted in new growth each time irrigation was resumed, and these flushes were quite differ­ent from the normal cycle (3).

It is not clear which factors determine the number of growth flushes. It has been shown that there is no chilling requirement for the sprouting of citrus buds (16). Sprouting takes place at any time when soil temperatures fise above 12°C. In the coastal plairt of Israel, sprouting begins, irrespective of air temperature, between February 4 and 15, at which time soil temperatures are about 12°_13°C.

The duration of the flushes varies, as do the intervals between them. Whereas Cooper et a1. (6) stated that the spring flush was of the longest, duration, Krishnamurti and co-workers (l0) noted that the main summer flush was the longest.

It has also been shown that, under long-day condition,s (16-hours illumination), the period between flushes is shorter than under short-day (8 hours illumination) condi­

tel diJ

tions (14). Bertossi (2) reported the influence of the ob duration of illumination on a tissue culture of lemon stems. gn During a 12-hour illumination the same rhythm of flushe~, sh, (five) appeared as in intact plants; after changing to sh, continuous lighting, the growth of the tissue became an almost uninterrupted phase of proliferation. hil

ofFrom the results of research work in our Department (5, re~7, 11), it became apparent that the growth flushes are

governed by a promotion - inhibition balance. The rate of nu thtaccumulation of inhibiting substances ("Total Phenolic lorCompounds") determines the cessation of growth and, with

it, the termination of a flush. During the period between m,flushes, the amount of the inhibiting substances decreases. talIn this mechanism, many details still have to be hi~elucidated. As noted above, two to five flushes in citrus gr<occur in subtropical regions, with 1~)Tlgest interval between duthe first and second flush, whereas in the tropics, growth

continues almost uninterruptedly, Temperature seems to be a decisive factor. From Table

2 it is evident that temperatures between the first and second flush in the subtropical regions are markedly lower than in the tropics. We may therefore suggest that high

I

./ TABLE 2. ;.'J

"j;" '0 Average monthly temperatures (oC) in various citrus growing areas during the period from first to second growth flu~h

* September - December (spring in southern hemisphere)

temperatures favor the decomposition of inhibiting sub.. stances and decrease the rate of their accumulation. This is, of course, only circumstantial evidence, which has to be substantiated by further research.

SHOOT-r:LONGATION AND INCREMENT GROWTH OF TREES

After a prolonged period of rest (conditioned by low temperatures or drought), citrus buds have been induced to differentiate into flowering branches (1, 9). It is a common observation that a flush after such a phase cf rest produces a great number of branches with relatively small number of short internodes. These branches therefore remain relatively short (5, 7,10).

The flushes produced in summer under conditions of high temperatures are of a different character. The number of buds sprouting is much smaller than after a prolonged rest, but the individual branches developing have a greater number of internodes, and the internodes are longer: hence, the branches produced under high temperatures are much longer (5, 7).

From these observations, it becomes evident that the major increment in the growth of the citrus trees generally takes place during the summer flushes (5, 13). Conditions of high temperatures and low humidity may lead to reduced growth in summer (6, 10), and to the major increment during other growth flushes.

In tropical humid regions, the flushes always have the characteristics of the summer flushes of the more subtropi­cal areas. It is therefore to be expected that the increment rafe of growth in tropical regions will be higher than that in subtropical regions. Because of this growth behavior, citrus

trees in tropical regions have a more straggly growth than in subtropical regions, v/here the trees are more compact :s~~

also Rain, ref. I).

OBSERVATIONS ON THE DEVELOPMEN r OF TREES ;

UNDER DIFFERENT CLIMATIC CONDITIONS

Nursery Stage

Nursery practices differ widely in the various citrus regions, and it is quite difficult to find a common denominator so that the development of the seedlings and budded plants can be compared. In the folloWing compari· son, the author took into account his observations in those nurseries where the seeds were planted in seedbeds, the seedlings transferred to nursery rows, where they were budded after reaching adequate size, and the budlings left to develop until large enough for planting. Taking intD account also the different growth rates of seedlings of different species, Rough Lemon was chosen for the comparison.

It is interesting to note, that the rate of devlopment of the nursery plants is quite closely correlated with the heat units at various sites (Table 3). Whereas with 2500-3500­H.U. it takes the seedling about 12-15 months to be ready for budding (12 mm stem diameter at 10 cm above ground), in the warmest areas of Columbia and Ceylon (5700 H.D.), 9 months are sufficient. The development of the budling after budding depends largely on whether budding is carried out before the dormancy period or under conditions which allow for immediate sprouting. In the former case, another 9-12 months have to be added to allow for the budling to develop into a tree ready for planting; in such a case, the budded tree will be ready for planting within 4 to 6 months. In the coastal area of southern Ecuador, where temperatures

---

, TABLE 3. I

Heat units and nursery development of cit;us (.i'­"f

I:_

t".'

,l!,nn~al No. of months I LGcation Heat units until budded tree is

(OC) ready for planting ( I

Riverside (California) 1700 30 ,;.r

:."!'

,:,-:... .,

~_\

24 ­ 30 24 - 30 24 18 15 12 ­ 15

3. Also in Ecuador, In a Tahiti Lime plantation from laye[s, 4 years old, the rows were almost closed a:td the trees were 3 to 3.5 m high (4700 H.U.). The spacing in this plantation was 6 X 6 m.

1. A lemonime (lemon X lime hybrid) at Colombo, Ceylo;1, 9 months after budding, had a height of about 2 ill and a width of about 1.50 m (5500 H.U.)

L Washington Navel trees (Frost's nucellar, from Califor nia), 2 years after budding, at the University farm at Milagro, near Guayaquil, Ecuador; reached a height of 2.50 m (4700 H.U.)

2500 2600 3300 4400 5700 5700

............., ....... -.

Fig. 1. Frost Nucellar Washington navel orange Irees. 2 years after budding. University Farm at Milagro, near Guayaquil, Ecua­dor. Height 2.5. Meters (4700 heat units).

Nairobi (Kenya) Rehovot (Israell Jinja (Uganda) 5ta. Rosa (Ecuadc~)

Mannar (Ceylon) Girardot (ColornbiJ)

are iit He lowe. (4500 H.U .), under the influence of the cold Hum00ldt Stream, the development of the trees until planting takes a little longer .than in the Carribbean coastal area of 2olombia. Here, temperature is evidently the determining factoi, because the Colombian coastal area lies a, about i 00 N and the citrus area of southern ccuadcr at 30" u

Tree development in the grove: Bain (1) has stated that in Trinidad, a five to eight year-old tree attains the same size as a ten year-old tree in California.

The very high rate of growth under tropical conditons IS

illustrated by the following:

I;,­

-, ';;'1

i I

)j

'-1 X

.:.:..

In, i a

)r· at of

rs, es ilis

Fig. 2. Four year old Washington navel orange on Rough lemon stock in Colombia S.A. at an elevation of about 1400 meters. Trees were 3 meters high and 3 meters wide (2000 heat units).

~-.

Fig. 3. Three year old Washington navel trees on Rough lemon root in Magdalena Province of Colombia S.A. (Caribbean zone)_ Trees 4 meters high and 4 meters wide (heat units 5700).

4. In Colombia, at an elevation of about 1400 m, in a 4-year-old Washington Navfll grove on Rough Lemon stock, the trees w~re ::s m high and about the same wid~h

(250C H.D.).

5. The highest growth rate was exhibited in a grove in the Magdalena Province in the Caribbean area of Colombia. A 3 year-old Washington }.favel orchard, budded to Rough Lemon and planted at 6 X 6 m distances, had developed 4-m high and 4-m wide trees. This area re­ceives about 5700 heat units per year - about three and a half times as much as does Riverside, California.

In contrast to the above observations, the author found a very poor development of citrus trees at the Tumbaco Experiment Station, near Quito, in Ecuador, at an elevation of 2200 m.

Twelve-year-old Valencia trees on Sour orange (no tristeza is yet present in that area of Ecuador) were about 2.50 m high and 2 m wide. Climatological data indicate th2-1

observations of the present author, seem to lead to the conclusion that accumulated temperatures (heat units) above the physiological threshold for dtrus trees (12.S°C) are the decisive factors in the growth rate. Light (intensity, length of day, and quality) seems to have a secondary influence under grove conditions.

For the rate of development as dependent on tempera­ture a sigmoid curve is to be postulated. In the "minimum" range (1000-1400 H.D.) it is low, rising at an increasing rate until about 6000 H.D. .

The highest experienced temperatures have not yet shown to limit the growth rate, 8.5 at no place did the heat 5. units per annum ~xceed 5700. This cor:-esponds to an annual average temperature, of 28.0°C which is still quite below the upper limit for growth of 38°C, according to Webber (18). We may therefore also conclude that, under natural condi­tions, there exists no upper temperature limit for citrus cultivation. 6.

7.

8.

9.

Fig. 4. Twelve year old Valencia orange trees or sour orange root in Ecuador. Tumbaco Experiment Station near Quito at an elevation of 2200 meters (heat units 1000).

at that location the average temperature for every month of the year is above 12.5°C, but 1Il only one month surpasses 17.5°, and the heat units received are about 1000. It is interesting to note that adjacent to the citrus grove, a Fuerte avocado orchard of the same age evinced absolutely normal development. The trees, planted at 6 X 6 m distances, had covered the entire space of the grove.

CONCLUSIONS

Research work carried out by many workers and the

REFERENCES

1. Bain, F.M. 1949. Citrus and and climate. Calif. Citrog. 34(9): 382;

(10):426.

2. Bertossi, F. 1960. Ritmo autonomo

Emone coltivato in Pavia, 17, 210-221.

di vitro.

crescita Atti

del Ist.

tessuto Bot. Univ.

de

3. Bielorai, H. and Levy, Y. 1967. The Influence of Various Moisture Regimes en

the Water Requirement, Yield and Salt Accumu­lation in the Soil of Irrigated Grapefruit Groves in the Northern Negev (Gilat, 1967/66). Pre!. Rep. Nat. Univ. Inst. Agr., Rehovot. No. 572. (Hebrew, with English summary).

4. Chailahjan, M.M. and Nekopova, T.V. 1952. The influence of the length of day and light in·

tensity on the growth of citrus plants. Doklady Akad. Nauk. S.S.S.R. 86, 865-68.

5. Cohen, A. 1963. Physiological Aspects of Stock-Scion Relation·

ships in Citrus Seedlings. Ph.D. thesis, Hebrew Univ. Jerusalem. (Hebrew with English Sum­mary).

6. Cooper, W.C., Peynado, A., Pmr, J.R., Hilgeman, R.R and Cahoon, G.A.

1963. Tree growth and fruit quality of Valencia orange in relation to climate. Proc. Am. Soc. Hart. Sci. 82,180·192.

7. Goell, A. 1964. Vegetative Growth of Citrus Branches. M.Sc.

thesi~, hebrew Univ. of Jerus<\lem. (in Hebrew).

8. Gonzales-Sicilia,~.

1960. El ..cultivo de los Agrios. ~nst. Nac. de Invest. Agro'fi:, Madnd,

9. Iwasaki, T. and Owada, A. 1960. Studies of the control of alternate bearing. II.

The effect of environmental conditions during winter on the number of flowers and the growth of shoots. Jour. Hart. Ass. Japan, 29 (1): 3746.

10. Krishnamurti, S., Randhawa, G.S. and Sivaraman, Nain. 1960. Growth studies in some Citrus species under

sub-tropical conditions. Indian Jour, Hart. 17: 171 ..184.

de iv.

11. Mendel, K. and Cohen, A. 1962. Methods for the Rapid Evaluation of Rootstocks

for Citrus. Spec. Bull. Nat. Univ. Inst. Agne., Rehovot. No. 46.

12. Monselise, S.P. 1951. Growth analysis of citrus seedlings. 1. Growth of

Sweet Lime seedlings in dependence upon mu­mination. Palest. Jour. BOL, Rehovot Ser., 8: 54-75.

13. Motial, V.S. 1965. Studies in the vegetative growth in Kagzi Lime.

Proc. Indian Ac. Sci., Sect. B. 61,262-66.

14. Piringer, A.A., Downs, R.G. and Borthwick, H.A. 1961. Effect of photoperiod and kind of supplemental

light on growth of three species of Citrus and Poncirus tri/oUnla. Proc. Am. Soc. Hort. Sci, 77, 202·210.

15. Singh, G.P., and Ghoze, S.P. 1965. Studies on the growth behaviour of different

citrus species and cultivars in the nursery. Indian Jour. Eort. 22: 266-276.

16. Stathakopoulos, N.P. and Erickson, L.C. 1966. The effect of temperature on bad-break in

Ponicirus trifoliata, Proc. Am. Soc. Hort. SC::. 89: 222-227.

:;7. Wamer, R.M. 1966. Photoperiod growth responses of five citrus

rootstocks in Hawaii. Proc. XVI] Int. Hart. Congr., Vol. ~: 602.

18. Webber, H,J. 1948. Plant Characteristics and Climatology: In: H.J.

Webber' and L.D. Batchelor (eds.). The Citrus Industry, Vol. I, pp. 41-69.

19. Young, R.H. 1961. Influence of day length, light intensity and

temperature en growth, dormancy and cold.. hardiness of Red·blush grapefruit trees. Proc. Am. Soc. Hort. Sci., ,78, 174·180.

o