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Quality of Pelargonium graveolens cuttings as affected by the rooting medium
Scientia Horticulturae, 19 (1983) 379--385 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
379
QUALITY OF PELARGONIUM GRA VEOLENS CUTTINGS AS AFFECTED BY THE ROOTING MEDIUM
A. ALTMAN and D. FREUDENBERG ~
Department of Horticulture, The Hebrew University of Jerusalem, Rehovot 76 100 (Israel) ~Present address: Nahalal, Israel (Accepted for publication 15 July 1982)
ABSTRACT Altman, A. and Freudenberg, D., 1983. Quality of Pelargonium graveolens cuttings as affected by the rooting medium. Scientia Hortic., 19: 379--385. The effect of 5 rooting media on rooting characteristics and on growth of stem cuttings of Pelargonium graveolens under standard mist propagation was investigated. Perlite was found to be superior to all other media and supported the greatest fresh weight accumulation of both roots and new leaves. The numbers of adventitious roots and leaves were equal in both perlite and standard peat:perlite mixture. The poorest root formation occurred in soil medium, while peat was especially deleterious for new leaf development. Both root and shoot development were intermediate in cuttings planted in sand. Considerable differences and changes were observed in the pH of the various rootingmedia. It is concluded that these d~fferences represent a direct effect on the rooting process, and that substrate characteristics are of the utmost importance for the quality of rooted cuttings.
INTRODUCTION
In addition to the array of endogenous physiological and morphological factors which affect root formation in cuttings (Altman, 1972; Haissig, 1974; Hartmann and Kester, 1975), environmental conditions during rooting may prove critical for the quality of the cutting. Water relations of the top-shoot system (e.g. mist vs. humid-tunnel propagation) and the physical conditions at the basal portion of the cutting (e.g. use of various rooting media) are the 2 most important environmental factors. The present paper deals with the latter. The m o d e m use of detached media in nurseries enables the selection of a great variety of substrates which differ considerably in physical and chemical characteristics (Baker, 1956; Furuta, 1974; Bunt, 1976). The optimization of a rooting-substrate for cutting production is thus dependent on the proper combination of the following factors: water content, air economy
0304-4238/83/$03.00
© 1983 Elsevier Science Publishers B.V.
380 and drainage properties, nutrient balance, pH and buffer capacity, heat balance, and physical stability, as well as other characteristics (De Boodt and Verdonck, 1972; Bunt, 1976; Goh and Haynes, 1977). Of all these, the first 2 are complementary and are of major importance to root development and cutting-establishment. Since no single substrate fulfills all the abovementioned requirements, several mixes have been developed. Combinations of perlite (or vermiculite and expanded polystyrene flakes) and peat have become especially popular in cutting-production of ornamentals. However, considerable differences between the quality of cuttings grown on various media combinations are evident (Poole and Waters, 1972; Conover and Poole, 1974), depending on the plant species and on the specific environmental conditions of the nursery. In the following, we report the effect of 5 media on rooting characteristics of P e l a r g o n i u m g r a v e o l e n s stem cuttings under standard mist propagation. MATERIALS AND METHODS R o o t i n g c o n d i t i o n s . - - Sub-terminal stem cuttings o f P e l a r g o n i u m g r a v e o l e n s were prepared in mid-June. The cuttings were ca. 12 cm in length,
and consisted of 2 nodes and 1 leaf {the basal leaf was removed). Untreated cuttings were planted in trays with 5 media: peat (horticultural grade); perlite (horitcultural grade, No. 4); peat:perlite (1:1, " d r y " volumes); coarse quartz sand (pre-washed with tap water); and local soil {dark brown vertisol). The cuttings were maintained throughout in an uncontrolled greenhouse, under intermittent mist (60 s "on", 20 min "off"). Air temperatures were in the range 24--31 ° C, and medium temperatures were 3--4°C lower. All experimental treatments (media) consisted of 3 randomized replicates (trays) with 20 cuttings in each replicate. Ten cuttings of each replicate were uprooted and analyzed after 24 days of rooting, and the remaining 10 were analyzed after 37 days of rooting, in order to assess the effect of this extended period on root development. G r o w t h data. - - The number of primary adventitious roots, as well as the total fresh and dry weight of the root system, were recorded at each samplingdate. Dry weight was positively correlated with fresh weight of roots, and thus only the latter is presented. Visual rating of the quality and color of the original leaf was also recorded (see legend for Table III). The newly-formed leaves were removed on t h e final sampling-date, and their number and fresh weight were recorded. Standard errors of the means were calculated for all treatments. - - The water-holding capacity and the air space of the substrates were calculated from the weight of a known volume of substrate at "container capacity", and after being dried at 105°C. For pH determination,
Rooting-media.
381
10 g of substrate at container capacity were shaken with 50 ml distilled water for 3 h and the acidity of the slurry was measured. RESULTS While rooting-percentage of Pelargonium graveolens cuttings was 100 on all 5 rooting-media, significant differences were found in the quality of rooting. This was assessed by the n u m b e r of adventitious roots and by their fresh weight. Initial r o o t formation in cuttings r o o t e d in either perlite or peat was considerably better, as compared with standard peat:perlite medium, whereas local soil adversely affected r o o t formation (Table I). However, it is evident that additional r o o t formation in the period 24--37 days was better on the peat:perlite medium. Thus, final number of roots on different media was in the following order: peat:perlite = perlite > peat = sand > soil. The effect of rooting-medium on the total mass of adventitious roots (Table II) usually agrees with the former data, the differences being even greater. Thus, perlite was found to be superior to all other media, while r o o t growth in local soil was very poor. The intensive growth of roots on sand and soil media during the period 24--37 days did n o t compensate for initial p o o r growth. Final fresh weight of roots was in the following order: perlite > peat:perlite > sand = peat > soft. In addition to its direct effect on r o o t formation, the rooting-medium considerably affected several parameters of shoot development (Table III). Accelerated senescence of the original leaf {that was left on the cutting) was f o u n d with sand, and eventually also in cuttings rooted in soil. A different developmental response was found with the new leaves which emerged after root formation and cutting-establishment; both perlite and peat:perlite media supported maximal development of new leaves (number and weight), whereas peat adversely affected it. Final fresh weight of the new growth was thus in the following order: peat:perlite = perlite > sand = soil > peat. The differential effect of the rooting medium on r o o t and shoot developTABLE I R o o t f o r m a t i o n ( n u m b e r ) in Pelargonium graveolens cuttings in different r o o t i n g media. A d v e n t i t i o u s r o o t s were c o u n t e d after 2 4 a n d 37 days o f rooting. Data are c o m p a r e d w i t h standard peat:perlite m e d i u m Medium
Perlite Peat Peat:perlite Sand Local soil
24 days
37 d a y s
No. of roots
% of standard
No. of roots
% of standard
6.1 5.5 4.5 4.3 2.3
136 122 100 96 51
8.9 7.3 9.3 6.8 3.8
96 78 100 73 41
± ± ± ± ±
0.8 0.7 0.7 0.7 0.6
± ± ± ± ±
0.5 0.6 0.5 0.8 0.7
% increase, 2 4 - - 3 7 days
46 33 107 58 65
382 TABLE II The effect of different rooting media on fresh weight of roots of Pelargonium graveolens cuttings. Fresh weight was recorded after 24 and 37 days of rooting. Data are compared with standard peat: perlite medium Medium
24 days Fresh weight
37 days % of Fresh standard weight
% of standard
0.52 0.21 0.29 0.09 0.03
179 72 100 31 10
136 52 100 66 26
(g)
Perlite Peat Peat:perlite Sand Local soil
± 0.13 ± 0.08 ± 0.10 ± 0.02 ± 0.01
(g)
1.80 0.68 1.32 0.87 0.34
± 0.23 ± 0.13 ± 0.27 ± 0.25 ± 0.12
% increase, 24--37 days
246 224 355 867 1033
TABLE III Leaf quality and shoot growth of Pelargonium graveolens cuttings on different rooting media. The quality of the original leaves which were retained on the cuttings was recorded after 24 and 37 days of rooting (on a scale of 1 = yellow to 3 = healthy green); the number and fresh weight of newly developed leaves was determined at the time of uprooting (37 days) Medium
Quality of original leaf
Newly developed leaves
24 days
37 days
Number
% of standard
2.8 2.0 2.7 1.4 2.8
1.6 ± 0.2 1.6 ± 0.2 1.5 ± 0.3 0.9 ± 0.2 1.1 ± 0.2
3.3 ± 0.4 1.9 -~ 0.3 3.2 ± 0.4 3.0 ± 0.4 2.3 ± 0.4
103 59 100 94 72
Fresh weight
% of standard
(g) Perlite Peat Peat:perlite Sand Local soil
± 0.1 ± 0.1 ± 0.1 ± 0.3 + 0.i
1.5 0.7 1.6 1.0 1.0
± 0.2 ± 0.2 ± 0.3 ± 0.2 ± 0.3
94 44 100 63 63
m e n t is r e f l e c t e d in t h e r o o t / n e w leaves ratio o f the c u t t i n g s (Fig. 1). T h r e e d i s t i n c t g r o u p s are e v i d e n t : a high r o o t / l e a v e s ratio o f cuttings g r o w n in perlite (1.25), a m e d i u m r a t i o ( 0 . 8 - - 0 . 9 ) with p e a t , p e a t : p e r l i t e , a n d sand, a n d a v e r y l o w r o o t / l e a v e s ratio o n soil (0.35). In an a t t e m p t t o clarify t h e e f f e c t o f the m e d i u m o n r o o t i n g a n d establishm e n t o f cuttings, several p a r a m e t e r s were a n a l y z e d . W a t e r - h o l d i n g c a p a c i t y a n d air-space values were in close a g r e e m e n t with the already-established values f o r these m e d i a ( B u n t , 1 9 7 6 ) , a n d n o significant changes in t h e temp e r a t u r e o f t h e 5 m e d i a were f o u n d . Media pH, h o w e v e r , were m a r k e d l y d i f f e r e n t a n d c h a n g e d c o n s i d e r a b l y d u r i n g t h e r o o t i n g p e r i o d (Fig. 2). Peat a n d p e a t : p e r l i t e h a d an initially l o w p H , rising o n l y later, whereas sand med i u m was initially h i g h l y basic. T h u s , p H values d u r i n g t h e first 1 0 - - 1 2 d a y s o f r o o t f o r m a t i o n were b e l o w 5 in p e a t a n d p e a t : p e r l i t e , n e u t r a l in perlite, a n d basic in soil a n d sand.
oL 1.0
383 PERLITE
PEAT
Lf} W
PEAT: PERLITE SAND
I.J
~0.5
m
SOIL
o oce-
Fig. 1. Root/new leaves ratio of Pelargonium graveolens cuttings rooted in different media. Ratios were calculated from fresh weight of roots and of newly formed leaves (Tables II and III) after 37 days. 9
8 i
_D C)
,,,6
4 i
0
DAYS
24
37
Fig. 2. p H changes of the rooting medium. Initialp H of media, as well as its change during the rooting-period, were determined under standard conditions. Data are averages of 4 separate determinations for each medium. DISCUSSION
Since s t e m c u t t i n g s o f Pelargonium graveolens r o o t easily, d i f f e r e n c e s in p e r f o r m a n c e o n v a r i o u s r o o t i n g - m e d i a c a n be ascribed t o a d i r e c t e f f e c t o f t h e s u b s t r a t e o n t h e basal p o r t i o n o f t h e c u t t i n g , r a t h e r t h a n t o i n d i r e c t or earlier p h y s i o l o g i c a l changes. This is f u r t h e r stressed b y t h e f a c t t h a t t h e
384
water balance of the shoot does not seem to play a role, since mist was used throughout. The large differences in the quality of the root system (Table I and II) and in shoot characteristics (Table III) do indeed indicate the importance of this direct substrate effect. Improved root formation and growth on perlite and peat:perlite was probably related to the superior aeration and drainage of these substrates (Furuta, 1 9 7 4 ; J a c k s o n , 1 9 7 4 ; Bunt, 1976), which are important for the first phase of root initiation. This is supported by the fact that perlite, which allows maximal aeration (Jackson, 1974), was especially advantageous during the first 24-day period, both with regard to the number of roots (Table I) and to their mass (Table II). It is well established that initial inhibition of root formation may result in an additional, secondary, wave of root intiation (Kefford, 1973), as was indeed found with cuttings planted in sand and soil (Table II). Top growth of a cutting may reflect earlier growth of the root system, but other environmental factors can also be involved. Thus, while new leaf development on perlite and peat:perlite closely agrees with the superior root development on these media, peat was especially deleterious to leaf growth (Table III). Soil, on the other hand, allowed moderate leaf development although root growth was lowest. Since the above cannot be explained solely by differences in the water/air relationship of the various rooting media, other factors are probably involved. Mechanical impedance and reduced porosity is one such factor which may restrict root formation (Nicolosi and Fretz, 1980), as found in the present study with respect to soil. The great differences and changes in substrate pH (Fig. 2) may be another factor in cutting production (Conover and Poole, 1974). At present, it is not clear why the low pH of peat was especially deleterious for shoot development.
REFERENCES Altman, A., 1972. The role of auxin in root initiation in cuttings. Proc. Int. Plant Propag. Soc., 22: 280--294. Baker, K.F. (Editor), 1956. The U.C. system for producing healthy container-grown plants. Univ. Calif. Agric. Exp. Stn. Manual 23. Bunt, A.C., 1976. Modern Potting Compost. George Allen and Unwin, London. Conover, C.A. and Poole, R.T., 1974. Influence of media and fertilizer rates on Aglaonema 'Fronsher'. Proc. Fla. State Hortic. Soc., 77: 177--183. De Boodt, M. and Verdonck, O., 1972. The physical properties of the substrates in horticulture. Acta Hortic., 26: 37--44. Furuta, T., 1974. Environmental Plant Production and Marketing. Cox Arcadia, CA. Goh. K.M. and Haynes, R.J., 1977. Evaluation of potting media for commercial nursery production of container-grown plants. N.Z.J. Agric. Res., 20: 363--370. Haissig, B.E., 1974. Influence of auxin and auxin synergists on adventitious root primordium initiation and development. N.Z.J. For. Sci., 4: 311--323. Hartmann, H.T. and Kester, D.E., 1975. Plant Propagation, Principles and Practices. Prentice-Hall, NJ.
385 Jackson, D.K., 1974. Some characteristics of perlite as an experimental growth medium. Plant Soil, 40: 161--167. Kefford, N_P., 1973. Effect of a hormone antagonist on the rooting of shoot cuttings. Plant Physiol., 51: 214--216. Nieolosi, R.T. and Fretz, T.A., 1980. Evaluation of r o o t growth in varying medium densities and through dissimilar soil surfaces. HortScience, 15: 642--644. Poole, R.T. and Waters, W.E., 1972. Evaluation of various potting media for growth of foliage plants. Proc. Fla. State Hortic. Soc., 85: 395--398.
379
QUALITY OF PELARGONIUM GRA VEOLENS CUTTINGS AS AFFECTED BY THE ROOTING MEDIUM
A. ALTMAN and D. FREUDENBERG ~
Department of Horticulture, The Hebrew University of Jerusalem, Rehovot 76 100 (Israel) ~Present address: Nahalal, Israel (Accepted for publication 15 July 1982)
ABSTRACT Altman, A. and Freudenberg, D., 1983. Quality of Pelargonium graveolens cuttings as affected by the rooting medium. Scientia Hortic., 19: 379--385. The effect of 5 rooting media on rooting characteristics and on growth of stem cuttings of Pelargonium graveolens under standard mist propagation was investigated. Perlite was found to be superior to all other media and supported the greatest fresh weight accumulation of both roots and new leaves. The numbers of adventitious roots and leaves were equal in both perlite and standard peat:perlite mixture. The poorest root formation occurred in soil medium, while peat was especially deleterious for new leaf development. Both root and shoot development were intermediate in cuttings planted in sand. Considerable differences and changes were observed in the pH of the various rootingmedia. It is concluded that these d~fferences represent a direct effect on the rooting process, and that substrate characteristics are of the utmost importance for the quality of rooted cuttings.
INTRODUCTION
In addition to the array of endogenous physiological and morphological factors which affect root formation in cuttings (Altman, 1972; Haissig, 1974; Hartmann and Kester, 1975), environmental conditions during rooting may prove critical for the quality of the cutting. Water relations of the top-shoot system (e.g. mist vs. humid-tunnel propagation) and the physical conditions at the basal portion of the cutting (e.g. use of various rooting media) are the 2 most important environmental factors. The present paper deals with the latter. The m o d e m use of detached media in nurseries enables the selection of a great variety of substrates which differ considerably in physical and chemical characteristics (Baker, 1956; Furuta, 1974; Bunt, 1976). The optimization of a rooting-substrate for cutting production is thus dependent on the proper combination of the following factors: water content, air economy
0304-4238/83/$03.00
© 1983 Elsevier Science Publishers B.V.
380 and drainage properties, nutrient balance, pH and buffer capacity, heat balance, and physical stability, as well as other characteristics (De Boodt and Verdonck, 1972; Bunt, 1976; Goh and Haynes, 1977). Of all these, the first 2 are complementary and are of major importance to root development and cutting-establishment. Since no single substrate fulfills all the abovementioned requirements, several mixes have been developed. Combinations of perlite (or vermiculite and expanded polystyrene flakes) and peat have become especially popular in cutting-production of ornamentals. However, considerable differences between the quality of cuttings grown on various media combinations are evident (Poole and Waters, 1972; Conover and Poole, 1974), depending on the plant species and on the specific environmental conditions of the nursery. In the following, we report the effect of 5 media on rooting characteristics of P e l a r g o n i u m g r a v e o l e n s stem cuttings under standard mist propagation. MATERIALS AND METHODS R o o t i n g c o n d i t i o n s . - - Sub-terminal stem cuttings o f P e l a r g o n i u m g r a v e o l e n s were prepared in mid-June. The cuttings were ca. 12 cm in length,
and consisted of 2 nodes and 1 leaf {the basal leaf was removed). Untreated cuttings were planted in trays with 5 media: peat (horticultural grade); perlite (horitcultural grade, No. 4); peat:perlite (1:1, " d r y " volumes); coarse quartz sand (pre-washed with tap water); and local soil {dark brown vertisol). The cuttings were maintained throughout in an uncontrolled greenhouse, under intermittent mist (60 s "on", 20 min "off"). Air temperatures were in the range 24--31 ° C, and medium temperatures were 3--4°C lower. All experimental treatments (media) consisted of 3 randomized replicates (trays) with 20 cuttings in each replicate. Ten cuttings of each replicate were uprooted and analyzed after 24 days of rooting, and the remaining 10 were analyzed after 37 days of rooting, in order to assess the effect of this extended period on root development. G r o w t h data. - - The number of primary adventitious roots, as well as the total fresh and dry weight of the root system, were recorded at each samplingdate. Dry weight was positively correlated with fresh weight of roots, and thus only the latter is presented. Visual rating of the quality and color of the original leaf was also recorded (see legend for Table III). The newly-formed leaves were removed on t h e final sampling-date, and their number and fresh weight were recorded. Standard errors of the means were calculated for all treatments. - - The water-holding capacity and the air space of the substrates were calculated from the weight of a known volume of substrate at "container capacity", and after being dried at 105°C. For pH determination,
Rooting-media.
381
10 g of substrate at container capacity were shaken with 50 ml distilled water for 3 h and the acidity of the slurry was measured. RESULTS While rooting-percentage of Pelargonium graveolens cuttings was 100 on all 5 rooting-media, significant differences were found in the quality of rooting. This was assessed by the n u m b e r of adventitious roots and by their fresh weight. Initial r o o t formation in cuttings r o o t e d in either perlite or peat was considerably better, as compared with standard peat:perlite medium, whereas local soil adversely affected r o o t formation (Table I). However, it is evident that additional r o o t formation in the period 24--37 days was better on the peat:perlite medium. Thus, final number of roots on different media was in the following order: peat:perlite = perlite > peat = sand > soil. The effect of rooting-medium on the total mass of adventitious roots (Table II) usually agrees with the former data, the differences being even greater. Thus, perlite was found to be superior to all other media, while r o o t growth in local soil was very poor. The intensive growth of roots on sand and soil media during the period 24--37 days did n o t compensate for initial p o o r growth. Final fresh weight of roots was in the following order: perlite > peat:perlite > sand = peat > soft. In addition to its direct effect on r o o t formation, the rooting-medium considerably affected several parameters of shoot development (Table III). Accelerated senescence of the original leaf {that was left on the cutting) was f o u n d with sand, and eventually also in cuttings rooted in soil. A different developmental response was found with the new leaves which emerged after root formation and cutting-establishment; both perlite and peat:perlite media supported maximal development of new leaves (number and weight), whereas peat adversely affected it. Final fresh weight of the new growth was thus in the following order: peat:perlite = perlite > sand = soil > peat. The differential effect of the rooting medium on r o o t and shoot developTABLE I R o o t f o r m a t i o n ( n u m b e r ) in Pelargonium graveolens cuttings in different r o o t i n g media. A d v e n t i t i o u s r o o t s were c o u n t e d after 2 4 a n d 37 days o f rooting. Data are c o m p a r e d w i t h standard peat:perlite m e d i u m Medium
Perlite Peat Peat:perlite Sand Local soil
24 days
37 d a y s
No. of roots
% of standard
No. of roots
% of standard
6.1 5.5 4.5 4.3 2.3
136 122 100 96 51
8.9 7.3 9.3 6.8 3.8
96 78 100 73 41
± ± ± ± ±
0.8 0.7 0.7 0.7 0.6
± ± ± ± ±
0.5 0.6 0.5 0.8 0.7
% increase, 2 4 - - 3 7 days
46 33 107 58 65
382 TABLE II The effect of different rooting media on fresh weight of roots of Pelargonium graveolens cuttings. Fresh weight was recorded after 24 and 37 days of rooting. Data are compared with standard peat: perlite medium Medium
24 days Fresh weight
37 days % of Fresh standard weight
% of standard
0.52 0.21 0.29 0.09 0.03
179 72 100 31 10
136 52 100 66 26
(g)
Perlite Peat Peat:perlite Sand Local soil
± 0.13 ± 0.08 ± 0.10 ± 0.02 ± 0.01
(g)
1.80 0.68 1.32 0.87 0.34
± 0.23 ± 0.13 ± 0.27 ± 0.25 ± 0.12
% increase, 24--37 days
246 224 355 867 1033
TABLE III Leaf quality and shoot growth of Pelargonium graveolens cuttings on different rooting media. The quality of the original leaves which were retained on the cuttings was recorded after 24 and 37 days of rooting (on a scale of 1 = yellow to 3 = healthy green); the number and fresh weight of newly developed leaves was determined at the time of uprooting (37 days) Medium
Quality of original leaf
Newly developed leaves
24 days
37 days
Number
% of standard
2.8 2.0 2.7 1.4 2.8
1.6 ± 0.2 1.6 ± 0.2 1.5 ± 0.3 0.9 ± 0.2 1.1 ± 0.2
3.3 ± 0.4 1.9 -~ 0.3 3.2 ± 0.4 3.0 ± 0.4 2.3 ± 0.4
103 59 100 94 72
Fresh weight
% of standard
(g) Perlite Peat Peat:perlite Sand Local soil
± 0.1 ± 0.1 ± 0.1 ± 0.3 + 0.i
1.5 0.7 1.6 1.0 1.0
± 0.2 ± 0.2 ± 0.3 ± 0.2 ± 0.3
94 44 100 63 63
m e n t is r e f l e c t e d in t h e r o o t / n e w leaves ratio o f the c u t t i n g s (Fig. 1). T h r e e d i s t i n c t g r o u p s are e v i d e n t : a high r o o t / l e a v e s ratio o f cuttings g r o w n in perlite (1.25), a m e d i u m r a t i o ( 0 . 8 - - 0 . 9 ) with p e a t , p e a t : p e r l i t e , a n d sand, a n d a v e r y l o w r o o t / l e a v e s ratio o n soil (0.35). In an a t t e m p t t o clarify t h e e f f e c t o f the m e d i u m o n r o o t i n g a n d establishm e n t o f cuttings, several p a r a m e t e r s were a n a l y z e d . W a t e r - h o l d i n g c a p a c i t y a n d air-space values were in close a g r e e m e n t with the already-established values f o r these m e d i a ( B u n t , 1 9 7 6 ) , a n d n o significant changes in t h e temp e r a t u r e o f t h e 5 m e d i a were f o u n d . Media pH, h o w e v e r , were m a r k e d l y d i f f e r e n t a n d c h a n g e d c o n s i d e r a b l y d u r i n g t h e r o o t i n g p e r i o d (Fig. 2). Peat a n d p e a t : p e r l i t e h a d an initially l o w p H , rising o n l y later, whereas sand med i u m was initially h i g h l y basic. T h u s , p H values d u r i n g t h e first 1 0 - - 1 2 d a y s o f r o o t f o r m a t i o n were b e l o w 5 in p e a t a n d p e a t : p e r l i t e , n e u t r a l in perlite, a n d basic in soil a n d sand.
oL 1.0
383 PERLITE
PEAT
Lf} W
PEAT: PERLITE SAND
I.J
~0.5
m
SOIL
o oce-
Fig. 1. Root/new leaves ratio of Pelargonium graveolens cuttings rooted in different media. Ratios were calculated from fresh weight of roots and of newly formed leaves (Tables II and III) after 37 days. 9
8 i
_D C)
,,,6
4 i
0
DAYS
24
37
Fig. 2. p H changes of the rooting medium. Initialp H of media, as well as its change during the rooting-period, were determined under standard conditions. Data are averages of 4 separate determinations for each medium. DISCUSSION
Since s t e m c u t t i n g s o f Pelargonium graveolens r o o t easily, d i f f e r e n c e s in p e r f o r m a n c e o n v a r i o u s r o o t i n g - m e d i a c a n be ascribed t o a d i r e c t e f f e c t o f t h e s u b s t r a t e o n t h e basal p o r t i o n o f t h e c u t t i n g , r a t h e r t h a n t o i n d i r e c t or earlier p h y s i o l o g i c a l changes. This is f u r t h e r stressed b y t h e f a c t t h a t t h e
384
water balance of the shoot does not seem to play a role, since mist was used throughout. The large differences in the quality of the root system (Table I and II) and in shoot characteristics (Table III) do indeed indicate the importance of this direct substrate effect. Improved root formation and growth on perlite and peat:perlite was probably related to the superior aeration and drainage of these substrates (Furuta, 1 9 7 4 ; J a c k s o n , 1 9 7 4 ; Bunt, 1976), which are important for the first phase of root initiation. This is supported by the fact that perlite, which allows maximal aeration (Jackson, 1974), was especially advantageous during the first 24-day period, both with regard to the number of roots (Table I) and to their mass (Table II). It is well established that initial inhibition of root formation may result in an additional, secondary, wave of root intiation (Kefford, 1973), as was indeed found with cuttings planted in sand and soil (Table II). Top growth of a cutting may reflect earlier growth of the root system, but other environmental factors can also be involved. Thus, while new leaf development on perlite and peat:perlite closely agrees with the superior root development on these media, peat was especially deleterious to leaf growth (Table III). Soil, on the other hand, allowed moderate leaf development although root growth was lowest. Since the above cannot be explained solely by differences in the water/air relationship of the various rooting media, other factors are probably involved. Mechanical impedance and reduced porosity is one such factor which may restrict root formation (Nicolosi and Fretz, 1980), as found in the present study with respect to soil. The great differences and changes in substrate pH (Fig. 2) may be another factor in cutting production (Conover and Poole, 1974). At present, it is not clear why the low pH of peat was especially deleterious for shoot development.
REFERENCES Altman, A., 1972. The role of auxin in root initiation in cuttings. Proc. Int. Plant Propag. Soc., 22: 280--294. Baker, K.F. (Editor), 1956. The U.C. system for producing healthy container-grown plants. Univ. Calif. Agric. Exp. Stn. Manual 23. Bunt, A.C., 1976. Modern Potting Compost. George Allen and Unwin, London. Conover, C.A. and Poole, R.T., 1974. Influence of media and fertilizer rates on Aglaonema 'Fronsher'. Proc. Fla. State Hortic. Soc., 77: 177--183. De Boodt, M. and Verdonck, O., 1972. The physical properties of the substrates in horticulture. Acta Hortic., 26: 37--44. Furuta, T., 1974. Environmental Plant Production and Marketing. Cox Arcadia, CA. Goh. K.M. and Haynes, R.J., 1977. Evaluation of potting media for commercial nursery production of container-grown plants. N.Z.J. Agric. Res., 20: 363--370. Haissig, B.E., 1974. Influence of auxin and auxin synergists on adventitious root primordium initiation and development. N.Z.J. For. Sci., 4: 311--323. Hartmann, H.T. and Kester, D.E., 1975. Plant Propagation, Principles and Practices. Prentice-Hall, NJ.
385 Jackson, D.K., 1974. Some characteristics of perlite as an experimental growth medium. Plant Soil, 40: 161--167. Kefford, N_P., 1973. Effect of a hormone antagonist on the rooting of shoot cuttings. Plant Physiol., 51: 214--216. Nieolosi, R.T. and Fretz, T.A., 1980. Evaluation of r o o t growth in varying medium densities and through dissimilar soil surfaces. HortScience, 15: 642--644. Poole, R.T. and Waters, W.E., 1972. Evaluation of various potting media for growth of foliage plants. Proc. Fla. State Hortic. Soc., 85: 395--398.