Studies of vegetative propagation of the lychee (Litchi chinensis ...

Studies of vegetative propagation of the lychee
(Litchi chinensis Sonn.) with special reference to
graftage
W. S. ABUTIATE & N. Y. NAKASONE
(W.S.A.: Crops Research Institute, P.O. Box 3785, Kumasi, Ghana; N. Y.N.: Department of Horticulture,
University of Hawaii, Honolulu, Hawaii)
SUMMARY
Studies of rooting of stem cuttings, grafting upon
air-layered rootstocks under three photoperiods, and
histology and graft-union anatomy are reported for three
cultivars of lychee (Kwai Mi, Brewster and Hak lp).
NAA-Na, IBA and their mixtures did not produce
significant differential rooting in any of the concentrations
used. IBA, however, effected greater numbers and
greater length of roots per cutting than NAA-Na. Rooting
generally was poor in both Kwai Mi and Brewster
under mist and within a polyethylene enclosure. Under
the same conditions Hak lp failed to root. Probable
reasons for the poor rooting are suggested. Starch levels
in the three subjects did not correlate with percentage
rooting observed except in Brewster which rooted without
mist in the polyethylene enclosure. Probable causes
for the rooting responses in the three cultivars are
advanced. Graft takes were equally low under both the
8-hour day and the normal day. There was no success
under a 16-hour regime. Brewster was more graftcompatible
with Kwai Mi than with Hak lp. Probable
reasons are examined. The healing process in the lychee
graft and the ontogeny of the contributing tissues are
also presented. Only secondary vascular tissues were
found to contribute callus in the healing process. Callus
was contributed by the scion and the stock, with greater
amount being contributed by the stock in side-grafts.
Original scientific paper. Received 16 Mar 72; revised
10 Aug 72. (This paper was based on a thesis submitted
by the senior author in 1966 in partial fulfilment of the
requirements for the M.Sc. degree at the University of
Hawaii.)
RESUME
Al!UTIATE, W. S. & NAKASONE, N. Y.: Etudes sur la
multIplication des litchis (Litchi chinensis Sonn.) par voie
vegetative, particulierement par greffage. Les auteurs ont
etudil~ l'enracinement de boutures et la greffe sur des
marcottes de porte-greffes, soumis a 3 differentes photoperiodes
chez 3 varietes de litchi (Kwai Mi, Brewster et
Hak lp); l'histologie et l'anatomie des tissus de jonction
ont ete examinees. Les hormones NAA-Na, IBA et leurs
melanges n'ont pas montre de difference entre eux quant
a l'augmentation de l'enracinement a aucune des concentrations
utilisees. Cependent, IBA a determine Ie
developpement de racines plus nombreuses et plus
longues des boutures que Ie NAA-Na. Generalement,
l'enracinement a ete faible a la fois chez les Kwai Mi et
les Brewster plantes dans du fumier, dans des pots de
polyethylene. Dans les memes conditions, Hak lp ne
s'est pas enracine. Les auteurs donnent des raisons
probabIes pour expliquer ces faibles resultats. II n'a pas
ete observe de correlation entre la teneur des boutures en
amidon et Ie pourcentage d'enracinement chez les 3
varietes en experience, sauf chez Brewster qui s'est
enracine dans des pots de polyethylene sans fumier. Les
auteurs envisagent les causes probables de ces reactions
d'enracinement chez les 3 varietes. La reussite des
greffes a egalement ete faible sous Ie regime de 8 heures
d'eclairage par jour, ou de l'eclairage normal; elle a ete
nulle sous Ie regime de 18 heures. Les greffons de
Brewster se sont montres plus compatibles avec les
Kwai Mi qu'avec les Hak lp; les raisons probables de ce
fait ont ete examinees. Le processus de cicatrisation et
l'ontogenese des tissus impliques dans Ie greffage des
litchis sont presentes dans ce travail. II a ete observe que,
seul, Ie tissu vasculaire secondaire (liber) contribue a la
formation du cal dans la procedure de cicatrisation. Le
greffon et Ie porte-greffe contribuent tous deux a la
formation du cal; dans les greffes laterales (par approche)
c'est Ie porte-greffe qui en forme la plus grande partie.

W. S. Abutiate & N. Y. Nakasone (1972) Ghana Jnl agric. Sci. 5,201-211
Introduction Incompatibility between stock and scion has
Litchi chinensis (Sonn.), a subtropical fruit tree, also been put forward by Mergen (1954) as another
belongs to the family Sapindaceae, the Soapberry possible explanation for graft failures. Other
family. The tree is evergreen, low-branching and workers (Buck, 1953; Kostoff, 1928; Saas, 1933)
round-topped with pinnately-compound leaves have dwelt on the origin of the unifying callus
borne on generally brittle branches. Growth tissue, the absence of which results in graft failure.
occurs in flushes, there being several flushes in a Venning (1949), in his study of the anatomy and
year. The small flowers are apetalous and are borne secondary growth in the axis of the lychee, stated
on leafless terminal inflorescences. All evidence that successful grafting depends upon the activpoints
to the probability that lychee is native in ities of the vascular cambium.
Southern China where its cultivation is well Rapid multiplication of new cultivars in many
established. Its culture has spread to part of South plants is accomplished universally by cuttings,
Mrica, Hawaii and Florida (Chadler, 1958). budding or grafting methods. The need for
The plant is propagated commercially by air- accurate diagnosis of the causes of graft failures,
layering. There has been very little success with especially in hard-to-root or hard-to-graft subjects,
grafting and rooting of cuttings, even with the aid seems worthwhile.
of rooting hormones. Many reasons have been put This investigation was an attempt to elucidate
forward by workers to explain the low success of the causes of side-graft failures in the lychee and
vegetative propagation in various plants. Fahmy the ways and means of overcoming them to achieve
(1952) states that successful graftage involves the commercially feasible propagation.
interplay between the external and internal
environment of the plant or part of the plant used.
Carbohydrate, the main energy source fOl plant
activity is thought to be one of the limiting factors
in the successful vegetative propagation of plants
(Carlson, 1929; Kraus & Kraybill, 1918; Schrader,
1924; Starring, 1923). Working with macadamia,
Jones & Beaumont (1937) recorded an increase
from 10% to 75-80 % graft takes with girdled
scions. They also found that starch accumulation
rarely exceeded 0·4 to 0·5 % of the branch dry
weight in non-flowering branches of lychee but
when branches were girdled for 3-4 weeks, starch
reserves rose to 11·4 %.
Even though photoperiodism has not been
shown to improve graft take, its beneficial effects
have been shown in the rooting of cuttings, seed
germination and abscission (Nitsch, 1957). Photoperiodic
effect on cambial activity has also been
shown experimentally by Mollart (1954). However,
Snyder (1955) working with Taxus cuspidata failed
to find any significant photoperiodic effect on
cuttings of this subject. Since the accumulation of
photosynthates in plant parts depends in part on
the amount and quality of light received, one
might expect daylength, through its effect on
carbohydrate synthesis to influence vegetative
propagation, especially grafting and rooting of
cuttings when plant parts high in carbohydrates
are employed.
Materials and methods
The study was divided into two parts. The first
part deals with the effect of root-inducing hormones
on root development in the girdled and
non-girdled stem cuttings, whilst the second part
involves the effect of girdled and non-girdled
scionwood and daylength on graft take.
The experimental plants consisted of three
popular cultivars of lychee, Kwai Mi, Hak Ip and
Brewster, grown at Kona and the Poamoho Branch
Stations.
Rooting experiments
Suitable branches of the three cultivars were
girdled both at Poamoho and Kona in March and
April 1965. Thirteen to 15-em cuttings with two
to three leaves were taken from both girdled and
non-girdled branches at Kona on 4 June, treated
with the appropriate concentration of NAA-Na
and IBA and set in vermiculite with mist and without
mist in a polyethylene enclosure. Similar
cuttings were taken from Poamoho on 22 June and
set under the above regime on 23 June.
The experiment was set up in a randomized
block design with four replications of 10 treatments.
Each treatment consisted of 15 cuttings for
the Kona material but six to 10 for the Poamoho
material. Treatments were as follows: Control,

2000, 5000 and 10 000 ppm each of NAA-Na
and IBA separately and 2000, 5000 and 10000
ppm mixture of equal parts ofNAA-Na and IBA.
Treatments were prepared as powder to which
10% Dithane M-45 fungicide was added. Both
vermiculite and air temperatures were recorded at
9 am, 12 noon and 3 pm (local time) at 2-day
intervals for 8 weeks and thereafter at 1O-day
intervals. Relative humidity within the polyethylene
enclosure was recorded by a hygrothermograph.
At termination of the experiments on 9 & 17
November for the Kona and Poamoho subjects
respectively, the cuttings were dug up, and the
number rooted, the number of roots per cutting,
the average length of roots, the number callused
and the number dead were recorded.
Grafting experiments
Rootstocks for these experiments were obtained
from the Poamoho Experimental Station. Four
hundred and thirty suitable branches were selected
on each of the three cultivars and air-layered.
When enough roots developed, the air-layers were
harvested and potted in 3-gallon cans and set in
shade until a new flush of growth appeared, after
which they were acclimatized. In September 1965,
70 air-layers each of Kwai Mi, Hak Ip and
Brewster were transferred into nursery rows on
the Manoa Campus Experimental Farm. The
remaining air-layers were left in the cans for the
photoperiod experiments.
Scionwood for the grafting experiments also was
obtained from the three cultivars at Poamoho. For
scionwood, branches 0·6-1·0 em in diameter were
selected from mother trees and girdled on 9 Oct 65.
Girdled and non-girdled scionwood were harvested
on 9 December, and 8-10-em scions were sidegrafted
to 60 each of the three stock cultivars under
normal daylength. For the 8- and the 16-hour day
photoperiods only Hak Ip rootstock was used with
girdled scions from the three cultivars.
All rootstocks were side-grafted on 10 December
and then transferred to their respective photoperiod
regimes. The 16-hour day plants received
9·5 h sunlight daily and 6·5 h supplementary light
from two 100-watt incandescent bulbs suspended
0·9 m above the tops of the plants.
The experiments were terminated on 10 Mar 66
and percentage takes were recorded for each treatment.
Successful grafts were then harvested, fixed
in Craf III solution for 5 days and then transferred
to 70 % ethyl alcohol until sectioned. Sections were
cut on the sliding microtome at 25fL without
embedding, stained in Safranin and Fast Green
and mounted in Canada Balsam.
Histological studies
For histological studies inarching technique was
employed. However, a few Kwai Mi and Brewster
side-wedge grafts were also made. One hundred
and forty air-layers of the three cultivars in cans
were inarached in different combinations on
5 Nov 65. The first grafts were harvested 2 weeks
later and then at 10-day intervals thereafter until
January 1966. The last harvest was taken on
10 March, 115 days after inarching. All grafts
were fixed, sectioned, stained and mounted as
previously described.
Sample preparation and carbohydrate determination
Girdled and non-girdled sample twigs from
Kona and Poamoho were harvested at the same
time of taking cuttings for rooting. Twigs were
chopped up, oven-dried at 60°C for 12 h and
ground in a Wiley Mill with a 4-mm mesh.
Similar twigs used as scionwood in the grafting
experiments were also taken for analysis. For these
latter determinations, girdled twigs were sampled
at 3-week intervals until scions were taken for
grafting at 9 weeks. Samples taken from nongirdled
twigs on each date served as controls. The
samples were prepared as already described. Two
determinations were made for each sample and the
mean recorded.
Sugar was extracted from 2 g samples with 90
em 3 of 80 % ethyl alcohol. Total sugar was then
estimated in 5 em 3 aliquots according to the
Shaffer-Somogyi Micro Method (Horwitz, 1960).
For starch determination, the residue from each 2 g
sample after sugar extraction was digested with
diastase solution for 30 min at 38°C, then refluxed
with concentrated hydrochloric acid for 2 h.
The resultant solution was filtered and 2 cm 3
aliquots used in the determination of the reducing
power of sugar (Horwitz, 1960). The Shaffer-
Somogyi Dextrose- Thiosulphate Equivalent Table
(Horwitz, 1960) was used for the estimation of
total sugar. A factor of 0·90 (glucose to starch) was
used to convert percentage sugar to starch.

204 W. s. Abutiate & N. Y. Nakasone (1972) Ghana Jnl agric. Sci. 5,201-211
Results for total carbohydrates were analysed Rooting percentages obtained with the Poamoho
statistically following the methods outlined by cuttings under mist with any of the hormonal
Snedecor (1962). treatments were very low. Rooting was better with
no mist in the polyethylene enclosure. The highest
Rooting studies
Four weeks after the Kona cuttings were set,
callusing was clearly visible on a few girdled
branch cuttings of Kwai Mi in the mist box.
Callusing in Brewster under mist and in the polyethylene
enclosure was apparent at 5 and 6 weeks,
respectively. Leaves were retained in the majority
of the Brewster and Kwai Mi cuttings up to 10
weeks but were shed thereafter.
Results showed very low percentage rooting in
both Kwai Mi and Brewster cultivars with and
without mist, irrespective of hormonal treatment.
The highest percentage rooting obtained under
mist and the corresponding total carbohydrate
analyses for girdled and non-girdled scionwood
are shown in Table 1. Cuttings taken from nongirdled
branches of both Kwai Mi and Brewster
rooted respectively better than those taken from
girdled branches and rooted in the polyethylene
enclosure.
Even though percentage total carbohydrates was
higher in Hak Ip than in Brewster, the former did
not root. On the whole, Kwai Mi rooted slightly
better than Brewster. Percentage rooting did not
tally well with levels of carbohydrates in the
cuttings. Results, however, showed that carbohydrate
accumulation was fastest in Kwai Mi and
slowest in Brewster.
Kona
TABLE 1
percentage rooting obtained with no mist in the
polyethylene enclosure and the corresponding
per cent total carbohydrate analyses of girdled and
non-girdled scions are shown in Table 1. There
was better correlation between total carbohydrate
content and corresponding percentage rooting
obtained in the Brewster cultivar. In the case of
Kwai Mi, better rooting was obtained with
material from non-girdled branches.
Grafting studies
Very few graft takes were obtained under any of
the photoperiod regimes. In almost all cases, only
previously prepared scions showed any success.
Results of graft takes under normal day are presented
in Table 2. Non-girdled Kwai Mi scion
gave 10% successful unions on Brewster stock.
All grafts under the 16-hour photoperiod failed
while under the 8-hour regime, only 20 % of
girdled Brewster scion and 10% Kwai Mi each on
Hak Ip stock were successful. Graphs showing the
results of the chemical analyses for total sugar in
girdled and non-girlded stems of the three lychee
cultivars used as sources for scionwood for the
grafting studies are shown in Fig. 1.
Total percentage sugar was less than 1% dry
weight in all cases. The total sugar accumulation
curves for Kwai Mi and Hak Ip for girdled and
non-girdled stems were similar.
Total Percentage Carbohydrate Analyses and Percentage Rooting for Girdled and Non-Girdled Stems of
Three Cultivars of Lychee Grown at Kona (Hawaii Islanli) and at Poamoho (Oahu, Hawaii)
Rooting % % Total carbohydrates1 Station Nature of
stem KwaiMi Hak Ip Brewster KwaiMi Hak Ip Brewster
Poamoho
··1
··1
Girdled' 21·7 0 1·7
Non-girdled 5·0 0 3·3
Girdled' 33·3 0 55·0
Non-girdled 60·0 0 5·0
1 Percentages based on dry weight.
, Branches girdled for 11 weeks before cutting.
** Means for determinations significant at P = 0·01.
11·00
9·14
8·88
2·46
10·82
8·73
9·08
1·97
10·05**
4·77**
10·41**
2·34**

Vegetative propagation ofthe Iychee (Litcni chinensis 5onn.)
TABLE 2
Percentage Successful Gaft Unions under
Normal Day for Three Cultivars of Lychee
Girdled scion
Rootstocks
Brewster I Kwai Mi Hak Ip
Brewster
Kwai Mi
..
..
40
40
0
0
10
0
Hak Ip ., 20 0 0
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W. S. Abutiate & N. Y. Nakasone (1972) Ghana Jnl agric. Sci. 5,201-211
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Vegetative propagation of the Iychee (Litchi chinensis Sonn.)
contents. The contribution of the ray cells to the
callus could also not be ascertained.
Once the callus was formed, cell differentiation
within it proceeded rapidly. A bridging callus from
a Brewster stock 64 days after grafting is shown in
Fig. 7. By the 64th day, vessels and xylem ray cells
were well developed in the callus (Fig. 8). Other
tissues such as sclereids (Fig. 9) developed later.
The differentiation of the bridging callus into
permanent tissues in lychee corroborated the
findings of Mendel (1936) who observed that in
citrus, the primary callus is not a transitory tissue
which is destroyed but is transformed through
differentiation into permanent tissue. Cambium
regeneration in all the grafts occurred between the
74th and the 115th day after grafting. The determination
of the exact time when the cambium
differentiation started could not be ascertained due
to the insufficiency of successful unions for
sectioning.
Within this period (74th to the 115th day) the
two callus projections, one from each side of the
bark (Fig. 10) grew actively and eventually met.
Pith cells (Fig. 10) did not contribute to the graft
union. By the 115th day the healing process was
completed and the cambium regenerated (Figs
11 and 12). The extent of callus development in
Kwai Mi and Brewster side-wedge grafts harvested
115 days after grafting is also shown in Figs 13,
14 and 15.
In all cases callus was contributed by stock and
scion but the former contributed a greater portion
towards the eventual healing of the wound in the
case of side-wedge grafts. In the case of approachgrafts
callus contribution seemed to depend upon
the cultivars used. Where a fast growing cultivar
such as Brewster was approach-grafted to a slow
grower such as Hak Ip, the greater contribution
was made by the fast grower.
Discussion
The results of the various experiments showed a
cultivar trend in the three subjects. A few cuttings
from both girdled and non-girdled branches of
Kwai Mi and Brewster from Kona and Poamoho
rooted, whereas none of the Hak Ip cuttings
rooted in any of the experiments. As pointed out
earlier Hak Ip is the slowest grower among the
three cultivars. The slow growth rate may be due
to slow differentiation of tissues in the stem and
Fig. 7. Transverse section through a 64-day-old callus
tissue (ct) from Kwai Mi scion approach-grafted to
Brewster rootstock (R) (x 38).
Fig. 8. Detailed structure ofthe callus tissue (ct) from the
Kwai Mi scion showing vessels (U) (X 136).
Fig. 9. Further detailed structure ofthe callus tissue showing
well-developed sclereids (m) (x 635).
branches coupled perhaps with other factors not as
yet determined. Histology of the graft union
between Hak Ip and the other two cultivars also
revealed the slow rate of proliferation of callus
tissue, a condition which may explain the rooting
failures.

Fig. 10. Transverse section through a graft union showing
the bridging callus tissue (ct) advancing from the scion
(s) and the rootstock (R) together with the inactive
pith cells (p) at this stage (x 219).
Fig. II. Transverse section through a 115-day-old graft
union showing the developing cambial zone (cz) from
the Kwai Mi scion (5) and the Hak Ip rootstock (R)
(x 9).
Fig. 12. Transverse section through the parenchymatous
cells (n) of the cambial zone showing their detailed
structure (x 139).
Fig. 13. Transverse section through a 115-day-old sidegraft
union showing the callus tissue (ct) developing
from Kwai Mi scion (5) on Hak Ip rootstock (R) (x II).
Fig. 14. Transverse section through a side-graft union of
Brewster scion (5) on Kwai Mi rootstock (R) showing
the extent of the developing callus tissue (ct) 115 days
after grafting (x 12).
Fig. 15. Transverse section through a 115-day-old sidegraft
union of Brewster scion (5) on its own rootstock
(R) showing the extent of the bridging callus tissue (ct)
(x 217).

With the other cultivars, it was noticed that
there was a new flush of leaves 4 weeks after the
cuttings were set. Since a source of energy is
required for this process, it is likely that the small
carbohydrate reserves in the cuttings were used up
for this initial growth, thus depleting the reserves
which could have been drawn upon for root
development. This carbohydrate depletion theory
may explain the rooting failures in Kwai Mi and
Brewster.
Even though the percentage of successful rooting
was low with either NAA-Na or IBA in both
Kwai Mi and Brewster, nevertheless, IBA consistently
induced a higher number and greater
length of roots per cutting than NAA-Na. This
suggests that IBA may be more suitable for rooting
lychee cuttings than NAA-Na. Traub (1937) also
found IBA particularly useful with L. chinensis and
others like Psidium guajava. Perhaps at the same
concentration, NAA-Na may be more toxic to
lychee cuttings than IBA. Doran (1941) found in
his experiments that naphthalene-acetic acid
(NAA), at a given concentration, was more toxic to
cuttings of most species than IBA or indoleacetic
acid (lAA).
Since callus formation was generally slow in the
three cultivars, desiccation of the cuttings,
especially within the polyethylene enclosure, may
have contributed to rooting failures.
The results of carbohydrate analyses on stems
taken for rooting showed some correlation with
rooting percentages obtained in Kwai Mi and
Brewster. Better rooting was obtained with higher
rather than lower starch content in the stems.
Cultivar differences undoubtedly played a part in
the success of rooting obtained; for even though
Hak Ip showed a slightly higher starch content in
the stems than Kwai Mi, there was no rooting
under any environment. Here rooting response
seems to be correlated with factors other than
starch level only.
The important role played by carbohydrates in
the rooting of cuttings has been shown by Murneek
(1941), Reid (1926) and Shippy (1930). These
investigators generally found high correlation
between carbohydrate levels in stem cuttings and
rooting facility. Brandon (1939), however, failed
to find the relationship between starch content and
ease of rooting in species of the genus Rosa. The
results of this study did not, on the whole, sustain
4'
the finding that high carbohydrate level in stem
cuttings is correlated with facility of rooting.
Unpublished reports in the Department of
Horticulture, University of Hawaii, have indicated
that when treated with IAA and planted in an
unheated propagation bed, only 10 or 20 % of
lychee cuttings rooted, but if the propagation bed
was maintained at 3Q-32°C, root formation was
rapid and large numbers of roots were formed. The
reports concluded that for rooting lychee cuttings,
treatment with IAA and heated propagation beds
were essential.
Cooper & Knowlton (1939) obtained 100%
rooting oflychee cuttings under 100 % humidity in
propagating boxes. In the study reported here, the
average daily relative humidity was 78 % and
temperature 25°C within the polyethylene enclosure.
The conditions in the enclosure were
perhaps not ideal for rooting oflychee cuttings and
the low percentage rooting obtained was perhaps
due in part to the unsuitable conditions for the
cuttings.
From the results of the side-wedge grafting
experiments, it seemed that Brewster may be more
readily grafted on Kwai Mi than on Hak Ip. Since
Brewster and K wai Mi are faster growers than Hak
Ip, graft success was perhaps the result of more
rapid development of the unifying callus from
these cultivars compared with Hak Ip. The percentage
graft take under normal day recorded
using Brewster girdled scions, coincided at 9
weeks with the highest level of starch (Fig. 2) in
the stems at this time. If graft take was solely
dependent on the level of starch in the stems, then
in Kwai Mi the graft failures may be explained by
assuming that scionwood collection was ill-timed.
The starch level in prepared scionwood was highest
at 6 weeks and lowest at 9 weeks when the scionwood
was taken for grafting. The starch level alone
cannot explain the observed results in the Hak Ip.
Failure may be more aptly explained on the basis
of relatively low rate of growth of this cultivar,
coupled with factors other than starch level.
Various investigators have described the origin
of callus tissue in the healing process of various
tree species. Mendel (1936) and Juliano (1941)
have all described callus tissue as originating from
the parenchymatous cells from the medullary and
phloem rays and the cortex. Similar observations
were made by Artschwager (1941), Bradford &

210 W. S. Abutiate & N. Y. Nakasone (1972) Ghana Jnl agric. Sci. S, 201-211
Sitton (1929) and Swarbrick (1926). In this study, Buck, G. J. C1?53).The histological development o~the
the secondary cambial derivatives were observed to bud graft union In roses. Proc. Am. Soc. hort. Set. 62,
'b call fi . b th '" 497-502.
contn ue to us ormatIOn ut e partICIpatIOn
of the ray cells in the healing process could not be
clearly established. Crafts (1934) and Bradford &
Sitton (1929) further observed that the vascular
cambium also contributed cells to the graft union
but in this study there was no conclusive evidence
to establish the cambium as directly contributing to
callus formation.
As observed also by Mendel (1936) and Saas
(1933) the pith did not contribute callus in the
healing process of the lychee grafts. The results
of the side-wedge grafts also corroborated the
findings of Mendel (1936) that both the stock and
scion may contribute callus in the healing process.
From the growth behaviour of the lychee, Venning
(1949) postulated that successful unions may
depend upon the chances of any two active cambial
areas being in juxtaposition. Since there are no
external indicators to cambial activity in this stem,
success of union will undoubtedly depend upon
the chances of two active cambial areas being in
contact.
The results of this study have indicated that
successful grafting may depend upon the interplay
between a number of factors including cambial
activity in the two symbionts, the level of carbohydrates
in the stems and cultivar characteristics.
Both rooting of suitable stem cuttings with the
aid of hormones and side-grafting of old stocks
using prepared scions may be used only to a
limited extent. For large-scale propagation, however,
young seedlings are preferred since a higher
percentage of successful unions may be obtained.
Recent work by Kadman & Slor in Israel has
clearly established this fact.
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Brandon, Dorothy (1939) Seasonal variations of starch
content in the genus Rosa and their relation to propagation
by stem cuttings.J. hort. Sci. 17,233-253.
Carlson, M. C. (1929)Microchemical studies of rooting
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