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

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Unpublished reports in the Department of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 &