Studies of vegetative propagation of the lychee (Litchi chinensis ...
Studies of vegetative propagation of the lychee (Litchi chinensis ...
Studies of vegetative propagation of the lychee (Litchi chinensis ...
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With <strong>the</strong> o<strong>the</strong>r cultivars, it was noticed that<br />
<strong>the</strong>re was a new flush <strong>of</strong> leaves 4 weeks after <strong>the</strong><br />
cuttings were set. Since a source <strong>of</strong> energy is<br />
required for this process, it is likely that <strong>the</strong> small<br />
carbohydrate reserves in <strong>the</strong> cuttings were used up<br />
for this initial growth, thus depleting <strong>the</strong> reserves<br />
which could have been drawn upon for root<br />
development. This carbohydrate depletion <strong>the</strong>ory<br />
may explain <strong>the</strong> rooting failures in Kwai Mi and<br />
Brewster.<br />
Even though <strong>the</strong> percentage <strong>of</strong> successful rooting<br />
was low with ei<strong>the</strong>r NAA-Na or IBA in both<br />
Kwai Mi and Brewster, never<strong>the</strong>less, IBA consistently<br />
induced a higher number and greater<br />
length <strong>of</strong> roots per cutting than NAA-Na. This<br />
suggests that IBA may be more suitable for rooting<br />
<strong>lychee</strong> cuttings than NAA-Na. Traub (1937) also<br />
found IBA particularly useful with L. <strong>chinensis</strong> and<br />
o<strong>the</strong>rs like Psidium guajava. Perhaps at <strong>the</strong> same<br />
concentration, NAA-Na may be more toxic to<br />
<strong>lychee</strong> cuttings than IBA. Doran (1941) found in<br />
his experiments that naphthalene-acetic acid<br />
(NAA), at a given concentration, was more toxic to<br />
cuttings <strong>of</strong> most species than IBA or indoleacetic<br />
acid (lAA).<br />
Since callus formation was generally slow in <strong>the</strong><br />
three cultivars, desiccation <strong>of</strong> <strong>the</strong> cuttings,<br />
especially within <strong>the</strong> polyethylene enclosure, may<br />
have contributed to rooting failures.<br />
The results <strong>of</strong> carbohydrate analyses on stems<br />
taken for rooting showed some correlation with<br />
rooting percentages obtained in Kwai Mi and<br />
Brewster. Better rooting was obtained with higher<br />
ra<strong>the</strong>r than lower starch content in <strong>the</strong> stems.<br />
Cultivar differences undoubtedly played a part in<br />
<strong>the</strong> success <strong>of</strong> rooting obtained; for even though<br />
Hak Ip showed a slightly higher starch content in<br />
<strong>the</strong> stems than Kwai Mi, <strong>the</strong>re was no rooting<br />
under any environment. Here rooting response<br />
seems to be correlated with factors o<strong>the</strong>r than<br />
starch level only.<br />
The important role played by carbohydrates in<br />
<strong>the</strong> rooting <strong>of</strong> cuttings has been shown by Murneek<br />
(1941), Reid (1926) and Shippy (1930). These<br />
investigators generally found high correlation<br />
between carbohydrate levels in stem cuttings and<br />
rooting facility. Brandon (1939), however, failed<br />
to find <strong>the</strong> relationship between starch content and<br />
ease <strong>of</strong> rooting in species <strong>of</strong> <strong>the</strong> genus Rosa. The<br />
results <strong>of</strong> this study did not, on <strong>the</strong> whole, sustain<br />
4'<br />
<strong>the</strong> finding that high carbohydrate level in stem<br />
cuttings is correlated with facility <strong>of</strong> rooting.<br />
Unpublished reports in <strong>the</strong> Department <strong>of</strong><br />
Horticulture, University <strong>of</strong> Hawaii, have indicated<br />
that when treated with IAA and planted in an<br />
unheated <strong>propagation</strong> bed, only 10 or 20 % <strong>of</strong><br />
<strong>lychee</strong> cuttings rooted, but if <strong>the</strong> <strong>propagation</strong> bed<br />
was maintained at 3Q-32°C, root formation was<br />
rapid and large numbers <strong>of</strong> roots were formed. The<br />
reports concluded that for rooting <strong>lychee</strong> cuttings,<br />
treatment with IAA and heated <strong>propagation</strong> beds<br />
were essential.<br />
Cooper & Knowlton (1939) obtained 100%<br />
rooting <strong>of</strong><strong>lychee</strong> cuttings under 100 % humidity in<br />
propagating boxes. In <strong>the</strong> study reported here, <strong>the</strong><br />
average daily relative humidity was 78 % and<br />
temperature 25°C within <strong>the</strong> polyethylene enclosure.<br />
The conditions in <strong>the</strong> enclosure were<br />
perhaps not ideal for rooting <strong>of</strong><strong>lychee</strong> cuttings and<br />
<strong>the</strong> low percentage rooting obtained was perhaps<br />
due in part to <strong>the</strong> unsuitable conditions for <strong>the</strong><br />
cuttings.<br />
From <strong>the</strong> results <strong>of</strong> <strong>the</strong> side-wedge grafting<br />
experiments, it seemed that Brewster may be more<br />
readily grafted on Kwai Mi than on Hak Ip. Since<br />
Brewster and K wai Mi are faster growers than Hak<br />
Ip, graft success was perhaps <strong>the</strong> result <strong>of</strong> more<br />
rapid development <strong>of</strong> <strong>the</strong> unifying callus from<br />
<strong>the</strong>se cultivars compared with Hak Ip. The percentage<br />
graft take under normal day recorded<br />
using Brewster girdled scions, coincided at 9<br />
weeks with <strong>the</strong> highest level <strong>of</strong> starch (Fig. 2) in<br />
<strong>the</strong> stems at this time. If graft take was solely<br />
dependent on <strong>the</strong> level <strong>of</strong> starch in <strong>the</strong> stems, <strong>the</strong>n<br />
in Kwai Mi <strong>the</strong> graft failures may be explained by<br />
assuming that scionwood collection was ill-timed.<br />
The starch level in prepared scionwood was highest<br />
at 6 weeks and lowest at 9 weeks when <strong>the</strong> scionwood<br />
was taken for grafting. The starch level alone<br />
cannot explain <strong>the</strong> observed results in <strong>the</strong> Hak Ip.<br />
Failure may be more aptly explained on <strong>the</strong> basis<br />
<strong>of</strong> relatively low rate <strong>of</strong> growth <strong>of</strong> this cultivar,<br />
coupled with factors o<strong>the</strong>r than starch level.<br />
Various investigators have described <strong>the</strong> origin<br />
<strong>of</strong> callus tissue in <strong>the</strong> healing process <strong>of</strong> various<br />
tree species. Mendel (1936) and Juliano (1941)<br />
have all described callus tissue as originating from<br />
<strong>the</strong> parenchymatous cells from <strong>the</strong> medullary and<br />
phloem rays and <strong>the</strong> cortex. Similar observations<br />
were made by Artschwager (1941), Bradford &