From the Archives
of the Rare Fruit Council of Australia
by Dave Hodge - Cairns Branch
Top-Working
Lychees - The Result
Scientific
name: Litchi
chinensis
Family:
Sapindaceae
The
article 'Top Working Lychees' that appeared in the RFCA Newsletter No.
80 of May, 1993, described a top-working project aimed at quickly
converting large, unmanageable Tai So Trees over to the new super
variety Fay Zee Siu. That article must be read in conjunction with this
one to get the full story.
So how did it
all work out?
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Picture 1.
A tree one year and ten months after Top-Working Fay Zee Siu onto Tai
So. |
Picture 2.
The slower growth of single trees planted back into old tree sites.
These are older than the tree in Picture 1. |
Only
a bunch or two of fruit was picked off the Top-Worked trees so don't
expect much fruit for the first two years at any rate. However, it will
be interesting to see if any fruit is produced in the third year. But
don't expect miracles!
Is
top-Working Expensive?
Capital Cost
Yes,
it is expensive in planting material. The capital cost is high but the
benefits could outweigh this cost eventually. The previous article in
Newsletter No. 80 describes how four or five potted marcots were
approach grafted to the suckers around each stump. That is $80-$100 per
stump at $20 a potted marcot. There is no gain without pain!! Cheaper
if you marcot your own trees, of course.
Replanting vs
Top-Working
What
must also be taken into account is the slower growth and longer time
involved to get trees into production when replanting into old tree
sites.
Time is Money!
Consider
the cost of your time over the number of years it takes to get such
trees into bearing. The cost of irrigating, fertilizing, weed control,
spraying and mowing, etc., is much the same, but the lag time to get
the new trees into production should be considerably reduced by
Top-Working instead of replanting. Furthermore, earlier yields from
Top-Worked trees should be higher, because of the larger tree size and
increased vigour.
Why So Much
Vigour?
Why
are the Top-Worked trees so vigorous? Partly, perhaps, because of the
vigorous Fay Zee Siu variety and partly, perhaps, because of the extra
vigour imparted to it by the massive Tai So root system now around 20
years old. But I think it is also very largely due to the high
population of actively-growing mycorrhiza fungi in the soil on the old
Tai So root system.
Transverse section of part of a root of the Scots pine (Pinus sylvestris),
showing the Piliferous layer, surrounded by ectotrophic Mycorrhiza.
Note some of the fungal hyphae penetrating between the cells.
Mycorrhiza
What
is mycorrhiza? It is a beneficial fungus which lives on the roots of
certain trees. The fungus is supplied with nutrients by the tree and in
return it helps the tree to absorb moisture and nutrients from the soil.
This
is known as a symbiotic relationship, each helps the other to the
mutual benefit of both. One cannot live without the other.
Oh the wonders of nature! I believe the Lychee to be a tree highly
dependant on its mycorrhiza for optimum growth and cropping.
Mycorrhiza
has been observed on Lychee roots, but unfortunately I have no picture.
But here are two of this beneficial fungus on Pine tree roots to show
what it looks like.
By Top-Working in the manner described in the Newsletter No. 80 we take
full advantage of the presence of this mycorrhiza.
When Absent
Growth May be Slower
Now
look carefully at Picture 2. These trees were planted back into old
tree sites, but only after the trees were removed and the sites
fallowed for a while before being replanted. In other words, any roots
and their mycorrhiza left in the soil were dead by the time the new
trees were planted. Some mycorrhiza die very quickly once the host tree
is removed. Hence the new trees tended to struggle initially to get
established. The fact that they are of a less vigorous variety makes
them look even worse when compared with the Top-Worked trees.
The Effect of
Vigour
Picture
3 illustrates what I believe to be the immediate effect of mycorrhiza
on initial growth. Notice that the growth from the approach graft in
the middle is not as vigorous as the two branches arising from below
the graft.
In this illustration the potted marcot was planted in the ground next
to the stump and approach grafted onto a sucker.
The
Tai So stump and its root system, kept alive by all the suckers, would
have had plenty of active mycorrhiza fungi in the soil. These would
rapidly colonise the roots of the Fay Zee Siu marcot and immediately
help it to absorb nutrients and moisture. Hence the rapid growth from
below the graft while the graft was becoming established.
Well, that's my theory anyway!
The
approach grafted marcot at about 15 months. Note the strong shoots
arising from below the graft. Is this due to the beneficial effect of
the mycorrhiza?
Recommendation
One
occasionally sees marcots which die some time after potting up, even
though they grew initially, and also potted marcots which survived
planting in the orchard, but died later on even though good care was
taken of them.
Could this be partly due to the lack of mycorrhiza fungus in the
potting mix and/or lack of the fungus in the orchard soil?
Would
establishment and growth in the pot and later on in the orchard be
improved if the mycorrhiza was present right from the start?
Personally I think it would and I would recommend as follows:
Scrape
away the leaves from under old established Lychee trees and dig out the
topsoil and fibrous roots. Add about 20% of this to the potting mix
when potting up rooted marcots. Also put a couple of handfuls per hole
when planting out. Mixing soil with the peat moss when marcotting may
also be beneficial. Always use the soil fresh from under the tree,
don't store it for any length of time or the mycorrhiza may deteriorate.
Is This
Practical?
I
realize the practicality of doing this on a large scale is perhaps
doubtful from a nurseryman's point of view. It may only be worthwhile
if one is experiencing high numbers of deaths in the nursery or loss of
trees after planting. For small numbers, it might be worth giving it a
go.
Marcots retained in their pots. Once the approach graft has taken, the
marcot is removed and can be used again.
A not-so-good
Alternative
As
can be seen from Picture 4, instead of planting the Fay Zee Siu marcot
in the ground, the pot on the right was placed on the ground next to
the stump and the pot on the left on top of the stump.
The
advantage here is that once the approach graft has taken, the marcot is
cut off below the graft and can then be used again elsewhere. As it
would be fairly pot-bound by now it would probably be better to plant
it in the ground next time. Tease out the roots before planting.
The
main disadvantage of this method, which I have observed, is that it is
more difficult to keep all the pots watered, especially if a great
number of trees are being Top-Worked.
If not kept adequately
watered, you can expect some graft failures. For a good take, they
really should be watered by hand, individually.
Putting a
sprinkler above the tree may work but the dense sucker foliage tends to
deflect the water to some extent. Pots need to be level, of course, and
some may need to be placed on boxes or bricks to bring them up to the
sucker for grafting.
Feed the Pots
If
the potting mix is very porous, as most peat-based mixes are, nutrients
tend to rapidly leach out. Perhaps it would be better to mix soil with
the peat as previously described, but at a higher rate, to act as a
buffer if this method of Top-Working is to be employed. Top-dress each
pot regularly with a soluble fertilizer to keep the marcot actively
growing for a good take.
In my opinion, if not given good care
and attention, this is not such a good method as planting the marcot in
the ground. As it is isolated from the soil, it misses out on what I
think is the beneficial effect of the abundant mycorrhiza in the soil
around the stump. The resulting tree tends to be smaller initially.
Experimental
Graft Failures
Ah yes, we must always talk about the failures
as well as the successes. Thus we learn by practical experience!
As
described in the original article in the May 1993 Newsletter, I tried
out two alternative methods of Top-Working: Cleft grafting and Chip
budding.
Cleft grafting was a complete failure, all the scions died, so I guess
we can forget that method.
Out
of about a dozen Chip buds, only two grew. As with all Chip budding,
the take can be considerably improved providing the bud wood is
especially grown for the job.
I took my bud wood off mature cropping
trees, which is not the way to go, but I had no choice. Just wandering
around the orchard snipping shoots off here and there is definitely not
on! I found it very hard to find the ideal wood.
Bud wood for Chip budding must be produced on young, vigorous bushes
which are kept hard-pruned and well-fertilized.
Hedge-pruned
bushes, in fact. This produces vigorously flushing wood which is taken
off when it still has some green colour and when the axillary buds are
nice and prominent. It is impossible to find this sort of wood on large
fruiting trees in any quantity.
Unless you can get this sort of
wood, forget about budding. However, if you can, then this could be a
promising alternative method of top-working as it is quick and easy to
do.
The Best
Method So Far
No
doubt about it. Approach grafting with potted marcots is 100%. So, in
my opinion, if you want to Top-Work either old or young trees over to a
better variety, and if you want a big tree quickly, then that is the
way to go as described in the RFCA Newsletter No. 80 of May 1993.
Compatibility
Watch
compatibility. Not all varieties are compatible with each other when
grafted. Apparently, from what I have read, early vigorous varieties
are compatible with each other. Similarly with mid-season and with
late, slow-growing varieties. But there is incompatibility between
these three groups. See the DPI for more information on that. But we do
know that Fay Zee Siu is compatible when grafted onto Tai So. I will
keep you posted on how the Top-Worked trees have performed in the
future.
So, if you want to give it a go, then the best of luck!! !
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