Lodoicea germination

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Figure 1. Germinated seedling

A large percentage of the palms being grown for the Townsville Palmetum have been raised from seed, so the arrival of yet another seed batch is hardly a matter to cause any concern. They are usually cleaned and sown within hours without disturbing the everyday course of events in the nursery. However the arrival of five Coco-de-mer (Double Coconut) seeds was an occasion in stark contrast to the normal seed acquisition and was both preceded and followed by time consuming efforts by a multitude of people.

Simply obtaining the seeds was no easy matter, much correspondence and the generosity of the Seychelles Forestry Department saw five wooden boxes eventually arrive at Townsville airport. The seeds had been sent pregerminated, individually packed in boxes. Unfortunately the growing cotyledonary outgrowth, which carries the embryo into the soil, had been damaged on three of the seeds during transit. Two however were in perfect condition.

After much discussion and a search of the available literature on Locoicea germination, which proved scant, it was decided to sow the seeds in containers specially built for the task. These containers are in the form of a cylinder with a base made of galvanized weldmesh, lined with woven weed-mat, a type of heavy shade-cloth used for weed suppression. The dimensions of the containers is 1.5 x 1.5 metres.

Trying to find information on Lodoicea germination is an exercise involving interpreting various authors dubious statements, mere rumours and heresay. There seem to be no published accounts of the germination process that can be used and trusted. Various authors state that the cotyledonary outgrowth or "root" penetrates as much as 4m before a leaf is formed. Some authors state that the seedling requires a certain period of time to attain the leaf-emergence state. This period varied in the literature from 1 year to 3 years.

Reasons for the scarce and varying statements on Lodoicea germination are due no doubt to the seeds rarity, cost and size: the latter being a reason why many writers suggest planting the ungerminated seed directly into the ground in its permanent site. This leads to a certain variance in stated germination times as there is then no way of knowing when germination begins and therefore how long the seedling takes to form. No doubt the method of planting directly in the ground often leads to false impressions of just how deep the seedling penetrates.

In devising a way of accommodating the germinating seeds, I decided to study palms that are related to Lodoicea. In the collection we had already germinated various Latania, Hyphaene and Borassus species as well as Borassodendron machadonis and Bismarckia nobilis. In all these palms the seed germinates rapidly and forms a tuberous extension of the cotyledon which carries the embryo out of the seed and plants it deep in the soil. In all of these seedlings it was found that the cotyledon suddenly ceased its tuberous downward growth at a point and then grew a whorl of slender lateral roots. The apex of the cotyledon then continued downwards as a reduced radicle, whilst a growing point formed just above the lateral-root whorl. As soon as the lateral roots attained any length, the tuberous cotyledon was seen to fissure externally due to the formation of leaves within. These leaves grow upwards for some distance before rupturing the cotyledon. In Latania and Borassodendron the first emergent leaf is palmate, whilst Hyphaene, Borassus and Bismarckia have undivided blade-like first leaves.

An interesting feature of these genera is that the downwards growth of the cotyledon (under our conditions at least) approximated the length of the first emergent lear blade with Bismarckia being somewhat shallower and Hyphaene somewhat deeper.

It was therefore established that the base of the plant, where the lateral roots formed would be about as deep as the leaf-blade length + some cm depending on the genus. If Lodoicea were to behave like its relatives then a depth of 1.5 metres should be ample as the first emergent leaf blade is normally between 1 and 1.5m long.

Using this estimate as a guide, we set about making the massive containers. Past experience with the galvanised mesh "baskets" indicates that their transport with a forklift and truck to the site and placement in the planting hole is relatively simple. On site the sides are cut off with bolt-cutters and the plant is filled around with the base remaining under the plant, causing no detriment.

The next problem to overcome was the choice of germination medium. As I had previously had success with Hyphaene germination and further trials with other Borassoid genera proved, a well-drained medium consisting primarily of peanut shells seemed to be most suitable. The mix was modified to contain some sand, peat and osmocote in the following formula:

1 part peanut shells 1 part river sand 1/2 part peat moss + 250 grams osmocote to 1 cubic metre of mix.

This was then poured into the baskets up to 30cm from the top. The seeds were seated upon this with the cotyledon placed centrally facing down. The seeds were then covered with peanut shells, drenched with fungicicle and left for some weeks.

The seeds were planted on the 29th August with cotyledons 3-5cm long. By the 30th September it became obvious that the three that were damaged during transit would not survive, however the two that were undamaged had sunk the cotyledon some 15cm into the medium, a growth rate of about five millimetres a day.

The warmer weather that followed saw the growth increase to nearly one centimetre a day so that by the 1st January the cotyledons had reached down over a metre and were gradually thickened to a maximum of 7cm about 60cm down. I carefully dug down to the apex at regular intervals to watch this process and inspect for any threatening infestations. By the 30th January the cotyledons had nearly reached the bottom of the container and I began to doubt that they had enough room. By the 1st March however, I decided to raise the seedlings and dug down only to find an astonishing whorl of lateral roots about 15 millimetres in diameter radiating out from the apex, below which continued a similar sized radicle. The seedlings were raised by 15 cm as a precaution.

After another month the lateral roots had extended into the medium some 60cm and were producing their own secondary laterals. This whorl was situated 1.25m from the seed. At this time it was noticed that the tuberous cotyledon was beginning to fissure, the surface of the fissures showing a callous-like growth, no doubt a mechanism to aid in screening out invasive fungi. It seemed that leaves were being formed inside the cotyledons in the same manner as the other Borassoids.

Qn the 25th May 1987, I discovered leaf shoots rupturing the cotyledon only 20cm below the seed. From the initiation of germination on the 8th August, 1986 until 25th May, 1987 when the leaf became obvious is a period of 289 days, a lengthy time-span for any seedling, but considering the size of the plant, its huge tuberous cotyledon and massive roots, it does not seem overly slow.

Some conclusions based on our experience with Lodoicea and the other Borassoids can be summarised here. Firsfly, the cotyledons growth is greatly increased in both rate and size by the use of a light, friable medium which should contain some structural materials to hold it up and open. In this way we have found peanut shells to be perfect, but other longlasting organic or synthetic materials could just as easily be used. Secondly, it appears unnecessary to plant any of the Borassoids directly in the ground as it is certainly possible to grow them in containers initially, providing it is deep enough. Container-raising of the seedlings also allows greater control of the seedlings health and growth, and being portable, they can be moved if needed. Finally, once germination begins, Borassoid palms establish rapidly if given the right conditions which are: good drainage at all times, warmth, a medium of slightly acid to neutral pH and plenty of depth.

Contributed by:

Robert Tucker, Townsville Palmetum.
(from Palms & Cycads No. 22, Jan-Mar 1989.)
Rolf Kyburz, (Figure 1)

External Links:

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