Herewith a few comments on tropical agriculture from practical experience in Uganda, East-Africa, which I consider have some bearing on Rare Fruit growing in Australia.

In my thick-headed youth, I spent around ten years in the Western part of Uganda, Toro Province which borders Zaire (The Belgian Congo as it was in those good old colonial days). The border passes ever the top of the 17,000 ft Ruwenzori Mountains (Mountains of the Moon). Few people know that right on the equator in the middle of tropical Africa there is a mountain range complete with a permanent snow cap and glaciers.

Not much in the way of Rare Fruits up there, except a somewhat unpalatable species of Rubus (blackberry/raspberry). Being right next to the Congo. I and my bachelor friends used to go there occasionally for the more sophisticated night life enjoyed by the Belgians. I have noticed in past numbers of the newsletter references to tree fruits, including large-fruited species of Annona (custard apple), to be found in the Congolese rainforest, and I have often been asked if I ever went there to look for rare fruits. Well, not really. We would take our girl friends over there for salubrious weekends. The sort of fruits we were after did not grow on trees. As a young colonial in Darkest Africa, I have many fond memories of such events.

A point of interest worth mentioning is that the Ruwenzori National Park and its adjoining Parc Nationale du Albert (old name) did, at one time, contain the highest density of game animals in the whole of Africa. I doubt if it still does. The higher rainfall in that area always ensured year-round feed for the animals, of which there was a great variety.

The melting snows on the Ruwenzori Mountains and the surrounding lakes and rivers are one of the sources of the River Nile. The two southernmost sources are rivers on the eastern side of the Virunga Mountains in Rwanda and Burundi: African countries few people have heard about, to the south of Uganda.

At the northern end of the Ruwenzori range is a place called Bundabugio on the banks of the Semeliki River, which at that point forms Uganda's western border. There used to be a DPI experimental station there some years before my time. There they introduced Cocoa (Theobroma cacao) as a possible cash crop for the locals. It didn't take off, why, I never found out, but the trees were still there and growing strongly. They were not growing under shade but in full sun and un-irrigated. All the trees had developed an umbrella-shaped crown and were packed with fruit on the main limbs inside the trees. Despite neglect, they were doing very well on their own.

Another place I saw Cocoa growing was on Salama Estate just east of the capital, Kampala. I was employed there for a time by the Uganda Development Corporation to commence a Tea Improvement Program by clonal selection. Whilst there, I was asked to experiment with Cocoa, and directed to clear about three acres of rainforest underbrush, leaving the main trees so that their canopy provided shade for the developing cocoa trees. Well, that was the idea anyway.

In years gone by, the previous owners, from memory the Buchanan family of whiskey fame, had planted cocoa in a patch of forest on the estate. This was never followed up in later years and the forest grew back again, but some of the cocoa trees had survived. From the best of these we took seed, as they seemed to do well in that area, for the nucleus of our planting. Seed was extracted from the fruit and immediately sown in pots. Seed viability, from memory, is only of short duration, something like coffee. The nursery was lightly shaded.

When sufficiently grown, the best seedlings were planted out in rows beneath the trees. They grew reasonably well at first, but eventually they were repeatedly attacked by leaf-eating bugs from the surrounding forest, to the point where some trees were completely defoliated. Any new leaves that formed were immediately chewed off. Not so good. Too much shade seemed to slow the growth, making them susceptible to insect attack.

Cocoa needs shade initially, until established. After giving the problem some thought, I persuaded our General Manager for us to try again away from the forest on a nearby estate, but this time with shade we could control. We used bananas instead. In Australia, a similar type of mixed planting of Avocado trees and bananas has worked well in the Coffs Harbour area, as reported in Newsletter No.32 page 16 entitled "Companion planting at Coffs Harbour".

Africans in Uganda grow the Matoke, or Cooking banana, as their staple diet. So plenty of banana offsets were available for our experimental plot. A grassy area in more open country was selected and the Cocoa and bananas planted in alternate lines in well-prepared, deeply-ripped ground. Everything took off and grew vigorously, as was expected. To control the shade, we merely lopped the bananas and used the loppings as mulch for the cocoa trees. According to the above-mentioned article, bananas provide about 25 tonnes of organic matter per hectare each year. It all looked very promising indeed. The block was not irrigated, the abundant rainfall being sufficient.

Unfortunately around about that time there appeared on the horizon a certain gentleman from the army, a Mr Idi Amin. A very large fellow indeed, over seven feet tall and massively built. Eventually I was introduced to him, and during our discussion, it became obvious to me that this was a very dangerous character. Not long afterwards, I decided to leave the country at the end of my contract. Funnily enough, after some years, he also left Uganda. He "emigrated" to Saudi Arabia and I to South Australia. Thus our paths diverged. So I never found out what happened to my experimental plot of cocoa.

I noticed an article in the Australian of 25.3.93, that the State Government has set aside $15,000 to study the viability of a cocoa bean processing plant in Innisfail. Apparently there are a number of cocoa trees growing well in that town. Bear in mind that in 1991, Australia imported $60 million worth of cocoa product for chocolate manufacture. The processing plant could produce up to $40 million worth chocolate liquor, cocoa butter and powder. Sounds good, however it all depends on how much the grower is going to get for his crop.

In 1991, I noticed in the paper that cocoa was A$1,744 per tonne at exchange rates prevailing at that time. According to H.F. Macmillan's Tropical Planting and Gardening, yields of around 2.5t/ha are possible. Presumably, as in Uganda, at wide spacing and unirrigated. At the above price, this translates into $4,360 per hectare ($1,744 per acre). I question the viability of cocoa at this price unless by closer planting, irrigation and other modern management practices the yield can be increased and through some sort of Cooperative factory arrangement, the price to the grower can be improved. He will need a lot more than $1.74/kg to make a living out of a perennial tree crop like cocoa with all the attendant capital outlay and ongoing costs of production associated with tree crops.

There is a young cocoa tree or bush growing well without shade in the Lakes area of the Flecker Botanic Gardens in Cairns near Greenslopes St, but I don't think it's labelled. There are or were several fruits on it. There is also a line of healthy-looking trees on a property near Mossman that apparently have stood up well to past cyclones. So cocoa seems to grow here quite well and especially under irrigation.

There was cocoa growing in the Coastal Plains Research Centre of the DPl near Darwin. The larger trees were about 5 years old in 1990 and were in flower at the time (February). They were irrigated and shaded by Glyricidia trees.

Near the aforementioned Salama Estate in Uganda, there was a DPI Research Centre growing cocoa in an experimental block. The young cocoa trees in this planting started to die out here and there over a period of time. On examination of the dead trees, it was suspected that they were infected with either Fusarium or Verticillium Wilt (Black Heart disease), both soil-borne diseases. The heart wood of the trees had turned black so we suspected Verticillium Wilt. The shade trees were all quite healthy and showed no sign of infection. These were a legume, possibly Glyricidia. The block had previously had several crops of cotton on it and we surmised, as cotton is susceptible to Wilt, that a heavy carryover of Wilt disease in the soil had infected the cocoa.

Wilt diseases, especially Black Heart, are present in orchards down south, and I have no doubt they are also present in Far North Queensland. Black Heart has many alternative hosts, both herbaceous and woody, and is very persistent in the soil. Affected trees can look healthy but remain slightly stunted and unproductive for some time before finally dying, following a period of stress such as temporary waterlogging. This is a problem that should be borne in mind when planting cocoa here. I would suggest plant only in well-drained soil, and in not-as-well-drained soil, hill up rows before planting. Incidentally, what happened to the cocoa variety trial at Kamerunga Research Station?

I also read somewhere that the Northern Territory DPI at Berrimah Research Centre is experimenting with another type of cocoa, commonly called CUPUASSU (Theobroma grandiflorum) Seventy five seedlings were planted, but I don't know when. This is said to be superior to cocoa, with a higher price but lower yield. lt is supposed to be caffeine-free, therefore good for health products. The ripe pods apparently fall to the ground (ordinary cocoa pods have to be cut off) so maybe they could be mechanically sweep-harvested, something like almonds or cider apples. The cupulate (not sure what this is exactly - perhaps the raw chocolate?) of Cupuassu does not turn white or spoil in storage compared to ordinary cocoa. The DPI intend to make chocolate from it. A good import substitute.

In Uganda, we fermented a small amount of beans in boxes, as is done overseas and sent a sample to the manufacturers in the UK for assessment. Apparently the reports were quite favourable, but I left the country soon afterwards.

As with most cultivated tree crops, higher-yielding clones and varieties are available either here or overseas. Some clones are vegetatively propagated by cuttings taken only from specially managed nursery trees grown for that purpose. In Uganda, we experimented with rooting cuttings from selected higher-yielding trees. I don't know what varieties/clones we have here, but considering the high capital cost of establishing an orchard and the bag time before coming into full bearing, it is to be hoped that only the best available selected material will ultimately be supplied to growers for planting.

Illustration of the life cycle of root knot nematodes.

The company I worked for in Uganda was mainly engaged in growing tea. On Salama Estate, we needed to expand our tea acreage into old coffee land where uneconomic coffee trees had been removed and the land left fallow. Unfortunately, in this replant situation, we ran straight into a problem with Root Knot Nematodes (Meloidogyne javanica) a soil-borne pest which causes the familiar swellings on the roots of infested vines, tomatoes and carrots etc. (also sometimes called eelworm), a world-wide problem. The tea was very slow to grow and took a long time to become established. This was probably the problem with the coffee in the first place!

The Tea Research Institute at Kericho in Kenya had an outstation on Salama Estates with the same nematode problem. They decided to try out the well-known remedy espoused by adherents of organic growing methods of planting Marigolds between the crop rows, in this case between the rows of young tea plants. The belief is held that the root exudate, or whatever, from the marigolds encourages the nematode cysts to hatch out, but then they all die because they cannot live on the marigolds roots, or that the roots are toxic to the nematode - something like that anyway.

Well, the Research Station looked like a flower garden by the time they'd finished. Being only a small area, they could afford the price of imported seed. However, our Estate was a different matter. We needed too many kilos of seed.

Illustration of the root system of a tomato plant infested with root knot nematodes.

In my travels around the district, I had noticed a wild and robust growing species of native marigold which tended to appear once a piece of ground was worked up. I had it correctly identified and then collected seed. I sowed a small plot, collected more seed from that and then sowed a larger plot and so on until I had enough seed. I then sowed a large area in old coffee ground, and once it had grown up and set seed, I rotary hoed it all in. I allowed the area to re-seed in this way three times, followed by ripping and rotary hoeing to incorporate the marigold trash as a soil-enriching cover crop and one that was supposedly toxic to nematodes.

The soil in the plot ended up just like compost - full of organic matter to a good depth. Absolutely ideal and all ready for planting more tea. The reader must understand that all this process took a comparatively short time because of the regular rainfall in that part of Uganda and the very free-draining soil.

Before planting, I had another soil test (nematode count) done to check if I had got rid of all those damned nematodes. Back came the results and would you believe it, the nematode count was almost as bad as when we had started. The result was the same on the Research Station. So don't tell me you can get rid of nematodes by planting marigolds, or certainly not in this case at any rate.

In the end I solved the problem, to some extent, by selecting tea clones which appeared to have some degree of nematode tolerance (no lumps on the roots and better growth). Not easy, a long and involved process, but it was the only way to get tea established in nematode-infested soil.

Tea clonal selection, as previously mentioned, was my main job with the Uganda Development Corporation. The best tea bushes are selected, usually for vigour and yield, tested for fermentability (quality potential), propagated from cuttings (rooting test - ease of propagation), planted out in replicated trial plots from which yields were recorded and tea made for market appraisal. Successful clones were then mass-propagated for future plantings. Interesting and rewarding work. Tea has traditionally been grown from seed for over 200 years. But there is tremendous genetic diversity between seedlings. In a tea plantation grown from seed, about a third of the tea bushes are responsible for producing more than half the crop. The rest are hangers-on which only take up valuable space. With clonal selection, one selects not only for high yield but also for superior quality in the cup. Thus our best tea clones in Uganda produced more than three times the average crop and fetched a much higher than average price on the market because of their excellent quality.

In Central America, for example, seedling progeny resulting from crossing certain cocoa clones have given huge increases in yield and an improvement in the quality of the final product.

Nearer to home in South Australia, two of my main R&D programmes in the South Australian DPI were clonal selection in wine grapes and apricots and the adoption of resistant rootstocks for both. By combining selected clones, higher yields were obtained and better quality fruit.

Clonal selection should be given top priority when propagating Rare Fruits, and to this end, the Cairns Branch is currently conducting a survey of its members with one of the aims being the identification of those superior clones. That is, trees, often seedlings, with a higher and more consistent cropping history and producing superior quality fruit.

This is just as important to the home gardener as it is to the commercial grower.

The identification and selection of better rootstocks should also be a priority. What's below ground is just as important as what's up top.

Rootstocks considerably influence the growth and cropping capacity of fruit trees, a point which seems to have escaped many Rare Fruit Growers. Typical examples amongst temperate fruits are the growth-regulating and increased cropping capacity imparted to apple trees on Malling rootstocks and others; the resistance of plum rootstocks to Black Heart disease for apricots on heavy soils and the vastly increased yields imparted to wine and table grapes as a result of grafting virus-tested clonal vines onto Ramsey rootstocks. Ramsey, a hybrid vine rootstock, was selected for its vigour and resistance to Root Knot nematodes in replant areas (the dreaded nematode again). So why not a similar clonal selection and rootstock programme for each of the Rare Fruits? The more active participation of our commercial grower and backyard gardener members along with nurseryman to identify such clones and rootstocks would be of considerable benefit to us all.

This article is intended to point up some of the pitfalls in growing tropical crops and the benefits of clonal selection. It is based on my own practical experience in Africa and elsewhere. Hopefully, it will be of some help. In doing so, it has brought back many happy memories of Darkest Africa.

Dave Hodge, Cairns Branch

DATE: November 1993

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