91av

GREENING the desert has so far been mostly a matter of giving ordinary
crops enough water to grow. Technology, such as computer-controlled drip
irrigation, has reduced the amount of water needed. Selection for new varieties,
for example tomatoes and melons that flourish in brackish water, allows
growers to use water of lower quality. But by and large the effort has been
in changing the desert to suit the crops, rather than the other way round.
Yosef Mizrahi, professor of plant physiology and horticulture at the Ben
Gurion University of the Negev in Beersheva, is trying to change all that.
He is trying to find and develop new perennial plants for arid areas, to
grow desert orchards.

‘The last fruit tree of the desert that we domesticated was the date
palm,’ Mizrahi said, ‘and that was over 2000 years ago.’ Most scientists,
Mizrahi says, don’t want to work on fruits, especially new fruits, because
of the time it takes to get results. And results, at least in terms of the
number of papers published are limited too. ‘One paper more or less is no
problem to me,’ Mizrahi says, ‘And I am young enough to see such a programme
through.’ So in 1984 he began what he thinks will be a 20- to 25-year research
programme, one that he believes will culminate in the domestication of rare
and wild fruit and nut trees for the desert.

The first step for Mizrahi and his colleague James Aronson, an economic
botanist and plant hunter, was to survey the world’s deserts, looking for
the many trees harvested by the local people. One tree is the monkey orange,
Strychnos cocculoides, of the Kalahari. The local !Kung people will travel
long distances to visit a monkey orange tree in fruit. Those fruits are
large, like big round avocados, and, like avocados, they are still unripe
when they fall to the ground. After a few days the thick shell turns orange,
indicating that the fruit inside is no longer green. The !Kung break them
open and scoop out the juicy flesh that surrounds the seeds, rather like
a pomegranate. It tastes, according to people who have tried it, like a
combination of citrus and pineapple, and it is very refreshing.

Another approach was to look for plants that are already cultivated
to some extent, but are underdeveloped and poorly researched. They might
have a small local market, but they are not globally important. One of these
is the white sapote, Casimiroa edulis, the fruit of a tree native to Mexico
and Central America. Growers in California who specialise in rare fruits
do have orchards of white sapote, but Mizrahi thinks there may be much greater
demand, if he can improve the supply.

From their travels abroad and sifting through anthropology libraries,
Mizrahi and his team narrowed the field down to some 27 candidates. Among
them were the monkey orange and the marama bean, which has bulbs that taste
like asparagus and seeds reminiscent of almonds. But these, and others,
are taking a back seat for the moment while Mizrahi and his team focus most
of their attention on six of the most promising species: mongongo nuts,
yeheb, ber, white sapote, pitahaya agria and marula . In global terms, each
of these, although important to the local people who use it, is not important
economically. Mizrahi thinks they have been unfairly ignored, for all the
wrong reasons.

The old view, he pointed out, was always that these local foodstuffs
were somehow inferior, that people ate them because they had no choice and
would rather munch on a Golden Delicious than savour their own monkey oranges.
‘This is all wrong,’ Mizrahi said. ‘These could be the fruits of the future.
Look what they did with the Kiwi fruit.’

Mizrahi sees no limit to the potential of his candidate species. He
is scathing about how little some people have made of their local crops.
Botswana, with a million people, is two-thirds desert. Perhaps it is no
surprise, then, to learn that it imports almost all its food. But the country
is blessed with hundreds of wild plants that are not merely edible, but
tasty and nutritious too. As for the Kalahari desert, Mizrahi says: ‘If
you ask me, this is no desert. They could create a virtual Heaven on Earth
with their average annual rainfall of 300 to 400 millimetres. If only we
had that much rainfall in the Negev.’

To help the people of Botswana to grow Heaven on Earth, Mizrahi is introducing
them to new crops. He is also part of a cooperative venture to take farmers
from Botswana to Israel, where they learn how to make the most of desert
agriculture and then return to apply what they have learnt in their own
desert. He has also been combing Botswana for plants that he can develop
into new crops.

The idea is to import seeds, grow them on, and so begin the long and
painstaking process of creating new orchard crops for the desert. Four years
into that agenda, Mizrahi can report some successes and some failures. Not
surprisingly, each of the six guinea-pig plants raised new and different
obstacles.

The first problem was simply to obtain the seed. The Department of Plant
Protection at Israel’s Ministry of Agriculture, conscious of the country’s
economic dependence on the crops it grows, is very careful about importing
plants that might harbour diseases or pests. Ber, which is already grown
extensively in India, came in as grafted material, but the ministry still
insisted that it must be kept for a year at a special quarantine station.
For the other species, seeds, which also had to be grown in quarantine,
were the answer. Some were easy to acquire. Growers of rare fruits in California
supplied seeds of good varieties of white sapote, and already had a considerable
fund of expertise on how to grow them. Marula, a large fruit related to
the mango, proved more of a problem.

Mizrahi and his team visited southern Africa with a shopping list of
desirable qualities in the fruits they sought. The local people, who collect
marula from trees in the wild, knew a great deal about the individual trees,
and could tell Mizrahi where a particular fruit had been gathered. The people
were aware, for example, that some trees always produce particularly aromatic
fruit, while others have the more characteristic sweet-and-sour taste. Some
trees can be relied on to produce a heavy crop, others do not produce as
much. With the help of the Taswana people, Mizrahi chose seeds from fruits
that were likely to have the qualities he needed, and took them back to
Israel.

The next stage was to germinate the seeds, and that created further
problems. Of a thousand ripe mongongo nuts, not one germinated. Mizrahi
and his colleague, Avinoam Nerd, broke the shells of a further batch but,
again, none germinated. Piercing the testa, the hard coat around the seed,
which often works on other nuts by allowing the seed to absorb water, had
no effect either. ‘Then we heard a claim that ethylene would break the dormancy,’
Mizrahi recalled. Ethylene certainly has a role in making fruit ripen, but
few people had suspected that it could wake up seeds. Yet just one minute’s
exposure to ethylene was enough to trigger germination in 80 to 100 per
cent of mongongo nuts.

Marula posed a similar sort of problem: none of the seeds germinated
even under ideal laboratory conditions. This time, ethylene did not help.
Even in the wild there appears to be a problem. The population of marula
trees in some parts of southern Africa is highly unstable, with many old
individuals and almost no young ones. In the wild, it is enough that a seedling
replaces an old tree every century or so, but this rate of reproduction
is not enough for a programme of domestication. Why marula should germinate
so rarely remains a mystery, but one that can be sidestepped in the laboratory.
The obstruction is mechanical. The outer seed coat contains a well-defined
region called the operculum. With the operculum intact, the seed cannot
absorb water and does not germinate. Remove the operculum, and, as Mizrahi
says, ‘you get great germination, 200 per cent or more, because each seed
contains two or three embryos’.

Great reluctance to germinate is hardly surprising among desert trees.
One of the best adaptations to intermittent drought is to spread reproduction
over several years, in the hope that some seeds will germinate at a propitious
time. But Mizrahi refuses to speculate on why mongongo nuts should need
a breath of ethylene to start them into growth, or where that ethylene might
come from in the wild. ‘The tree only needs to do it once,’ he points out,
while he needs to do it hundreds of times every year to provide enough seedlings
for research. If ethylene will provide germinating seedlings, that means
one fewer practical problem to solve.

Once the seeds have sprouted the young trees are grown in pots in quarantine
greenhouses until the Department of Plant Protection gives them a clean
bill of health. Then they go out to suffer the trials of real life at one
of the experimental farms run by the Ben Gurion University of the Negev.

There are four experimental farms. Besor lies 40 kilometres east of
Beersheva near the Gaza strip. Ramat-Negev is a similar distance south.
Neot Hakikar is at the northern end of the Arava valley, just south of the
Dead Sea, and Qetura is further south in the Arava, about 50 kilometres
north of Eilat. Although all are, broadly speaking, in the Negev desert,
each enjoys a different climate and quality of water.

At the orchards, each tree receives food and water via a highly-developed
‘fertigation system’. Water carrying essential nitrogen, phosphorus and
potassium, as well as iron and other trace elements, drips through specially
designed holes in an irrigation hose onto the roots of the plants. At regular
intervals scientists measure the growth and development of the trees, trying
to relate them to the climate, soil and water at each plot.

Yehib, unfortunately, failed to thrive. It germinated well enough, and
grew up in the quarantine nursery, but it did not establish itself when
moved to the orchards. Some places were simply too cool. Besor, for example,
can have 100 days a year in which the temperature does not climb above 10
Degree C, and in two consecutive years the yehib trees there died in the
spring, after a cold spell. Even at the warmer places, however, most of
the yehibs suffered yellowing of the leaves and then died. Only at Qetura
have a few trees survived.

The cause of death is still not clear. It probably has something to
do with damage caused to the roots by transplanting. In the nursery, Mizrahi
discovered, the roots of the yehib grow 15 centimetres while the shoots
grow only 1 centimetre. This may not be surprising for a desert plant whose
first priority is water, but it creates difficulties for people who want
to transplant them.

Despite the setbacks, several small yehib trees at Qetura are now more
than three years old. They are continuing to grow, albeit slowly, and in
future it may be possible to multiply vegetatively these survivors, which
might be genetically distinct from those that failed. If the survivors flower
and set seed, Mizrahi will try to plant the seed directly into the ground,
so the shrub can get on with building its root system without disturbance.

Marula did much better than yehib. The trees grew well at all the orchards,
and even in the salty soil of Neot Hakikar the trees showed no signs of
leaf burn, although they grew more slowly than at the other sites. At Qetura,
three-year-old trees, male and female, came into bloom and set fruit.

Mongongo, despite coming from the same semiarid regions of southern
Africa as marula, did not do as well. Once seeds had been induced to germinate
they grew well, and the seedlings transplanted successfully to all the orchards.
Almost all showed symptoms of iron deficiency, but responded well to extra
iron. At Neot Hakikar, however, the plants turned yellow, showing symptoms
typical of damage caused by salt, and all of them died. So mongongo, unlike
marula, will not tolerate much salt in the soil. It did grow quite well
at Qetura, where the quality of the water is similar but the predominant
ions are calcium and sulphate, rather than sodium and chloride. The best
trees are at Besor, which is the coolest and wettest of the sites.

Pitahaya agria, like so many cacti, germinated well but grew very slowly.
Even in the ideal conditions of the nursery it took two years for the seedlings
to reach a height of 10 to 15 centimetres, the bare minimum for successful
removal to the orchards. There the plants have grown well, with shoots growing
to a height of 160 centimetres after three years. They have not flowered,
however. ‘We probably need to learn a lot more about the induction of flowering
in these species,’ Mizrahi conceded.

White sapote, like mongongo, germinated and grew well in the nursery,
but succumbed to the high salinity at Neot Hakikar. Indeed, only the columnar
cacti and ber really thrived at Neot Hakikar. Ber, unlike the other species,
is already at an advanced stage of development, with several well-known
cultivars available in India. Mizrahi imported two of these, called Gola
and Seb, and grafted them onto rootstocks of Ziziphus spina-christi, which
is native to Israel, and Z. abyssinica. The grafted trees have grown well
at all four sites, and on both rootstocks.

Mizrahi is beginning to learn which species will do well under different
conditions, and soon he hopes to start selecting for the qualities that
will make his trees a commercial success rather than a horticultural curiosity.
But there are other aspects of the enterprise that need to be tackled at
the same time. Some of the fruits, for example mongongo and marula, are
dioecious, that is, male and female flowers grow on separate trees. Males,
while vital as sources of pollen, and therefore fruit, are not productive.
How many males will be needed to ensure that all the female trees produce
fruit? And if the flower is pollinated by an insect, how will the tree do
if that insect does not live in Israel?

The other side of the insect coin is pests. Bringing exotic plants into
a country poses two risks; first that those new plants may harbour diseases
that will attack already established crops, and secondly that indigenous
animals will turn their attention to the new source of food. Either way,
the new fruit programme would be in trouble. Already, a survey in South
Africa and Namibia has discovered that one in five marula fruits is unusable
because it is infected with the larvae of a moth; is that moth, or one like
it, going to be a problem for marula trees elsewhere? Most important of
all, if the fruits of these trees are ever to find a market outside their
immediate neighbourhood, then there is much more to be learnt than simply
how to grow them. The whole process of ripening, and eventual decay, needs
careful study.

Many of the fruits we are already familiar with ripen on the tree; the
marketers have to delay ripening so that they have time to transport the
fruit to the shops. Desert fruits like marula are often unripe when they
fall. They then pass through a series of biochemical changes that can affect
the colour, texture and taste of the fruit before they are finally ripe.
At what stage do they taste best? Mizrahi has been working with other researchers
on this side of fruit growing, and has established, for example, that although
ber goes through at least six identifiable stages of ripening, it is best
to eat at stages three or four.

Then there is the question of shelf life. ‘We need two weeks,’ Mizrahi
says. The fruit is harvested in, say, the Arava Valley, and is packed and
graded on day one. It needs another two days to reach the airport, and a
further two days to reach the distribution centres of the big supermarkets
in Europe and North America. Another day sees the fruit on the shelf, and
it has to last for at least another seven days, because on average people
shop once a week. All these links in the export chain have been carefully
investigated for the fruits we already eat, but they will need to be re-examined
for new items. To do so, the fruit growers will create a model of the export
chain within the country, duplicating the conditions of each link until
they are satisfied that they can get the fruit to market in perfect condition.

There remains one potentially insuperable obstacle: taste. People are
notoriously conservative about what they eat. Will we ever snap up marula
juice, or sit roasting mongongo nuts round a crackling fire? ‘We believe
in R and D,’ Mizrahi said. ‘Research and development. Research will create
the fruits, development will create the market.’ Mizrahi is unshakably optimistic,
but that question of taste remains.

As he steered me through the nurseries and greenhouses that are his
laboratories, Mizrahi made a detour to an unprepossessing tree growing a
short distance from the road. It was a ber, laden with fruits. ‘Here, try
one,’ Mizrahi urged. I did, and I have to say that unless you are fond of
blandness, the texture of stringy apricots and an overwhelming taste of
mouth-puckering tannin, ber is not my idea of the fruit of the future. At
least, not yet.

* * *

ASSORTED FRUIT AND NUTS FOR DRY LANDS

White sapote, the fruit of Casimiroa edulis, is probably the closest
to commercialisation of all Yosef Mizrahi’s candidates. The trees are evergreen,
and the large seed is surrounded by sweet, creamy flesh. The fruit is already
grown for market in Mexico and California, and has been the subject of intensive
research in New Zealand and Australia. There are a score or more varieties:
some crop heavily, others have fruit resistant to bruising and with a long
life in storage, others bear fruit almost all year round; but no one variety
yet combines all those qualities into one fruit, so there is scope for a
conventional breeding programme in search of a superior variety.

Yehib is an African plant, native to the very arid desert of Somalia.
The shrub (Cordeauxia edulis) grows throughout dry regions of the country,
and its nuts, which are easy to shell and apparently very tasty, are a staple
item in the local diet. But it has other uses too. The leaves provide forage
for animals, and yehib is also used as a dye and as a source of firewood.
The National Range Agency of Somalia has designated several reserves to
protect the species, and is sponsoring studies of domestication, though
the effectiveness of these measures remains unclear.

Marula, Sclerocarya birrea, is another fruit native to southern Africa,
and related to the mango. The fruits are green when they fall, and ripen
on the ground. Local people prefer to pound the fruits and drink the resultant
juice, and probably get some 80 per cent of their vitamin C from this source.
Different trees produce fruits with different flavours. Some are sweet,
others sour, yet others aromatic. Some fruits produce a juice that is thick
and grainy, while others are more liquid. Unfortunately, for people who
like marula juice the best juice, that is thick and grainy, is not often
associated with the preferred sweet-and-sour flavour.

Pitahaya agria is the fruit of a columnar cactus, Stenocereus gummosus.
Cacti are not a prominent part of the diet anywhere in the world, although
the prickly pear, Opuntia ficus-indica, does have a small market. The prickly
pear suffers two drawbacks that pitahaya agria does not. It is prickly even
when ripe while pitahaya loses its spines as it becomes ready to eat. And
whereas prickly pears are full of hard, inedible seeds, pitahaya seeds are
small and edible, like those of figs. The flesh has a texture and taste
something like that of a banana.

Mongongo nuts are the fruits of Ricinodenron rauteanenii, a large tree
that is a member of the Euphorbia family. It provides shelter for campsites,
and one of the staple items in the diet of the !Kung. While the men are
off hunting, often unsuccessfully, the women easily gather bushels of mongongo
nuts. The average !Kung eats about 300 nuts a day, receiving 1260 calories
and 56 grams of protein, equal to almost half a kilogram of steak. Mongongo
nuts provide the !Kung with about a third of their diet, and as one !Kung
asked, ‘Why should we plant (crops) when there are so many mongongo nuts
in the world?’ Yet the rest of the world has hardly heard of, let alone
tasted, this provident nut.

Ber, like white sapote, is already cultivated in a minor way. The task
now is to evaluate its horticultural potential on a wider scale. The tree
is called Ziziphus mauritania, and is a close relative of the jujube tree
(Z. jujubus), whose boiled fruits were valued as an early Chinese throat
remedy.

The fruits have an astringent taste and a fibrous texture, and the leaves
can also be used as forage for animals, making it doubly useful as a crop.
The plant tolerates salts and is already widely grown in India.