Halophytes

O'Leari stated in 1987:

''Although economic consideration of halophytes and other salt-tolerant plants is just beginning, they are now receiving increased attention in arid regions where intensive irrigation has led to salt soils or where water shortages are forcing use of marginal resources such as brackish underground water''.

The issue should be updated in the new millennium due to the increasing actions causing desertification. Furthermore, production of salt tolerant plants is one of the ways to utilise the waste saline lands around the world (Gallagher 1985).

''Salt is vital for human body. Iodine daily requirement derives from vegetable, rice or fish. For some people living in the most impoverished areas in high altitude or far from the sea this in not possible. Iodine once present in the soil has long since leached away, causing catastrophic effects for public health. Iodine deficiency can lead to neurological disorders, deafness, psychomotor retardation, brain damage, mental defi ciency, and retarded growth. In Tibet raw salt is freely available in salt lakes, but it is the main cause of the nation's high level of retarded growth, goitre, and neurological impairments, because it is non-iodised salt. The Australia's Overseas Aid Program has provided over $2 million to support the elimination of iodine deficiency in Tibet, distributing iodised oil capsules to vulnerable groups'' (Focus-AusAID 2006, p. 11).

Halophytes (plants that grow in soils or waters containing significant amounts of inorganic salts) can harness saline resources that are generally neglected and are usually considered impediments rather than opportunities for development (Aronson 1989).

''In searching for crops for saline agriculture, those that currently comprise the bulk of human food should be considered as models -maize, wheat, rice, potatoes, and barley. If these major crops can be grown using saline resources, or if new tolerant crops that are acceptable substitute can be developed, the world's food supply will have a more diverse and vastly expanded base''(Pasternak 1987, p.275).

Halophytes have been evaluated as potential crops for direct seawater or brackish water irrigation. They can be developed in three areas: in coastal deserts using seawater for irrigation, in inland salt deserts using saline underground or surface water, in arid-zone deserts using brackish drainage water for irrigation. Halophytes grown in desert environments showed levels of biomass and seed production comparable to conventional crops.

Scientists exploring seashores, estuaries, and saline seeps have found thousands of halophytes with potential use as food, fuel, fodder, fibber, and other products. Although the direct consumption of halophytes by humans and animals can be limited, the seeds of many of them are being considered as new sources of grains or vegetable oils (Hinman 1984).

Some conventional crops, such as sugar, fodder, date palm and culinary beets have halophytic ancestors, so they can be irrigated with brackish water.

Barley is the most salt tolerant cereal grain. Rice cells subjected to salt stress and then grown to maturity have progeny with improved salt tolerance, up to 1% salt.

There are also a number of plants that, although not halophytes, have sufficient salt tolerance for use in some saline environments.

The use of water with salt levels equal to, and even exceeding that of seawater for irrigation of various food, fuel, and fodder crops has been reported by many researchers including Boyko (1996), Somers (1975), Iyengar (1982), Epstein (1985), Gallagher (1985), Glenn and O'Leary (1985), Pasternak (1987), Yensen (1988) Aronson (1989). These scientists have produced grains oilseed; grass, tree, and shrub fodder; tree and shrub fuel-wood; and a variety of fibre, pharmaceutical, and other products using highly saline water.

Plants can use salt water at their disposal or they can even be irrigated with it. In India twenty species of trees were planted in a trial using saline water (EC = 4.0-6.1 dS/M) for irrigation and nine of them were growing well after 18 months (Yensen 1988).

It is very difficult to exploit all the possibilities related to salt tolerant species, since it is unlikely that any species will meet all the requirements: although selection is usually based on performance in a similar environment, some species ''travel'' poorly (Glenn 1985, p.51). Some show extreme variation in regard to source and some perform remarkably well far outside their native climate; some require different levels of salinity during the span of their life: responses are variable at seedling, vegetative or reproductive stages. Adult plants can tolerate salt water better than younger plants, others tolerate medium root salinity and not salt spray, other tolerate salt in leaves and bubble aeration.

Many halophytes have a special and distinguishing feature - their growth is improved by low levels of salt. Other salt-tolerant plants grow well at high salt levels but beyond a certain level, growth is reduced. With salt-sensitive plants, each increment of salt decreases their yield.

Some halophytes require fresh water for germination and early growth but can tolerate higher salt levels during later vegetative and reproductive stages. Some can germinate at high salinities but require lower salinity for maximum growth. Some grow well on permanently wet areas, other's best growth occurs where the soil dries out in the summer.

Some halophytes contain too much salt for consumption, but a solution is to extract leaf protein from the salt-containing foliage (Table 1). Leaf protein can be used to enhance the protein content of many food products, i.e. in Mexico it is used to make fortified spaghetti (Carlsson 1983).

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