Panel 6: Miscellaneous

Panel leader: Fernando Riveros

PEST RODENTS, POTENTIAL HAZARD FOR PROSOPIS TAMARUGO

Jaime Rodríguez
Professor
Management of Wild Fauna
University of Chile

Man, with the help of technological development, has transformed and modified vast extensions of land. These modifications are frequently not in harmony with nature, causing profound alterations in the ecosystems, the effects of which become evident in the long term through the proliferation of weeds and pests, or by the problems encountered by the species in their adaptation to the altered ecosystem.

Environmental alterations modify the balance of nature, in such a way that the new balances are normally not desirable to man.

The wild fauna pests, as they are perceived by man, are generally the product of anthropical alterations of the ecosystem.

A wild fauna species is considered a pest when, being either indigenous or exotic, affects man's interests in a negative way, jeopardizing his health, producing general nuisance and destroying food, fibers or resources desired by man (Howard 1983).

A vertebrate species is considered a pest when it affects man's interests or well-being (Elias & Valencia, 1983).

The pest vertebrates result when man joins animals with vegetation or other animals with which they have not had a chance to evolve.

When man modifies the physical form of the environment, he frequently causes early stages in plant succession. These changes may affect in unpredictable ways the dynamics of the native wild fauna species present (Howard 1983).

Among the pest vertebrates, rodents are the most conspicuous group in Latin America. As an example, rodents (rats and squirrels), in Colombia, caused damage ranging from 4% to 77% in the largest coconut producing areas (Elías & Valencia 1973).

The main groups in terms of damage caused in Latin American agriculture are the Cricetidae or rats and mice from the “new world”, the cosmopolitan rodents (Rattus rattus, R. norvegicus and Mus musculus, family Muridae) and those from the family Geomydae.

Some species from other families are recognized as pests in localized areas.

At the Central Zone in Chile, in the Acacia caven steppes, it is customary to find damage on bark and leaves caused by the native rodents Abrocoma bennetti and Octodon degus, which feed on the phloem and leaves of this leguminous species (Meserve, Martin & Rodríguez 1983).

In Atriplex repanda crops, a major fodder shrub for arid and semi-arid regions, Octodon degus causes considerable damage both to the leaves and the stem of this shrub, as it not only consumes it, but uses it to build dens under its shelter.

During the past three years, serious damage has been detected in Pinus radiata plantations caused by indigenous pest rodents, among which the most relevant is Octodon bridgesi, whose biology and ecology are presently being studied (Rodríguez & Murúa 1984).

The damage caused by these rodents is in the form of wounds on the stem or branches. These wounds are the product of the introduction of the incisor teeth in the bark, which the rodent normally does sitting on the verticils or from the ground.

Damage can extend from the base of the stem up to four meters from the ground, reaching higher as the tree grows older (Rodriguez 1983).

Beneath recently damaged trees it is common to find a large amount of bark particles fairly regular in size, ranging from 0.6 to 1 cm in length and 1.5 to 4.0 cm wide.

A tree can be attacked in different opportunities from 2 to 12 years of age, which increases the possibilities of death, as the rodents continue extracting bark from places adjacent to those that have already been damaged. The likelihood of complete girdling of the tree is thereby increased, threatening the tree with certain death from sap flow interruption.

If girdling is provoked above the first verticils and these remain alive, the crown dies from the girdle up, and a new crown is formed, consequently losing the tree its original shape. This affects normally those trees with smaller diameter (Rodríguez & Herrera 1983).

The wounds produced by rodents on Pinus radiata can be spotted from a certain distance, as they are covered by a resin layer which acquires a very typical whitish color. Those wounds not readily covered by resin or callous outgrowth, can be easily infected by lignivorous fungi.

General damage to Pinus radiata is considerable, with 92.4% of the trees affected in a certain stand (Herrera 1983).

This figure may vary depending on the location of the plots, as, generally speaking, damage distribution is concentrical. The percentage of damage in the stand was 43.12%, considering only the trees affected to a maximum degree. Mortality reached 15% and the volume loss of the trees amounted to 34.3%.

Rodents attack independently of the tree diameter, being a given width of the wound more damaging for trees of larger diameter.

During the past year, damage has been detected on the bark of Prosopis tamarugo caused by rodents at the Refresco Farm in the Tamarugal Pampa. The damage consists of intense debarking, particularly at the branches.

This debarking can become a complete girdling, provoking the death of twigs, branches and even the tree itself. It must be pointed out that Prosopis tamarugo fruit is also consumed, not only on the branches, but on the ground as well. This affects fodder availability for livestock.

The tamarugo forest constitutes a very unstable ecosystem due to its low diversity, a fact which favors the appearance of pest vertebrates, particularly in light of the extremely low amount of predators.

The above indicates that rodents constitute a major actual and potential pest for Prosopis tamarugo, being one of the main constraining factors for the increase of this important desert fodder resource.

REFERENCES

ELIAS D.J., VALENCIA G.D. (1973). Control de roedores en el cocotero. ICA Informe 8 : 5, 6— 13, 14.

ELIAS D.J., VALENCIA G.D. (1983). La agricultura latinoamericana y los vertebrados plagas. Symposium: Zoologia Económica y vertebrados como plagas de la Agricultura. IX Latin American Congress on Zoology. Arequipa, Peru. p. 24–28.

HERRERA G.L. (1983). Evaluación y control de daños producidos por roedores en plantaciones jóvenes de Pinus radiata D. Don, en la VII Región. Thesis for Forestry Eng. Deg., Universidad de Chile. 200 p.

HOWARD W.E. (1983). Aspectos ecológicos del control de plagas vertebrados. Symposium: Zoología Económica y vertebrados como plagas de la agricultura. IX Latin American Congress on Zoology. Arequipa, Peru.

MESERVE P., MARTIN R., RODRIGUEZ J. (1983). Feeding ecology of two Chilean caviomorphs in a central Mediterranean savanna. J. Mann, 64 (2) p. 322–325.

RODRIGUEZ J. (1983). Evaluación preliminar del daño ocasionado por roedores en plantaciones de pino insigne. Curso de capacitación Universidad de Chile. Facultad de Ciencias Agrarias, Veterinarias y Forestales. Escuela de Ciencias Forestales. 14 pp.

RODRIGUEZ J., HERRERA L. (1983). Evaluación del daño ocasionado por Octodon bridgesi en plantaciones de Pinus radiata. Abstracts IX Latin American Congress on Zoology. Arequipa, Peru.

RODRIGUEZ J., MURUA R. (1983). Evaluación y alternativas de control del daño ocasionado por roedores en plantaciones de pino insigne (Pinus radiata D. Don.) en la VII y VIII Región. Primer informe de Avance 56 pp.

AN ALTERNATIVE UTILIZATION OF THE TAMARUGAL PAMPA

Mauricio Meyer
Fundación Chile

1. INTRODUCTION

This analysis intends to describe sheep stock raising at the Tamarugal Pampa from a private standpoint.

The economic profile in this report was developed within the framework of a Fundación Chile study in July, 1978, under the direction of Dr. Edmundo Acevedo, named “Pre-feasibility study on desert development”.

The trials and experiments conducted by CORFO at the Refresco Farm were taken into consideration, together with the opinions and experiences of all the specialists who had taken part in these activities.

Particularly relevant were the observations made by the Agronomist Mr. Italo Lanino, who at the time held a post at the Northern University in Iquique.

The analysis made considered the utilization of 20,000 ha planted with tamarugo (Prosopis tamarugo Phil.) by double-purpose Corriedale sheep.

The plantation was managed by dividing it into 400-ha modules under the supervision of a shepherd, with a total of 1,612 head obtaining the water from a well located at the center of the module.

The inclusion of a services and administration compound is also envisaged, where general coordination and management support for each module will be provided, together with such chores as shearing and others.

Within this basic framework, some direct costs and investments arise at each module, as well as indirect ones pertaining to the central compound, such as veterinarian, vehicles, shearing sheds, consumption of supplies, etc.

Costs and investments have been updated in this report to the price correlation between inputs and outputs as of May 1984. A cash flow was likewise made to obtain more relevant economic indices to enable comparisons. The value of the land and the plantations was not included in the investments.

2. TECHNICAL DATA

This alternative is based on the utilization of meat and wool Corriedale sheep at a stocking rate of 4.03 head per ha, which is equivalent to approximately 0.4 F.U./ha. This means 1,612 head over 400 ha, with a lambing rate of 80% and average mortality of 5%. Breeding is made with 12 rams at a cost of US$ 113.6 each, which are renewed every year.

Estimated production is 28 kg of meat for ram and ewe lambs, 45 kg for ewes and 60 kg for rams. Wool yield is estimated at an average of 2 kg per animal.

The estimated prices for meat were generally reduced by 40% with respect to the live animal prices placed marketplace during the 1983–84 season, to account for possible oversupply, losses and trading costs.

Wool has likewise been entered at a 25% lower price, considering that its quality is somewhat inferior.

3. SALES INCOME

The basis for calculation is as follows:

The average weighted price was US$ 0.31 per kg, and the price of wool was estimated at US$ 1.30/kg, which gives a total income of US$ 4,160 for the 3,200 kg produced.

Summary of Sales Income

4. INVESTMENT AND COST STRUCTURE

The investment and cost structure in a full-production year is as follows:

4.1 Investments

4.2 Costs

5. ECONOMIC INDICATORS

6. SENSITIVITY

Sensitivity was accounted for by reducing the price of meat and wool products, and animal productivity, by 20%. Additionally, total costs and investments were increased by 20%.

Sensitivity Analysis

It may be observed that this alternative is very sensitive to both the price of products and productivity of the animals, as a 20% decrease in any of them makes the NVA at 12% be negative. Such is not the case when investments and/or production costs are increased by 20%.

Another sensitivity that was computed is that of reducing the animal load to two head per ha, thereby decreasing sales income, investment in animal stocks and the cost of feed and supplies by 50%. The remaining costs decrease in a small measure. The internal rate of return obtained in this case was 5.5%.

CASH FLOW FOR SHEEP RAISING AT THE TAMARUGAL PAMPA
US$

UNICEF, ACTION AND SCOPE

María Rosa Duhart
UNICEF
Santiago, Chile

According to modern historians —Toynbee among them—, the origin of the civilizations in the Nile, Indus and Tigris-Euphrates valleys could be linked to the increasing aridity of the surrounding area, which forced the herders of the steppes and savannas to move to the valleys, where they had to irrigate and cultivate the land. From the very dawn of pre-history, the climatic changes have brought about major social innovations, when not downright convulsions.

The rupestrian art in the deserts shows that the droughts which formed them are very recent, and the common denominator of this art, either unearthed at Sahara or the Atacama Desert, is that it reflects a life with plenty of livestock and, consequently, plant cover to support the animals.

Currently, between 36% and 43% of the Earth's area is rated as desertic, including vast extensions of South America —such as the Pacific Coast, shared by Peru and Chile— and the Brazilian North East.

The dynamic process which deserts are undergoing —their growth and the movements they force on the local population— demands the attention of UNICEF, on account of the tragic effects often resulting from such processes, as, for instance, in the African Sahel.

In addition to the proper deserts, vast areas are threatened by desertification, ranging in degree from moderate to high, such as a considerable portion of the Argentine pampa and the Brazilian North East.

According to conservative estimates, arid zones and their advance affect 384 million people directly or indirectly. This population accounts for 12% of the world's total and belongs mostly to Third World countries, which suggests that the precariousness of their natural environment is further burdened by a lack of economic means.

Desertification processes represent a struggle in which man and land are engaged. It must be admitted that man himself, or the increase of his population and that of his livestock, contributes to the expansion of the deserts. And, yet, he suffers the worst consequences of such process, by having to be satisfied with the leftovers of the land.

From its conception to the present day, UNICEF has helped in the search of solutions when man has been ravaged by war, catastrophes, disease, and ecological and economic crises.

In 1946, as an emergency fund, UNICEF contributed with food and medicine for the European children surviving in the wake of World War II. Once this situation had been taken care of, the Fund turned its attention to the Third World children living in a permanent state of emergency: their living standards are their daily burden.

In the outskirts of the scintillating Latin American cities, in the countryside, in the crowded urban centers of Asia, in the villages lost in Central Asian mountains or in the Andes, those suffering the worst consequences of underdevelopment and most greatly affected by any kind of crisis are the women and the children.

It is on these grounds that UNICEF, whose main concern is children, is interested as well in all that surrounds them: the mother, the family, the community. While the battle is presently being waged against infant mortality —still scandalously high in many parts of the world— UNICEF is working towards offering today's children the opportunity for a dignified life in the future, and giving them the tools to make their own contribution to the solution of tomorrow's problems.

To this end, UNICEF resorts to any and all resources and methods, particularly those requiring imagination and creativity. These two “ingredients” are essential to solve the enormously complex problems faced with scant monetary funds.

These solutions, falling within the bracket of those rated as simple technologies, employing abundant labor and little capital, are —perhaps— the answer of the Third World to the problem of underdevelopment.

Although UNICEF has not taken part in projects related to tamarugo, it constitutes a good example of the type of solutions it encourages: something so simple as a tree having the capacity for checking the advance of the deserts, increasing livestock raising possibilities —and, therefore, providing milk in those areas where water is scarce— and, last, and as a result of the foregoing, raising the standard of living. These experiences have, furthermore, a clear potential for horizontal cooperation and offer a new approach to the transference of technology.

Throughout the world, UNICEF is lending its support to projects fostering the use of appropriate technology. In Chile, through CIDERE: in the Bio Bio Region, in joint work with local business companies, UNICEF has backed projects such as the utilization of pita, a plant similar to agave and jute, used as raw material for a number of handicrafts, which has the additional capability of checking the advance of sand dunes; the collection and subsequent export of hip rose which, besides embodying an income of foreign currency equivalent to 4 million dollars annually, offers an occupation to about 20 thousand people. Other projects seek the utilization of some aquatic plants invading lakes and lagoons as fodder; the construction of floating piers for unloading small-scale fishing; the cultivation of champignon mushrooms in abandoned mines is being studied, together with a commercial bourse for the exchange and reutilization of industrial waste; sawdust heaters for domestic use and portable metal kilns to make charcoal are being manufactured. Even a prefabricated micro-hydroelectric plant has been devised.

Throughout the rest of the world, there are innumerable such projects promoted by UNICEF. The stress is laid on those which make the woman's load lighter. Thus, clay cooking stoves are being developed in Africa and Asia to replace the traditional three stones surrounding the bonfire. Modified bicycles use their gears for a host of different mills, wind energy is being harvested, particularly to provide water to those villages lacking its supply, such as those located in arid zones.

Waste water continues to be one of humanity's worst enemies, transmitting most of the disease that affects and kills Third World children. Last year, UNICEF made contributions to supply drinking water and improve waste water elimination in 97 countries. Roughly 75 thousand water supply systems were completed, benefiting nearly 13 million people, 40% of which were children.

The goal of UNICEF is to reduce to half —despite the economic crisis which has undermined the funds available for social expenses in most developing countries— the 40 million infant deaths, which could perfectly be prevented completely.

The prevention of these deaths embodies a proper “pro-children revolution”, a revolution which UNICEF proposes but does not patronize. There are other United Nations organizations deeply involved in it, such as the World Health Organization. This revolution is feasible through the use of appropriate technologies in the field of health, and a profound worldwide cultural change. To see it through, the cooperation of governments, international agencies, non-government organizations, mass media and men of good will is a essential.

There are four measures which, combined, have the capacity for saving 20 million children every year and, at the same time, keeping the growth of the world's population under control.

These steps entail, in a sense, a return to traditional ways, when the health and well-being of the children depended on their family and comunity and not on a wellfare organization which, unfortunately, in the Third World is not always present, nor is it at the service of the most needy.

Oral rehydration replaces advantageously the costly treatment of intravenous rehydration of the hospitals. With a simple mix of salts and sugar, which can be homemade or acquired for a very low price, a mother can prevent her child's death from dehydration induced by diarrhea.

According to a recent study by the Harvard International Development Institute, which analyzed several hundred nutritional programs, “in the common cases of moderate malnutrition in children from 6 months to 24 months of age, the children look entirely normal, but their height is low for their age, they have fewer defenses and, consequently, are easy prey to disease. A child who takes only 60% of the necessary energy requirements may not present external symptoms of hunger, other than his frequent wish to suckle.”

A study on the Philippines reveals that 58% of the mothers of children affected by second to third degree malnutrition stated that they believed their children were growing and developing well. At the same time, a series of studies indicates that over half of the malnutrition cases occur at households where there is no absolute scarcity of food. The reason for not giving the necessary amount of food to the undernourished children is that the mothers ignored that the children were actually in that condition and did not realize that they have special nourishing requirements. For this reason, the simple act of bringing this matter to the attention of the mother —the person best suited to prevent and treat it— could be one of the easiest and most important measures to promote the healthy and normal development of many million children during their more vulnerable years. An appropriate aid is already available to show the mother when her children are undernourished: the growth charts, costing the equivalent of ten cents of a dollar, can help the mother make sure whether her child is growing normally or not.

Another cornerstone of this revolution pro-children is the promotion of lactation by the mother. Artificial lactation has been introduced in the Third World, many times fueled by commercial interests which do not take into account the damage it can cause in newborn children. Recent studies conducted in India and Canada have shown that infants feeding on artificial milk were three times more prone to diarrhea and twice more to being affected by respiratory disease (the two main causes for infant mortality) than those feeding on their mother's milk. It has been shown in Chile that the probability of death for children feeding on artificial milk is two to three times greater during their first year. In the Philippines, the encouragement of mother milk instead of artificial milk among the newborn at the Baguio Hospital reduced clinical infections by 88%, diarrheic infections by 93%, and infant mortality by 95%. At times it is necessary to state that “modern” does not always mean “better”. Lactation by the mother, besides being the ideal nourishment, at the best hygienic conditions and the perfect temperature, protects the infant against a host of infectious disease and, additionally, gives it the sensorial stimulation necessary for sound psycological development. A major secondary benefit is that it acts as a natural contraceptive, providing no supplementary nourishment is given to the child.

The nourishment of the child at weaning is equally important and the education of the mother, in this respect, is essential. It is often necessary to overcome the barrier set by enormous commercial advertising campaigns offering food with no nutritional value at exorbitant prices.

Every six seconds, a child dies and another is left handicapped by sickness susceptible to immunization. Many others are affected by ailments which impede their healthy normal development. Only 10 to 20% of the children in the world are immunized against the six mortal sicknesses susceptible to prevention: measles, tetanus, whooping cough, diphtheria, poliomyelitis and tuberculosis. The total cost of immunization per child, including transportation and services, amounts to 5 dollars. The immunization of each and everyone of the 100 million children who are born every year in the developing world would cost about 500 million dollars, which is equivalent to the cost of only a dozen of the more sophisticated modern jet fighters.

These four strategies —watching the child's development, promoting lactation by the mother, oral rehydration therapy and universal immunization— have common features. All of them entail small costs, are presently available, can be applied universally, and can show rapid results.

Additionally, they are the main components of the primary attention of health. These measures turn the people into informed actors, capable of procuring their own and their families' well being, instead of being passive dependent recipients.

The most effective feature is that the combination of these four simple measures attacks the most important problem of infant health at worlwide scale: the synergic alliance of malnutrition and infection, presently taking a toll of millions of young lives during their critical years of physical and mental development.

We have seen these four measures separately. But when they are associated, they can act in a concerted and synergic way to attack the mortal alliance of malnutrition and infection. A child feeding on maternal milk and immunized is less prone to diarrheic infections. A child with fewer diarrheic episodes has a lower probability of being undernourished. A better nourished child is less prone to infection. Likewise, each time a weight loss or an infection can be prevented —by means of immunization, maternal feeding, oral rehydration therapy, or by a watchful control of the child's development— this mortal cycle is broken, these setbacks get farther apart in time, the period of recovery is extended and the defenses against infection or weight loss become more effective, making the occurrence of such events more remote. To summarize, the combined potential of these four main strategies can have an effect considerably greater than the simple addition of their single contributions.

Whenever possible, these four basic measures must be supported by other factors to help children survive.

The education of the women is very important. The educational level of the mother is a determinant factor in infant mortality rates. For instance, in Pakistan and Indonesia, the infant mortality rate of children whose mothers had attended four years of school was 50% lower than among illiterate mothers. In a study on eleven countries conducted by CELADE, Latin American Center for Demography, it was found that the influence of the mother's education on the survival probabilities of their children was even more determining than the household income.

The supplementary nourishment programs for high risk groups, such as pregnant women, wet nurses and children at weaning are another great contribution to the stated goals.

The education of mothers with greater knowledge and means to space their pregnancies wider apart in time is an essential contribution to family planning in favor of health.

Currently, through experiments conduted at a small scale in all regions of the world, it has been demonstrated that the combination of these measures can reduce infant mortality to a half worldwide. But to make this a reality, these measures must be applied at the remotest corners of the Third World, reaching all those sectors below the poverty line.

The potential is there. The opportunity can and must be used. To this end, the political decision of all the governments is mandatory, together with the catalyzing power of all the international agencies, the generous contribution of all the non-governmental organizations, all the knowledge which the scientific community can furnish, and the infinite minute contributions by individuals of good will. It is important to realize that the pro-children revolution is not a property of UNICEF, nor of any other institution or government in particular. If it has to belong to someone, let it be the future generations, which, thanks to today's gigantic effort, will be able to live in a different culture, just like those nomadic tribes which, when they came to settle at the Nile, the Indus and the Tigris-Euphrates, laid down the foundations of our civilization.

BIOLOGIC NITROGEN FIXATION IN PROSOPIS TAMARUGO AND PROSOPIS ALBA

María Elena Torres
Researcher
Technologic Research Institute, INTEC
Santiago, Chile

INTRODUCTION

Nitrogen fixing trees have major economic potential. Among these, stand out the leguminous Prosopis species which, on account of their high nitrogen fixation rates, enhance soil productivity. Additionally, their pods constitute good fodder for livestock (1).

An efficient symbiosis plant-specific Rhizobium is required to obtain good nitrogen fixation. The strain to be used as inoculum must be highly competitive and effective with the corresponding host plant, must have good survival rates and tolerance to adverse environmental conditions, such as drought, salinity, acid soils, etc.

There is presently little knowledge regarding the Prosopis-Rhizobium symbiosis, the micro-organism itself, and the effectiveness of the different Rhizobium strains from various Prosopis species.

The first data on the possibility of nodulation in trees of the genus Prosopis and, consequently, on nitrogen fixation, dates from 1972 (2). Only as recently as 1976 the correlation between the presence of nodules, dry matter production and nitrogen fixation was demonstrated in experimental trials (3).

This paper describes the isolation of native Rhizobium strains from the Tamarugal Pampa and their selection. The latter is made basing on its capacity for producing root infection and its effectiveness in nitrogen fixation for leguminous trees of the species Prosopis alba and Prosopis tamarugo.

MATERIALS AND METHODS

Rhizobium Strains

Dr. Felker, CKWRI, Texas A & I University, provided the strains F-1 and F-2, isolated from mesquite nodules. Strains C-1 and C-2 (indigenous strains) were isolated from Prosopis tamarugo nodules at the Tamarugal Pampa, desert zone in the North of Chile, located between 19°33' and 22°30' South Latitude. The sampled sector ranks as one of the driest areas in the world, at an altitude of some 1,000 above sea level.

Culture Media

The Rhizobium strains were kept in agar and manitol, yeast extract and congo red. The composition of the medium was as follows: K₂HPO₄, 0.5 g; MgSO₄. 7 H₂O, 0.2 g; NaCl, 0.1 g; Difco yeast extract, 1 g; Manitol, 10 g; Agar, 15 g; per liter of distilled water.

The culture medium used for isolating Rhizobium had the same composition, save for a 70%-replacement of manitol by arabinose.

The media were sterilized by autoclave for 15 minutes at 121°C.

Jensen Medium

Nitrogen-free agar culture medium, with the following composition: CaHPO₄, 1.0 g; K₂HPO₄, 0.2 g; MgSO₄, 7 H₂O, 0.2 g; NaCl, 0.2 g; FeCl₃, 0.1 g; agar, 15.0 g; trace elements, 1 ml, per liter of distilled water. It was sterilized by autoclave for 15 minutes at 121°C.

Trace element solution: B, 0.05%; Mn, 0.05%; Zn, 0.005%; Mo, 0.005%; Cu, 0.002%. The solution was prepared in distilled water and acidulated with concentrated HCl drops, to facilitate the dissolution of the elements. It was sterilized by autoclave for 15 minutes at 121°C.

Preparation of inoculum

The inoculum was prepared cultivating the selected micro-organisms in a maintenance medium, at 28°C. The cultivated material was harvested and diluted in peptone water. Dilutions were standardized between 10⁷ and 10⁸ cells/ml.

Seed Treatment

Seeds were obtained from Refresco Farm trees (CORFO-SACOR, Tamarugal Pampa). The Prosopis alba and Prosopis tamarugo seeds were soaked in concentrated sulphuric acid for 10 and 8 minutes, respectively.

Isolating Rhizobium from the Nodules

Soil and other contaminants were washed off from the collected root material. The selected nodules were surface-sterilized by dipping them 3–5 sec in ethanol at 95°C. They were subsequently soaked for four minutes in 0.1% acidified mercuric chloride solution (0.5 ml concentrated HCl per 100 ml solution).

After rinsing five times with sterile distilled water, the nodule was smashed and mixed with 0.5 ml of sterile distilled water, and the resulting dilution was sown in Petri dishes with yeast-manitol arabinose agar with Congo red.

Once growth was observed in these dishes, the material was sown in slant containing yeast-manitol agar with Congo red maintenance medium.

An infection test was carried out with the purpose of preselecting Rhizobium strains according to their capacity for nodulating Prosopis alba and Prosopis tamarugo plants. This trial was made in 200-mm-tall, 30-mm-diameter tubes, to which Jensen medium was added. The seeds treated with acid and germinated in Petri dishes with agar were implanted in the tubes with Jensen medium and inoculated with the Rhizobium strains. This process was carried out under controlled temperature conditions (28° to 30°C). The 14-hour daily photoperiod was achieved with 40 W fluorescent lamps and supplemented with Agrolight (Westinghouse) lamp tubes. The infection trial was made with 12 replications for each of the isolated strains.

Effectiveness Trial

This trial was conducted in a growth chamber with temperatures between 29° and 35°C; 14-hour daily photoperiod and 30–40% relative humidity.

The seeds and inoculum were prepared as described above. Pots with vermiculite were used (previously washed with abundant drinking water and then with distilled water), irrigated with a nitrogen-free nutritive solution, with the following composition: K₂SO4 anhydrous, 436 mg; MgSO₄ anhydrous, 493.6 mg; Ca (H₂PO₄)₂, 117 mg; CaSO₄, 272 mg; and sequestrene 138 Fe (Fe-EDTA complex, Ciba-Geigy Corp.) 83 mg per liter of distilled water. This solution, additionally, contained the following micronutrients: H₃BO₃, 150 μg; ZnSO₄. 7H₂O, 13 μg; MnSO₄ . H₂O, 85 μg; (NH₄)₆Mo₇O₂₄ . 4H₂O, 13 μg; CuSo₄ . 5H₂O, 12 μg, per liter of distilled water pH was adjusted to 6.0 and sterilized by filtration.

Nitrogen was added to this same nutritive solution for the control plus nitrogen. This solution contained, additionally: Ca(NO₃)₂ . 4H₂O, 385 mg; KNO₃, 96.2 mg; (HN₄)₂SO₄, 48.1 mg.

Salinity Tolerance Trial

This trial was carried out with the same methodology and conditions described above. The test was made using different salinities in the solutions employed for irrigation, starting in the second month after the trial was implanted in pots. In salinity trials it is customary to use sodium, calcium and magnesium salt mixes. However, only sodium chloride was used in this trial, as the calcium and magnesium salts would precipitate the phosphorus in the nutritive solution, and leguminous plants are very demanding in their phosphorus requirements.

0.9% sodium chloride solution was added to the normal nutritive solution.

The following treatments were tried to test the effectiveness and salinity tolerance of the symbiosis plant-Rhizobium both for Prosopis alba and Prosopis tamarugo:

Control - non inoculated seed (4 replications)
Control - non inoculated seed + nitrogen (4 replications)
Inoculated seed - foreign strain (6 replications)
Inoculated seed - indigenous strain (6 replications)

Total nitrogen dosis for the non inoculated + nitrogen treatment was 420 mg.

Pots were arranged in randomized blocks. Six months after the beginning of the trial the appearance and size of the plant were evaluated, together with the dry weight of the shoot and the amount of nitrogen fixed by each plant, by the Kjeldahl method.

RESULTS

Infection Trial

Tamarugo and algarrobo plants inoculated with Rhizobium strains specific for the Prosopis species isolated at the Tamarugal Pampa, were evaluated in their capacity for forming nodules 12 weeks after inoculation. Eight indigenous strains isolated were tested.

This evaluation was made by:

• Observing nodule presence or absence

• Nodule aspect and number in each algarrobo and tamarugo plant

• Plant general appearance

Table 1 shows the findings for the infection test in the eight strains evaluated, (C₁ to C₈).

TABLE 1
Infection test with native Rhizobium strains in Prosopis alba and Prosopis tamarugo

(1) Average results for twelve replications

Nodules appeared from the fifth to the sixth week after inoculation, generally in new secondary roots. Nodules from the C₂ and C₃ strains showed excellent appearance and size. Their cross section showed a rich red color inside, indicating the presence of leg-hemoglobine and, consequently, nitrogen fixation by the plant. Nodules produced in the C₆ and C₇ treatments proved small.

CONCLUSIONS

— Of the eight Rhizobium strains isolated at the Tamarugal Pampa, only strains C₂, C₃, C₆ and C₇ would be effectively micro-organisms from the genus Rhizobium. Of these, only C₂ and C₃ are infective enough to be considered in the “assessment of ‘efectiveness’ or capacity for fixing nitrogen” stage by the nodulated plants. The selected strain was C₂, on account of its earlier nodulation compared with C₃. In other leguminous plants early nodulation is associated with greater effectivity and higher productivity.

Effectiveness of Rhizobium Strains in Prosopis alba and Prosopis tamarugo

The trial was evaluated six months after its inception, assessing the response of the different strains tested by:

• Observing nodule presence or absence

• Aspect, color, size, number and position of the nodules in the root

• Dry weight of the plant

• Nitrogen content in the plant

Tables 2 and 3 show the findings for the effect of inoculation in Prosopis alba and Prosopis tamarugo, with the native strain C₂ and the foreign strains F-1 and F-2.

TABLE 2
Assessment of nitrogen fixation effectiveness in Prosopis alba inoculated with different Rhizobium strains (1)

(1) Average for 4 to 6 replications.
(2) Number of nodules not quantified, as most plants only had two or three of them.
(3) Seeds inoculated upon germination.
(4) Seedlings inoculated eight weeks after germination.

Not all the inoculated plants showed nodulation. Basing on the general appearance, results showed good correlation between dry matter and nitrogen fixed. The nodules grew always at the secondary roots, very near the point from which tap roots develop. All nodulated plants had only 2–3 nodules, very small but with good appearance and red inside. The individual character of the nodules is typical of the morphology indicated for P. alba.

The strain which showed better results in terms of dry matter yield, even outperforming the nitrogenated control, is the indigenous strain isolated from the Tamarugal Pampa. It did show, however, a low nitrogen rate, which would indicate low specific nitrogenase activity by the nodules.

The treatments responded well to inoculation, fixing a greater amount of nitrogen than the controls, although dry matter yield was similar. This could be due to the short duration of the trial. Larger differences among the responses may be obtained with longer treatments.

To conclude, it may be stated that the plants fix atmospheric nitrogen, showing good development in a nitrogen-free medium. This indicates efficient performance by the nodules.

It is worth mentioning that Prosopis alba plants showed a difference in nodulation rates depending on the date of inoculation. Plants inoculated eight weeks after germination showed 100% nodulation, in contrast with the other treatment, which only showed 75% and 67% nodulation.

TABLE 3
Assessment of nitrogen fixation effectiveness in Prosopis tamarugo inoculated with different Rhizobium strains (1)

(1) Figures are averages for three replications. Many plants were lost to fungal attack.
(2) The number of nodules was not quantified, as most plants only showed 2–3 nodules.
(3) Seeds inoculated upon germination.
(4) Seedlings inoculated eight weeks after germination.

Tamarugo seedlings, in general, looked sickly and weak.

There was a remarkable difference between the control treatment and inoculated treatments, not as much in size as in foliage development. Indeed, dry matter yields exceeded manifold those of control plants. The highest yield was obtained with the nitrogen treatment, followed by the F-1 inoculation treatment, although this strain was the one that showed the smallest nodulation rate.

The nitrogen fixation rate was quite even for all the treatments, except for the control plus nitrogen, which showed exceptionally high rates.

In general terms, nodulation rates are very much lower for tamarugo than for algarrobo. Small nodules, with good color and appearance, were observed in the lateral roots.

Prosopis tamarugo showed no remarkable differences derived from the date of inoculation, except for the F-1 treatment. This may well be due to phytopathologic problems.

Assessing the effect of salinity on nitrogen fixation by Prosopis alba and Prosopis tamarugo inoculated with different Rhizobium strains

The trial was evaluated six months after inception.

The effect of salinity on nitrogen fixation was evaluated as per:

• Nodule presence or absence

• Nodule appearance, color, size, number and position in the root

• Plant appearance and size

• Plant dry weight

• Amount of nitrogen in the plants

Tables 4 and 5 present the findings for the effect of salinity on nitrogen fixation in P. alba and P. tamarugo.

TABLE 4
Effect of salinity on nitrogen fixation by Prosopis alba inoculated with different Rhizobium strains (1)

(1) Figures are averages for four and six replications.
(2) The number of nodules was not quantified, as most plants only showed 2–3 nodules.
(3) Seeds inoculated upon germination.
(4) Seedlings inoculated eight weeks after germination.

The plants showed acceptable appearance, both in size and dry matter yields. All treatments evidenced better response than the non-inoculated control.

There was no correlation between dry weight and nitrogen fixation rates, particularly with treatment C₂.

If dry matter yields are compared for salt and salt-free treatments (Tables 2 and 4), it may be observed that the salt treatment gives better yields, despite the different nitrogen fixation rate.

Nodules had good appearance and developed always in secondary roots.

TABLE 5
Effect of salinity on nitrogen fixation for Prosopis tamarugo inoculated with different Rhizobium strains (1)

(1) Figures are averages for three replications. Many plants were lost to fungal disease.
(2) Number of nodules was not quantified, as most plants only showed 2–3 nodules.
(3) Seeds inoculated upon germination.
(4) Seedlings inoculated eight weeks after germination.

Plant appearance was generally poor, although dry matter yield is good if compared with the non-inoculated control treatment; however, performance fell below the values observed for the Non-inoculated + Nitrogen treatment.

This trial showed poor nodulation and plant survival rates.

The 0.9% salt treatment was less effective in P. tamarugo than the salt-free treatment (Tables 3 and 5). The comparison of these trials evidences better response by inoculated plants than by the non-inoculated control, although dry matter yield falls well below that for the Non Inoculated + Nitrogen. Nitrogen fixation rate was as expected for this kind of treatment.

The low survival observed for P. tamarugo seedlings under the conditions of this type of trials was attributed to fungal attack.

DISCUSSION AND CONCLUSIONS

This study has evidenced the existence of nodules in Prosopis plants belonging to a natural ecosystem.

These nodules were only observed on those trees growing in soils lacking available nitrogen.

As regards the general methodologic aspects of the nitrogen fixation trials for leguminous plants of the species Prosopis, it may be pointed out that these should be conducted with ambient temperature ranging from 28°C and 35°C. At temperatures below 26°C there is no nodulation.

The Leonard Jar system, frequently used in nitrogen fixation trials for leguminous plants, did not prove convenient for Prosopis, due to the high water regime involved in this system. It was therefore necessary to replace it with the vermiculite pots as inert support.

Another remarkable aspect is the poor development of the Prosopis tamarugo plants. This may have been due to the susceptibility of this species to attack by various types of fungi; the same was not observed for Prosopis alba.

The following may be mentioned among the specific conclusions from this research work:

• Four micro-organism strains of the genus Rhizobium were isolated starting from Prosopis tamarugo nodules from a natural ecosystem.
• Only one of the isolated strains, labelled C₂, was selected on acount of its infective capacity and its precocity in nodule formation.
• It was found that inoculating seeds upon germination or inoculating them as eight-week-old seedlings does not visibly affect the nodulating capacity of the plants. The behaviour of the P. alba and P. tamarugo plants inoculated with indigenous strains or reference strains (provided by Dr. Peter Felker) was erratic. Nodulation rates ranged freely from 100% to 25%. It is interesting to observe that seedlings inoculated eight weeks after germination can nodulate.
• The native strain C₂ selected is able to fix nitrogen, as shown by the trials conducted, but performs better in dry weight of P. alba than in that of P. tamarugo.
• As regards the effect of salinity upon nitrogen fixtioncapability, P. alba has better development prospects on soils with 0.9% salt than in treatments without salt, with better response to the indigenous strain than to the control strain.

P. tamarugo could not develop efficiently in a salt treatment with 0.9% concentration under the trial conditions.

	Excavation of a tamarugo looking for Rhizobium nodules.
	View of the planted tamarugo forest.

Research study of the Arid Zone Project of the Development Division of the Production Development Corporation of Chile (CORFO).

REFERENCES

1. NATIONAL ACADEMY OF SCIENCES, U.S. 1977. Leucaena, promising forage and tree crop for the tropics. Washington D.C. 115 p.

2. FELKER P., CLARK P.R. 1980. Nitrogen fixation (acetylene reduction) and cross inoculation in 12 Prosopis (mesquite) species. Plant and Soil 57, 177–186.

3. BAILEY A.W. 1976. Nitrogen fixation in honey mesquite seedlings, J.Range Management 29, 479–481.

4. NATIONAL ACADEMY OF SCIENCES, U.S. 1979 Microbial Processes: Promising Technologies for Developing Countries. Washington, D.C.

5. PEPPLER H.J. 1967. Microbial Technology. Reinhold Publishing Corporation.

6. NUTMAN P.S. 1978. Breeding for high symbiotic effectiveness in red clover. Rothamsted Ann rev.

7. VINCENT J.M. 1970. A manual for the practical study of root-nodule bacteria. International Biological Programme Handbook No. 15. Oxford. Blackwell Scientific Publications, 164 p.

8. Short intensive course on “Rhizobium technology” held from July 7 to 26, 1980, at the Universidad Federal do Rio Grande do Sul, Brazil (sponsored by MIRCEN, UNEP, UNESCO).

9. FELKER P. Personal communication.