Mexico has incorporated the goal of sustainable development in its National Development Plan 1995-2000. Yucatan and other regions are expected to promote strategies that are ecologically friendly, socially equitable and economically viable. The henequen selection programme could make a contribution to these goals in Yucatan, using relatively simple biotechnologies rather than genetic engineering.

Plant biotechnology is potentially a useful tool to solve a number of agronomic problems. However, crops that are less commercially viable receive less attention from research and development than commercially more lucrative ones. This is the case for some agaves from the arid and semi-arid zones of Mexico, which play a significant role in a number of regional economies and yet have been largely neglected by commercial research and development (R&D). They are particularly relevant as a cash crop for small farms in regions where other species are difficult to grow. Although in some areas agaves are exploited in the wild, sometimes endangering natural populations, most agave cultivation is based on inefficient management systems with low yields and poor economic returns. Simple and inexpensive biotechnologies such as tissue culture, rather than genetic engineering with its problems of social acceptance and potential environmental hazards, could offer considerable benefits. They can be applied to solving specific problems such as the low productivity of agave cultivation, caused by unavailability of optimal varieties and healthy starting materials.

Agaves could play an increasingly important role in the future of arid and semi-arid agricultural systems for a variety of reasons: they are physiologically and morphologically adapted to cope with water scarcity; their long root systems are efficient for the conservation of soil; they can be intercropped with other economically important species; they can serve as fences and wind barriers; and it is possible to obtain a variety of products from them such as fibres, cellulose for pulping, chemical substances and spirits such as tequila (see box).

Rise and decline of henequen production

Henequen is slow-growing with a long life cycle of up to 20 years, flowering only once towards the end of its life. Probably because the plant has an uneven chromosome set, most seeds are infertile. Propagation occurs principally through subterranean shoots. The plant is unusual in being highly productive under harsh ecological conditions of water and soil scarcity such as are found in the henequen growing area of Yucatan.

The African and South American production of fibre comes from a few clones of sisal (Agave sisalana, a close relative of henequen) smuggled out of Mexico towards the end of the nineteenth century. Although there are no records, it is quite likely that the present production of henequen in Yucatan is based on only a few clones selected when the henequen industry began to grow.

Moreover, the limited sexual reproduction that might occur in the fields is prevented by the farmers themselves by cutting off the flower stalk as soon as it begins to develop because otherwise it uses the stored sugars and the leaves dry up. Genetic variability is therefore limited. However, recent observations of morphological (phenotypic) variability in the field, and the analysis of variability at the molecular level, have revealed that in spite of being a vegetatively propagated species, a limited degree of variability does occur in the agave plantations from which selection of traits can be made.

Combing tissue culture and nursery-propagation

In the henequen industry, technological innovation is slow. First, because traditional ideas about how henequen should be cultivated are very deeply rooted, especially amongst small-scale farmers. Second, there is no effective extension system to transfer new ideas to the producers.

The implementation of a typical breeding programme would be plagued with difficulties because of the long life cycle of henequen (12 to 20 years to flower) and its very limited sexual reproduction.

Micro-propagation, a technique for multiplying plants vegetatively through the in vitro culture of their cells, tissues or organs, offers the possibility of speeding up multiplication of outstanding individuals by reducing the time it takes to produce new generations from years to months. This technology makes the large-scale production of elite clonal lines possible. In addition, it produces pathogen-free plants that are more vigorous and faster growing than field-produced plants.

Micro-propagation is more expensive than traditional adventitious shoot production. Clones multiplied in nurseries cost only 20 per cent of the cost of laboratory-produced plants, which makes the in vitro production of millions of plants economically unfeasible. However, the in vitro plants grow stronger and generate about three times more shoots in the nursery than field propagated ones.

By combining both methods, micro-propagation can be used to produce vigorous elite lines as a starting material for a cheap multiplication in nurseries, in order to provide sufficient, high quality planting material to re-establish the henequen plantations.

The agave programme at CICY

In 1980, the Centro de Investigación Científicia de Yucatán (Centre for Scientific Research of Yucatan, CICY) initiated a research programme that covered all aspects of the biology and product-use of henequen: the physicochemical properties of cellulose materials, steroid chemistry, botanical, ecological and genetic studies as well as the in vitro culture of agaves. The latter has produced technologies for their efficient propagation. CICY has taken the initiative to test the benefits of combining tissue culture (micro-propagation) with nursery-propagation by developing experimental nurseries and plantations together with growers.

In 1994, field testing of 150 clonal lines began through a collaborative agreement with a number of henequen growers through the Union for Agricultural Credit. After carefully selecting the most outstanding mother plants from the growers’ plantations, CICY cloned and produced 300,000 micro-propagated plants, which were then propagated in nurseries. Monthly morphometric evaluations of the plants have been done, over a period of five years, in eight nurseries and eight experimental fields, over a total of 65 hectares, to characterize the clonal lines and compare their performance with that of field-produced plants.

CICY is implementing a system to distribute elite micro-propagated plants to the nurseries of four associations of small and large-scale farmers so that they can propagate the plants themselves and distribute them among their members at almost the same cost as traditional, field-produced ones.

Because CICY is a publicly funded research institution, an arrangement was set up with the grower associations to minimize costs. The collaborating grower associations have contributed to the programme by covering the operating costs of the experimental nurseries and plantations, and have helped to finance the research, while CICY has paid the costs of the technical evaluations. This way CICY also ensures that its elite lines are managed in the same way as the field propagated plants used as controls.

Preliminary results from the elite lines

Lines are considered as elite mainly because of their larger number and larger size of the leaves and faster production of adventitious shoots.

The results obtained so far from measurements in the nursery and the plantation seem promising. In the nursery, the main effect is the greater propagation capacity of the clonal lines which yield an average of 5.6 shoots per plant per year compared to only 1.5 produced by the field propagated ones.

The clonal lines also show faster growth in the plantation. After three years they have almost doubled their height and produced an average of 81 leaves per plant, while the field plants have only increased their height by 48 per cent and produced 60 leaves. In addition, the total foliar area of the clonal plants is more than double that of the field-produced ones, from which a proportionally higher fibre content can be expected.

The in vitro treatment with hormones seems to be responsible for the greater propagating vigour of micro-propagated plants; however, as controls show, the other characteristics seem to result from the selection. So far no problems, such as greater susceptibility to disease, have been detected and it seems unlikely that they will be, since selection of healthy material was carried out in plantations where microbial diseases are normally present at low densities.

It is difficult to evaluate how much the variability of a henequen population could be affected by the introduction of micro-propagated lines since in vitro grown plants are in fact only being multiplied faster by basically the same vegetative procedure that generates new plants in the field. However, the recommended procedure is to introduce several hundred new clones every year. In fact, this is almost an obligatory practice since lines are never subcultured in vitro more than six or seven times, generating only 3000 to 6000 individuals per clone. Additionally, the selected clones are mixed by the growers in the nurseries so that every single hectare of plantation contains materials from several clones.

As yet, the main impacts derived from the clonal lines are:

• The 300 per cent increase in adventitious shoot production allows growers to replant their plantations with elite material far more rapidly than expected.
• An added advantage over the traditional propagation methods of cutting the adventitious shoots from the base of potentially diseased plants, is that the elite materials are disease-free and will help to prevent the spread of disease. However, the impact that the use of these materials will have on the prevention of losses to fungal and bacterial infections is difficult to measure and will also depend on residual pathogen pressure in the field to which healthy in vitro grown plants are exposed.
• The overall faster growth of the clonal lines has enabled these plants to reach harvesting earlier than normal. Instead of five years normal harvest time, clonal lines only take three years.
• In vitro multiplication produces plants that are more homogeneous morphologically and physiologically. This synchronizes growth so that the plants reach the various production stages at the same time, thereby making all the agricultural procedures more simple and efficient. A concentrated demand for labour might be a disadvantage for small-scale farmers with other crops, but for henequen the harvesting is at present very inefficient as farmers have to walk considerable distances between the plants looking for leaves that are long enough to be cut. A more synchronized growth would increase efficiency considerably without causing side effects. This is even more the case because henequen leaves do not have to be harvested immediately after they reach the correct length. Farmers can wait up to four month without any adverse effects for the plants.
• The most important measure of productivity in henequen plants is fibre yield. The first harvests suggest that an increase can be expected in the content of fibre in the leaves. In addition, the increase in both the number of leaves and their size suggests that the total yield per hectare at the end of the plant’s life cycle could be more than double in the elite lines. It is, however too early to make definitive projections; for example, it is not known if the crop produces a predetermined number of leaves in its life independently of how long it lives, nor is it possible to estimate the maximum fibre content. The increased rates might be temporary and not a reflection of inherited traits.
• Finally, as elite individuals grow faster, their first leaves can also be harvested, adding some 8 per cent to the total production. An important but unquantifiable benefit is that by harvesting these leaves and not allowing them to dry and accumulate as highly inflammable material around the base of the plant, as usually happens, the risk of fire is considerably reduced. Currently, several thousand hectares of henequen are lost to fire each year.

Although the initial costs of planting elite henequen are 25 per cent above the price of field-propagated adventitious shoots, economic studies show that the additional costs will be more than compensated for by the increased production. Projections suggest that economic returns, at the end of fifteen years, may be double those from field-produced plants. The savings brought about by reducing the preharvest period by two years are particularly important for increasing the profitability of henequen production.

The plants produced by CICY with public funds have not been protected in any way. Therefore they will be further available to the grower associations for nursery propagation and distribution amongst their members. As soon as sufficient material is available, the cost of improved plants should be no higher than unimproved ones. Additionally, the government is currently supporting the establishment of nurseries in order to increase the availability of high-quality planting material.

Government programmes to stimulate the agricultural production of henequen consist of direct payments to the farmers who carry out certain activities such as planting new areas with henequen (US$ 73 per hectare in 1998), rehabilitating old henequen plantations (US$ 60 per hectare) and establishing nurseries (US$ 2500 per hectare). Compensation of US $85 per hectare is paid to farmers who lose plantations because of fires.

The challenge of sustainable development

The challenge to promote strategies that are considered ecologically friendly, socially equitable and economically viable is no small task in an area where the infertile soils and long dry season have severely limited agricultural development. Unemployment is a chronic problem for the rapidly growing and largely underprivileged population of 1.5 million people in Yucatan, of which between a quarter and a third is rural. Ways of increasing opportunities, work productivity and living standards to meet the criteria of sustainable development are difficult to find. Although in itself it is not a solution to this enormous problem, the henequen selection programme could potentially make a substantial contribution.

Most small-scale henequen growers will not be able to stay in business for long if they cannot improve their productivity. The increased income from using elite material could also have a much needed multiplication effect, because in a situation of lacking employment opportunities and low purchasing power, any extra money that stays in the communities will benefit the local economy. The application of CICY’s technology can also help to keep the henequen industry alive in Yucatan by improving its competitive position in relation to Brazil.

Furthermore, the medium and large-scale producers will be able to pay their workers higher wages to keep them from either migrating to the cities or working for the maquiladoras. These subsidiary factories of foreign companies have established themselves in Mexico to take advantage of its cheap labour. They do not have to pay taxes and generally the workers only earn the minimum wage of US$ 3.50 per day. Because of its location, Yucatan is well placed for companies interested in exporting to the American market and the number of maquiladoras in Yucatan has increased greatly over the past few years.

Cultivating elite henequen plants can be considered as ecologically sustainable; it does not imply cutting down forests or losing germplasm because the new plantations will be developed by rehabilitating abandoned areas that were once under henequen and that are of little use for other crops.

In the last few years, various factors combined have given henequen a brighter outlook. International calls for more sustainable methods of production and for a reduction in pollution have slightly increased the demand for natural fibres, of which the competitive position has also been boosted by the recent rise in oil prices. Here henequen serves doubly because it is not only biodegradable and can substitute plastic for several purposes, but it also requires no fertilization, no irrigation, and little herbicide because half of the weeding is still done by hand.

In addition, the state government of Yucatan has introduced new programmes to promote rural activities including henequen production and processing because of the present fibre shortage. Although interest in the crop has thus been rekindled and growers are keen to establish new plantations, they are faced with a lack of high quality planting material and a need to increase their productivity in order to stay in the market. For the first time in many years there is a real demand from henequen producers for new and appropriate technology. This has been stimulated by the activities of CICY, using relatively simple biotechnologies for the genetic improvement and large-scale reproduction of henequen.

Outlook

Although it is clear that medium and large-scale producers who already have planted some 200 hectares with this material will be the first to benefit from the elite plants, the small growers associations are not being excluded. They recently planted 500,000 elite shoots in their nurseries.

So far there are no technical reasons to suggest that the technology may fail. However, the extent to which the selected lines are used and the speed with which they are diffused amongst the growers, will depend on two factors:

First, on convincing the growers to abandon the traditional practice of using materials of unknown quality that also might be infected, and to make an initial investment in the elite plants, and second, on how much government support is given to promote them and help paying the costs of establishing the required number of nurseries. The present government terminates its period in 2001 and it is difficult to foresee how much support rural development will get in the future. The increased productivity of the elite plants and their economic benefits should determine their final impact.
Amarella Eastmond* & Manuel L. Robert**

*Autonomous University of Yucatan, Unit for Social Sciences, Calle 61 No. 525 por 66 y 69, Mérida, Centro C.P. 97000, Yucatán, Mexico.
Fax (+52) 99 285 115; E-mail espencer@tunku.uady.mx
**Centre for Scientific Research of Yucatan (CICY), Biotechnology Unit, Calle 43 No. 130 Col. Chuburna de Hidalgo, Mérida, C.P. 97200, Yucatán, México.
Fax (+52) 99 813 900

The work reported here was supported by Cam BioTec and Mexico’s National Council for Science and Technology (CONACYT).

Sources
Eastmond, A., Herrera, J.L. and Robert, M.L. (in press), La biotecnología aplicada al henequén: alternativas para el futuro. CICY: Mérida, Yucatán.

Eastmond, A. and Robert M.L. (1992), "Biotecnología y Agroecología ¿Paradigmas opuestos o complementarios?" Agrociencia serie Fitocienca, Vol. 3, pp. 7-22.

Robert, M. L., Herrera J. L., Contreras F. and Scorer, K. N. (1987), "In vitro propagation of Agave fourcroydes Lem". Plant Cell, Tissue and Organ Culture, Vol. 8, pp. 37-48.

Robert. M. L., Herrera, J. L., Chan J. L. and Contreras, F. (1992), "Micropropagation of Agave spp." In: Y.P.S. Bajaj, (ed.) Biotechnology in Agriculture and Forestry, Vol.19, Springer-Verlag, p. 306-329.