Agrobiodiversity: functions and threats under global change D 3.4 81 Wood and Lenne (1997), generally favourable agricultural sites and tended not to be centres of diversity. The farmer’s varieties of various species are often only superior, or at least competitive, under poorer ecoclimatic conditions. Most ofthe studies that have looked at these issues come to the conclusion that yield (or rather potential yield) is the most important criterion from the farmer’s perspective for selecting a variety alongside the actual product (Heisey and Brennan, 1991). However, Brush (1995) found that many farmers plant high-yielding varieties without giving up on the traditional farmers’ varieties altogether; mainly because the latter are of a particularly high quality (protein content, taste). Having said that, one can assume that the replacement of old varieties by new ones will continue. It is crucial to note that the continued substitution of old varieties does not automatically have to lead to a loss in genetic diversity if one takes timely and sustained conservation measures to take care ofthe genotypes, that have at that stage become ‘genetic resources’ (Heisey et al, 1997) Issue area 4: Agricultural and economic policy Behind the direct causes of change in agrobiodiversity (issue areas 1–3) are the causes that were cited in the introduction to this section such as – extreme weather conditions and climate fluctuations, – disappearance and degradation of resources, – pollution, – population growth, – political unrest and war. Different policy areas intervene here. Agricultural and economic policies set the parameters for market activities and technological development in the agricultural sector.Areas for action include protection of intellectual property rights (eg variety protection, patent rights), promotion of research, agricultural pricing policy, subsidies, food laws or foreign trade policies. The agricultural sector is therefore an economic area in which most states in the world intervene to a particular degree in a regulatory fashion. In light ofthe diversity ofthe possible instruments available to agricultural and economic policy, it is evident that the influence ofthese policy areas on agrobiodiversity is extremely complex. It also appears necessary in this context in future to examine agricultural and economic policy measures with regard to their influence on – management intensity in agriculture, – diversity of species breeding, – diversity in procurement and trade, and – level and use of public funding in agricultural research. Generally it can be stated that agro-sciences must tackle as a priority the task of informing political decision makers with regard to which individual measures will have what potential impact on agrobiodiversity. In many areas there is a need for fundamental research since we have only just scratched the surface in terms of even recording agrobiodiversity. The biggest problem, however, is that biological diversity in agro-ecosystems is generally not the goal of an individual farm and is rarely even the goal of agricultural policy. That applies particularly wherever the elements of agrobiodiversity have (today) no known ‘function’ or where they do not contribution towards increasing or stabilizing agricultural production. Maintaining current and latent agrobiodiversity must be made a particular policy goal as is demanded in the Convention on Biological Diversity. D 3.4.5 Measures to conserve agrobiodiversity Strategies for conserving agrogenetic resources Modern agriculture has profited immensely from the diversity that has arisen during the history of land use (Box D 3.4-3). Its success, however, has essentially contributed to the loss of that diversity (Miller et al, 1995). In order to be able to adapt to changing environmental conditions and to achieve sustainable production increases (Section E 3.3.4) agricultural systems are, and will remain, dependent on biological diversity. Strategies that make active use ofthe ecological functions of agrobiodiversity should be pursued as a matter of priority, since measures to preserve genetic resources have no more than a precautionary character, even when organized in an optimum fashion. If current biodiversity cannot be maintained, conservation measures must attempt to preserve the biological diversity of plants, animals and microorganisms. According to Frankel (1983), there are two options in response to the question of what is the appropriate strategy for preserving a species: 1. Establish or conserve a habitat in which the species can survive and evolve further, without being actively influenced in that respect. This option is rarely open to components of agrobiodiversity. It will become more limited in future (Brush, 1995). 2. If these habitats are not available, but the species or their varieties and breeds are to be prevented from dying out, then they must be transferred to collections, eg botanical gardens or gene banks.
82 D The use of genetic and species diversity Box D 3.4-3 The gene pool concept Harlan and de Wet (1971) first put forward the idea ofthe gene pool. The concept divides cultivated plants andtheir relatives and wild species into a primary, secondary and tertiary gene pool. The measure of relationship is the possibility of crossing the species: • The primary gene pool contains all representatives ofthe cultivated species. • Plants in the secondary gene pool can be crossed with the cultivated plant species under consideration and produce fertile hybrids; the plants do not however belong to the cultivated plant species under consideration. • The tertiary gene pool comprises species that can no longer be crossed in the classic sense with the cultivated species, but only with the help of in-vitro techniques such as embryo rescue or protoplast fusion. Since genes can be transferred across species barriers using genetic engineering methods, the gene pool concept has been ‘diluted’. The ability of a species to hybridize with another is no longer the exclusive criterion for whether gene transfer is possible. Callow et al (1997) therefore discuss whether hybridization with ‘cultivated species’ is still a suitable criterion for regarding a species as a genetic resource since genetic engineering methods in principle allow us to see any organism as a source of valuable genes. The gene pool concept however, does continue to provide a basis for designing collection and conservation strategies for genetic resources. Theoretically, the following strategies may be derived form those two options (Table D 3.4-3): 1. In-situ conservation in the case of agricultural crops means more or less intensive management. There are gradations of difference from ‘no management’ (eg core zones in a national park), over ‘minimal management’ to ‘intensive management’ (when conservation is only possible if the present human-influenced state is also preserved at the same time). In-situ or on-farm conservation relate to conserving genetic resources in agricultural or horticultural situations, such as the traditional household garden (‘conuco’). 2. Ex-situ conservation takes place in gene banks, botanical and zoological gardens and aquaria. For the conservation of plants, there are many different available measures. These include seed collections, field collections, in-vitro tissue cultures, pollen conservation, protoplast cultures and cryoconservation. Animals are kept in captive populations; sperm, eggs and embryos can be conserved cryogenically. With regard to conservation strategy, one can differentiate between crops and livestock on the one handandthe wild portion of agrobiodiversity on the other hand. Whilst the latter have to be kept in situ, this approach is only possible for the former in exceptional cases since these generally depend on human assistance for survival. Their long-term preservation is possible in situ, on farm or ex situ (Kosak, 1996). On-farm conservation generally only takes place in ‘traditional’ agriculture that is characterized by crop diversity. In modern or industrial agriculture that is characterized by genetically homogeneous highyielding plant varieties and animal breeds of just a few species, diversity must be conserved ex situ. Brush (1995) proposes that in isolated areas in the centres of domestication, in which small-scale farming is still the only possibility, systematic in-situ and on-farm conservation could be introduced to supplement ex-situ conservation. This is not just the conservation ofthe status quo, but rather allows evolutionary processes to continue. Examples of conservation strategies for particular cultivated plant species • Wheat: Worldwide almost 800,000 wheat (Triticum) accessions are being kept ex situ (FAO, 1996b). Many ofthe accessions are historic farmers’ varieties. Although there are certainly some duplicates among the 800,000 accessions, sheer numbers clearly show that systematic in-situ or onfarm preservation of this diversity would be impossible from an organizational standpoint. Two biological characteristics predestine wheat for ex-situ conservation strategy: 1. Wheat is self-fertilizing; that means elaborate measures to manage pollination or isolate plots can be dispensed with. 2. The samples have only to be planted every 25 years for regeneration. That is sufficient to preserve germinating capacity. • Cassava: Cassava (manioc) is a species that reproduces by vegetative propagation.Worldwide there are around 28,000 accessions in ex-situ collections, 23 per cent of which are historic farmers’ varieties, and 9 per cent are modern varieties or nucleus stocks (FAO, 1996b). It may be assumed that the collections constitute more of a random selection than a complete collection. Furthermore, the cassava clones have to be replanted every year. The conservation of habitats in which a large diversity of cassava is cultivated is therefore the best strategy for conservation. The two examples indicate how one might proceed in order to define the optimum conservation strategy for a given species.