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Giuseppina Morico, Fabrizio Grassi and Carlo Fidegpina Morico, Fabrizio Grassi and Carlo Fideghelli
Introduction
"The plant genetic resources for food and agriculture (PGRFA) represent the basis for world food security. "
Horticultural crops comprizing fruit and nut crops, vegetables, food legumes, roots and tubers, medicinal, aromatic and ornamental plants are only part of the total genetic diversity of PGRFA; nonetheless they contribute greatly both to satisfying food security and to integrate and diversify dietary needs of mankind. In fact, in some regions of the world, horticultural crops are important staples.
In recent decades the awareness of a high degree of genetic erosion led to the establishment of seed and field genebanks located both in developed countries (poor in genetic resources) and in developing countries (rich in genetic resources).
Even more recent is the the concept of dynamic in situ conservation, which allows the conserved material to evolve.
This report highlights that research and technology have neglected
minor and underutilized horticultural species of particular importance
for subsistence farming systems in developing countries, and for
preserving environment and socio-economic fabric in marginal areas
of developed countries. A review of the main conventional and
alternative conservation systems, methods of characterization,
evaluation and utilization ostems, methods of characterization,
evaluation and utilization of horticultural genetic resources
is reported.
Overview of horticultural genetic resources
Plant genetic resources for food and agriculture (PGRFA) are as part of the biological wealth indispensable for securing world food supplies, alleviating poverty and sustaining rural development. PGRFA, in its modern definition, includes resources which contribute to people's livelihoods by providing food, medicine, feed for domestic animals, fibre, clothing, amenity, shelter and energy etc., even though more emphasis has been given to the PGRFA which contribute most to food security. Within the plant kingdom around 350,000 species have been classified, of which 70,000 are considered edible plants, even though mankind has utilized only about 7,000 of these for food. Given this enormous repository, it is remarkable that as few as 30 plant species account for about 95% of the world's calories and protein intake (tab.1).
The so-called major crops, identified as being of great importance for food security in one or more regions, include different horticultural crops (potato, sweet potato, cassava, yam, beans, coconut, tropical fruits) (tab. 1).
The other crops are considered minor and under-utilized even though they fulfill several functions: some (fonio, taro, bambara groundnut, breadfruit, etc.) contribute to food security for specific regions, etc.) contribute to food security for specific regions or localities; others crops improve the nutritional value of human diet (vegetables, fruits) due to their vitamin and mineral content, or are important to dietary diversification or promote health (medicinal plants).
A species that has not been fully exploited in terms of its potential use is by distinction underutilized. The main reason 'potentially useful crop species' rarely attract interest from agricultural research is the financial constraint on research; funding agencies are not in favour of work on crops of unproven potential and unknown commercial value.
To solve the problems associated with increasing agricultural biodiversity, science should pay more attention to valuable indigenous species grown locally for centuries. This diversification should include minor and underutilized species in developed countries and minor, underutilized and subsistence crop species in the developing countries.
Horticultural crops, which are only a part of PGRFA, are characterized
by a wide and heterogeneous range of species. In fact, five different
major groups can be identified: fruit and nut crops, vegetables,
food legumes, roots and tubers, and lastly the ornamental and
medicinal group (tab. 2).
Centres of origin of the main horticultural crops
One of the first scientists to become aware of the importance of plant genetic diversito become aware of the importance of plant genetic diversity was the great Russian plant explorer and geneticist Nikolai J. Vavilov. His geographical survey revealed that the most cultivated plants are linked to one of seven basic geographical centres of origin. Almost one third of the world's species originated in Southeastern Asia and most of the main fruit and vegetable crops come from the east and west Asiatic centre and Mediterranean centre of origin, while roots and tubers and tropical fruit trees are concentrated in the Central American and Andean centres.
Clearly, major crops such as potato, apple, orange, grape, banana, and tomato which originated from very different parts of the world, are now grown over vast land areas often extending into altitude and latitude that bear little resemblance to their original habitats.
This adaptation of major crop species to different locations and growing conditions has taken many generations of selection and breeding, initially by individual farmers, and more recently by plant breeders and research institutions responsible for genetic improvement programmes.
On the other hand, for minor and underutilized species, production areas mostly correspond to their original centre of diversity (olives, capers, carob, fig, strawberry-tree and other Mediterranean small fruits).
The genetic diversity is contained in different types of genetic material such as "populations", &quonetic material such as "populations", "landraces" and "stable varieties".
Population is a heterogeneous genetic entity formed by different genotypes able to survive varying conditions; this definition is not only applied to wild populations but can also be extended to landraces.
Landraces, also called farmers' varieties, are heterogeneous populations of crop plants grown by traditional farmers.
Modern varieties, obtained by plant breeding, are genetically
homogeneous populations highly adapted to modern uniform agricultural
management techniques. This genetic uniformity is the result of
intensive selection for the genotype that best meets modern production
and market needs.
Genetic vulnerability and genetic erosion
The intensive activity of genetic improvement, together with the technological development of agricultural inputs, has led in developing countries to the replacement of many local varieties by a few uniform modern cultivars. The genetic uniformity of cultivars of a widely grown crop makes them uniformly susceptible to biotic or abiotic hazards, and this genetic vulnerability may lead to complete crop loss. The factors that influence the degree of vulnerability are the extent of the areas devoted to a single cultivar and the similarity between cultivars.
An example of the high degree of uniformity is evident in apple. Most of of the high degree of uniformity is evident in apple. Most of the world's production is based on two cultivars, 'Delicious' and its red sports and 'Golden Delicious', with recent expansion based on their seedlings.
Cultivar replacement is reported to be the main cause of genetic erosion around the world.
Among other causes of genetic erosion are: land clearing, over-exploitation
of species, population pressure, environmental degradation, overgrazing,
legislation/policy, changing agricultural systems.
Major temperate fruit trees
Ex situ living collections of major fruit trees are present in most of the countries interested in these crops. But the genetic diversity present in these collections is often characterized by the presence of duplicate accessions in several living collections. This fact is probably due to the incomplete characterization data and documentation available, sometimes also caused by the difficulties encountered in interpreting publications, workshops and symposium proceedings in the different languages used.
The common limitations, at present, of the fruit tree collections are:
Storage - high costs involved in the establishment and maintainance of living field collections around the world. Protocols for in vitro collections have already been developed for some species, while for other species some preliminary results have been obtained, but er species some preliminary results have been obtained, but there is the need to improve expertise, methods and facilities to increase the use of in vitro storage.
Characterization - up to now most of the characterization data have been achieved using morphological markers and agronomic traits.
Around the world several projects are underway to build genome maps, for example the European Union projects "Prunus genome mapping" and the "Malus genome mapping".
Collection activities
As mentioned before, the old representative cultivars and the
modern commercial cultivars are safely maintained in ex situ collections,
while gaps have been identified primarily for germplasm of wild
relatives of cultivated fruit trees. The under-representation
of wild germplasm in ex situ collections, particularly from their
centre of origin, is of particular concern in so far as such material
is likely to contain a rich genetic diversity.
Minor temperate and nut fruit trees
Minor temperate and nut fruit trees have generally been relatively neglected by the scientific community. They have been considered low income crops and so little genetic improvement work as been conducted to improve existing cultivars. These crops still maintain a wide genetic base that makes them suitable for cultivation in marginal areas.
Collecting and conservation acton in marginal areas.
Collecting and conservation activities involving these kind of species are only recent and there still remains much to do to fill the remaining gaps in existing collections. Collecting expeditions should be urgently made in the different existing ecosystems to collect the wild genetic material adapted to the various climatic conditions.
The conservation, characterization and utilization of these minor
species is an important objective, allowing diversification of
agro-food production by the use of a greater number of species
and cultivars, tolerant to pests and diseases, and requiring fewer
chemical treatments in line with a more friendly agriculture not
hampering enviromental conditions.
Subtropical and tropical fruit and nut species
In developing countries subtropical and tropical fruit growing has generally had a marginal or subsistence role. Only recently, with increasing tourism in tropical countries and the commercial exchange with developed countries, fruit growing has passed from a traditional management system to an industrial one, even though this is true only for some countries of South-East Asia and Central America, which have adequately sustained agricultural research (Thailand, Malaysia, Indonesia, Ecuador, Brazil, etc.). Musa is among the most important crops in the developing world in terms of gross value of production.
Among sub-tropical and trss value of production.
Among sub-tropical and tropical fruit trees the most important crops for food security around the world are banana/plantain, coconut and mango, considered high income commodities. As consequence, a certain amount of research has been performed on these crops by private and public research institutions. Collecting expeditions have been made to gather wild material of Musa spp. in South-east Asia and parts of Africa.
Ex situ collections have been established around the world. In particular, for banana/plantain there are about 10,500 accessions in genebanks worldwide, the biggest of which is held by the International Network for the Improvement of Banana and Plantain-INIBAP (10%).
For the many minor tropical fruit and nut species present in their centre of diversity, little if not anything is being done to collect, preserve and characterize this enormous amount of unique genetic diversity, that is a source of food for the local populations. The recent International Technical Conference on PGR, stressed the need for every country to establish national programmes, according to their scientific and financial resources, to preserve such precious local material for future generations.
Examples of fruit species that have the potential for exploitation include Artocarpus communis, Solacca edulis, Mangifera koetijape, Dimocarpus longanan, Artocarpus adoratissimus, Dimocarpus molesianus,, Artocarpus adoratissimus, Dimocarpus molesianus, Canarium odontophyllum.
There is expected to be very diverse genetic variability in the
wild range of indigenous fruits yet to be discovered, as there
are so many seedling trees in the wild or semi-wild conditions.
Besides the imperative need to conserve as much as possible the
indigenous fruit species, their potential could be exploited,
namely as new fruit trees, as multi-purpose trees, as rootstocks
and as sources of germplasm for improving exisisting cultivated
fruit crops.
Vegetable
More than 1000 plants may be used as vegetables, 350 of which are used on a larger scale. Vegetables differ in their edible plant parts; it may be leaves, buds, roots, tubers, bulbs, stalks, sprouts, flowers, fruits or seeds. For the USA, 100 species are mentioned as being used as vegetables; for China it is more than 200 species and sub-species of 29 different plant families; for tropical vegetables almost 300. The above data make one conclude that the number of vegetables commonly consumed on a large scale is about 200-300, worldwide, with regional concentrations.
One of the most interesting initiatives carried on in Europe was the funding of the European Community project that initiated the coordinated collection of valuable Brassica germplasm in EU countries. The importance of this project is connected to the fact that severatance of this project is connected to the fact that several grown and imported vegetablels belonging to Brassica spp, and in particular six Brassica species (kale, cauliflower, cabbage, brussel sprouts, kohlrabi, broccoli) derive from the wild cabbage Brassica oleracea.
In these countries the objectives of breeding programmes are oriented towards the utilization of genetic diversity not only to obtain high yielding cultivars, but also to such other traits as taste, colour, nutritional value, ripening season, resistance to plant diseases and to unfavourable climatic conditions.
In developing countries, where hunger prevails, primary importance is given to the production of subsistence crops, rich in proteins, fats and carbohydrates. On the contrary, the contribution of traditional vegetables to alleviating micro-nutrient deficiencies is greatly underestimated.
Around the world, only a small portion of the vegetable landraces has been collected and evaluated.
The chances of genetic erosion, in particular for landraces, wild
related species, located in marginal and isolated areas, suggests
using existing protected areas (National Parks, Reserves, etc.)
for the conservation of wild vegetables present in their natural
habitats, thus providing protection of germplasm at the lowest
possible cost.
Root and tuber crops
Potato and sweet potato belong to the crops
Potato and sweet potato belong to the most important crops for food energy supply worldwide.
At the subregional level cassava (Manihot esculenta) and yam (Dioscorea spp.) are major food crops and represent the dietary needs of millions of the world's poorer people.
Generally all the countries (Africa, and South-Eastern Asia) that are heavily dependent on tuberous crops, are the relatively poor economically. The FAO Committee on World Food Security reported in 1986 that there was a 'frequent absence of a coherent policy framework for the traditional food sector particularly for roots and tubers' in Africa (FAO, 1986).
Unfortunately, tuber crops have generally been denied the infrastructural
support necessary for their full promotion and development. Such
support includes research, dissemination, subsidies and organized
production, processing and marketing facilities.
Food legumes
Food legumes, above all beans, are particularly important to food security in Central America and Africa (West, East and Southern).
According to the FAO World Information Early Warning System (WIEWS) database, food legumes are the next largest category of preserved germplasm, after cereals, constituting about 15% of the global accessions stored ex situ.
A core collection for Phaseolus, based on a sophisticated agro-ecological classificaolus, based on a sophisticated agro-ecological classification of Latin America, has been developed by CIAT in Colombia.
Wild species have been documented as significant sources of genes for tolerance or resistance to drought, heat, cold, golden mosaic and other diseases.
Core collections of common bean , defined at CIAT and in the USA
using passport, ecoclimatic and molecular marker data are increasingly
used for evaluation and breeding.
Medicinal, aromatic and ornamental plants
The great diversity of plants in general, has to be and can be saved and used not only for nutritional value, but also for their contribution to health and for improving peoples'lives satisfying their esthetic and culinary needs. The existence of undiscovered pharmaceuticals for modern medicine, estimated approximately in 328 drugs, has often been cited as one of the most important reasons to protect tropical forest and plants in general.
The Tropical-Equatorial Countries have a rich heritage of traditional knowledge of the uses of plants as medicines. It is through a trial and error process that local people selected the plants for their medicinal values. Many indigenous plants are known to have diuretic, hypotensive, symatolytic, tranquillizing, antineoplastic, antiprotozoan, insecticidal, aphrodisiac, contraceptive and anti-tumor properties.
At present, most of medicinal plant genetic resources
At present, most of medicinal plant genetic resources exist in the wild and are not receiving effective attention by Scientific Community and National Governments.
Before they are lost completely, through destruction of their
natural habitats and by an intensive extractive process by Pharmaceutical
Companies, there is an urgent need to: collect as much as possible
the indigenous medicinal plant resources and assemble them in
ex situ collections; botanically and taxonomically identify these
resources and characterize them; fully and properly document this
information; evaluate and test them for their medicinal properties
before they are utilized; establish international collaborations
particularly for the chemical analyses for their medicinal values.
Ornamental plant genetic resources
Like the medicinal and spice species genetic resources of ornamental plants in developing countries grow wild in the rainforest habitats, most of which are being destroyed because of massive logging operations. Thousands of ornamental plant species have yet to be discovered, identified and documented.
At present, botanical gardens are the only ex situ sites where ornamental plants are conserved.
In the Countries rich in diversity of ornamental genetic resources there is a need to: closely monitor all living plants, a government policy put in place protecting all ornamental plants frnt policy put in place protecting all ornamental plants from being collected illegally.
In order to provide easy access to these valuable resources for
the 1.500 botanical gardens worldwide this kind of information
should be readily available.
The role of research in the conservation, characterization and utilization of horticultural genetic diversity
In situ conservation
In situ conservation differs from ex situ conservation as it allows plant species to grow in their natural environment and thus allows evolutionary processes, which are the base of genetic diversity and plant adaptability, to continue.
For such a reason, in situ conservation can be considered a dynamic system most suitable to preserve adaptability. It allows the evolution of populations, conserving genetic variability, which continues to originate from mutations and gene flow (pollen and seed exchange within and between populations).
Outside protected areas and national reserves, in situ conservation is carried on at the farm level, particularly in developing countries, where landraces and locally improved material are cultivated, utilized and conserved as parts of traditional farming systems.
On-farm conservation programmes are of particular importance in developing countries in order to maintain local genetic diversity and to provide food for loco maintain local genetic diversity and to provide food for local consumption and local markets, where local livelihoods depend on subsistence farming.
There is, however, increasing interest in promoting on-farm conservation in countries with modern agriculture, such as Europe and North America. For instance the European Union regulation 2078/92 provides financial assistance to farmers for the cultivation and propagation of useful plants adapted to local conditions and threatened by genetic erosion (local cultivars and landraces, etc.) using more traditional, organic and integrated farming systems compatible with the requirements of the protection of the environment and the maintenance of the countryside.
Some scientific approaches have been developed in order to define
priorities for what and where to conserve. One based on a biological
criteria and the other based on a socio-economic criteria.
Fig. 1 Methodological approaches to define in-situ conservation
priorities
Ex situ conservation
Ex situ conservation or static conservation aimed at maintaining, unvaried, plant genetic material, is not subject to the evolutionary processes that occur in natural habitats. The most common types of ex situ conservation are seed gene-banks and field gene-banks.
At present about 6 million accessions are stored in ex situ collections worlion accessions are stored in ex situ collections worldwide. Taking into consideration duplication among collections the estimate of unique accessions is reduced to about 1-2 million.
According to the data available from FAO World Information and Early Warning System (WIEWS) the accessions belonging to the major group of crops present in genebanks comprise cereals 40%, food legumes 15%, vegetables, roots and tubers, and forages 10% each; aromatic, medicinal, spice and ornamental plants are seldom found in ex situ long-term public collections (fig. 2). Generally the latter groups of species are conserved as living collections in the 1,500 botanical gardens around the world. By so doing, botanical gardens fill an important gap in ex situ conservation collections by ensuring the protection of a wide range of horticultural species which otherwise would not receive any particular attention from traditional gene-banks mostly involved in the conservation of food crops.
Ex situ collections are based on the final use of the accession. Base collections are intended for long term conservation. Active collections on the other hand are used for the exchange of genetic material; and breeder's working collections are used primarly for genetic improvement.
Another concept of collection is the core collection, aimed at improving management efficieon, aimed at improving management efficiency and at reducing gene-bank operating costs. This represents for part of an entire collection, with a minimum of repetition, the genetic diversity of a crop species and its wild relatives.
The main functions of a genebank are: the acquisition of germplasm through collecting missions or by introduction from or exchange with other institutions; its conservation, including the preparation of material for storage, monitoring its viability in storage and regeneration of the accessions when needed; the distribution of samples to users; the study of the conserved resources, their characterization and preliminary evaluation; and the documentation of information on the collecting, registration, characterization, evaluation and management of the accessions in the genebank.
The methods used for in situ conservation include seed
genebanks, living genebank (tab. 3) in vitro conservation
and cryo-preservation, pollen storage, conservation of DNA.
Characterization and evaluation
Adequate germplasm conservation and its future efficient utilization require an accurate characterization and evaluation of the material, obtainable through the use of diversity markers.
The minimum data to be recorded for single accessions by genebanks include country of origin, collection site, species name, and local name, the so-called passp site, species name, and local name, the so-called passport data. Extensive guidelines to record this type of data have been published by the International Plant Genetic Resources Institute (IPGRI).
The next step is characterization (phenotypic markers) which corresponds to the recording of those traits which are highly heritable and can be seen by eye and are expressed in all environments.
The last step concerns the evaluation of the agronomic traits which are too genetically complex to be identified by the primary characterization.
Biochemical markers, such as isozyme and storage proteins can increase the number of qualitative markers.
A very detailed characterization of diversity totally independent
from the environment can be obtained with technologies that operate
directly at the DNA level and this is done using molecular markers.
Utilization
The main goal to be achieved by conservation of genetic resources is their present and future utilization for the benefit of mankind.
Some significant results have been obtained by using wild relatives
of domesticated plants in breeding programmes, exploiting the
traits acquired by the co-evolving of wild relatives with pests
and diseases. An example of this is the tomato, in which several
wild species have been used as gene donors: Lycopersicon hirsutum
and L. pimpinellifolium for fungus resistance;
Other examples that underline the importance that wild horticultural
genetic resources may have in breeding programmes are:
= vegetables, where it has been found that wild forms have high
contents of mineral substances, proteins and Vitamin C compared
to cultivated vegetables;
= wild apples collected by USA expeditions (1989-1993) in the
Republic of Kazakhstan, Vavilov's centre of origin for cultivated
apples; in a screening of 1600 seedlings for resistance to apples
scab (Venturia inaequalis (Coske) Wint), cedar apple
rust (Gymnosporangium juniperi-virginianae Schwein),
and fire blight (Erwinia amylovora (Burr) Winslow et
al.) more than 10% of the seedlings were resistant to one or more
of the three diseases.
Documentation and information
The functions that documentation and information provide by means
of a database system include:
providing an accessible inventory of the material held in the
collection;
allowing the determination of the presence of duplication or gaps
in the collection and consequently the planning of further collection
efforts or exchange;
providing a tool for an efficient management of the collection
(monitoring viability, quantity and location of seed, or the location
of stock in field collections);
giving the possibility of choosing the appropriate material to
use in breeding and research programmes;
providing information to coordinate global activity on genetic
resources.
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