Part 1. Centers of Origins of Crop Plants and Agriculture

Back to Vavilov: Why Were Plants Domesticated in Some Areas and Not in Others? - J.G. Hawkes
Vavilov's Theories of Crop Domestication in the Ancient Mediterranean Area - A.A. Filatenko, A. Diederichsen and K. Hammer
Archaeobotanical Evidence for the Beginnings of Agriculture in Southwest Asia - G. Willcox
Syrian Origins of Safflower Production: New Discoveries in the Agrarian Prehistory of the Habur Basin - J. McCorriston

Back to Vavilov: Why Were Plants Domesticated in Some Areas and Not in Others? - J.G. Hawkes

Behind this rather simplistic title of my paper lie a number of problems - some clearly answerable without much difficulty, and others which are not yet answered and perhaps never will be.

We as biologists, ethnologists and geneticists pay tribute to the genius of Nicolay Ivanovich Vavilov - his enormous width of understanding and innovative vision. We may well consider him to be the 'Darwin of the 20th century' with just as enquiring a mind and capacity to recognize the basic similarities between several apparently quite distinct phenomena as Darwin had done in the 19th century.

Whereas Darwin (1868) studied the diversity of all living organisms known to science, Vavilov directed his vision toward domesticated plants just as had Alphonse de Candolle (1882) before him. Clearly, Vavilov's depth of enquiry was much greater than that of de Candolle, to whom he pays tribute.

Vavilov was basically a geneticist and plant breeder, approaching the problems of cultivated plant species in terms of the diversity within and between them that might be put to practical ends. For this reason Vavilov was not particularly interested in diversity as such, but only in the diversity that could be put to practical advantage.

If we consider the world flora, even a quick survey will show us that there are many areas of plant diversity which have little to do with cultivated plant origins. Thus, the 'fynbos' plant formation on the very southernmost tip of South Africa is extremely diverse. In quite a small area one can find hundreds of species in quite distinct genera and even plant families. These are very attractive and colorful but were never brought into cultivation by the indigenous people. They were not at all edible and are known today as beautiful and extraordinary examples of plant evolution. A rather similar flora exists in southern Australia, and again, none of its species was brought into cultivation.

To take other examples, let us consider the vast tropical rainforests of South America, Africa and Asia. These differ from the fynbos in that many plants have been used, perhaps for millennia, for food, medicine, clothing and in some instances building materials. But were any of these domesticated? Perhaps a few, such as cassava, pineapple, peanuts, etc., but these were plants from the drier forest margins, and occurred only in certain regions. Several nuts and fruits were gathered for food. They were gathered, eaten and used in a variety of ways. Again, the vastly rich fruit-tree floras of South East Asia were of immense value to the people of such areas but their actual cultivation is comparatively recent.

Let us look at another example, namely the wild spring bulb flora of the central and southern European mountains. These plant communities are very diverse and extremely beautiful, with their bulbs, annuals, shrubs and trees. Few were eaten by humans - in fact the plants themselves had developed mechanisms to prevent their being eaten, such as poisonous or bitter roots, bulbs, etc. and spiny leaves and branches. None of these was domesticated in ancient times.

Much further north in northern Europe and the steppes of Asia, as well as the northern part of North America and the southern part of South America, the species diversity diminishes very greatly. There are only a few species able to survive, grazed by wild and domesticated cattle, but these are not of direct use to humans as food, only through their horses and cattle.

We thus have a curious paradox; namely, that there is considerable wild plant diversity up to about 45-50°N latitude in Europe, Asia and North America, and southward to 35-40°S latitude in the southern continents, apart from desert and semi-desert areas. However, only in certain areas between 45°N and 30°S latitudes were potential crop plants actually domesticated. This problem was not really solved by Vavilov, or by his predecessor de Candolle and others. Why was only part of the world's plant diversity domesticated?

Vavilov noted that the centers of origin of cultivated plants occurred mostly in mountainous regions between the Tropic of Capricorn (23°28') south of the equator and about 45°N of the equator in the Old World. In the New World crop domestication occurred between the two tropics (Cancer and Capricorn) approximately. In all cases agricultural origins and primitive diversity occurred in high and complex mountain regions. Why only these?

Let us now return to the process of domestication. How did plants become domesticated despite their evolutionary processes to protect them from being eaten by the development of various defensive mechanisms such as poisons, bitter substances, etc.? One strategy of survival adopted by many plants is to produce so many seeds that even if most of them are eaten enough will remain to provide for the next generation. And the plants that do this superbly well are grasses. To a lesser extent those that do this quite well are herbaceous legumes. This, then, may be the solution to the problem of how humans began the process of domestication. Hunter-gatherers took and ate the natural surplus and left enough seeds (probably by chance) to provide for the next generation. Later, when non-shattering mutants occurred by chance, these were adopted automatically by the primitive farmers. From this point evolution under domestication began to take place.

As far as can be seen from the literature, Vavilov did not consider these points in any detail. What he did do - and that superbly well - was to pinpoint the exact areas where crop plant diversity showed us the centers of origin of world crops.

Vavilov considered that “as a rule the primary foci of crop origins were in mountainous regions, characterized by the presence of dominant alleles.” In his work entitled The Phytogeographical Basis for Plant Breeding (Vavilov 1935) he summarizes and pulls together all his previous work on centers of origin and diversity. In this he recognizes eight primary centers, as follows.

I. The Chinese Center - in which he recognizes 138 distinct species of which probably the earlier and most important were cereals, buckwheats and legumes.

II. The Indian Center (including the entire subcontinent) - based originally on rice, millets and legumes, with a total of 117 species.

IIa. The Indo-Malayan Center (including Indonesia, Philippines, etc.) - with root crops (Dioscorea spp., Tacca, etc.) preponderant, also with fruit crops, sugarcane, spices, etc., some 55 species.

III. The Inner Asiatic Center (Tadjikistan, Uzbekistan, etc.) - with wheats, rye and many herbaceous legumes, as well as seed-sown root crops and fruits, some 42 species.

IV. Asia Minor (including Transcaucasia, Iran and Turkmenistan) - with more wheats, rye, oats, seed and forage legumes, fruits, etc., some 83 species.

V. The Mediterranean Center - of more limited importance than the others to the east, but including wheats, barleys, forage plants, vegetables and fruits -especially also spices and ethereal oil plants, some 84 species.

VI. The Abyssinian (now Ethiopian) Center - of lesser importance, mostly a refuge of crops from other regions, especially wheats and barleys, local grains, spices, etc., some 38 species.

VII. The South Mexican and Central American Center - important for maize, Phaseolus and Cucurbitaceous species, with spices, fruits and fibre plants, some 49 species.

VIII. South America Andes region (Bolivia, Peru, Ecuador) - important for potatoes, other root crops, grain crops of the Andes, vegetables, spices and fruits, as well as drugs (cocaine, quinine, tobacco, etc.), some 45 species.

VIIIa. The Chilean Center - only four species - outside the main area of crop domestication, and one of these (Solarium tuberosum) derived from the Andean center in any case. This could hardly be compared with the eight main centers.

VIIIb. Brazilian-Paraguayan Center - again outside the main centers with only 13 species, though Manihot (cassava) and Arachis (peanut) are of considerable importance; others such as pineapple, Hevea rubber, Theobroma cacao were probably domesticated much later.

After this brief survey it seems quite clear that out of the very wide range of plant diversity in the tropical and warm temperate regions of the world our major food crops have come mainly from high mountain valleys, isolated from each other to a large extent and with a very great habitat range. Here people made selections of wheat, barley, oats, rye, potatoes and maize which were eventually cultivated.

These plants were weeds or possessed the syndrome of not being able to compete well with climax vegetation. Hence they grew in areas where nature or humans had reduced competition from other species, were noticed, eaten, resown by chance and eventually became domesticated. Several other weedy plants were never or only temporarily domesticated, remaining as weeds but often hybridizing by chance with the cultivated ones and thus enhancing their diversity.

It seems that the restricted access of the mountain valleys and the wide range of altitudes helped to produce and select the diversity needed for domestication. Similar selection pressures even in unrelated crops produced similar types of adaptation, a process developed by Vavilov into his Law of Homologous Series. Because such adaptation in only partially related crops must surely have been due to mutations on distinct loci in each crop, this writer feels that a more correct title might have been the Law of Analogous Series. However, the phrase has persisted as Homologous Series and we must retain it as just one of the extraordinarily innovative ideas put forward by the great genius, N.I. Vavilov.

Conclusions

In this brief review of the history of plant domestication we can see clearly that it took place mainly in mountainous regions more or less within or near the tropics. It is still difficult to understand why it took place in those regions and nowhere else, when plant diversity elsewhere was so high. While not proposing to give a final answer, I believe the following points are relevant.

First, we can eliminate areas such as the 'fynbos' of South Africa where there was little or no production of starchy seeds or tubers for the people to eat.

Second, we have to consider the vast resources of tropical forests. In these it seems that there were no processes leading to domestication, since abundant food was there to be gathered in the form of fruits, nuts and starchy tubers throughout the year.

Third, we must consider the areas of the southern European plains and mountains with abundant ornamentals, and some seeds and bulbs for gathering, but probably not enough to provide food throughout the year.

Fourth, we have the high mountain areas mainly between the Tropics of Cancer and Capricorn. These areas are seasonal in climate, with a wide range of temperature and rainfall due to differences of altitude and aspect. Here were closed ecological systems of grasses and legumes where mutant forms could thrive and become established. Here also were isolated human communities exerting their own selection pressures for larger seed size, adaptation to drought, humidity and extremes of climate. These were ideal conditions for mutations and selections, especially for large seed size and adaptation to environmental extremes.

Weedy relatives of the crops were also present, adding to the genetic diversity by random mating with the primitive crops themselves. In the crop I know best -potatoes - one can find not only a range of ploidy, from diploid to pentaploid, but clear evidence for crosses between weed species and cultivated ones as well as the natural introduction of frost resistance from wild species into the cultivated ones.

To sum up, it seems clear to me that evolution of domesticates is very much promoted by the factors of varied microclimate, aspect, altitude, restricted habitats and human selection which are all present in the intertropical mountain zones of the Old and New Worlds. Such a wide range of natural and human selection pressures is not available to the same degree of intensity in other world regions. Vavilov was the first investigator to study and understand these systems and to use them as a basis for present and future plant breeding. At the same time, since Vavilov was not only a geneticist and plant breeder, but also a man of wide interests and intelligence, he was able to provide a theoretical background to interpret crop genetic diversity in all its aspects and thus to make it available for the whole world.

References

Darwin, C. 1868. The variation of animals and plants under domestication. London, UK. de Candolle, A. 1882. Origins de Plantes Cultivées. (English edition 1886). Paris, France [in French].

Vavilov, N.I. 1935. Theoretical Basis for Plant Breeding, Vol. 1. Moscow. Origin and Geography of Cultivated Plants. Pages 316-366 in The Phytogeographical Basis for Plant Breeding (D. Love, transl.). Cambridge Univ. Press, Cambridge, UK.

Vavilov's Theories of Crop Domestication in the Ancient Mediterranean Area - A.A. Filatenko, A. Diederichsen and K. Hammer

Introduction

The papers by Nicolay Ivanovich Vavilov, elucidating the origin and geography of cultivated plants, have served as a systematic collection of such work with plants and its presentation to the world in general. The first fundamental paper by Vavilov, Centers of origin of cultivated plants, was dedicated to Alphonse de Candolle, the first person in the history of science to pose questions concerning independent centers of origin (Vavilov 1935). Vavilov's (1920) work on the homologous series was recently re-recognized (Hammer and Schubert 1994) but his work on the centers of origin continues to be discussed (Zhukovsky 1968; Zeven and de Wet 1982; Harris 1990).

Methods used by Vavilov for determining the centers of type-formation (centers of origin) of cultivated plants

For the purpose of establishing the centers of type-formation or the centers of diversity the 'differential phyto-geographical method' was applied (Vavilov 1935). It can be described by the following steps:

1. A strict differentiation of the plants studied into Linnaean species and intraspecific groups by all available means of various disciplines beginning with morphology, agrobotany, phytopathology, cytology and recently by molecular methods.

2. Delimitation of the distribution areas of these plants and, if possible, also of the distribution areas in the remote past when communication and seed exchange were more difficult than at present.

3. A detailed determination of the composition of the varieties and races of each species, and a general system of the genetic variability within the different species.

4. Establishment of the distribution of the genetic variability of the forms of a given species as far as regions and areas are concerned, and the establishment of the geographical centers where these varieties are now accumulated. Regions of maximum diversity, usually also including a number of endemic types and characteristics, can also be centers of type-formation.

5. For a more exact definition of the center of origin and type-formation it is necessary to establish the geographical centers of concentrations of species that are botanically closely related as well.

6. Finally, the establishment of the areas of diversity of wild subspecies and species that are closely related to the cultivated species in question should be used for amendment and addition to the area defined as area of origin, when the differential method for studying races is applied to them.

Vavilov's original concepts

In 1940 Vavilov stated that the method of differential taxonomy offers an opportunity to trace the dispersal of many cultivated plants. It demonstrates their stages of evolution with respect to both the initial origin and their introduction into cultivation within different areas. It shows their relation to wild subspecies and species, but also demonstrates the subsequent evolution under domestication of these plants when dispersed from the basic centers and undergoing changes under new conditions and the further effects of natural and artificial selection.

The studies of the origin of different cultivated plants led Vavilov to the establishment of new concepts, i.e. primary and more ancient crops in contrast to secondary ones, allowing him to characterize with good precision the centers where agriculture originated and the pathways along which it was dispersed.

The study of the laws of the geographical distribution of plant resources on earth and the establishment of the enormous infraspecific diversity of the majority of crops allowed not only a determination of their localization but also offered an opportunity to ascertain the period of origin of the plants most important for cultivation. In 1924 Vavilov wrote: “The history and origin of human civilizations and agriculture are, no doubt, much older than what any ancient documentation in the form of objects, inscriptions and bas-reliefs reveals to us. A more intimate knowledge of cultivated plants and their differentiation into geographical groups helps us attribute their origin to very remote epochs, where 5000 to 10,000 years represent but a short moment” (Vavilov 1992).

The number of centers listed in Vavilov's papers increased dramatically during a comparatively short period from three in 1924 to five during 1926, six in 1929, seven in 1931 and eight in 1935, but was again reduced to seven in 1940. Each publication appeared to be the result of consideration of additional data (Vavilov 1924, 1929, 1931, 1932, 1935, 1938, 1940).

In 1932, Vavilov wrote: “Many historical problems can be understood only because of the interaction between man, animals and plants.” Centers differ with respect to the concentration of specific variation. Vavilov attached great importance to data indicating regions of major concentration of specific and generic variation. During the arrangement of these regions according to the richness of cultivated floras, the Chinese center was put in first place and the Hindustani one in second (Vavilov 1934). More recent data (1940) led to the necessity for changing these places: 33% of all cultivated plant species are to be found concentrated in the southern Asiatic tropical center, which at Vavilov's time nourished up to one-fourth (now one-third) of the population of the world. In eastern Asia, the second most important center, 20% of the number of species of cultivated plants are grown. As far as the number of species introduced into cultivation is concerned, southwestern Asia follows with 14%. However, Vavilov attached a particular importance to that center since the composition of what is cultivated in the territory of Russia is a consequence of the influence from Asia in general and specifically from Asia Minor in a wide sense and Inner Asia. He determined the boundaries of that center.

In the papers published in 1934 and 1935, the division of southwestern Asia into two centers is suggested: the Middle Asian one and one covering Asia Minor. In 1937, the Middle Asian center was renamed the Inner Asian one. It belongs to one of the five major regions where cultivated plants originated in Asia and includes northwestern India, Afghanistan and the mountainous parts of Turkistan (Uzbekistan, Tajikstan and a part of Turkmenistan). This name, however, does not agree with the centers of origin or with their subdivision in Vavilov's later papers. Its appearance is explained by the fact that during that period and until recently, the exact spatial-geographical borders of Inner Asia had not been clearly outlined (Grach 1984).

After rejecting the division of the southwestern Asiatic center, Vavilov (1938, 1940) discussed the composition of the complex of species formed by cultivated plants within the territory in question. He refers to the close relationship between Cis-Caucasus and Asia Minor: “An enormous potential of species and even of genera is concentrated there, constituting genetically distinct units” (Vavilov 1938). In addition to quantitative characteristics, Vavilov concentrated his attention on the specific composition of cultivated plants for each of which endemic genera, species and even forms occurred.

Vavilov used equally the terms 'center', 'focus' and also 'area' of origin. Their definition is important: the geographical centers are basic and independent foci where agricultural crops originated but are also geographic areas where cultivated plants are grown. Passing from one of Vavilov's papers to another concerning the problem of the origin of cultivated plants, it is possible to conclude that the terms 'center' and 'focus' are mainly associated with large territories. In his last papers, he writes about 'areas of basic origin of cultivated plants' and about the conventional concept of 'center of origin' such as suggested by Darwin.

Summing up the data concerning the hundreds of cultivated plants from all over the world resulting from the systematic collection by the All-Union Institute of Plant Industry (VIR), Vavilov wrote in 1935: “We can now speak with a considerably greater accuracy than dreamed of ten years ago about the eight ancient and basic centers of agriculture in the world, or, more accurately about the eight independent areas where plants were initially taken into cultivation.”

E.N. Sinskaya's approach

After Vavilov's untimely death in Saratov in 1943, Sinskaya continued his work concerning the establishment of borders for the centers of cultivated plants and for the specification of the relationship between the centers (areas).

Sinskaya noted that several amendments can be made to Vavilov's theories concerning the centers of origin of cultivated plants but they amount only to a correction of details. “The basic composition of cultivated plants, typical of this or that center, remains stable” (Sinskaya 1966).

As far as the historical character of Vavilov's works toward the establishment of the centers of agricultural crops is concerned, Sinskaya calls our attention to the prevalent use of the expressions “historical-geographical area” or “geographical areas of the historic development of a cultivated flora” which appear regularly in Vavilov's papers from 1924 to 1940 (see also Karpyceva and Sokolova 1987).

Sinskaya elaborated a more detailed approach to the analysis of the cultivated plants in their centers of origin. This approach is based on a differentiated characterization of the endemism the various taxa have in a given area which are divided into the following categories:

· genera originating from the area

· genera having one of their centers of origin or their most important secondary center of origin in the given area

· species strictly endemic for the given area

· species endemic to the given area, but having their first origin in another area

· species having one of their centres of origin or their most important secondary centre of origin in the given area.

The development of important genera (such as Triticum, Secale, Hordeum, Beta, Brassica, Daucus, Lens, Linum, Olea, Mandragora, Pisum, Melilotus and many others), which include the major proportion of all crops, forms the basis for agricultural production in countries around the Mediterranean, but most of them are intensively grown in Asia as well as in Southwest Asia. Phytogeographical studies have revealed that compared with the areas of Africa south of the Mediterranean, there is a characteristic cultivated flora that is not less rich than those in other centers where agriculture arose. Many cultivated plants have undergone very old but secondary development there, e.g. in Ethiopia.

While further developing Vavilov's ideas about the centers of origin, Sinskaya (1966) singled out the African region for the historic development of cultivated flora. Ancient Mediterranean elements (actually both Mediterranean and Southwest Asiatic ones) predominated in the composition of the cultivated flora of Ethiopia but are not sharply delimited from those of other African areas. Elements from South Asia also occur there.

This area is rather an area of introduction than of distribution of cultivated plants to other places. Sinskaya (1966, 1969) calls such territories “dependent areas”, to which belong not only Ethiopia, but also North America, where agriculture developed on the basis of Mexican and Central American crops and, later on, that of crops from the Old World. In central and northern Europe, on the Russian steppes and in Siberia, agriculture is based primarily also on cultivated plants, introduced from the subareas Southwest Asia and Mediterranean, etc. The agriculture of the “dependent areas” underwent a certain period of development and, therefore, is not limited, judging by the large quantity of plants introduced into cultivation from less rich, wild flora of these territories.

During his work on the question of the origin of cultivated plants Vavilov himself only once used the term 'gene-center'. It was for his lecture at the International Congress of Genetics at Berlin in 1927. This term, however, is often used today possibly because it is easy to pronounce. Nevertheless the name 'gene-center' is quite abstract which subsequently gave rise to several misunderstandings of the theory of the centers of origin of cultivated plants. The botanical investigations concerning the centers of origin still continue and the collections gathered are being thoroughly studied at VIR.

Table 1. Geographical areas of historical development of cultivated flora (after Sinskaya 1966, 1969).

Basic areas of origin	Subareas
I. Ancient Mediterranean	Southwest Asia 1a. Anterior Asia (Transcaucasus, Asia Minor, Near East, West Iran) 1b. Middle Asia (Turkistan, Afghanistan, East Iran, North West India, Pakistan) Mediterranean
II. East Asia	Northeast Asia (Japan, Manchuria) Southeast and Central China
III. South Asia	South China, India and Sri Lanka Malesian
IV. Africa
V. New World	Central America South America

The origin of cultivated plants, in particular of wheats (Triticum L.)

Vavilov referred emphatically to the division of the globe into floristic regions and subregions such as those accepted by conventional phytogeography for elaborating the geographic origin of cultivated plants.

The origin of cultivated wheat is located in the Ancient Mediterranean (syn.=Old Mediterranean) which includes, according to Vavilov's last paper (1940), the Mediterranean region and Southwest Asia. The latter was divided by Vavilov (1935) into Asia Minor in a broader sense and Inner Asia. Sinskaya (1966, 1969) considers these territories as subareas of the Ancient Mediterranean (Tables 1, 2). Many species, genera and families which were responsible for the development of cultivated plants originated from these subareas. Nevertheless, every subarea has its characteristics due to the ecological conditions and the richness of the flora of wild and cultivated plants as well as to the ancient history of agriculture. The area of origin of wheat is Southwest Asia. The greatest amount of endemic species and a huge amount of different intraspecific taxa is found there. The greater the distance from this primary area of origin, the less diversity of the species is observed.

From 26 species of the genus Triticum the following species are found in Anterior Asia and are endemic wild plants: T. urartu, T. araraticum and T. dicoccoides. Endemic cultivated plants are: T. timopheevii, T. zhukovskyi, T. carthlicum, T. karamyschevii, T. ispahanicum, T. macha, T. vavilovii and T. sinskajae. Triticum turanicum and the wild einkorn T. boeoticum mainly occur there. Sinskaya (1969) considers T. sphaerococcum a further species, which occurs in northwest India, as an endemic species (Table 2).

A second group of Southwest Asian wheat originated in the Near East subarea but then spread to other areas. They were later replaced, at the beginning of the century, by higher-yielding species and therefore can only be found as relics isolated from each other. They are: Triticum monococcum, T. dicoccum, T. aethiopicum and T. spelta (Sinskaya 1969; Padulosi et al. 1996). These species, which are at present to be found in areas far away from each other, were more intensively developed in other subareas of the Ancient Mediterranean. Triticum aestivum and T. compactum were intensively developed in Middle Asia and subsequently spread all over the world. Triticum durum and T. turgidum developed in the more central and western parts of the Ancient Mediterranean, particularly close to the sea coast. East of this area of origin, on the other hand, the process of formation of the further wheat varieties is not observed. A.M. Gorskyi during his expedition to Sinkiang (Western China) found a new endemic wheat named T. petropavlovskyi (Dorofeev et al. 1979). Vavilov had completed the investigation of Sinkiang in 1929 and regarded this western part of China as one of the geographically most isolated peripheral sites of Triticum.

Fig. 1. Geographical regions of development of cultivated flora. Adapted from Sinskaya (1969).

Table 2. Distribution of the species of wheat in the Ancient Mediterranean area of origin of cultivated plants (after Dorofeev et al. 1979).

Subarea			Dependent area
Mediterranean †(147)	Southwest Asia		Ethiopia (250)‡
	Anterior Asia (412)	Middle Asia (260)
T. boeoticum (16)§	T. boeoticum (57) T. urartu (6) T. araraticum (13) T. dicoccoides (25)
T. monococcum (13)	T. monococcum (14) T. sinskajae (1)
T. dicoccum (7)	T. dicoccum (15) T. ispahanicum (2) T. karamyschevii (3) T. timopheevii (4) T. militinae (2) T. zhukovskyi (1) T. macha (14) T. vavilovii (7)		T. dicoccum (8)§
T. spelta (14)	T. spelta (14)	T. spelta (19)
T. durum (80)	T. durum (75)	T. durum (8)
T. turanicum (4)	T. turanicum (34)	T. turanicum (7)
T. turgidum (34)	T. turgidum (54) T. carthlicum (18)	T. turgidum (3) T. jakubzineri (1)
T. polonicum (11)	T. polonicum (14) T. sphaerococcum (17)	T. polonicum (3)	T. polonicum (6)
T. compactum (13)	T. compactum (40)	T. compactum (64)
T. aestivum (25)	T. aestivum (59)	T. aestivum (142) T. petropavlovskyi (4)	T. aestivum (33) T. aethiopicum (203)

Number of taxa which occur in the given subarea: ^† number of botanical varieties per area;^§ number of botanical varieties per species.

^‡ Species of wheat, e.g. Ancient Mediterranean elements of northeast African flora.

		Subarea
		Mediterranean	Southwest Asia		Dependent area
			Anterior Asia	Middle Asia	Ethiopia‡
Hordeum vulgare†
	subsp. vulgare	14/3	7	21/3	38/8
	subsp. distichon	10/1	18/2	7	38/20
Pisum§
	P. formosum	-	1	-	-
	P. fulvum	1	1	-	-
	P. sativum	8	7	9	-
	subsp. abyssinicum	-	-	-	1
Beta vulgaris¶		9	5	5	-
Lens††		63/3	-	54/9	2/2

Species of different crops, e.g. Ancient Mediterranean elements of northeast African flora. Number of varieties: ^† Lukjanova et al. 1990; ^‡ total/endemic varieties;^§ Makasheva 1973; ^¶ Krasochkin 1960; ^†† Barulina 1930.

Other crops

The diversity of barley (Hordeum vulgare) is more evenly spread across the Ancient Mediterranean area and several infraspecific taxa are endemic to Ethiopia (see Table 3). The botanical varieties of the genus Pisum are also more or less evenly spread in the Ancient Mediterranean area of origin (Table 3).

Several monographs dealing with many different crops have been published by the VIR. Such work is important not only for studies on centers of origin of cultivated plants but also for theoretical and practical agronomy. Such work is the basis for searching for initial material for plant breeding. These monographs are based on: (1) previous publications, (2) a thorough investigation of the accessions of the collection which were not included in previous work, and (3) data obtained through new experimental methods, e.g. physiological, phytopathological, genetical, molecular and other research. But all research done to study plants can only produce useful results if the botanical identification of the material is carried out at the intraspecific level. This rule being basic for scientific work in this field, however, is often neglected.

Taxonomic studies in the tradition of Vavilov, based on the investigation of variation within a species, have also been carried out in Gatersleben (e.g. Mansfeld 1950, 1951; Hanelt 1972; Gladis and Hammer 1992; see Hammer et al. 1994).

Recently information on coriander has been provided by Diederichsen (1996). The detailed investigation of the variation of the species Coriandrum sativum by several characters caused the author to divide this species into several groups (so far called ecological types), which are connected with the geographical origin in the Ancient Mediterranean area.

The infraspecific classification (Hanelt 1986; Hanelt and Hammer 1995) helps to indicate areas where different types of a given species are to be found. It also is an excellent method to single out and preserve rare accessions in a collection. However in the case of wheat a very interesting group - T. durum convar. villosum - collected by Vavilov in Syria, Jordan and Lebanon is untraceable in the collection at VIR. It was an extremely xerophytic type with a very hairy ear and similar leaves. A herbarium specimen of it exists at VIR but even that is threatened.

The extinction of durum wheat without ligula (T. durum convar. aglossicon Flaksb.) from Cyprus was prevented. In its area of origin on Cyprus this type is already extinct. In bulk populations of wheat accessions single plants of this type occurred. Such plants were singled out and received their own number in the VIR catalogue.

In the 1960s and 1970s the landraces collected by VIR staff in the Caucasus comprised more than ten botanical varieties. Of these only one or two are still part of the VIR collection. The VIR collection of Ethiopian wheats has also lost many varieties. Every botanical variety has to be preserved as a single accession, if the original landrace, which contained several varieties, is not reproduced under the conditions which are similar to its natural area of origin (Hammer 1992).

The taxonomical category 'varietas' was introduced by Fr. Alefeld (1866) and Fr. Körnicke (1885) for crop plants and is based on the differentiation by distinct characters. This category makes it possible to orientate quickly and properly in the diversity of a given area. At the same time such classification delivers clear information for the given species with respect to the Law of Homologous Series in variation (Vavilov 1920; Sinskaya 1964).

The basic taxonomical category, however, is the species. For geobotanical investigations in wild plants the use of more detailed categories, i.e. infraspecific taxa, is not essential. In the early days researchers concentrated on the level of the genera; later the species level was elaborated. At present taxonomists of cultivated plants should focus on the infraspecific level.

The taxonomical classification of cultivated plants depends on the methods on which it is based, and the attention which was paid to a given species. In general the economic relevance of a species favors scientific interest.

The classification of wheats

As early as 1935 Vavilov stated that “a basic handicap of all genetic investigation in wheat, as well as in other plants, is the accidental choice of the material... and the neglect of the wide range of geographical variation.”

For crops, which have a short history of domestication, the characterization of a cultivar can be as general as for the botanical species. Wheat has been the basic element of food for humans for 10,000 years, and is to be found nearly all over the world. The resulting range of variation of wheat, as evident from Table 4, is astonishing. The formation of new infraspecific varieties is a continuous process during cultivation of the species. The modern techniques used in plant breeding of today never led to formation of such varieties. The latest systematical overview for wheat was finished in 1979 (Table 4), and it differs from the system established by Flaksberger in 1935 (Table 5). In particular, the latest system was cleared of contradictions and inconsistencies. The first successful approach to such a classification of wheat was done by Flaksberger in 1915. The system proposed by Percival (1921) does not differ very much from the latter. The ideas about the infraspecific differentiation of the species T. aestivum were very much changed owing to the expeditions of Vavilov to Central Asia, Iran, Afghanistan and India.

Table 4. Taxa in the genus Triticum (according to Dorofeev et al. 1979).

Species	Subsp.	Convar.	Subconvar.	Var.	Forms	Ecological groups
T. aestivum	2	3	4	194	15	23
T. aethiopicum	3	5	-	203
T. araraticum	2	-	-	13
T. boeoticum	2	-	-	61
T. carthlicum	-	-	-	18	3
T. compactum	2	3	4	96	2	9
T. dicoccoides	-	3	-	25
T. dicoccon	4	4	-	64	2
T. durum	2	6	3	120	30	12
T. ispahanicum	-	-	-	2
T. jakubzineri	-	-	-	1
T. karamyschevii	-	-	-	2
T. macha	-	2	2	14
T. monococcum	-	-	-	14	6	7
T. petropavlovskyi	-	-	-	4
T. polonicum	2	2	-	41	1	3
T. sinskajae	-	-	-	1
T. spelta	2	2	-	55	-	2
T. sphaerococcum	-	-	-	17
T. timopheevii	-	-	-	4
T. turanicum	-	-	-	20	-	2
T. turgidum	-	2	-	71	-	5
T. urartu	-	-	-	6
T. vavilovii	-	-	-	7
T. zhukovskyi	-	-	-	1
Total = 25	21	32	13	1054	59	63

Table 5. Taxa in the genus Triticum (according to Flaksberger 1935).

Species	Subsp.	Proles	Sub-proles	Groups	Greges	Var.	Forms
T. aestivum (T. vulgare)	2	15	5	5	25	128
T. carthlicum						10	2
T. compactum	2	3	1	1	21	68
T. dicoccoides	2	3				25	22
T. dicoccon	5	6	3		4	65	8
T. durum	2	21	10	11	35	131	15
T. macha				2		8
T. monococcum		3			11	2	11
T. polonicum	2				9	24
T. spelta		2			9	3
T. sphaerococcum						6
T. spontaneum	2					23	46
T. timopheevii						2
T. turgidum		2	5			19	138
Total = 14	19	58	19	19	133	633	104

The enormous diversity of wheat in Southwest Asia caused Vavilov to revise the value of the investigated characters of wheat for systematics. He noted that the endemic wheats are characterized by complexes of traits, which themselves are connected with distinct areas.

The endemic forms of Pamir Mountains, for example, can be distinguished by eligulatum forms and forms with more or less inflated ears. The characters themselves are connected with each other. By studying variability in wheat, Vavilov determined the hierarchy of characters according to their taxonomic value.

In the species T. aestivum there is a complex of characters connected with difficult threshing and stiff ears. These traits are always accompanied by several others: rough stalks and ears, xerophytic type. Such wheat is typical of southwestern Asia [subsp. hadropyrum (Flaksb.) Tzvel.]. Types with easy threshing ability, on the other hand, are peculiar to Europe and areas of less continental climate of Asia (subsp. indoeuropaeum Vav.). These are the two main geographical groups of wheat, which can be distinguished. Vavilov and Flaksberger (1935) regarded them as subspecies, using different names for them.

The study of the variation led to a more detailed insight, and allowed complete description of the geographical-botanical structure by an ecogeographical system of classification. This system also uses the more detailed taxonomical unit 'varietas'. The necessity to use more detailed taxonomical units was stressed by Sinskaja (1966), Hawkes (1970), Skvortsov (1971) and others.

The results of such a classification for T. aestivum are shown in Box 1. The Asian subspecies (subsp. hadropyrum) contains three groups of different geographical origin.

After the analysis of the European subspecies (subsp. aestivum) as well as the Asian subspecies (subsp. hadropyrum) it became obvious that the awned varieties of T. aestivum mostly belong to the semi-rough-eared type of wheat.

Box 1 shows that the Asian subspecies is of greater polymorphism. In particular, Middle Asia is a subarea of intense evolution of different types of T. aestivum. The subspecies aestivum is younger. Not consisting of so many ecogeographical groups, it is, nevertheless, characterized by very contrasting ecological groups. Length of the vegetative period, winter hardiness, resistance to diseases and other characters vary to a great extent. This subspecies covers a greater area, and stretches all over the European continent. The European subspecies has been affected by different types of ecological conditions, by different types of agriculture and by modern plant breeding.

Places with a long tradition of wheat cultivation, resulting in special ecogeographical types, could be singled out. At present these landraces are to a great extent used as basic material in plant breeding.

Triticum compactum, having much in common with bread wheat (T. aestivum), was widely cultivated in the past and concurrently developed in environments similar to those of bread wheat; thus it repeats the polymorphism of bread wheat (Box 2).

Box 1. Infraspecific classification of Triticum aestivum L.

Box 2. Infraspecific classification of Triticum compactum Host

Reduction of the area of distribution of T. compactum, which took place in the remote past, and restriction of cultivation of this wheat mainly to mountainous zones led to elimination of sharply contrasting groups. No distinct isolation of subspecies is observed within this species. Flaksberger (1935) supposed that the process of differentiation in T. compactum had stopped in those distant historical times when cultivation of this wheat started to be replaced by more productive bread wheat.

The system of infraspecific classification of T. durum is completely different. This wheat species is, after T. aestivum, the species with the widest range of geographic distribution (Box 3). Virtually different is the differentiation pattern of the second most important wheat species in terms of distribution, T. durum (Box 3). There is no complicated branching structure like the one observed in bread or compact wheats. The area of durum wheat stretches along the Old Mediterranean from west to east.

Durum wheat has no distinctly isolated ecological groups. The most definite are morphological differences in khoranka wheats (subsp. horanicum), which are characterized by a certain genetic isolation (in crosses with proper durum wheat, anomalies and sterility of the progeny may be observed). This feature preconditioned their separation into a subspecies of T. durum, known as subsp. horanicum Vav. Basically durum wheat is united by the presence of numerous common traits having similar manifestations along the whole stretched area of its distribution. However, separate distinct features and their sets have a local character, i.e. they are geographically attributed: isolation of groups regulated by selection took place long ago. To describe such type of infraspecific structural subunits the taxon of 'convarietas' (group of varieties) was used. The intraspecific classification of other wheat species (T. aethiopicum, T. turgidum and T. polonicum) is less complicated and the number of botanical varieties is limited (Boxes 4 and 5). Owing to the indiscrete continuity of evolutionary processes there are almost always transitional forms (most easily preserved by humans in the case of self-pollinators).

Box 3. Infraspecific classification of Triticum durum Desf.

Box 4. Infraspecific classification of Triticum aethiopicum Jakubz.

Box 5. Infraspecific classification of Triticum turgidum L. and Triticum polonicum L.

Conclusions

For the identification and preservation of the global crop genetic diversity it is necessary to:

· develop infraspecific classifications for all crops with a relevant variation

· make inventories of genebank collections according to the most detailed and reliable classification available

· work out a unified system of classification units with due respect to the specific features of cultivated plants (at the present stage it would be sufficient to use the system presented by the International Code of Botanical Nomenclature)

· make the ecogeographic zoning of the earth more precise by defining boundaries of regions, subregions, areas of influence, etc., and accomplish detailed inventories of cultivated plant diversity in these territories.

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Archaeobotanical Evidence for the Beginnings of Agriculture in Southwest Asia - G. Willcox

Introduction

Over the past ten years much new evidence has to come to light which has enabled us to explain in more detail the transition from plant-gathering to plant production in Southwest Asia. It is now clear that this important change, which led ultimately to a significant increase in population, urbanism in Mesopotamia and Egypt, the civilizations of Greece and Rome and eventually industrialization, occurred gradually over a long period in a geographically wide area. Over 30 sites have provided a corpus of botanical evidence for the plants used during this period. These plant remains themselves have provided several hundred radiocarbon dates.

Archaeobotanical evidence indicates that the process of domestication may have been slow (Willcox 1995), and finds indicate that domestic and wild cereals occurred as mixtures on several early Neolithic sites over a period of at least a millennium (Table 1). Archaeobotanical finds and field studies show clearly that late Epipalaeolithic and early Neolithic distributions of wild cereals were much more extensive (Hillman 1996) and that the cereals collected differed on the various sites according to variations in local conditions which favored certain cereals (barley on poor dry soils, for example). These differences can be seen prior to and just after cultivation began. But once cultivation became systematic, favorable soils would have been chosen as would preferred crops. For example, emmer became more widespread at the expense of einkorn. Sites geographically separated with long sequences appear to show gradual evolution toward domestication, which may have occurred independently.

Methods

Archaeobotanical samples have been obtained from 35 sites (see Fig. 1) in southwestern Asia from the crucial period 20,000 to 8500 BP (non-calibrated). The quantity and quality of the archaeobotanical information vary considerably between sites. Because biological decomposition is rapid in the aerobic archaeological sediments of this area, archaeobotanists rely on plant materials which have been rendered stable through charring in hearths or other fires. These remains are recovered by flotation and sieving. Under the best circumstances large-scale flotation has obtained thousands of charred seeds, fruits and fragments of charcoal within the chronological framework of a site. At worst no sampling was carried out or only a few chance finds were collected. This makes comparisons between certain sites difficult.

Concerning the archaeobotanical criteria for morphological domestication and cultivation, not all archaeobotanists agree on the best criteria. The solid rachides in barley and naked wheats are clear indicators for archaeobotanists. However, the more primitive hulled wheats such as einkorn and emmer are more problematical. For the archaeobotanist the distinction between domestic and wild hulled wheats is based on the disarticulation scar left by the abscission layer. The break occurs in the same place on the rachis, and on domestic modern material it is rough or torn and on wild material it is smooth. However, with ancient carbonized remains the surface is very often too poorly preserved to allow this distinction.

Grain size is another criterion used, because domestic grains are generally more plump (van Zeist and Roller 1994). Plump barley grains, unknown in the wild, occur with fragile rachis fragments on a number of sites, e.g. at D'jade, Mureybit and Jerf el Ahmar. These are not considered to be evidence of domestication. However there is some reason to reconsider these finds in the light of modern semi-solid rachis barley which occurs in Syria. The author has collected specimens of semi-solid rachis, two-row 'black' barley near Bosra in southern Syria. The disarticulation scar is similar to that of wild barley, and the rachis fragments would be difficult to distinguish from wild types in carbonized material. This morphological type could explain why domestic-type grains occur with apparent wild-type rachis fragments.

As for evidence for cultivation, one might expect digging tools to provide the answer. However, for the moment this is not the case and it is possible that these tools were wooden and have not survived. Archaeobotanical research has concentrated on the presence of weed assemblages (Hillman et al. 1989; Colledge 1994). At present there are no solid results but sites with wild cereals are sometimes accompanied by an assemblage which resembles that of a weed flora. The most common taxa in these assemblages include the following: Adonis, Aegilops, Astragalus, Avena, Bromus, Bupleurum, Camelina, Centaurea, Centranthus, Coronilla, Fumaria, Galium, Glaucium, Hordeum, Lathyrus, Lithospernum, Lolium, Malva, Papaver, Polygonum, Reseda, Silene, Valerianella and Vicia. It is difficult to be sure that these taxa really represent a weed assemblage because these plants make up part of the original steppe flora, and identification at the species level is rarely possible. On the other hand, what one might expect is an increase in the frequency of these taxa at the expense of other steppe plants which were not preadapted to become part of the weed flora.

Archaeobotanical results

A summary of archaeobotanical results is given in Table 1. Several late Palaeolithic hunter-gatherer cultures have been recognized in Southwest Asia for the period 20,000-12,000 BP. Archaeobotanical evidence from this period is sparse because hunter-gatherers are mobile and thus archaeological deposits are superficial, which does not favor survival of carbonized plant remains. The early part of this period coincides with the glacial maximum in Europe. High-altitude pollen sites in Turkey and Iran indicate steppe conditions. Further south near the Mediterranean, conditions were more favorable. The earliest evidence for grain exploitation comes from widely separated sites: Ohalo II (Kislev et al. 1992) near the sea of Galilee, dated to 19,000 BP, is the earliest find (wild pulses, emmer and barley) and corresponds to the glacial maximum. Wild grasses were recovered from Wadi el-Jilat 6 (a little later in date) in the Jordan steppe. At Franchthi cave in Greece, dated to 12,500 BP, wild barley and pulses were found (Hansen 1991). These sites are all that has been found of what was probably a widespread phenomenon. It is probable that these hunter-gatherers roamed widely in the region. Wild cereals and pulses would have become more and more abundant during the late glacial climatic amelioration. Groundstone tools, originally used perhaps for ochre, may have been adapted for cereal processing.

Table 1. Presence of the major cereals, pulses and tree species from sites in the eastern Mediterranean (adapted from Nesbitt and Samuel 1996). There is considerable chronological overlap between sites, particularly for the later periods. Note that lentils are very frequent; domestication appears over a wide area during the last half of the 10th millennium BP. Oak is also well represented.

Site	Date BP non-cal.	Einkorn w†	emmer w†	barley w†	einkorn d†	emmer d†	naked wheat d†	barley 2r d†	barley 6r d†	Aegilops w†	lentil ?†	pea ?†	bitter vetch ?†	oak w†	almond w†	Pistacia w†	flax ?†	Reference
Ohalo II	19,000	-	O‡	O	-	-	-	-	-	-	O	-	-	A‡	O	O	-	Kislev et al. 1992
Franchthi	12,400-9000	-	-	O	-	-	-	-	-	-	O	O	O	-	O	O	-	Hansen 1991
Hayonim	12,300-11,900	-	-	O	-	-	-	-	-	-	O	-	O	-	-	-	-	Hopf and Bar Yosef 1987
Wadi Hammeh 27	12,200-11,900	-	-	O	-	-	-	-	-	-	O	-	-	W‡	-	O	-	Willcox 1991 a; Colledge 1994
Abu Hureyra 1	11,000-10,000	O	-	O	-	-	-	-	-	-	O	-	O	W	W	O	-	Hillman et al. 1989
Hallan Çemi	10,600-9900	-	-	-	-	-	-	-	-	-	O	-	O	-	O	O	-	Rosenberg et al. 1995
Mureybit I-III	10,200-9500	O	-	O	-	-	-	-	-	-	O	-	-	W	-	O	-	van Zeist & Bakker-Heeres 1984
Qermez Dere	10,100-9700	-	-	O	-	-	-	-	-	-	O	-	O	-	-	O	-	Nesbitt 1995
Netiv Hagdud	10,000-9400	-	-	O	-	-	-	-	-	-	O	-	-	-	-	-	-	Bar-Yosef et al. 1991
Jerf el Ahmar	9800-9700	O	-	O	-	-	-	-	-	O	O	O	O	W	O	O	-	Willcox 1996
M'lefaat	9800-9600	?‡	-	O	-	-	-	-	-	O	O	-	O	-	-	O	-	Nesbitt 1995
Tell Aswad la	9700-9600	-	-	O	-	?	-	?	-	-	O	O	O	-	O	O	-	van Zeist & Bakker-Heeres 1984
D'jade	9600-9000	O	-	O	-	?	-	-	-	O	O	O	O	W	O	O	-	Willcox 1996
Cayönü mr	9500-9200	?	?	-	-	-	-	-	-	-	O	-	-	W	O	O	-	van Zeist and de Roller 1994
Jericho PPNA	9500-9000	-	-	?	?	?	-	?	-	-	O	-	-	-	O	O	-	Hopf 1983
Mureybit IV	9400-8500	O	-	O	-	-	-	-	-	-	O	-	-	W	-	O	-	van Zeist & Bakker-Heeres 1984
Cafer Höyük XIII-X	9400-9000	O	O	-	O	O	-	-	-	-	O	O	O	W	O	O	-	Willcox 1991c; de Moulins 1993
Tell Aswad Ib	9300-8800	-	-	O	-	O	-	?	-	-	O	O	-	-	-	O	-	van Zeist & Bakker-Heeres 1984
Cayönü gp bp ch	9200-8500	O	O	?	O	O	-	?	-	-	O	O	O	W	O	O	O	van Zeist and de Roller 1994
Nevali Cori	9200	-	-	?	O	-	-	-	-	O	O	O	O	-	O	O	-	Pasternak 1995
Ain Ghazal	9000-8500	-	-	-	-	O	-	O	-	-	O	O	-	W	-	O	O	Rollefson et al. 1985
Jericho PPNB	9000-8500	-	-	O	O	O	-	O	-	-	O	O	-	-	-	-	O	Hopf 1983
Cafer Höyük IX-VI	9000-8400	O	-	-	-	O	-	-	-	-	O	-	-	W	W	O	-	de Moulins 1993
Nahal Hemar	9000-8200	-	-	-	-	O	-	O	-	-	O	-