Daniel Zohary

Distribution of wild wheats and barley.

If we accept the evidence at face value, we are led to conclude that emmer was probably domesticated in the upper Jordan watershed and that einkorn was domesticated in southeast Turkey. Barley could have been domesticated almost anywhere within the arc bordering the fertile crescent. All three cereals may well have been harvested in the wild state throughout their regions of adaptation long before actual farming began. The primary habitats for barley, however, are not the same as those for the wheats. Wild barley is more xerophytic and extends farther downslope and into the steppes and deserts along the wadis. It seems likely that, while all three early cereals were domesticated within an are flanking the fertile crescent, each was domesticated in a different subregion of the zone. Lest anyone should be led to think the problem is solved, we wish to close with a caveat. Domestication may not have taken place where the wild cereals were most abundant. Why should anyone cultivate a cereal where natural stands are as dense as a cultivated field? If wild cereal grasses can be harvested in unlimited quantities, why should anyone bother to till the soil and plant the seed? We suspect that we shall find, when the full story is unfolded, that here and there harvesting of wild cereals lingered on long after some people had learned to farm, and that farming itself may have orig inated in areas adjacent to, rather than in, the regions of greatest abundance of wild cereals. We need far more specific information on the climate during incipient domestication and many more carefully conducted excavations of sites in the appropriate time range. The problem is far from solved, but some knowledge of the present distribution of the wild forms should be helpful.

Beginnings of Fruit Growing in the Old World

The article reviews the available information on the start of fruit tree cultivation in the Old World. On the basis of (i) evaluation of the available archeological remains and (ii) examination of the wild relatives of the cultivated crops, it was concluded that olive, grape, date, and fig were the first important horticultural additions to the Mediterranean grain agriculture. They were most likely domesticated in the Near East in protohistoric time (fourth and third millennia B.C.) and they emerge as important food elements in the early Bronze Age. Domestication of all four fruit trees was based on a shift from sexual reproduction (in the wild) to vegetative propagation of clones (under domestication). Olive, grape, date, and fig can be vegetatively propagated by simple techniques (cuttings, basal knobs, suckers) and were thus preadapted for domestication early in the development of agriculture. The shift to clonal propagation placed serious limitations on selection and on fruit set under cultivation. We have examined the consequences of this shift in terms of the genetic makeup of the cultivars and traced the various countermeasures that evolved to ensure fruit set. Finally, it was pointed out that in each of these classic fruit trees we are confronted with a variable complex of genuinely wild types, secondary weedy derivatives and feral plants, and groups of the domesticated clones, which are all interfertile and interconnected by occasional hybridization. It was concluded that introgression from the diversified wild gene pool facilitated the rapid buildup of variation in the domesticated crops.

Domestication of plants in the old world : the origin and spread of domesticated plants in south-west Asia, Europe, and the mediterranean Basin

1. Current state of the art 2. Sources of evidence for the origin and spread of domesticated plants 3. Cereals 4. Pulses 5. Oil and fibre producing crops 6. Fruit trees and nuts 7. Vegetables and tubers 8. Condiments 9. Dye crops 10. Plant remains in representative archaeological sites Appendix A: Site orientation maps Appendix B: Chronological chart for the main geographical regions mentioned in the book References Index

GENETIC DIVERSITY AND ENVIRONMENTAL ASSOCIATIONS OF WILD BARLEY, HORDEUM SPONTANEUM , IN ISRAEL

The levels and patterns of adaptive genetic variation in natural populations of the wild progenitors of cultivated plants are still largely unknown. Yet such knowledge would contribute substantially to three important areas of inquiry. These are (1) the general static and dynamic properties of genetic variation in natural populations, (2) the evolutionary process of domestication, and (3) the utility of wild gene pools in future plant breeding. Thus Lewontin (1974), among others, has drawn attention to the advantages that natural plant populations possess as experimental materials; and Harlan (1975a, b) and Zohary (1969), for example, have stressed the need to collect and study the wild progenitors of crop plants from the viewpoints of domestication and exploitation. There are several reasons why wild barley, Hordeum spontaneum , is an ideal species for such studies. First, this species is the recognized progenitor of cultivated barley with which it can yield fully fertile hybrids (see Zohary, 1969). Second, it has the technical advantages of diploidy (2n = 14), predominant self-pollination, and an annual life cycle. Third, its ecology and distribution are already well known. It is widespread in the Near East Fertile Crescent where it occupies primary habitats as well as man-made, secondary formations. It constitutes an important component of open plant communities characteristic of the summer dry hilly belt arcing the Euphrates Basin and the Jordan Rift Valley (Harlan and Zohary, 1966, Zohary, 1969). In Israel, H. spontaneum is abundant,

GENETIC VARIATION IN NATURAL POPULATIONS OF WILD BARLEY (HORDEUM SPONTANEUM)

In order to evaluate the potential genetic resources of the wild relatives of crop plants, allozyme variation at 28 loci was determined for 28 Israel populations of Hordeum spontaneum, the progenitor of cultivated barley. Etectrophoretic properties of these loci and their variants are described. The enzyme loci exhibited a great range of polymorphism, from one to fifteen alleles per locus being detected. The average probability that two gametes drawn randomly from this collection would differ genetically at a locus was 0.19. The evidence indicates that natural populations of this species represent very rich reserves of genetic variability. The extent of differentiation between populations at each locus was compared with that shown by variation in spikelet morphology. The allozyme diversity was apportioned into 17% between regions, 32% between populations within regions, and 51% within populations. In contrast, spikelet variation occurred predominantly between populations. This indicated the species is highly differentiated in phenotype between regions, and presumably allozyme variation is involved in this differentiation. These results support field sampling and evaluation strategies which stress the sampling of more sites at the expense of reducing numbers per site.

Domestication of Pulses in the Old World

This article reviews the available information on the place of origin and time of domestication of the cultivated pea (Pisum sativum), lentil (Lens culinaris), broad bean (Vicia faba), bitter vetch (V. ervilia), and chickpea (Cicer arietinum). On the basis of (i) an examination and evaluation of archeological remains and (ii) an identification of the wild progenitors and delimitation of their geographic distribution, it was concluded that pea and lentil should be regarded as founder crops of Old World Neolithic agriculture. Most probably they were domesticated, in the Near East, simultaneously with wheats and barley (certainly not later than the sixth millennium B.C.). Bitter vetch shows a similar mode of origin. The evidence on the broad bean and the chickpea is much more fragmentary and the wild progenitors of these legumes are yet not satisfactorily identified. But also these two pulses emerge as important food elements in Bronze Age cultures of the Near East and Europe.

Outcrossing rates and heterozygosity in natural populations of Hordeum spontaneum Koch in Israel

SummaryThe extent of cross-pollination was estimated quantitatively in 26 populations of wild barley (H. spontaneum) in Israel, using allozyme variation at 22 polymorphic loci. Individual population estimates varied from 0 to 9·6 per cent outcrossing. The overall average was 1·6 per cent, with a 95 per cent confidence range of 0·8-2·7 per cent. The evidence indicated that outcrossing was significantly higher in populations growing in the more mesic (2·1 percent), than in the xeric regions (0·4 per cent). The average frequency of multilocus homozygosity for the 22 loci was 0·963 which was in agreement with the level expected under the observed high rate of self-fertilisation, indicating no heterozygous excess. However, the heterozygotes encountered, displayed a very high degree of multiple heterozygosity which arises from extensive gametic phase (or linkage) disequilibrium. In general, these results do not support the contention that the bulk of the genetic polymorphism found in H. spontaneum in Israel has arisen in recent times by periodic introgression from cultivated barley (H. vulgare L.). Rather they indicate that extensive genetic polymorphisms probably predates the domestication of the crop, and is maintained independently of introgression.

Unconscious Selection and the Evolution of Domesticated Plants

Two types of selection operate (and complement each other) in plants under domestication: (a) conscious or intentional selection applied by the growers for traits of interest to them; (b) unconscious or automatic selection brought about by the fact that the plants concerned were taken from their original wild habitats and placed in new (and usually very different) human-made or human-managed environments. The shift in the ecology led automatically to drastic changes in selection pressures. Numerous adaptations vital for survival in the wild environments lost their fitness under the new sets of conditions. New traits were automatically selected, resulting in the build-up of characteristic “domestication syndromes,” each fitting the specific agricultural environment provided by the farmer.The present paper assesses the evolutionary consequences of the introduction of the wild plants into several sets of contrasting farming situations. These include: (a) the type of maintenance applied, whether seed planting or vegetative propagation; (b) the plant organs for which the crop has been grown, whether they are reproductive parts or vegetative parts; (c) the impact of the system of tilling, sowing, and reaping on the evolution of grain crops; (d) the impact of the horticultural environment on fruit crops.

Genetic diversity and environmental associations of wild wheat, Triticum dicoccoides, in Israel

SummaryAllozyme variation in the tetraploid wild progenitor of wheat, Triticum dicoccoides, was studied for the proteins encoded by about 50 gene loci in 457 individuals representing 12 populations from Israel. Six spikelet morphological traits were measured in the same populations. The results indicate that: (a) 16 loci (= 32%) were monomorphic in all 12 populations, 15 loci (= 30%) were locally polymorphic, and 19 loci (= 38%) were regionally polymorphic. All polymorphic loci (but one) displayed high levels of polymorphism (≧ 10%). In Israel, the proportion of polymorphic loci per population, P, in wild wheat averaged 0.25 (range, 0.16–0.38), and the genetic diversity index, He averaged 0.07, (range, 0.03 – 0.12). (b) Altogether there were 110 alleles at the 50 putative loci tested (c) Genetic differentiation of populations included regional and local patterns: (i) The coefficients of genetic distance between populations were high (mean D = 0.10 range, 0.02 – 0.25), and indicated sharp genetic differentiation over short distances, (ii) Common (≧ 10%) but sporadic and localized alleles were frequent (76%), and (iii) Rare alleles were few (only 5 alleles). (d) The patterns of allozyme and spikelet variation in the wild gene pool were significantly correlated with, and partly predictable by, water factors, including those of precipitation, evaporation, and relative humidity as well as of soil type, (e) All six spikelet characters showed statistically significant variation among localities and (f) Allozymic variation was correlated with spikelet variation.These results suggest in T. dicoccoides: (i) the operation of natural selection in population genetic structure, (ii) local adaptive genetic differentiation caused by diversifying selection through climate and soil, and (iii) the guidelines for sampling these resources for use in wheat breeding programs.

Monophyletic vs. polyphyletic origin of the crops on which agriculture was founded in the Near East

The following comparisons between crops and their closely related wild relatives provide clues for discriminating between monophyletic and polyphyletic origins under domestication: (i) Presence or absence of patterns indicative of founder effects in the cultivated genepool, compared to the amount of variation present in its wild progenitor. (ii) Uniformity or lack of uniformity (within a crop) in genes governing principal domestication traits (traits that were automatically selected for once the wild progenitor was introduced into cultivation). (iii) Species diversity: The number of closely related (congeneric) wild species with similar potential for domestication, native to the area under consideration; and how many of them entered cultivation. The present paper evaluates the information available on the eight crops that founded Neolithic agriculture in the Near East; and arrives at the conclusion that emmer wheat Triticum turgidum L. subsp. dicoccum Schúbler, einkorn wheat T. monococcum L., pea Pisum sativum L., and lentil Lens culinaris Medik. were very likely taken into cultivation only once or – at most – a very few times. Also chickpea Cicer arietinum L., bitter vetch Vicia ervilia (L.) Willd., and flax Linum usitatissimum L. seem to have been domesticated in a similar way, but the evidence concerning them is much scarcer. Only for barley Hordeum vulgare L. are there indications that it has been domesticated more than once – but again only a very few times.