Basic loci in cultivation of certain crops in the past and modern times

In 1968 H. Brücher asked: "Gibt es Genzentren?" He proposed a negative answer, but was wrong. The geographical distribution of the majority of crops is not even over all parts of their areas. There are loci of great abundance and regions of small plantations. The abundance of individuals in the large plantation is a factor favouring the display of genetic variability (an increase of the mutation number). The variability of ecological conditions, the antiquity of cultivation and the possibility of interspecific hybridization in such loci promote genetic variability; but a uniformity of ecological conditions and strong selection (natural or artificial) can eliminate new genotypes arising and preserve the homogeneity of the initial populations. Therefore loci of great genetic variability (Genzentren) exist only in conditions favourable for agriculture (with weak natural selection) and in conditions of a primitive consumer agriculture (without strong artificial selection). Loci of genetic variability can be observed in the following regions of a past or existing plantation abundance: in the ancient primary regions of domestication of certain plants; in the regions of ancient large scale cultivation around the primary domestication centers; and in the secondary loci of abundance in conditions favourable for agriculture where certain crops migrated from their primary cultivation regions. Certain loci of abundance (ancient and modern) have no noticeable genetic variability in their different crops, which are relatively uniform there. Such loci of abundance without genetic variability are either disposed at the periphery of the area of the particular crop, with worse natural conditions than in the rest of the area (control by strong natural selection), or are new loci of abundance in conditions of commercial agriculture (control by regular plant-breeding).All loci of polymorphism (Genzentren) are undoubtedly a temporary historical phenomenon. The absence of regular plant breeding was an indispensable condition for the rise of genetic variability loci in the regions of plantation abundance of certain crops. In modern times plant breeding becomes an inevitable component of commercial agriculture. Thus new loci of abundance have no great genetic variability and ancient centres of polymorphism of different crops now go to ruin, giving place to plantations of the few best varieties. Loci of genetic variability are now a relic of the past, while loci of abundance with the few best varieties conform with the economics of modern world agriculture, which aspires to cultivate each crop in the regions where its production cost will be lower and to avoid areas with an expensive product.