育種學, 最近의 進步

Recent Advancement in Breeding Researches

The pollution and destruction of our environment, the increasing consumption of our limited natural resources, and the feeding of expanding world population are some of the most urgent problems present-day human being has faced. Moreover, along with the rapid progress of science and technology, the structure of agriculture, the cultivating conditions, and our taste for food are also rapidly changing. In view of these worsening and changing situations surrounding us, breeding works need to be implemented with quick pace so as to meet the ever changing demands. Two factors stand in the way hindering the rapid progress of breeding works: the long duration necessary for producing a variety and the increasing scarcity of useful genes available in the existing strains or varieties. In the last decade or so, however, many new knowledge and techniques have been developed in the basic fields of biological science―the androgenetic induction of haploid plant, in vitro culture of plant cell, somatic cell hybridization, transformation of character of living organism by non-sexual means, genetic manipulation at the level of DNA, or the use of synthetic gene, etc. These techniques might be successfully used in shortening the breeding period or in introducing the useful genes from distantly related organism. In olden times our ancestors selected the seed or seed-stocks for next year’s use simply from plants displaying large grain, abundant yield, good taste and quality, disease resistance, or bearing beautiful and showy flowers. Although they had no knowledge on science and technology and were not aware of the means of handling each plant generation scientifically, thousands of varieties were produced during the long history of agriculture. Turning to the present century, Mendel’s laws of heredity were rediscovered and reconfirmed, and Johannsen’s pure line theory and de Vries’ mutation theory of evolution were simultaneously proposed. Genetics based first on gene and later on chromosomes was established. With the knowledge on heredity and variation being accumulated, breeding works were implemented systematically based firmly on scientific foundation. Thus during the first half of 20th century, tens of thousands of varieties were produced in every field of agriculture, much more varieties than those differentiated from the beginning of agricultural husbandry to the end of 19th century. With the clarification on the principles of heredity and variation being made, concepts of evolution, which were so confused and controvertial until the 19th century, were also rectified and evolution was studied under firmer scientific basis. Since 1940’s the genetics based on gene analysis and karyology, which contributed so much to the improvement of agricultural varieties, has faded to become classic science and was instead replaced by, on the one hand, microbial genetics combined with biochemistry and later on with molecular biology and, on the other, by hereditary studies of not. individual plant but of Mendelian population, the latter contributing much to breeding in the selection of polygenic quantitative characters. Genetics transferred in 1960’s to the molecular biologists’ hands later developed in 1970’s into new field, the so-called genetic engineering, in which genetic material was manipulated at DNA level. Biochemical and molecular genetics which concerned so much with the nature of gene and seemed hardly related with the improvement works of plant varieties might in future contribute to the development of new breeding techniques with the coming of new era of genetic manipulation and synthetic gene. Biology of in vitro culture of cell, tissue and organ has played, or will play, considerable role in the elevation of breeding technique. This paper has reviewed the major basic researches which were sucessfully utilized in various breeding programmes in the first half of this century, also reviewed the development and diversifi