The Indian Society of Genetics and Plant Breeding was established in 1941 in recognition of the growing contribution of improved crop varieties to the country's agriculture. Scientific plant breeding had started inIndia soon after the rediscovery of Mendel's laws of heredity. The Indian Agricultural Research Institute set up in 1905 and a number of Agricultural Colleges in different parts of the country carried out some of the earliest work mostly inthe form of pure-line selections. In subsequent years, hybridization programmes in crops like wheat, rice, oilseeds, grain legumes, sugarcane and cotton yielded a large number of improved cultivars with significantly higher yields. A turning point came in the 1960s with the development of hybrids in several crops including inter-specific hybrids in cotton. And when new germplasm with dwarfing genes became available in wheat and rice from CIMMYT and IRRI, respectively,Indian plant breeders quickly incorporated these genes into the genetic background of the country's widely grown varieties with excellent grain quality and other desirable traits. This was to mark the beginning of modem agriculture in India as more and more varieties were developed, characterized by a high harvest index and response to modem farm inputs like the inorganic fertilizers . India's green revolution which has led to major surpluses offood grains and othercommodities like sugar and cotton has been made possible by the work of one of the largest groups of plant breeders working in a coordinated network.

When trying to solicit authors for this book it became apparent that the causal factors for heterosis at the physiological and biochemical level are today almost as obscure as they were 30 years ago. Though biometrical-genetical analyses point to dispersion of complementary genes - not overdominance - as the major cause of the phenomenon, plant breeders' experience still suggests a cautious, pragmatic approach to the dominance-overdominance controversy in breeding hybrid cultivars. Thus we are faced with a striking discordance between our limited comprehension of the causal factors and mechanism of heter osis on the one hand, and the extensive agricultural practice of utiliza tion of hybrid vigor on the other. Such utilization is the result of the economic value of hybrid combinations displaying superior yields and qualities as well as stability of performance, of benefits derived in breeding programs, and of the enhanced varietal protection of proprietary rights. No comprehensive and critical analysis of the phenomenon of heterosis in economic plants has been published for the last three decades since the now classical book Heterosis, edited by J . W. Gowen (Iowa State College Press, Ames, Iowa, 1952). The present book attempts to fill the gap and to assess the status of our present knowl edge of the concept, the basis, the extent, and the application of heterosis in economic plants.

Explore the momentous contributions of hybrid crop varieties with worldwide experts. Topics include an overview, quantitative genetics, genetic diversity, biochemistry and molecular biology, methodologies, commercial strategies, and examples from numerous crops.

Zytologie.