Distant Hybridization Of Crop Plants

Wild taxa are invaluable sources of resistance to diseases, insects/ pests, nematodes, temperature extremes, salinity and alkalinity stresses, and also of nutritional quality; adaptation; genetic diversity and new species. Utilization of wild relatives of a crop depends largely upon its crossability relations with cultivated varieties. Sev eral wild species are not crossable with the commercial cultivars due to various isolation barriers. Furthermore, in a few cases, hybridiza tion is possible only in one direction and reciprocal crosses are not successful, thus depriving the utilization of desired cytoplasm of many species. However, techniques have been developed to over come many barriers and hybrid plants are produced. New crop species have been developed by overcoming the F 1 sterility and producing amphidiploids and such crops are commercially being grown in the field. The segregation pattern ofF 1 hybrids produced by distant hybridization in segregating generations are different from the intervarietal hybrids. In former cases, generally, unidirectional segregation takes place in early generations and accordingly, selec tion procedures are adopted. In most of the cases, backcross or modified backcross methods have been followed to utilize wild species, and thus numerous types of resistance and other economical attributes have been transferred in the recurrent parents. Protoplast fusion has been amply demonstrated in a number of cases where sexual hybridization was not possible and, as a result, hybrids have been produced.

Many of our current agricultural crops are natural or agricultural hybrids (between two or more species), or polyploids (containing more than one genome or set of chromosomes). These include potato, oats, cotton, oilseed rape, wheat, strawberries, kiwifruit, banana, seedless watermelon, triticale and many others. Polyploidy and hybridization can also be used for crop improvement: for example, to introgress disease resistance from wild species into crops, to produce seedless fruits for human consumption, or even to create entirely new crop types. Some crop genera have hundreds of years of interspecific hybridization and ploidy manipulation behind them, while in other genera use of these evolutionary processes for crop improvement is still at the theoretical stage. This book brings together stories and examples by expert researchers and breeders working in diverse crop genera, and details how polyploidy and hybridization processes have shaped our current crops, how these processes have been utilized for crop improvement in the past, and how polyploidy and interspecific hybridization can be used for crop improvement in the future.

Global climate is considered to be biggest challenge to the agricultural/horticultural scientists because of the need for development of climate resilient crop varieties. It has also been felt that there is a need to double the present production of fruits and vegetables to over 500 million by 2050 and to meet the growing demand of all other horticultural commodities. The presence of narrow genetic base in cultivated species is one of the major impediments for the plant breeder to develop variety/varieties for wide adaptability and yield. Hence, the utilization of wild relatives and land races in breeding programmes is the need of hour as the reservoirs of potential genes, which can be transferred to the cultivated species through hybridization. Several studies have proved that there is pre and post fertilization barriers which can be overcome through techniques such as embryo rescue, protoplast fusion, alien addition lines, alien substitution lines and ploidy manipulations, etc. The wide hybridization has been proved to be a potential method for developing many stable varieties, which can withstand various biotic and abiotic stresses. Developed and commercialized several intergeneric and interspecific hybrids in fruits, vegetables, flowers, plantation crops medicinal and aromatic plants across the globe. This book would be a valuable documents to the policy makers, researchers and more precisely to the students who are interested in pursuing the higher studies in the field of distant hybridization in horticultural crops.

Genetic engineering and biotechnology along with conventional breeding have played an important role in developing superior cultivars by transferring economically important traits from distant, wild and even unrelated species to the cultivated varieties which otherwise could not have been possible with conventional breeding. There is a vast amount of literature pertaining to the genetic improvement of crops over last few decades. However, the wonderful results achieved by crop scientists in food legumes’ research and development over the years are scattered in different journals of the World. The two volumes in the series ‘Alien Gene Transfer in Crop Plants’ address this issue and offer a comprehensive reference on the developments made in major food crops of the world. These volumes aim at bringing the contributions from globally renowned scientists at one platform in a reader-friendly manner. The 1st volume entitled, ‘Alien Gene Transfer in Crop Plants: Innovations, Methods and Risk Assessment” will deal exclusively with the process and methodology. The contents of this volume have been designed to appraise the readers with all the theoretical and practical aspects of wide hybridization and gene transfer like processes and methods of gene transfer, role of biotechnology with special reference to embryo rescue, genetic transformation, protoplast fusion and molecular marker technology, problems such as cross incompatibility and barriers to distant hybridization and solutions to overcome them. Since wild and weedy relatives of crop plants may have negative traits associated with them, there are always possibilities of linkage drag while transferring alien alleles. Therefore, problems and limitations of alien gene transfer from these species will also be discussed in this series. Further, the associated risks with this and assessment of risks will also be given due weightage.

This richly illustrated volume describes how somatic hybrids can contribute to the improvement of crops. It comprises 24 chapters dealing with interspecific and intergeneric somatic hybridization and cybridization, providing valuable tools for plant breeders.