Agronomy and Horticulture Department


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Copyright 1995 American Society for Horticultural Science. Used by Permission.


Diseases of horticultural crops have always been a concern of crop producers, processors, merchandisers, and consumers because of reductions in yield and product quality. Excessive chemical application to control diseases of some crops has been a health concern in some countries. Some diseases pose a major constraint, or even a threat, to the production of a crop in a region. Plant breeders, in association with plant pathologists, have had notable successes in breeding disease-resistant varieties, thus ensuring the economic production of a crop. There is now an increased need to breed for disease resistance of horticultural crops because of a loss of chemicals for disease control, environmental and human health concerns, the need to enhance economic competitiveness of horticultural producers and to reduce the genetic vulnerability of crops to pathogens, and an emphasis on using sustainable crop production systems. It is timely to review new concepts and strategies in breeding for disease resistance in horticultural crops in view of the new technologies that have been developed along with the continuing role of classical breeding. This colloquium was organized to review recent developments in classical and molecular approaches to breeding diverse horticultural plants for resistance to viruses, bacteria, and fungi. The reviews embody concepts, methods, strategies, and examples of current developments and successes that will interest breeders of all horticultural crops.

A comprehensive classical breeding program for disease resistance involving cooperation between breeders and pathologists encompasses most or all of the following areas: knowledge of the biology, strain, variation and virulence, and epidemiology of the pathogen; development of rapid inoculation methods with repeatable results; use of sets of differential varieties/lines (where available) to provide information on strain variation; easily applied and understood disease rating scales; identification of sources of resistance; knowledge of the genetics of resistance; development of effective selection and breeding schemes for resistance; and widespread evaluation of new lines along with controls in production areas to determine merit for release.

Many graduate students in plant breeding are now heavily involved in using the tools of molecular biology and tissue culture (molecular markers, gene tagging, molecular mapping, transformation methods, and regeneration of specific tissues into intact plants) in the laboratory. They also need to be well versed in the disciplines associated with classical breeding programs. The new tools need to become a part of the total plant breeding program. At this stage, breeders need to combine molecular and classical approaches in enhancing germplasm and developing crop varieties with desirable horticultural traits along with disease resistance. The goal of plant breeding is to enhance the welfare of a society through genetic improvement of crops, while at the same time improving breeding methods and advancing knowledge in attaining that goal. This perspective needs to be imparted to graduate students, administrators of land-grant institutions, and funding agencies because of the continued erosion of plant breeding programs. It is imperative for the future well-being of humanity that we continue to train plant breeders to meet the stated goal.