Towards Understanding and Manipulating Heterosis in Crop Plants — Can Molecular Genetics and Genome Projects Help?

Hybrid cultivars are bred and grown for a variety of reasons which include the favorable vigor of the hybrid progeny and systematic exploitation of heterosis. In their entirety, schemes for breeding and production of hybrid cultivars have steps at which new information or technology could make significant improvements to some of the steps, the overall system, and possibly, the product. Before some of the improvements are realized, however, it will be necessary to achieve a higher level of understanding of basic plant biology in the context of nature and agriculture. This may be an immense task and, depending on the objectives, it may be an unrealistic one; however, given the rate of change and new developments in the technical and information infrastructures for basic biological sciences, and the novel approaches they permit, it is becoming more difficult to delineate the possible from the impossible and the practical from the impractical. Thus, there is some reason to believe that new elements of basic biology, including molecular genetics, will enhance our understanding of heterosis and ultimately, our ability to exploit it further. How will molecular genetics help? At this time, identifying the paths to understanding a topic as complex as heterosis requires clairvoyance at many junctions because we often lack the basic information for making decisions, devising strategies and conducting tests. This is changing. There have been a few demonstrations that techniques and information derived from molecular genetics would benefit several aspects of the breeding and production of hybrid cultivars. Also, we are in the early stage of a flood of raw data from plant genome projects, major efforts destined to affect many areas of plant biology, biotechnology, and agriculture. As the data are distilled into information and assembled into technologies, some paths will emerge, and so will some obstacles. The purpose of this chapter is to assess some recent, current and future developments in molecular genetics and biology for their potential to improve our understanding of heterosis and hybrid breeding systems. To provide some context for the assessments, a few assumptions were made about the future: (i) crop productivity will become more dependent on crop genetics; (ii) basic knowledge of nature (plant biology and the supporting environment) will be central to crop-based agriculture; (iii) yield remains the primary goal (i.e., produce and protect plant biomass); and (iv) hybrid cultivars are for the general good of humanity. These assessments are based on recently established and evolving techniques (the recent past), current developments (the present) and their subsequent phases (the future).