Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2008
Publication Date: 7/4/2008
Citation: Wissuwa, M., Mazzola, M., Picard, C. 2008. Novel approaches in plant breeding for rhizosphere-related traits. Plant and Soil Journal 321:409-430
Interpretive Summary: Plant root systems have evolved several strategies to acquire nutrients and avoid diseases in natural ecosystems. In the domestication of plants for crop production, breeding programs have inadvertently diminished or eliminated the capacity of certain species to form associations with plant beneficial soil microorganisms or conduct specific basic functions such as acquisition of nutrients in the forms in which they naturally occur in soil. While the resulting crop varieties produce significantly higher yields than the predecessors when used in high-input production systems, these modern varieties have performed poorly in regions of the world that are dependent upon subsistence agriculture, which is typified by poor soil fertility and low-input production systems. Significant effort needs to be expended in the development of crop varieties with enhanced yield potentials but also the capacity to function in adverse production systems. Fulfilling this goal will require an overhaul of breeding programs to conduct the analysis of plant germplasm in realistic systems. It will also require a greater understanding of the plant processes which shield plants from biotic and abiotic stresses, and the corresponding genes that enable such functions. This will be required to efficiently introduce such traits into new crop varieties, whether that is attempted through traditional breeding programs or through the use of novel molecular methodologies.
Technical Abstract: Selection of modern varieties has typically been performed in standardized, high fertility conditions with a primary focus on yield. This may have contributed to loss of function of plant genes associated with efficient nutrient acquisition strategies and adaptation to soil-related biotic and abiotic stresses if such adaptive strategies resulted in a cost to the plant that compromised yield. Furthermore, benefits derived through interactions with rhizosphere associated soil organisms may have been made obsolete by provision of nutrients in high quantity and in readily available forms. Studies comparing older traditional varieties to modern high yielding varieties indeed showed that this has been the case. Given the necessity to efficiently use scarce and increasingly costly fertilizer inputs while also raising productivity on poorer soils, it will be crucial to reintroduce desirable rhizosphere-related traits into elite cultivars. Despite the considerable effort devoted to the identification of suitable donors and of genetic factors associated with beneficial rhizosphere traits, progress in developing improved varieties has been slow and largely confined to modifications of traditional breeding procedures. Modern molecular tools have only very recently started to play a rather small role. The few successful cases shown that novel breeding approaches using molecular tools do work in principle. When successful, they involve close collaboration between breeders and scientists conducting basic research and confirmation of phenotypes in field tests as a ‘reality check’. For novel molecular approaches to make a significant contribution to breeding for rhizosphere related traits applied breeding through more interdisciplinary research that addresses rather than avoids the complexity of plant-soil interactions.