- freely available
Agriculture 2012, 2(3), 211-227; doi:10.3390/agriculture2030211
Abstract: Yield losses occurring at the field level, whether due to plant diseases or abiotic stresses, reveal reduced stability of the crop yield potential. The paper argues that the stability of crop yield potential is a trait with a clear genetic component, which can be successfully selected for at the single-plant level and incorporated into high-yielding cultivars. Two novel selection equations with prognostic power are presented, capable to objectively phenotype and evaluate individual plants in real field conditions in the absence of the masking effects of interplant competition and soil heterogeneity. The equations predict performance at the crop stand through the key concept of coefficient of homeostasis and are equally useful for early generation selection and for nonstop selection within finished cultivars in order to continuously incorporate the adaptive (genetic or epigenetic) responses of plants. Exploitation of adaptive responses acquires particular importance in view of the climate change effects on crop productivity and the changing biotic or abiotic micro-environments. Cotton is used as a case study to highlight the potential of nonstop selection for increasing crop yield and for the gradual build-up of disease resistance. In addition, the paper envisions and proposes the formation of international networks of researchers focusing on specific diseases as, for example, the cereal root-rot or the cotton Verticillium wilt that will concurrently use the proposed strategy in their respective environments to select for resistant genotypes, while gaining a deeper understanding of the nature of the genetic or epigenetic changes at the phenotypic and genomic levels.
Over the past years the observed difference between potential and actual crop yields globally has emerged as a key issue demanding further consideration and action by the scientific community in order to improve food security [1,2,3]. On top of this, there have been many reports documenting a decrease in the annual yield gain and a stagnation of yields of major crops globally, because of either genetic or environmental reasons, including farm management practices [4,5,6,7,8]. Even in reports where the cause of stagnation is attributed primarily to environmental reasons, it becomes apparent that the high yields of the modern genetically improved cultivars cannot be stably maintained across seasons, years, and countries. The interaction between genetic composition and environment is such that the high potential yields are realized only in a limited range of optimal growing conditions or seasonal environments. In other words, a majority of cultivated, improved genotypes are not able to sustain their potential for high yields under a wider range of growing and often challenging conditions, where it actually is needed most.
To this, one can add the effects of global climate change that are certain to exacerbate the problem, for a variety of well-documented reasons extensively treated in recent literature, including increase in number and intensity of pest attacks, radical change in rainfall patterns, CO2 emissions, and others (e.g., [9,10,11]). The role of plant breeding to provide a range of solutions to the problem is pivotal and well recognized: Plant breeding is able to generate huge value relative to investment and offers an effective approach to improving food security .
Crop yield losses at the field level may be reduced by ensuring ideal growing conditions throughout the growing period or by developing genotypes that most efficiently exploit available resources. The second goal is certainly more relevant to the low-input conditions of the resource-poor farmers, who are primarily threatened by food insecurity, and will be the focus of the present article. The purpose is twofold: To provide insights into novel breeding concepts and equations whose application can accurately assess and incorporate genotypic stability of yield under field conditions, and to bring attent