 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 attention to the critical roles of yield stability and nonstop selection in mitigating and reducing crop losses. Cotton is used as a case study to illustrate both the potential to gradually incorporate resistance to pathogens much faster than in conventional breeding and the necessity of nonstop selection to improve the yield and homeostasis of cultivated varieties, especially during the annual propagation of breeder seed.
Research that led to the identification of yield stability as the critical factor that connects yield potential at the single-plant level with crop yield conditions has its origins in the development and applications of the Honeycomb field selection designs . The time course of this research, through some key publications that defined the principles which underlie the present cotton case study, can be briefly described as follows: An early important article  demonstrated the existence of a negative correlation between a plant’s yielding and competitive ability and showed that because of this, progress through selection in a breeding program is achieved when the evaluated plants are grown at distances excluding any interplant competition. Consequently, the unit of selection ceases to be the conventional, densely sown plot, becoming the individual plant grown in the absence of interplant competition. Subsequent work  measured for the first time the correlation between yielding and competitive ability, which was found to be high and negative. This negative correlation was interpreted as the main cause of variety degeneration and of selection inefficiency during the early, segregating generations of a breeding program. In the traditional densely-sown plots, where cultivar reproduction commonly occurs, there is preferential and gradual proliferation of genotypic forms that are high competitors-reduced yielders at the expense of high yielders-weak competitors. Another key finding was that the conditions, which maximize crop yield are those that minimize interplant competition.
The unique properties and est