t importantly, to effectively exploit drought-prone fields using lower seeding rates. It is envisioned that the crop performance of the varieties of the future will be density-independent.
Of particular interest also is that the superiority of genotypes selected in the absence of interplant competition is linked to their ability to develop deep and extensive root systems and exhibit fast early germination and growth . These properties enable plants to better withstand drought conditions and suffer less from weeds by covering the field before emergence and establishment of the weed majority.
In light of the growing evidence about the frequency, importance, and heritable nature of adaptive variation as a result of the genotype by environment (GE) interaction, the process of nonstop selection emerges as a key step to capture the plasticity of the genome and exploit this untapped, yet big reservoir of yield increasing potential. Even without considering the harsh reality of climate change, target environments are in a constant, often unpredictable, flux, and cultivated genotypes should be given the opportunity to keep up with adapting to their ever-changing microenvironments. The evidence is strong that the annual genetic gain from implementation of nonstop intracultivar selection can be larger compared to the average 1% annual genetic gain reported by most conventional programs [4,6,45,46,47,48,49,50,51,52,53,54]. As selection on a single plant basis is rather inefficient with conventional methods, the unique properties of the new equations can increase the efficiency of selection facing the confounding effects of competition, soil heterogeneity, heterozygosity, and GE interaction on single plant yields, while exploiting the constantly released adaptive variation. The outlined concepts demonstrate also a new dimension in breeding methodology, where the critical role of the environment is fully recognized and exploited during the selection process, since field selections based on the values of the two equations, bypass the subjective visual human evaluation, even during the earliest segregating generations. Further, the equations are very appropriate for accurately phenotyping whole plants under real field conditions, bridging the gap between molecular-genomic and phenotypic data.
Overall, three essential, yet unappreciated reasons for the observed gaps between actual and potential crop yield, concern reduced stability of performance that should have been incorporated during the early segregating stages of cultivar creation through appropriate breeding methodology, any prevalence of big genetic or acquired differences in the crop stand that increases the CV of individual plant yield, and failure to practice nonstop selection after the release of cultivar to avoid degeneration and incorporate useful adaptive (genetic or epigenetic) de novo variation.
The author gratefully acknowledges stimulating discussions with Apostolos C. Fasoulas, Aristotelian University, Greece, which contributed to the final form of the manuscript.
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