ns per line, for a total of 868 plants spaced at 100 cm. Using the selection equations and a selection pressure of 3.2%, seed was saved from the six superior lines in order to compose the material for the RCB trial of the following year.
Third growing season-2006: The selected six progeny lines, together with the original cultivar were tested in RCB trial of 3-row plots, 5 meters long, replicated four times in order to assess the genetic gain under standard crop stands. Plots were overseeded to be thinned later to 12 plants per m2. Only the central row was harvested.
Fourth growing season-2007: The two best lines in the RCB trial of the previous year, i.e., Lines 3 and 5, together with the control cultivar, were tested in a new RCB trial replicated six times to assess consistency of performance during a second year. Plots were overseeded to be thinned later to 12 plants per m2. Only the central row was harvested.
4.2. Intra-Cultivar Selection for Yield and Resistance to Cotton Verticillium Wilt
The second set of experiments concern selection for yield within the prevalence for many years in Greece cotton cultivar Sindos-80. Yield selection on a single-plant basis was combined with concurrent selection for resistance to Verticillium wilt. The experimental procedure is described in . Because of its overall significance, it is summarized here and the link to this concept article is outlined.
Intra-cultivar honeycomb selection was applied within Sindos-80 for three years leading to the development of the experimental variety Macedonia. Further honeycomb selection within Macedonia was applied for one year simultaneously in two contrasting environments, in a field heavily infected with cotton Verticillium wilt and in an infection-free site, using 150 × 150 cm plant spacing to exclude the masking effect of interplant competition. During the next year, a total of forty five (45) progeny lines originating from both selection environments, along with four controls (Acala S.J.5 and S.J.2, Macedonia, and Sindos-80), were grown in two environments, a heavily infected and a non-infected field.
This concept paper focuses on a new approach that can be used effectively during the early or later generations of a breeding program and, notably, in a nonstop manner to secure the continuous adaptation of cultivars to their target environments. The homeostasis or yield stability of a cultivar is a genetically controlled trait that can be selected for without sacrificing higher yields, and it is essential to bridge the gap between actual and potential yields, particularly in resource-poor farming areas. The concept of Coefficient of Homeostasis incorporates tolerance to a multitude of biotic and abiotic stresses, including the stress of higher planting densities. Genotypes that possess improved homeostasis are better able to exploit randomly distributed environmental resources (e.g., in rainfed agriculture where erratic rainfalls can nevertheless sustain production), and respond better to even limited amounts of fertilizers or chemical interventions for plant protection.
Importantly for the resource-poor farming areas, the new Equation A permits unbiased selection for high and stable yield on a single plant basis, a concept that leads to the creation of density-neutral cultivars. The denser the seeding rates in low-input agriculture, the higher the possibility that many plants in the crop stand will not make it to the end of their cycle to produce seeds because of the intense competition for resources within the stand. However, a genotype with improved homeostasis is capable of satisfactory production even under low seeding rates, thus, exploiting limited resources in a most efficient manner. Cultivars that are density-neutral have the capacity to fully exploit lower planting densities, maintaining high crop yields at lower seeding rates. This implies that farmers in resource-limiting environments can achieve high crop yields using a wider density range. An advantage that enables to avoid reseeding in the case of not-satisfactory stands and mos