rticular, they outyielded the more resistant Acala control (Acala S.J.5) by 140% in the non-infected field and by 40% in the infected field. The original mother variety, Sindos-80, is susceptible to Verticillium wilt, while Macedonia exhibited resistance similar to that of the Acala S.J.2. Importantly, the one year of selection in the infected site also revealed the existence of two low-yielding lines within the variety Macedonia, whose yield per plant was inferior to Acalas by 65%. These lines were even more susceptible to Verticillium than the original mother variety Sindos-80.
4. Experimental Section
4.1. Intra-Cultivar Selection for Yield Stability and Crop Yield Potential
In this set of experiments, the material used for applying selection was a leading, elite cotton cultivar, Celia. The study lasted four years, the first two were devoted to single-plant and progeny line selection within Celia and the subsequent two to the implementation of standard Randomized Complete Block (RCB) trials to assess the efficiency of selection in comparison to the original cultivar. All trials were grown at the Farm of the Aristotelian University at Thessalonica  under standard agronomic practices for the region and appropriate weed management.
First growing season-2004: Seven cotton cultivars, coded from 1 to 7, were grown in a replicated-7 honeycomb trial [Figure 1, code 13] with 133 plant positions per cultivar and 100 cm plant-to-plant spacing to exclude interplant competition. Seedcotton from all plants was picked up individually, weighed, and the individual plant seedcotton yields were transformed into unitless values based on the Plant Yield Index component of Equation A. Thirty plants from cultivar coded 3, i.e., Celia, were selected and advanced to the next year’s trials.
Second growing season-2005: Thirty progeny lines belonging to the 30 plants obtained after intracultivar selection and the original cultivar as control, were grown in a replicated-31 honeycomb trial [Figure 2, codes 1 to 31, 13] with 28 plant positions 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 gro