e line performance in RCB trials. Line 5, possessing the higher stability of performance, retained the average 20% superiority over Celia in the two years (Table 4), whereas Line 3 only during the first year. This emphasizes the importance of giving increased weight to the genetic component of homeostasis any time the breeder has to decide among entries with equal Equation A values.
|Rank no.||Design code no.||CH Value||Equation A value||Rank no.||Design code no.||CH Value||Equation A value||Rank no.||Design code no.||CH Value||Equation A value|
The efficiency of selection is also evidenced as the CH and equation values of the original cultivar are up to three and four times lower, respectively, than the top selected lines. Notably, a high CH value does not necessarily correspond to a similarly high Equation A value, as is the case with Line 16. This line, although similar in homeostasis to Line 3, had a lower equation value, which was reflected in its inferior performance at the RCB trials of the following season.
Two unappreciated sources of genetic variation exist within elite cultivars . The first stems from the negative correlation between yielding and competitive ability, which leads to a gradual cultivar degradation because of the gradual proliferation of low yielding-strong competing plants (yC) at the expense of high yielding-weak competing plants (Yc). This happens during the standard process of cultivar reproduction under dense stand [15,41]. The second overlooked source is the one produced by the interaction between genotype and environment, since the genome is capable of releasing adaptive variation by triggering off genetic or epigenetic mechanisms in response to environmental changes [27,28,29,30,31,32,33,34,35,36]. All the above justify the application of nonstop selection on the basis of Equation A to exploit this seemingly endlessly released variation for breeding purposes. In this way, the crop yield genetic potential of Celia, instead of remaining at the level of 12 Equation units, could have steadily increased above the 49 units of Line 3.
Table 2 ranks the top 30 of 868 cotton plants of the replicated R-31 honeycomb design on the basis of their unique and unitless Equation A values ranging from 36 to 65 units. Importantly, only four lines (5, 3, 16, and 6) are represented in the top 15 plants. These four lines are those with the highest CH values in Table 1, testifying again to the significance of selecting for the genetic component of stability of performance with reliable selection tools. Apparently, Equation A can be a more sensitive indicator during selection, as its resolution range is larger than the ranges of CH and PYI.
|Line no. of top plants||Equation A Values||CH||PYI|
Table 3 shows the results of a Randomized Complete Block trial in 2006, designed to verify under standard crop stands the identified differences among the top selected lines in the honeycomb trials. Mixtures of five plants from each of the top six lines were formed and compared to the original cultivar. Line 5, possessing the highest CH value, indicating higher stability of yield potential, significantly outyielded the original cultivar by 18.5%.
To further validate this superiority, a second RCB trial was grown in 2007 with six replicates and three treatments, i.e., Line-5 and Line-3 along with the original cultivar. Table 4 shows that Line 5 consistently and significantly outyielded the control with a superiority of 21.6% during the second testing season. Thus, the average across-year superiority of Line 5 over the original cultivar corresponds to a 20%.
|Line code no.||Replicates|
|Original cultivar||5.84||5.10||6.10||5.40||5.61 b||100.0|
CV = 9%, LSD0.05 = 0.78
|Line code no.||Replicates|
|Original cultivar||5.20||4.37||5.25||5.00||4.88||5.25||4.99 b||100.0|
CV = 7.4%, LSD0.05 = 0.56
This percentage acquires further significance compared to the commonly recorded 1% annual genetic gain in earlier and recent literature for crops like barley, oats, wheat, soybean, cotton, rice, potato, and even maize [4,6,45,46,47,48,49,50