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 [4,6,45,46,47,48,49,50,51,52,53,54]. Its significance increases even more considering the reality of climate change, affecting differentially various areas in the globe, and the necessity to effectively keep up with its accelerating genetic progress.
The results point to some important inferences with wider significance for breeding programs: The potential genetic variation for productivity and stability within cultivars seems to be large and inexhaustible, but goes undetected without the appropriate resolving tools. In order to effectively exploit this variation, avoid degeneration, and secure constant genetic gain, the nonstop intracultivar selection emerges as an essential process. The new selection and whole-plant field phenotyping equations offer unique properties for predicting the crop yield and stability of individual plants. This also involves the nonstop exploitation and incorporation of genes for resistance to biotic and abiotic stresses, permitting to effectively face pathogen selection pressure.
3.2. Intra-Cultivar Selection for Yield and Resistance to Cotton Verticillium Wilt
In the second set of experimental data, the application of the honeycomb selection for three consecutive years within Sindos-80 led to the development of the experimental variety Macedonia, which outyielded Sindos-80 by an average of 10% when tested at sixteen locations across Greece in standard RCB trials for two additional years . Although the variety Macedonia was developed using very high selection pressures (1.5%), its progeny lines retained the ability to further generate high genetic diversity. This was evident when honeycomb selection for yield potential per plant was simultaneously applied for one year in a site heavily infected with Verticillium and in a non-infected field. The process allowed the isolation of two lines with similar degree of Verticillium resistance as the resistant controls Acala S.J.5 and S.J.2. The two lines outyielded all controls (Acala S.J.5 and S.J.2, Macedonia, and Sindos-80) in both contrasting environments. In pa