Browsing by Author "Fasoulas, A.C."

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    Effects of competition and selection pressure on yield response in winter rye (Secale cereale L.)
    (1985) Kyriakou, D.T.; Fasoulas, A.C.
    Three intensities of mass honeycomb selection (14.3,5.3 and 1.6%) applied to an unselected rye population gave respectively an annual yield response of 0.28, -3.69 and -5.20% at 15 cm spacing, and of 4.07, 5.39 and 8.99% at 90 cm spacing. The negative response with competition was explained by strong negative correlation between competing and yielding ability which causes positive skewness because of transposition of low yielders and strong competitors from the left to the right tail of the distribution. The positive response in the absence of competition was mainly due to the increased genotypic differentiation which allowed effective discrimination between high and low yielding genotypes. The efficiency of the selection in the absence of competition was further improved by using the honeycomb designs which adjust soil heterogeneity and application of very high family and individual selection pressures. Two cycles of mass honeycomb selection increased the population yield by 29.4%, one cycle of mass plus one cycle of pedigree honeycomb selection did so by 34.5%. The results are discussed in relation to the selection response and to the efficiency of various breeding schemes
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    Effects of competition in the selection
    (1984) Fasoulas, A.C.
    Competition between plants interferes with the selection process: (1) by reducing genotypic differentiation and therefore progress through selection, (2) by imposing a limit on the number of environments and replicates when testing in early generations, both directly by reducing the number of seeds produced per plant, and indirectly through the establishment of field plots as experimental units, and (3) by making single-plant selection for yield unreliable, since competitive ability is usually negatively correlated with yielding ability. The detrimental effects of competition are overcome effectively by using wide spacings (i.e. 90 cm in wheat, 125 cm in maize) and the honeycomb field designs. With such designs a multisite and multireplicate screening of potential crosses and exceptional genotypes or families can be carried out in early generations. In this way annual progress will be maximized and the time needed to develop a new cultivar can be halved. Genes for adaptation and stability will be incorporated early in the programmes and both individual buffering and monoculture performance will be improved. Finally the scheme ensures a constant improvement of the cultivar, and paves the way for mechanizing and computerizing selection for yield