Variation within a bread wheat cultivar for grain yield, protein content, carbon isotope discrimination and ash content I.S. Tokatlidis a,* , J.T. Tsialtas b , I.N. Xynias c , E. Tamoutsidis b , M. Irakli c a Department of Agricultural Development, Democritus University of Thrace, 682 00 N. Orestiada, Greece b Technological Education Institute of W. Macedonia, 531 00 Florina, Greece c National Agricultural Research Foundation, Cereal Institute, 570 01 Thermi, Greece Received 25 November 2002; received in revised form 25 July 2003; accepted 28 July 2003 Abstract The study was undertaken to assess the variation within a bread wheat (Triticum aestivum L.) cultivar, primarily for grain yield, and the implications for wheat breeding. During the 1998–1999 growing season, cv. Nestos was established in a non- replicated (NR-0) honeycomb experiment, in the absence of competition (11 547 plants ha 1 ). Ten high yielding (H) and 10 low yielding (L) plants were selected, the seeds of which were used to form the respective H and L lines. The 20 lines, along with their original cultivar, were evaluated in two locations either in the absence of competition (11 547 plants ha 1 ) during the 1999–2000 season or under competition (5 000 000 plants ha 1 ) during the 2000–2001 season. Results showed significant differentiation between lines for grain yield, determined both in the absence of competition at the single-plant level, i.e. yield per plant (YP), and under competition at the crop yield level, i.e. yield per plot (CY). Significant differences between lines were also found for grain protein content (PC), grain carbon isotope discrimination (D), and grain ash content (ASH), either in the absence of competition or under competition. A positive relationship was found between YP and CY ðr ¼ 0:53; P < 0:02Þ . Results showed that selection within a bread wheat cultivar, under very low density and on the basis of individual plant grain yield, could be an effective way to either upgrade or maintain the cultivar, whereas the use of D or ASH as indirect selection criteria instead of grain yield was not supported by the study. # 2003 Elsevier B.V. All rights reserved. Keywords: Intra-cultivar variation; Density; Grain yield; Protein; Carbon isotope discrimination; Ash content 1. Introduction After a bread wheat cultivar is released, it is com- mon practice to maintain the breeder’s seed by the ‘‘ear to row’’ procedure. Thus ‘‘off-type’’ plants are removed or the best plants within each row are visually selected. Seed production under high density may favour cultivar degeneration because the rate of genotypes characterised as strong competitors–low yielders increases at the expense of weak competi- tors–high yielders (Fasoula and Fasoula, 2000) as a result of the inverse relationship between competitive and yielding ability (Janick, 1999). Therefore, Fasoula Field Crops Research 86 (2004) 33–42 * Corresponding author. Tel.: þ32-5520-28570; fax: þ32-5520-41191. E-mail addresses: itokatl@agro.duth.gr, itokatl@hotmail.com (I.S. Tokatlidis). 0378-4290/$ – see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0378-4290(03)00169-2