Variability within cotton cultivars for yield, fibre quality and physiological traits

Abstract

SUMMARYSelection within elite cotton cultivars is ineffective; it is believed that they are genetically homogeneous. Research in other crops, however, has verified significant intra-cultivar variation based either on phenotypic differentiation or molecular analysis techniques. The present study primarily investigated possible intra-cultivar variation for seedcotton yield. Honeycomb selection within three elite cotton cultivars, on the basis of single-plant seedcotton yield and under the ultra-low density of 1·2 plants/m2, was performed. From each cultivar, six selfed (hand-pollinated) plants were selected and seed of each selected plant constituted a separate line. The 18 first generation lines were evaluated in three locations at a density of 1·2 plants/m2. Within each line, the 10 selfed plants which yielded the highest were selected. Mixed seed from these selected plants constituted the respective second generation line. Offspring performance of the 18 second generation lines was also tested in three locations at a density of 1·2 plants/m2. The results were indicative of intra-cultivar variation, since significant differentiation between lines of each cultivar was found for seedcotton yield per plant, averaged across two years and three locations. Additionally, significant intra-cultivar variation was found for fibre quality properties (length and micronaire, but not strength and uniformity) averaged across two years in a single location, as well as for physiological traits (leaf carbon isotope discrimination, ash content and K concentration) averaged across two years and three locations. In comparison with the original cultivars the second generation lines had higher seedcotton yields supporting the existence of exploitable genetic variation. The conclusion was that honeycomb selection in the absence of competition could be an effective technique in breeders' seed treatment in order to avoid gradual degeneration and beneficially exploit any latent or newly developed genetic variation.

Density effects on environmental variance and expected response to selection in maize (Zea mays L.)

“…Inverse association between density and entry differentiation was also reported by, (Tokatlidis 2000), bread wheat (Triticum aestivum L.) (Fasoula 1990;Tokatlidis et al 2006), soybean (Glycine max (L) Merr.) (Fasoula and Boerma 2007), and upland cotton (Gossypium hirsutum L.) (Tokatlidis et al 2008). Fasoula and Tollenaar (2005) pointed out that at high densities uncontrollable environmental and soil variation can easily turn small differences into nonsignificant, but this is unlikely to happen with the large differences that occur at ultra-low densities.…”

Development of crop cultivars by honeycomb breeding

“…The implications of these results for plant breeding are crucial. First, they point out that the principal cause of cultivar degeneration is the negative correlation between yielding and competitive ability (Fasoula 1990;Fasoula and Fasoula 1997a;Boerma 2005, 2007;Tokatlidis et al , 2008b. Most importantly, cultivars of inbreeders, being mixtures of Yc and yC, encompass large amount of exploitable genetic variation and therefore are amenable to continuous improvement.…”

“…8 demonstrates, differentiation is maximized when plant density approaches the isolation environment, thus facilitating recognition of the superior genotypes and beneficially contributing to heritability. The isolation environment allowed the identification of even the within-cultivar limited genetic variation and application of effective single plant selection in maize, wheat, soybean and cotton (Fasoula 1990;Fasoulas 2000;Tokatlidis 2000;Boerma 2005, 2007;Tokatlidis et al , 2006Tokatlidis et al , 2008bTokatlidis et al , 2011. At high densities, uncontrollable environmental and soil variations can easily turn small differences into non-significant, but this is unlikely to happen with the large differences that occur in the isolation environment (Fasoula and Tollenaar 2005).…”

The Composition and Origins of Genomic Variation among Individuals of the Soybean Reference Cultivar Williams 82

“…Although the phenomenon of intracultivar heterogeneity has long been recognized in crop species (Byth and Weber, 1968), it is oftentimes ignored, as most researchers assume that elite cultivars are composed of relatively homogenous genetic pools (Fasoula and Boerma, 2007). However, a small number of studies have documented the phenotypic consequences of intracultivar genetic heterogeneity in inbred crop accessions, including studies in tobacco (Nicotiana tabacum; Gordon and Byth, 1972), maize (Zea mays; Higgs and Russell, 1968;Tokatlidis, 2000), wheat (Triticum aestivum; Tokatlidis et al, 2004), and cotton (Gossypium hirsutum; Tokatlidis et al, 2008).…”