Plant yield e ciency re ects the single-plant yield at low density that precludes interplant interference for resources. e role of plant yield e ciency in adaptation to water de cit was investigated in maize (Zea mays L.). Also investigated was whether yield of space-planted environments is transferable to densely seeded situations. Further, the correlation and genotype by environment (G × E) interaction of spaced and densely seeded plots were investigated. irty-one lines and 31 crosses among them were tested in three locations under dense stand and the ultra low density of 0.74 plants m -2 as well as in normal and de cit irrigation treatments. e dense stand was 4.44 plants m -2 in the water de cit regime and 6.67 plants m -2 (lines) and 7.84 plants m -2 (hybrids) in the normal water treatment. Hybrids of greater plant yield e ciency were less sensitive to water shortage. Among four hybrids yielding the same at normally irrigated dense stand (11.50 Mg ha -1 ), yield loss due to water shortage was 46% for that of the lowest plant yield e ciency (645 g plant -1 ) and 17% for that of the highest plant yield e ciency (880 g plant -1 ). Correlations between hybrid plant yield e ciency and gas exchange water-use e ciency in dense stand were signi cant. e low density ensured G × E interaction in the quantitative aspect only and thus was of higher heritability, placing emphasis on parental yield per se. Plant yield e ciency is a key element of hybrid ability to withstand water shortage and cope with environmental heterogeneity.Supplemental material available online. I.S. Tokatlidis, C. Tzantarmas, and A. Kargiotidou, Dep. of Agricultural Development, Democritus Univ. of Th race, Orestiada, 68200, Greece; C. Dordas, C. Pankou, F. Gekas, E. Ninou, I. Mylonas, and A. Lithourgidis, School of Agriculture, Aristotle Univ. of Th essaloniki, Th essaloniki, 54124, Greece; F. Papathanasiou, I. Papadopoulos, J.K. Petrevska, and I. Sistanis, Dep. of Agricultural Technology, Technological Educational Institute of Western Macedonia, Florina, 53100, Greece. Received 22 Nov. 2014. Accepted 1 Feb. 2015. *Corresponding author (itokatl@agro.duth.gr; itokatl@hotmail.com).Abbreviations: A, assimilation rate; ASI, anthesis-silking interval; G ´ E, genotype by environment interaction; HI, harvest index; PYE, plant yield effi ciency; T, transpiration; WUE, water-use effi ciency.Ability of a cultivar to tolerate crowding but also perform well at the single-plant level has been asserted to be a determinant element to its crop yield potential (Yan and Wallace, 1995;Fasoula and Tokatlidis, 2012). However, in maize yield more improvement has resulted from improving tolerance to high plant population densities rather than single-plant performance; the per plant yield under minimal competition for light, water, and nutrients remained unchanged (Tollenaar and Lee, 2002;Duvick, 2005). Transition to higher populations in combination with stagnation in yield capacity of individual plants resulted in hybrids characterized as density-dependent (Fas...

Plant yield efficiency (PYE) reflects the ability of the single-plant to respond to additional inputs and is fully expressed at the nil-competition regime (an ultra-low density to preclude inter-plant interference for inputs). The purpose of this study was to determine if PYE could prevent the erratic optimum plant density-yield interaction effect in maize (Zea mays L.). Seven hybrids were evaluated across five environments at four densities, under both the normal-input regime (NIR) and low-input regime (LIR). Plant yield efficiency was measured at the lowest density approaching the nil-competition regime (0.74 plants m -2 ), while crop (per area) yield potential was estimated at the highest density corresponding to the typical farming density in the NIR (8.89 plants m -2 ). In terms of optimum density, the hybrids varied extensively in the NIR (6.64-8.81 plants m -2 ) but performed similarly in the LIR (5.11-5.61 plants m -2 ). The hybrid displaying the highest PYE also had high harvest index (HI) and low anthesis to silking interval (ASI) and was proved the most stable according to various stability statistics including the genotype and genotype by environment (GGE) biplot model. In conclusion, crop yield by density interaction is a matter of hybrid. Hybrids with low PYE have inconsistent optimum density, which is a causal factor of yield loss in rainfed maize. High PYE improves hybrid flexibility and performance at low densities ultimately enhancing crop resilience to extremely fluctuating environments.Abbreviations: AMMI, additive main effect and multiplicative interaction; ASI, anthesis to silking interval; G × E, genotype by environment interaction; GGE, genotype and genotype × environment; HI, harvest index; LIR, low-input regime; NIR, normal-input regime; PYE, plant yield efficiency.

SUMMARYCultivated lentil (Lens culinaris L.) landraces offer a challenge to exploiting their genetic variability and deriving new pure-line varieties. For insect-transmitted viruses, low densities favour increased virus spread. The objective of the present work was to evaluate a selection procedure applied within a landrace under ultra-low plant density and low-input conditions toward the isolation of high-performing genotypes that escape virus infection. Field trials were conducted through four growing seasons (2006–2011) in the Democritus University of Thrace research farm in Orestiada, Greece. Selection of individual plants for high grain yield was applied for three generations, while virus presence was tested by enzyme-linked immunosorbent assay in the seeds used or the plants selected in each selection cycle. Early high plant-to-plant phenotypic variability, reflected by high coefficient of variation (CV) values, was partly attributed to virus infection. However, sister lines were consistently higher yielding and of lower CV than the mother population (MP). Second generation lines yielded up to 136 and 23% more than the source landrace at the ultra-low density and dense stand, respectively. Pea seed-borne mosaic virus was detected in the seeds of the MP, whereas bean yellow mosaic virus and bean leafroll virus were mainly involved in the subsequent selection rounds. In general, the highest-yielding plants were free of the viruses detected during experimentation. It was concluded that selection at ultra-low density of the highest-yielding plants from the sister lines with the lowest CV constitute an effective way to improve the health status of the seeds produced and result in high yielding and potentially virus-tolerant pure-line varieties.

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SUM M ARYIn a 5-year study (2004)(2005)(2006)(2007)(2008), the possibility of exploiting intra-cultivar variation in cotton (Gossypium hirsutum L.) was investigated. Honeycomb single-plant selection for seedcotton yield was employed within three cultivars at a low density of 1·15 plants/m 2 . First-and second-generation progeny lines (1GPLs and 2GPLs) were evaluated for seedcotton yield at low density at three sites, whereas third-generation progeny lines (3GPLs) were tested at the crop density of 10 plants/m 2 across two sites and 2 years. Significant differentiation for seedcotton yield was discovered within cultivar (cvar) Christina and cvar Corona at both low and crop densities, and within cvar Flora at low density. In addition, significant intra-cultivar heterogeneity for fibre quality properties was found at crop density. The 1GPLs and 2GPLs grown at low density showed increases in seedcotton yield of 16 and 19%, respectively, in cvar Christina, and of 2·6 and 3·7%, respectively, in cvar Corona. In cvar Flora, the 1GPLs and 2GPLs yielded 10 and 3·3% lower than the mother cultivar, respectively. When grown at standard crop density, across sites and years, 12 and 5·2% higher yield was obtained by the Christina-derived 3GPLs and the Corona-derived 3GPLs, respectively, when compared with the original cultivars. These results provide evidence that elite cultivars are not homogeneous but rather heterogeneous material, within which selections can be made to maintain or improve uniformity and further improve desirable agronomic traits.

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The study pertains to field experimentation testing seven maize (Zea mays L.) hybrids at four densities, across five locations under normal (NIR) and low-input (LIR) regimes. The main objective was to assess the prognostic value of plant yield efficiency by homeostasis (PYEH) for breeding purposes at ultra-low plant density to predict hybrid yield potential and stability. PYEH comprises plant yield efficiency (PYE) that reflects the ability of individual plants to exploit resources, and plant yield homeostasis (PYH) that indicates the crop’s ability to evade acquired plant-to-plant variability. The same hybrids were also evaluated for stability by commonly used parametric and non-parametric statistics based on data at low (LCD) and high crop densities (HCD). Hybrid stability focused on potential yield loss due to erratic optimum density (OD). Most methods produced conflicting results regarding hybrid ranking for yield and stability especially at LCD. In contrast, PYEH consistently highlighted high-yielding and stable hybrids, potentially able to reach the attainable crop yield (ACY) inter-seasonally irrespective of crop spacing. Low density is common practice under resource-deficit conditions, so crop adaptation to crop spacing is a viable option to overcome erratic OD that constitutes a root source of crop instability in rainfed maize. The results were further supportive of breeding at ultra-low density to facilitate the identification and selection of superior genotypes, since such conditions promote phenotypic expression and differentiation, and ensure repeatability across diverse environments.

BackgroundSpatial heterogeneity can have serious effects on the precision of field experimentation in plant breeding. In the present study the capacity of the honeycomb design (HD) to sample huge spatial heterogeneity was appraised. For this purpose, four trials were conducted each comprising a lentil landrace being screened for response to viruses.ResultsHuge spatial heterogeneity was reflected by the abnormally high values for coefficient of variation (CV) of single-plant yields, ranging 123–162 %. At a given field area, increasing the number of simulated entries was followed by declined effectiveness of the method, on account of the larger circular block implying greater intra-block heterogeneity; a hyperbolic increasing pattern of the top to bottom entry mean gap (TBG) indicated that a number of more than 100 replicates (number of plants per entry) is the crucial threshold to avoid significant deterioration of the sampling degree. Nevertheless, the honeycomb model kept dealing with variation better than the randomized complete block (RCB) pattern, thanks to the circular shape and standardized type of block that ensure the less possible extra heterogeneity with expanding the area of the block.ConclusionsOwing to the even and systematic entry allocation, breeders do not need to be concerned with the extra spatial heterogeneity that might induce the extra surface needed to expand the size of the block when many entries are considered. Instead, they could improve accuracy of comparisons with increasing the number of replicates (circular blocks) despite the concomitant greater overall spatial heterogeneity.