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.

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.

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