Wheat drought response strategies with special regards to root diversity

Wurzeldiversität ist eine wichtige Grundlage der Trockenresistenz. Weizengenotypen unterschiedlicher Ploidiestufe, Herkunft und Züchtungsintensität wurden bei unterschiedlicher Wasserversorgung verglichen. Sie zeigten hohe Variabilität in Wurzel- und Sprosseigenschaften, was zu verschiedenen Wasserversorgungsstrategien führte, z.B. dichte Oberbodendurchwurzelung, hohe spezifische Wurzellänge und tiefe Wurzelsysteme. Dicht wurzelnden Genotypen konnten Niederschläge in der Vegetationszeit am effizientesten aufnehmen. Die wenig genutzten Weizen unterschieden sich in ihrer Trockenreaktion von modernen Sorten: erstere zeigten höhere Assimilatverlagerung ins Wurzelsystem, während letztere ihre Wurzelmorphologie zu mehr Feinwurzeln verschoben. Die Ertragsreduktion durch Wassermangel wurde mit Passiouras konzeptionellem Modell analysiert. Trockenheit führte im Mittel zu 60 % Ertragsverlust, 37 % weniger Wasseraufnahme, 32,6 % geringerer Wassernutzungseffizienz und 14 % niedrigere Ernteindices. Die spät reifen wenig genutzten Weizen hatten durch ihr intensives Wurzelsystem und rasche Bodenbedeckung die höchste Wasseraufnahme. Die Pflanzeneigenschaften für hohe Wasseraufnahme waren jedoch mit Ertrag beschränkenden Eigenschaften verbunden, was das Züchtungspotential dieser Genotypen einschränkt. Geringe Chlorophyllkonzentration und Stomataleitfähigkeit zeigten eine Strategie des Wassersparens. Moderne Sorten dagegen hatten eine überlegene Wassernutzungseffizienz durch hohe Chlorophyllkonzentration und Stomataleitfähigkeit. Der Ernteindex war abhängig von Phänologie und dominierenden Ertragskomponenten: Zuchtsorten hatten aufgrund ihrer optimalen Reifezeit, reduzierter Bestockung und einer hohen Senkenkapazität der Körner eine höheren Ernteindex als genetische Ressourcen. Die Studie zeigte, dass innerhalb der modernen Sorten physiologische und Wurzeleigenschaften vorhanden sind, die für eine gezielte Verbesserung der Trockenresistenz genutzt werden können.Root diversity is considered important for drought resistance. Wheat genotypes of different ploidy levels, origins and breeding intensities were tested under contrasting water supply. Significant root and shoot trait variation was observed, leading to distinct water uptake strategies; e.g. dense topsoil rooting, high specific root length and deep rooting. Genotypes with a dominant surface root system benefited most from in-season rainfalls. Root systems of underutilized wheat contrasted with modern cultivars: while genetic resources responded to limiting water condition by allocating more assimilates to roots, advanced cultivars shifted their root morphology towards fine roots. Drought response strategies were analyzed by Passiouras yield-water framework with phenological, morphological, physiological, and root data. Limited water supply resulted in 60% yield loss and substantial reduction of water use (37%), water use efficiency (32.6%) and harvest index (14%). Late flowering underutilized wheats with large root system and vigorous ground cover showed greatest water use. Still there was a link of several water use traits with yield limiting behavior, constraining their potential role for better drought resistance. Lower chlorophyll concentration and stomata conductance of underutilized wheats also suggested a water saving strategy of transpiration with limited potential growth. Modern cultivars on the contrary had superior water use efficiency via high chlorophyll concentration and stomata conductance. Harvest index was strongly dependent on phenology and yield components: optimized flowering time, reduced tillering and strong grain sink of modern cultivars explained their higher harvest index compared to underutilized genetic resources. The study demonstrated that physiological and root traits within modern cultivars can be used for trait based crop improvement under water limited conditions.submitted by Alireza NakhforooshAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in dt. SpracheWien, Univ. für Bodenkultur, Diss., 2014OeBB(VLID)193136

Management of crop water under drought: a review

International audienceDrought is a predominant cause of low yields worldwide. There is an urgent need for more water efficient cropping systems facing large water consumption of irrigated agriculture and high unproductive losses via runoff and evaporation. Identification of yield-limiting constraints in the plant–soil–atmosphere continuum are the key to improved management of plant water stress. Crop ecology provides a systematic approach for this purpose integrating soil hydrology and plant physiology into the context of crop production. We review main climate, soil and plant properties and processes that determine yield in different water-limited environments. From this analysis, management measures for cropping systems under specific drought conditions are derived. Major findings from literature analysis are as follows. (1) Unproductive water losses such as evaporation and runoff increase from continental in-season rainfall climates to storage-dependent winter rainfall climates. Highest losses occur under tropical residual moisture regimes with short intense rainy season. (2) Sites with a climatic dry season require adaptation via phenology and water saving to ensure stable yields. Intermittent droughts can be buffered via the root system, which is still largely underutilised for better stress resistance. (3) At short-term better management options such as mulching and date of seeding allow to adjust cropping systems to site constraints. Adapted cultivars can improve the synchronisation between crop water demand and soil supply. At long term, soil hydraulic and plant physiological constraints can be overcome by changing tillage systems and breeding new varieties with higher stress resistance. (4) Interactions between plant and soil, particularly in the rhizosphere, are a way towards better crop water supply. Targeted management of such plant–soil interactions is still at infancy. We conclude that understanding site-specific stress hydrology is imperative to select the most efficient measures to mitigate stress. Major progress in future can be expected from crop ecology focussing on the management of complex plant (root)–soil interactions

Identification of Water Use Strategies at Early Growth Stages in Durum Wheat from Shoot Phenotyping and Physiological Measurements

Modern imaging technology provides new approaches to plant phenotyping for traits relevant to crop yield and resource efficiency. Our objective was to investigate water use strategies at early growth stages in durum wheat genetic resources using shoot imaging at the ScreenHouse phenotyping facility combined with physiological measurements. Twelve durum landraces from different pedoclimatic backgrounds were compared to three modern check cultivars in a greenhouse pot experiment under well-watered (75% plant available water, PAW) and drought (25% PAW) conditions. Transpiration rate was analyzed for the underlying main morphological (leaf area duration) and physiological (stomata conductance) factors. Combining both morphological and physiological regulation of transpiration, four distinct water use types were identified. Most landraces had high transpiration rates either due to extensive leaf area (area types) or both large leaf areas together with high stomata conductance (spender types). All modern cultivars were distinguished by high stomata conductance with comparatively compact canopies (conductance types). Only few landraces were water saver types with both small canopy and low stomata conductance. During early growth, genotypes with large leaf area had high dry-matter accumulation under both well-watered and drought conditions compared to genotypes with compact stature. However, high stomata conductance was the basis to achieve high dry matter per unit leaf area, indicating high assimilation capacity as a key for productivity in modern cultivars. We conclude that the identified water use strategies based on early growth shoot phenotyping combined with stomata conductance provide an appropriate framework for targeted selection of distinct pre-breeding material adapted to different types of water limited environments

Hyperspectral imaging: a novel approach for plant root phenotyping

Abstract Background Root phenotyping aims to characterize root system architecture because of its functional role in resource acquisition. RGB imaging and analysis procedures measure root system traits via colour contrasts between roots and growth media or artificial backgrounds. In the case of plants grown in soil-filled rhizoboxes, where the colour contrast can be poor, it is hypothesized that root imaging based on spectral signatures improves segmentation and provides additional knowledge on physico-chemical root properties. Results Root systems of Triticum durum grown in soil-filled rhizoboxes were scanned in a spectral range of 1000–1700 nm with 222 narrow bands and a spatial resolution of 0.1 mm. A data processing pipeline was developed for automatic root segmentation and analysis of spectral root signatures. Spectral- and RGB-based root segmentation did not significantly differ in accuracy even for a bright soil background. Best spectral segmentation was obtained from log-linearized and asymptotic least squares corrected images via fuzzy clustering and multilevel thresholding. Root axes revealed major spectral distinction between center and border regions. Root decay was captured by an exponential function of the difference spectra between water and structural carbon absorption regions. Conclusions Fundamentals for root phenotyping using hyperspectral imaging have been established by means of an image processing pipeline for automated segmentation of soil-grown plant roots at a high spatial resolution and for the exploration of spectral signatures encoding physico-chemical root zone properties

Peduncle breaking resistance: a potential selection criterion to improve lodging tolerance in Oat

Breeding for tolerance to lodging is an objective, but also a challenge, in oat (Avena sativa L.) breeding programs. A widely adopted method to assess breeding lines for tolerance to lodging is based on visual scoring of plant standability (1 = standing upright; 9 = completely lodged). The lack of sufficient lodging pressure due to weather or growing conditions often renders the visual scoring method ineffective. We present an alternative approach that allows selection for tolerance to stem lodging by screening for peduncle strength in the absence of lodging pressure. This approach also provides objective selection of lodging tolerance using a quantitatively measurable plant trait rather than subjective scoring of the lodged plants. Stem structural and mechanical properties of six oat cultivars with varying levels of lodging tolerance were tested at field experiments over 3 site-years under three nitrogen rates. Results suggested peduncle breaking resistance (PBR), measured below the panicle, as a potential selection criterion for stem strength and therefore lodging tolerance. Significant genetic variation among oat cultivars (p  0.73, p ≤ 0.05). This suggests that PBR provides a good estimation of the whole culm strength. Phenotyping of PBR can be easily integrated into breeding programs because of the ease of sampling and rapid measurement.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Deep soil exploration vs. topsoil exploitation: distinctive rooting strategies between wheat landraces and wild relatives

AimsDiversity of root systems among genetic resources can contribute to optimize water and nutrient uptake. Topsoil exploitation vs. deep soil exploration represent two contrasting ideotypes in relation to resource use. Our study reveals how rooting patterns changed between wheat wild progenitors and landraces in regard to these ideotypes.MethodsRoot (partitioning, morphology, distribution, elongation, anatomy) and shoot traits (dry-matter, leaf area, assimilation) of durum landraces, wild emmer and wild einkorn from Iran, Syria, Turkey and Lebanon were phenotyped using the GrowScreen-Rhizo platform. Distinctive rooting patterns were identified via principal component analysis and relations with collection site characteristics analyzed.ResultsShoot trait differentiation was strongly driven by seed weight, leading to superior early vigor of landraces. Wild progenitors formed superficial root systems with a higher contribution of lateral and early-emerging nodal axes to total root length. Durum landraces had a root system dominated by seminal axes allocated evenly over depth. Xylem anatomy was the trait most affected by the environmental influence of the collection site.ConclusionsThe durum landrace root system approximated a deep soil exploration ideotype which would optimize subsoil water uptake, while monococcum-type wild einkorn was most similar to a topsoil exploiting strategy with potential competitive advantages for subsistence in natural vegetation

Identification of water use strategies at early growth stages in durum wheat using modern shoot image phenotyping

The main challenges of plant production consist in mitigating the impact of climate change and guaranteeing sufficient food supply for the world’s fast-growing population. Integrating approaches across all scales of plant systems from molecular to field applications are necessary to develop sustainable plant production in the future. Phenotyping, the quantitative analysis of structure and function of plants, thereby, has become a major bottleneck.However, modern imaging technology provides new approaches to plant phenotyping for traits relevant to crop yield and resource efficiency. The ScreenHouse phenotyping facility at the Research Center Jülich was used to investigate water use strategies at early growth stages in durum wheat genetic resources combined with physiological measurements. 12 durum landraces from different pedo-climatic origin were compared to three modern check cultivars in a greenhouse pot experiment under well-watered (75 % plant available water, PAW) and drought (25 % PAW) conditions to identify different water-use strategies at early vegetative stages. During early growth, genotypes with large leaf area had high dry-matter accumulation under both well-watered and drought conditions compared to genotypes with compact stature. However, high stomata conductance was the basis to achieve high dry matter per unit leaf area, indicating high assimilation capacity as a key for productivity in modern cultivars. In independent experiments we analyzed root architecture changes in the same contrasting panel to reveal below-ground responses. We conclude that the identified water use strategies based on early growth shoot and root phenotyping by combined with detailed gas exchange analysis provide an appropriate framework for identifying water-use strategies and develop targeted selection of distinct pre-breeding material adapted to different types of water-limited environments

Root architecture simulation improves the inference from seedling root phenotyping towards mature root systems

Root phenotyping provides trait information for plant breeding. A shortcoming of high-throughput root phenotyping is the limitation to seedling plants and failure to make inferences on mature root systems. We suggest root system architecture (RSA) models to predict mature root traits and overcome the inference problem. Sixteen pea genotypes were phenotyped in (i) seedling (Petri dishes) and (ii) mature (sand-filled columns) root phenotyping platforms. The RSA model RootBox was parameterized with seedling traits to simulate the fully developed root systems. Measured and modelled root length, first-order lateral number, and root distribution were compared to determine key traits for model-based prediction. No direct relationship in root traits (tap, lateral length, interbranch distance) was evident between phenotyping systems. RootBox significantly improved the inference over phenotyping platforms. Seedling plant tap and lateral root elongation rates and interbranch distance were sufficient model parameters to predict genotype ranking in total root length with an RSpearman of 0.83. Parameterization including uneven lateral spacing via a scaling function substantially improved the prediction of architectures underlying the differently sized root systems. We conclude that RSA models can solve the inference problem of seedling root phenotyping. RSA models should be included in the phenotyping pipeline to provide reliable information on mature root systems to breeding research