Ancestral QTL Alleles from Wild Emmer Wheat Enhance Root Development under Drought in Modern Wheat

A near-isogenic line (NIL-7A-B-2), introgressed with a quantitative trait locus (QTL) on chromosome 7AS from wild emmer wheat (Triticum turgidum ssp. dicoccoides) into the background of bread wheat (T. aestivum L.) cv. BarNir, was recently developed and studied in our lab. NIL-7A-B-2 exhibited better productivity and photosynthetic capacity than its recurrent parent across a range of environments. Here we tested the hypothesis that root-system modifications play a major role in NIL-7A-B-2’s agronomical superiority. Root-system architecture (dry matter and projected surface area) and shoot parameters of NIL-7A-B-2 and ‘BarNir’ were evaluated at 40, 62, and 82 days after planting (DAP) in a sand-tube experiment, and root tip number was assessed in a ‘cigar-roll’ seedling experiment, both under well-watered and water-limited (WL) treatments. At 82 DAP, under WL treatment, NIL-7A-B-2 presented greater investment in deep roots (depth 40–100 cm) than ‘BarNir,’ with the most pronounced effect recorded in the 60–80 cm soil depth (60 and 40% increase for root dry matter and surface area, respectively). NIL-7A-B-2 had significantly higher root-tip numbers (∼48%) per plant than ‘BarNir’ under both treatments. These results suggest that the introgression of 7AS QTL from wild emmer wheat induced a deeper root system under progressive water stress, which may enhance abiotic stress resistance and productivity of domesticated wheat

Phenotypic plasticity and water flux rates of Citrus root orders under salinity

Knowledge about the root system structure and the uptake efficiency of root orders is critical to understand the adaptive plasticity of plants towards salt stress. Thus, this study describes the phenological and physiological plasticity of Citrus volkameriana rootstocks under severe NaCl stress on the level of root orders. Phenotypic root traits known to influence uptake processes, for example frequency of root orders, specific root area, cortical thickness, and xylem traits, did not change homogeneously throughout the root system, but changes after 6 months under 90 mM NaCl stress were root order specific. Chloride accumulation significantly increased with decreasing root order, and the Cl− concentration in lower root orders exceeded those in leaves. Water flux densities of first-order roots decreased to <20% under salinity and did not recover after stress release. The water flux densities of higher root orders changed marginally under salinity and increased 2- to 6-fold in second and third root orders after short-term stress release. Changes in root order frequency, morphology, and anatomy indicate rapid and major modification of C. volkameriana root systems under salt stress. Reduced water uptake under salinity was related to changes of water flux densities among root orders and to reduced root surface areas. The importance of root orders for water uptake changed under salinity from root tips towards higher root orders. The root order-specific changes reflect differences in vulnerability (indicated by the salt accumulation) and ontogenetic status, and point to functional differences among root orders under high salinity

Pruning of Acacia salicina trees irrigated with runoff water in arid zones

In arid and semi arid lands, forest and agricultural productions are declining due to water scarcity and drought. The objective of this study was to determine the effects of shoot pruning at different heights of acacia salicina lindl, grown in the Israeli Negev Desert and irrigated with runoff water. The specific objectives of this study were to examine the most appropriate pruning height, growth rate and biomass production, water use efficiency of A. salicina shrubs irrigated with floodwater and the water uptake rate and soil water content change at the different pruning height treatments. The trees were planted in 1993 in a 0.5 ha plot at a design of 1m between trees within the rows and 4 m between rows (1,250 trees ha-1). The trees were pruned at a height of 0.5m, 1.0m and 2.0m above soil surface and were compared to non-pruned trees (NP treatment, served as control treatment). Measurements of trunk diameter at a height of 0,3 m above soil surface, re-growth of new branches and soil water uptake by trees, using a neutron moisture gauge that has been previously calibrated in the field), were take every two weeks. Three pruning were carried out during the two years of the experiment. The first pruning was at the beginning of the experiment in March 2003, the second one in December 2003 and the third one in October 2004. Biomass measurements were taken after the second and the third pruning. A non-destructive biomass evaluation was carried out to the NP treatment by using a linear regression of cross Sectional Area (CSA) of trunk versus biomass yield developed from an adjacent plot of A. salicina of the same age. The results of the experiment indicate that more biomass was obtained from the 2,0 m pruning treatment followed by the 1,0 m. Water Use Efficiency had the same pattern. Under the condition of this experiment, the most appropriate pruning height for A salicina trees irrigated with floodwater is 2, 0 m

Hyperspectral Reflectance and Indices for Characterizing the Dynamics of Crop–Weed Competition for Water

Understanding the spectral characteristics of crops in response to stress caused by weeds is a basic step in improving the precision of agricultural technologies that manage weeds in the field. This research focused on the competition between corn (Zea mays) and redroot pigweed (Amaranthus retroflexus), a common weed that strongly reduces corn yield. The aim of this research was to characterize the physiological changes that occur in corn during early growth because of crop–weed competition and to examine the ability to detect the effect of competition through hyperspectral measurements. A greenhouse experiment was conducted, and corn plants were examined during early growth, with and without weed competition. Hyperspectral measurements were combined with physiological measurements to examine the reflectance and photosynthetic activity of corn. Changes were expected to appear mainly in the short-wave infrared region (SWIR) due to competition for water. Relative water content (RWC), chlorophyll content, photosynthetic rate, and stomatal conductance were reduced in the presence of weeds, and intercellular CO2 levels increased. Deeper SWIR light absorption occurred in the weed treatment as expected, accompanied by spectral changes in the visible (VIS) and near infrared (NIR) ranges. The results highlight the potential of using spectral measurements as an indicator of competition for water

Grafting as a Method to Increase the Tolerance Response of Bell Pepper to Extreme Temperatures

Fluctuations of winter and summer and day and night temperatures strongly influence shoot and root growth, as well as the whole plant tolerance to extreme soil temperatures. We compared the response of a commercial pepper ( L.) hybrid (Romance, Rijk Zwaan) to a range of soil temperatures when grafted to a new rootstock hybrid (S101, Syngenta), self-grafted, or ungrafted. The new rootstock hybrid was bred for enhancing abiotic stress tolerance. Plants were grown during winter and summer seasons in a plastic greenhouse with natural ventilation. Minirhizotron cameras and in-growth cores were used to investigate grafted bell pepper root dynamics and root and shoot interactions in response to extreme (low and high air and soil) temperatures. Soil and air temperatures were measured throughout the experiment. The variations of the grafted peppers and the ungrafted aboveground biomass exposed to low and high temperatures during winter and summer were higher in the Romance grafted on the S101 rootstock than in the self-grafted and ungrafted Romance. The plot of rootstock S101 accumulated Cl, and the rootstock efficiently allocated C into the leaves, stems, and roots and N into the leaves, stems, and fruits. These traits of rootstock S101 can be used to improve the tolerance of other pepper cultivars to low and high soil temperatures, which could lengthen the pepper growing season, as well as provide highly interesting information to plant breeders

Recognition of Orobanche cumana Below-Ground Parasitism Through Physiological and Hyper Spectral Measurements in Sunflower (Helianthus annuus L.)

Broomrape (Orobanche and Phelipanche spp.) parasitism is a severe problem in many crops worldwide, including in the Mediterranean basin. Most of the damage occurs during the sub-soil developmental stage of the parasite, by the time the parasite emerges from the ground, damage to the crop has already been done. One feasible method for sensing early, below-ground parasitism is through physiological measurements, which provide preliminary indications of slight changes in plant vitality and productivity. However, a complete physiological field survey is slow, costly and requires skilled manpower. In recent decades, visible to-shortwave infrared (VIS-SWIR) hyperspectral tools have exhibited great potential for faster, cheaper, simpler and non-destructive tracking of physiological changes. The advantage of VIS-SWIR is even greater when narrow-band signatures are analyzed with an advanced statistical technique, like a partial least squares regression (PLS-R). The technique can pinpoint the most physiologically sensitive wavebands across an entire spectrum, even in the presence of high levels of noise and collinearity. The current study evaluated a method for early detection of Orobanche cumana parasitism in sunflower that combines plant physiology, hyperspectral readings and PLS-R. Seeds of susceptible and resistant O. cumana sunflower varieties were planted in infested (15 mg kg-1 seeds) and non-infested soil. The plants were examined weekly to detect any physiological or structural changes; the examinations were accompanied by hyperspectral readings. During the early stage of the parasitism, significant differences between infected and non-infected sunflower plants were found in the reflectance of near and shortwave infrared areas. Physiological measurements revealed no differences between treatments until O. cumana inflorescences emerged. However, levels of several macro- and microelements tended to decrease during the early stage of O. cumana parasitism. Analysis of leaf cross-sections revealed differences in range and in mesophyll structure as a result of different levels of nutrients in sunflower plants, manifesting the presence of O. cumana infections. The findings of an advanced PLS-R analysis emphasized the correlation between specific reflectance changes in the SWIR range and levels of various nutrients in sunflower plants. This work demonstrates potential for the early detection of O. cumana parasitism on sunflower roots using hyperspectral tools