Association of Shoot and Root Responses to Water Deficit in Young Faba Bean (Vicia faba L.) Plants

Phenotyping revealed tolerance traits and genotypes for acidity and aluminum toxicity in European Vicia faba L

Soil acidity is a global issue; soils with pH <4.5 are widespread in Europe. This acidity adversely affects nutrient availability to plants; pH levels <5.0 lead to aluminum (Al3+) toxicity, a significant problem that hinders root growth and nutrient uptake in faba bean (Vicia faba L.) and its symbiotic relationship with Rhizobium. However, little is known about the specific traits and tolerant genotypes among the European faba beans. This study aimed to identify response traits associated with tolerance to root zone acidity and Al3+ toxicity and potentially tolerant genotypes for future breeding efforts. Germplasm survey was conducted using 165 genotypes in a greenhouse aquaponics system. Data on the root and shoot systems were collected. Subsequently, 12 genotypes were selected for further phenotyping in peat medium, where data on physiological and morphological parameters were recorded along with biochemical responses in four selected genotypes. In the germplasm survey, about 30% of genotypes showed tolerance to acidity and approximately 10% exhibited tolerance to Al3+, while 7% showed tolerance to both. The phenotyping experiment indicated diverse morphological and physiological responses among treatments and genotypes. Acid and Al3+ increased proline concentration. Interaction between genotype and environment was observed for ascorbate peroxidase activity, malondialdehyde, and proline concentrations. Genomic markers associated with acidity and acid+Al3+-toxicity tolerances were identified using GWAS analysis. Four faba bean genotypes with varying levels of tolerance to acidity and Al3+ toxicity were identified.

Increasing sustainability by intercropping legume crops with sugar beet under imposed water stress

The sustainable use of soil and water resources is a goal that should be pursued to attain food security. This investigation was implemented to compare the effects of three legume intercropping systems with sugar beet on (i) enhancing sugar beet yield under imposed water stress conditions, (ii) soil N contents, (iii) land and water use efficiencies, and (iv) farmers' net income. Two field experiments were carried out in the 2018/19 and 2019/20 seasons in the El‐Minia Governorate, Egypt. The treatments included the interaction between three irrigation treatments: required irrigation ((control, 100% ETc, RI) and two levels of imposed water stress (85% ETc (WS1) and 70% ETc (WS2)), and three intercropping systems: faba bean (FIS), chickpea (CIS) and lentil (LIS) intercropped with sugar beet. The results indicate that the application of implementing CIS and with RI attained higher average values of soil N content (SNC = 14.0 mg kg−1) and net income (NI = US$3,974 ha−1) than those obtained by sugar beet alone. Irrigation with WS1 and the implementation of CIS gave a value of SNC (12.3 mg kg−1) close to that obtained under sugar beet alone irrigated with RI. CIS irrigated with WS1 attained higher averaged values of land equivalent ratio (LER = 1.34), area time equivalent ratio (ATER = 1.28), land equivalent coefficient (LEC = 0.38), water equivalent ratio (WER = 1.12), negative value of change in water use (ΔWU < 0) and NI (US$3,602 ha−1) than those obtained under FIS or LIS irrigated with RI. In conclusion, implementing CIS and irrigation with RI can achieve the sustainable use of land and water. However, implementing CIS and irrigation with WS1 can realize soil improvement, conserve irrigation water and attain higher values of LER, ATER, LEC, WER, and NI than those obtained under FIS, LIS and sugar beet alone.

Responses of root system architecture to water stress at multiple levels: A meta-analysis of trials under controlled conditions

Plants are exposed to increasingly severe drought events and roots play vital roles in maintaining plant survival, growth, and reproduction. A large body of literature has investigated the adaptive responses of root traits in various plants to water stress and these studies have been reviewed in certain groups of plant species at a certain scale. Nevertheless, these responses have not been synthesized at multiple levels. This paper screened over 2000 literatures for studies of typical root traits including root growth angle, root depth, root length, root diameter, root dry weight, root-to-shoot ratio, root hair length and density and integrates their drought responses at genetic and morphological scales. The genes, quantitative trait loci (QTLs) and hormones that are involved in the regulation of drought response of the root traits were summarized. We then statistically analyzed the drought responses of root traits and discussed the underlying mechanisms. Moreover, we highlighted the drought response of 1-D and 2-D root length density (RLD) distribution in the soil profile. This paper will provide a framework for an integrated understanding of root adaptive responses to water deficit at multiple scales and such insights may provide a basis for selection and breeding of drought tolerant crop lines.

Wild Vicia Species Possess a Drought Tolerance System for Faba Bean Improvement

Faba bean (Vicia faba L.), a drought-sensitive crop, is drastically affected by drought stresses compromising its growth and yield. However, wild relatives of faba bean are considered a reservoir of potential genetic resources for tolerance against abiotic stresses. This study was conducted to characterize wild relatives of faba bean for identification of a specific tolerance system required for its improvement against drought stress. The study focused on physiological, biochemical, and anatomical responses of wild Vicia species under drought stress conditions. The experiment was carried out under various levels of drought stress imposed through different field capacities (FC) which included 80% FC ie (well-watered condition), 55% FC (moderate stress), and 30% FC (severe stress). When compared to plants grown in a control environment, drought stress significantly reduced the studied physiological attributes including soluble sugars (21.3% and 15.8%), protein contents (14.7 and 14.6%), and chlorophyll (8.4 and 28.6%) under moderate (55% FC) and severe drought stress (30% FC), respectively. However, proline content increased by 20.5% and 27.6%, peroxidase activity by 48.5% and 57.1%, and superoxide dismutase activity by 72.6% and 64.8% under moderate and severe stress, respectively. The studied anatomical attributes were also affected under drought stress treatments, including diameter of stem xylem vessels (9.1% and 13.7%), leaf lower epidermal thickness (8.05% and 13.34%), and leaf phloem width (5.3% and 10.1%) under moderate and severe stress, respectively. Wild Vicia spp. showed better tolerance to water-deficit conditions as compared to cultivated Vicia L. The observed potential diversity for drought tolerance in wild Vicia spp. may assist in improvement of faba bean and may also help in understanding the mechanisms of adaptations in drought-prone environments.

Inter-tissue and inter-organ signaling in drought stress response and phenotyping of drought tolerance

Plant response to drought stress includes systems for intracellular regulation of gene expression and signaling, as well as inter-tissue and inter-organ signaling, which helps entire plants acquire stress resistance. Plants sense water-deficit conditions both via the stomata of leaves and roots, and transfer water-deficit signals from roots to shoots via inter-organ signaling. Abscisic acid is an important phytohormone involved in the drought stress response and adaptation, and is synthesized mainly in vascular tissues and guard cells of leaves. In leaves, stress-induced abscisic acid is distributed to various tissues by transporters, which activates stomatal closure and expression of stress-related genes to acquire drought stress resistance. Moreover, the stepwise stress response at the whole-plant level is important for proper understanding of the physiological response to drought conditions. Drought stress is sensed by multiple types of sensors as molecular patterns of abiotic stress signals, which are transmitted via separate parallel signaling networks to induce downstream responses, including stomatal closure and synthesis of stress-related proteins and metabolites. Peptide molecules play important roles in the inter-organ signaling of dehydration from roots to shoots, as well as signaling of osmotic changes and reactive oxygen species/Ca²⁺ . In this review, we have summarized recent advances in research on complex plant drought stress responses, focusing on inter-tissue signaling in leaves and inter-organ signaling from roots to shoots. We have discussed the mechanisms via which drought stress adaptations and resistance are acquired at the whole-plant level, and have proposed the importance of quantitative phenotyping for measuring plant growth under drought conditions.