Drought and heat stress: insights into tolerance mechanisms and breeding strategies for pigeonpea improvement

MAIN CONCLUSION

Pigeonpea has potential to foster sustainable agriculture and resilience in evolving climate change; understanding bio-physiological and molecular mechanisms of heat and drought stress tolerance is imperative to developing resilience cultivars. Pigeonpea is an important legume crop that has potential resilience in the face of evolving climate scenarios. However, compared to other legumes, there has been limited research on abiotic stress tolerance in pigeonpea, particularly towards drought stress (DS) and heat stress (HS). To address this gap, this review delves into the genetic, physiological, and molecular mechanisms that govern pigeonpea's response to DS and HS. It emphasizes the need to understand how this crop combats these stresses and exhibits different types of tolerance and adaptation mechanisms through component traits. The current article provides a comprehensive overview of the complex interplay of factors contributing to the resilience of pigeonpea under adverse environmental conditions. Furthermore, the review synthesizes information on major breeding techniques, encompassing both conventional methods and modern molecular omics-assisted tools and techniques. It highlights the potential of genomics and phenomics tools and their pivotal role in enhancing adaptability and resilience in pigeonpea. Despite the progress made in genomics, phenomics and big data analytics, the complexity of drought and heat tolerance in pigeonpea necessitate continuous exploration at multi-omic levels. High-throughput phenotyping (HTP) is crucial for gaining insights into perplexed interactions among genotype, environment, and management practices (GxExM). Thus, integration of advanced technologies in breeding programs is critical for developing pigeonpea varieties that can withstand the challenges posed by climate change. This review is expected to serve as a valuable resource for researchers, providing a deeper understanding of the mechanisms underlying abiotic stress tolerance in pigeonpea and offering insights into modern breeding strategies that can contribute to the development of resilient varieties suited for changing environmental conditions.

Shade moderates the drought stress on saplings of Beneh (Pistacia atlantica Desf. subsp. mutica) in semiarid areas of Iran

Pistacia atlantica Desf. (Beneh) is an important woody species that has been facing significant challenges to its natural regeneration and reforestation in Iran. This study investigates the interaction of soil moisture and shade on growth, chemical contents, and morphological and physiological characteristics of Beneh saplings. One-year-old Beneh saplings were treated with varying amounts of soil moisture (20, 50, and 100% of field capacity) and shade (0, 30, and 50% of full sunlight) in a split-plot experiment of a randomized complete block design in semiarid conditions of the Alborz Research Station of the Research Institute of Forests and Rangelands (RIFR) in Iran. The results indicate that soil moisture significantly affects the water content of the leaf, total chlorophyll, proline content, activity of catalase enzyme, leaf dry biomass, leaflet area, and dry stem biomass in the leaf. Shade significantly affected total chlorophyll, catalase enzyme activity, specific leaflet area, relative water content of the leaf, proline content, dry root biomass, and leaflet area. The interaction of shade and soil moisture significantly affected seedling height, catalase enzyme activity, specific leaflet area, and nitrogen and potassium content of the leaf. Shade moderates the stress of drought on Beneh saplings, but shading of Beneh saplings is not recommended in conditions where there is no concern about soil moisture. These conclusions can be used to improve the production of Beneh saplings in nurseries.

Mechanistic insights of CRISPR/Cas-mediated genome editing towards enhancing abiotic stress tolerance in plants

Abiotic stresses such as temperature (high/low), drought, salinity, and others make the environment hostile to plants. Abiotic stressors adversely affect plant growth and development; and thereby makes a direct impact on overall plant productivity. Plants confront stress by developing an internal defense system orchestrated by compatible solutes, reactive oxygen species scavengers and phytohormones. However, routine exposure to unpredictable environmental stressors makes it essential to equip plants with a system that contributes to sustainable agricultural productivity, besides imparting multi-stress tolerance. The sustainable approach against abiotic stress is accomplished through breeding of tolerant cultivars. Though eco-friendly, tedious screening and crossing protocol limits its usage to overcome stress and in attaining the goal of global food security. Advancement on the technological front has enabled adoption of genomic engineering approaches to perform site-specific modification in the plant genome for improving adaptability, increasing the yield and in attributing resilience against different stressors. Of the different genome editing approaches, CRISPR/Cas has revolutionized biological research with wider applicability to crop plants. CRISPR/Cas emerged as a versatile tool in editing genomes for desired traits in highly accurate and precise manner. The present study summarizes advancement of the CRISPR/Cas genome editing tool in its adoption to manipulate plant genomes for novel traits towards developing high-yielding and climate-resilient crop varieties.

Biodiverse food plants in the semiarid region of Brazil have unknown potential: A systematic review

Food biodiversity presents one of the most significant opportunities to enhance food and nutrition security today. The lack of data on many plants, however, limits our understanding of their potential and the possibility of building a research agenda focused on them. Our objective with this systematic review was to identify biodiverse food plants occurring in the Caatinga biome, Brazil, strategic for the promotion of food and nutrition security. We selected studies from the following databases: Web of Science, Medline/PubMed (via the National Library of Medicine), Scopus and Embrapa Agricultural Research Databases (BDPA). Eligible were original articles, published since 2008, studying food plants occurring in the Caatinga. We assessed the methodological quality of the studies we selected. We reviewed a total of fifteen studies in which 65 plants that met our inclusion criteria were mentioned. Of this amount, 17 species, including varieties, subspecies, and different parts of plants, had data on chemical composition, in addition to being mentioned as food consumed by rural communities in observational ethnobotanical studies. From the energy and protein data associated with these plants, we produced a ranking of strategic species. The plants with values higher than the average of the set were: Dioclea grandiflora Mart. ex Benth (mucunã), Hymenaea courbaril L. (jatobá), Syagrus cearensis Noblick (coco-catolé), Libidibia ferrea (Mart. ex Tul.) L.P.Queiroz (jucá), Sideroxylon obtusifolium (Roem. & Schult.) T.D.Penn. (quixabeira). We suggest that the scientific community concentrates research efforts on tree legumes, due to their resilience and physiological, nutritional, and culinary qualities.

Proteomic Characterisation of Lupin (Lupinus angustifolius) Milk as Influenced by Extraction Techniques, Seed Coat and Cultivars

Lupin seeds are rich in proteins and other essential ingredients that can help to improve human health. The protein contents in both whole and split seeds of two lupin cultivars (Mandleup and PBA Jurien) were used to produce the lupin milk using the cheesecloth and centrifuge method. Proteins were extracted from the lupin milk using thiourea/urea solubilization. The proteins were separated by a two-dimensional polyacrylamide gel electrophoresis and then identified with mass spectrometry. A total of 230 protein spots were identified, 60 of which showed differential abundances. The cheesecloth separation showed protein extractability much better than that of the centrifuge method for both the cultivars. The results from this study could offer guidance for future comparative analysis and identification of lupin milk protein and provide effective separation technique to determine specific proteins in the cheese-making process.

Research Progress and Perspective on Drought Stress in Legumes: A Review

Climate change, food shortage, water scarcity, and population growth are some of the threatening challenges being faced in today's world. Drought stress (DS) poses a constant challenge for agricultural crops and has been considered a severe constraint for global agricultural productivity; its intensity and severity are predicted to increase in the near future. Legumes demonstrate high sensitivity to DS, especially at vegetative and reproductive stages. They are mostly grown in the dry areas and are moderately drought tolerant, but severe DS leads to remarkable production losses. The most prominent effects of DS are reduced germination, stunted growth, serious damage to the photosynthetic apparatus, decrease in net photosynthesis, and a reduction in nutrient uptake. To curb the catastrophic effect of DS in legumes, it is imperative to understand its effects, mechanisms, and the agronomic and genetic basis of drought for sustainable management. This review highlights the impact of DS on legumes, mechanisms, and proposes appropriate management approaches to alleviate the severity of water stress. In our discussion, we outline the influence of water stress on physiological aspects (such as germination, photosynthesis, water and nutrient uptake), growth parameters and yield. Additionally, mechanisms, various management strategies, for instance, agronomic practices (planting time and geometry, nutrient management), plant growth-promoting Rhizobacteria and arbuscular mycorrhizal fungal inoculation, quantitative trait loci (QTLs), functional genomics and advanced strategies (CRISPR-Cas9) are also critically discussed. We propose that the integration of several approaches such as agronomic and biotechnological strategies as well as advanced genome editing tools is needed to develop drought-tolerant legume cultivars.

Sensitivity of chickpea and faba bean to root-zone hypoxia, elevated ethylene, and carbon dioxide

During soil waterlogging, plants experience O₂ deficits, elevated ethylene, and high CO₂ in the root-zone. The effects on chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) of ethylene (2 μL L^-1 ), CO₂ (2-20% v/v) or deoxygenated stagnant solution were evaluated. Ethylene and high CO₂ reduced root growth of both species, but O₂ deficiency had the most damaging effect and especially so for chickpea. Chickpea suffered root tip death when in deoxygenated stagnant solution. High CO₂ inhibited root respiration and reduced growth, whereas sugars accumulated in root tips, of both species. Gas-filled porosity of the basal portion of the primary root of faba bean (23%, v/v) was greater than for chickpea (10%), and internal O₂ movement was more prominent in faba bean when in an O₂ -free medium. Ethylene treatment increased the porosity of roots. The damaging effects of low O₂ , such as death of root tips, resulted in poor recovery of root growth upon reaeration. In conclusion, ethylene and high CO₂ partially inhibited root extension in both species, but low O₂ in deoxygenated stagnant solution had the most damaging effect, even causing death of root tips in chickpea, which was more sensitive to the low O₂ condition than faba bean.

Waterlogging of Winter Crops at Early and Late Stages: Impacts on Leaf Physiology, Growth and Yield

Waterlogging is expected to increase as a consequence of global climate change, constraining crop production in various parts of the world. This study assessed tolerance to 14-days of early- or late-stage waterlogging of the major winter crops wheat, barley, rapeseed and field pea. Aerenchyma formation in adventitious roots, leaf physiological parameters (net photosynthesis, stomatal and mesophyll conductances, chlorophyll fluorescence), shoot and root growth during and after waterlogging, and seed production were evaluated. Wheat produced adventitious roots with 20-22% of aerenchyma, photosynthesis was maintained during waterlogging, and seed production was 86 and 71% of controls for early- and late-waterlogging events. In barley and rapeseed, plants were less affected by early- than by late-waterlogging. Barley adventitious roots contained 19% aerenchyma, whereas rapeseed did not form aerenchyma. In barley, photosynthesis was reduced during early-waterlogging mainly by stomatal limitations, and by non-stomatal constraints (lower mesophyll conductance and damage to photosynthetic apparatus as revealed by chlorophyll fluorescence) during late-waterlogging. In rapeseed, photosynthesis was mostly reduced by non-stomatal limitations during early- and late-waterlogging, which also impacted shoot and root growth. Early-waterlogged plants of both barley and rapeseed were able to recover in growth upon drainage, and seed production reached ca. 79-85% of the controls, while late-waterlogged plants only attained 26-32% in seed production. Field pea showed no ability to develop root aerenchyma when waterlogged, and its photosynthesis (and stomatal and mesophyll conductances) was rapidly decreased by the stress. Consequently, waterlogging drastically reduced field pea seed production to 6% of controls both at early- and late-stages with plants being unable to resume growth upon drainage. In conclusion, wheat generates a set of adaptive responses to withstand 14 days of waterlogging, barley and rapeseed can still produce significant yield if transiently waterlogged during early plant stages but are more adversely impacted at the late stage, and field pea is not suitable for areas prone to waterlogging events of 14 days at either growth stage.

A global experimental dataset for assessing grain legume production

Grain legume crops are a significant component of the human diet and animal feed and have an important role in the environment, but the global diversity of agricultural legume species is currently underexploited. Experimental assessments of grain legume performances are required, to identify potential species with high yields. Here, we introduce a dataset including results of field experiments published in 173 articles. The selected experiments were carried out over five continents on 39 grain legume species. The dataset includes measurements of grain yield, aerial biomass, crop nitrogen content, residual soil nitrogen content and water use. When available, yields for cereals and oilseeds grown after grain legumes in the crop sequence are also included. The dataset is arranged into a relational database with nine structured tables and 198 standardized attributes. Tillage, fertilization, pest and irrigation management are systematically recorded for each of the 8,581 crop*field site*growing season*treatment combinations. The dataset is freely reusable and easy to update. We anticipate that it will provide valuable information for assessing grain legume production worldwide.

Tolerance of three grain legume species to transient waterlogging

Waterlogging reduces the yield of food crops. Tolerance to waterlogging could vary between and within species. This study aimed to quantify tolerance to soil waterlogging in two divergent genotypes of pea (Pisum sativum), two of lentil (Lens culinaris) and a grasspea (Lathyrus sativus) control at germination and during vegetative growth. Following germination, seeds were grown for 14 days in soil waterlogged with the water table 10 mm below the surface, and then by draining the pots and allowing to recover for 21 days-to be compared with 35 days of continuous waterlogging. In both pea and lentil, the pair of genotypes contrasted widely with large-seeded pea genotype Kaspa and lentil genotype Nugget showing higher (2-fold) root porosity and less effect on shoot nitrogen content under waterlogging than the other genotypes (NPE and ATC). During recovery, the same two genotypes-Kaspa pea and Nugget lentil-also recovered better than their smaller-seeded species pairs. Soil waterlogging at 10 mm depth had no significant effect on shoot and root dry mass after 14 days. Root penetration into waterlogged soil was restricted to ∼100 mm depth and its distribution altered for pea and lentil genotypes but not for grasspea. Within the small sample studied, we demonstrated a significant genetic variation in both pea and lentil in tolerance to waterlogging after germination and subsequent recovery for the first time. Screening of additional pea and lentil germplasm for waterlogging conditions is clearly warranted.

Growth responses of cool-season grain legumes to transient waterlogging

Transient waterlogging reduces the yield of cool-season grain legumes in several parts of the world. The tolerance of grain legumes to waterlogging may vary between and within species. This study investigated the effects of 7 days of waterlogging and subsequent recovery (10 days) on plant growth to evaluate the variation in tolerance among 7 cool-season grain legume species, in sand culture in glasshouse experiments. Additionally waterlogging tolerance of 6 faba bean genotypes was also evaluated. Tolerance to waterlogging as indicated by root and shoot growth (as % of drained controls) was ranked as follows: faba bean > yellow lupin > grass pea > narrow-leafed lupin > chickpea > lentil > field pea. Faba bean produced adventitious roots and aerenchyma leading to increased root porosity (9% gas volume per unit root volume). Among the 6 faba bean genotypes screened, accession 794 showed the best waterlogging tolerance, but it was also the slowest growing accession, which might have contributed to apparent tolerance (i.e. growth as % drained control). It is concluded that waterlogging tolerance in grain legumes varied between and within species, with faba bean being the most tolerant. The variation in tolerance identified within the limited set of faba bean genotypes evaluated suggests scope for further genetic improvement of tolerance in this species.

Lupin: the largest grain legume crop in Western Australia, its adaptation and improvement through plant breeding

Between 500 000 and 1 000 000 tonnes of narrow-leafed lupins (Lupinus angustifolius L.) are produced in Western Australia each year. It has become the predominant grain legume in Western Australian agriculture because it is peculiarly well adapted to acid sandy soils and the Mediterranean climate of south-western Australia. It has a deep root system and root growth is not reduced in mildly acid soils, which allows it to fully exploit the water and nutrients in the deep acid sandplain soils that cover much of the agricultural areas of Western Australia. It copes with seasonal drought through drought escape and dehydration postponement. Drought escape is lupin’s main adaptation to drought, and has been strengthened by plant breeders over the past 40 years by removal of the vernalisation requirement for flowering, and further selection for earlier flowering and maturity. Lupin postpones dehydration by several mechanisms. Its deep root system allows it to draw on water from deep in the soil profile. Lupin stomata close to reduce crop water demand at a higher leaf water potential than wheat, but photosynthetic rates are higher when well watered. It has been proposed that stomata close in response to roots sensing receding soil moisture, possibly at a critical water potential at the root surface. This is an adaptation to sandy soils, which hold a greater proportion of their water at high matric potentials than loamy or clayey soils, since the crop needs to moderate its water use while there is still sufficient soil water left to complete its life cycle. Lupin has limited capacity for osmotic adjustment, and does not tolerate dehydration as well as other crops such as wheat or chickpea. Plant breeding has increased the yield potential of lupin in the main lupin growing areas of Western Australia by 2–3 fold since the first adapted cultivar was released in 1967. This has been due largely to selecting earlier flowering and maturing cultivars, but also to improved pod set and retention, resistance to Phomopsis leptostromiformis (Kühn) Bubák, and more rapid seed filling. We propose a model for reproductive development in lupin where vegetative growth is terminated in response to receding soil moisture and followed by a period in which all assimilate is devoted to seed filling. This should allow lupin to adjust its developmental pattern in response to seasonal conditions to something like the optimum that mathematical optimal control theory would choose for that season. This is the type of pattern that has evolved in lupin, and the task of future plant breeders will be to fine-tune it to better suit the environment in the lupin growing areas of Western Australia.

Grain yield and cadmium concentration of a range of grain legume species grown on two soil types at Merredin, Western Australia

Five grain legumes species, narrow-leafed lupin (Lupinus angustifolius L.), field pea (Pisum sativum L.), faba bean (Vicia faba L.), chickpea (Cicer arietinum L.), and yellow lupin (Lupinus luteus L.), were grown on 2 soil types, a red clay and red duplex soil, in the < 400 mm rainfall district of Western Australia. The study showed that chickpea, field pea and faba bean accumulated less cadmium (Cd) in dried shoots and grain than narrow-leafed lupin. Yellow lupin had Cd concentrations ~3 times higher in dried shoots and ~9 times higher in grain than narrow-leafed lupin. For both experiments, the ranking (lowest to highest) of mean Cd concentration (mg Cd/kg) in the grain was: chickpea (0.017) < field pea (0.024) = faba bean (0.024) < narrow-leafed lupin (0.033) < yellow lupin (0.300).