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Drought tolerance in higher plants can result in enhanced productivity, especially in case of carbohydrate storage root crop. Sweet potato has been reported as a drought-tolerant crop, while it is very sensitive to water shortage in the root initiation of cutting propagation and tuber initiation stages. In the present study, we aimed to alleviate the drought-tolerant abilities in sweet potato cv. Tainung 57 (drought-sensitive cultivar) using foliar glycine betaine (GlyBet) application as compared with drought-tolerant cultivar (cv. Japanese Yellow). Leaf osmotic potential in GlyBet applied plants under mild- (25.5% soil water content; SWC) and severe-water deficit (15.5% SWC) stresses was maintained through the accumulation of total soluble sugars as a major osmotic adjustment, thus stabilizing the photosynthetic pigments, chlorophyll fluorescence, net photosynthetic rate, and retaining the overall growth performances, i.e., shoot height, number, and length of leaves. In the harvesting process, storage root weight in water deficit stressed sweet potato cv. Tainung 57 (11.75 g plant−1) with 50 mM GlyBet application was retained in a similar pattern to cv. Japanese Yellow (12.25 g plant−1). In the present investigation, exogenous foliar GlyBet application strongly alleviated water deficit stress via sugar enrichment to control cellular osmotic potential, retain high photosynthetic abilities and maintain the yield of storage root yield. In summary, the regulation on total soluble sugar enrichment in water deficit–stressed sweet potato using GlyBet foliar application may play an important role in maintaining the controlled osmotic potential of leaves, thereby retaining the photosynthetic abilities, overall growth characters and increasing the yield of storage roots.

Assessing drought tolerance and the ability of plants to adjust to changes in available water resources is crucial for understanding current and future distributions of plant species. While turgor loss point (πtlp) has been recognized as a direct determinant of drought tolerance in woody plants, information on it for grassland species is largely missing. We first validated a rapid method to estimate πtlp for grassland species, using osmometry measurements (πtlp‐osm) of osmotic potential at full hydration (πo‐osm), originally proposed for woody species. We confirmed that πo‐osm was tightly positively related to πtlp measured by the classic pressure–volume curve (πtlp‐pv). Cell wall elasticity was not important in the maintenance of turgor and neither specific leaf area nor leaf dry matter content influenced πtlp. We then studied the relationship between πtlp‐osm measured under controlled conditions and species’ soil moisture affinity (Ellenberg indicator values) in 40 diverse grassland species from the full range of soil moisture conditions found in temperate grasslands. On a subset of 12 species, we studied the adjustment in πtlp‐osm to drought stress and recovery from drought. We hypothesized that dry grassland species are better adapted to drier conditions by having comparatively higher leaf drought tolerance (more negative πtlp) and a better ability to adjust to acute drought stress. We found that πtlp‐osm was unrelated to species’ soil moisture affinity. However, all species developed higher leaf drought tolerance by decreasing πtlp‐osm after seven weeks of drought stress. After only one week of recovery, all species reduced the leaf drought tolerance back to the πtlp‐osm level comparable with non‐stressed plants. Our results considerably extend the relationship between πo‐osm and πtlp, originally defined for woody species, and thus propose a yet unexploited direct method for assessing leaf drought tolerance via turgor loss point in herbaceous species. However, the lack of relationship between πtlp and soil moisture affinity suggests that, unlike in woody plants, leaf‐level drought tolerance in grassland plants does not fully translate into whole‐plant drought resistance, suggesting an importance of other drought resistance strategies. A plain language summary is available for this article. Plain Language Summary

Understanding local adaptation to climate is critical for managing ecosystems in the face of climate change. While there have been many provenance studies in trees, less is known about local adaptation in herbaceous species, including the perennial grasses that dominate arid and semiarid rangeland ecosystems. We used a common garden study to quantify variation in growth and drought resistance traits in 99 populations of Elymus elymoides from a broad geographic and climatic range in the western United States. Ecotypes from drier sites produced less biomass and smaller seeds, and had traits associated with greater drought resistance: small leaves with low osmotic potential and high integrated water use efficiency (δ13C). Seasonality also influenced plant traits. Plants from regions with relatively warm, wet summers had large seeds, large leaves, and low δ13C. Irrespective of climate, we also observed trade‐offs between biomass production and drought resistance traits. Together, these results suggest that much of the phenotypic variation among E. elymoides ecotypes represents local adaptation to differences in the amount and timing of water availability. In addition, ecotypes that grow rapidly may be less able to persist under dry conditions. Land managers may be able to use this variation to improve restoration success by seeding ecotypes with multiple drought resistance traits in areas with lower precipitation. The future success of this common rangeland species will likely depend on the use of tools such as seed transfer zones to match local variation in growth and drought resistance to predicted climatic conditions.

Sweet white lupin has a growing importance as a staple crop due to its rich protein and mineral content. Investigation of unfavorable environmental conditions at the seedling stage is critical for understanding and overcoming the challenges during germination and initial growth. In this study, the effects of salt and drought stress were investigated upon induction of NaCl and PEG6000 osmotic agents at iso-osmotic potential (0, -0.3 and -0.6 MPa) on seed germination and initial seedling growth in sweet white lupin (Lupinus albus L.). The research was carried out for 21 days under laboratory conditions according to a completely randomized plot design with 4 replicates. In order to assess the growth upon stress, germination percentage, mean germination time, germination rate index, shoot and root length, root/shoot length, shoot and root fresh weight, shoot and root dry weight, shoot and root dry matter content, root/shoot dry matter content, shoot and root water content and seedling vigor index parameters were measured. The results demonstrated that NaCl and PEG6000 solutions applied at the same osmotic potential had statistically significant effects on the measured germination and growth parameters. PEG6000 treatments at the same osmotic potential had more adverse effects on germination and initial seedling growth than NaCl treatments. In addition, shoot growth was more adversely affected than root growth in PEG6000 and NaCl treatments. The germination was limited in -0.6 MPa PEG6000 treatment and no subsequent seedling growth was observed. In this study, we documented that the white lupine's tolerance to drought during germination and initial seedling growth periods was lower than salinity at the same iso-osmotic potential and saline and arid soils showing an osmotic water potential of -0.6 MPa (12.7 dS m-1 EC and 22% PEG6000) are inhibitory for lupin germination and growth. This study lays the ground for further physiological and molecular studies on the effects of salt and osmotic stress on white lupins.

ABSTRACT Combretum leprosum Mart., commonly known as ‘mofumbo’, is used for medicinal purposes, recovery of degraded areas and apiculture. The objective of this study was to evaluate the effect of water stress on the germination and vigor of C. leprosum seeds as function of different temperatures. To compose the treatments, the substrate used was paper roll moistened with polyethylene glycol solutions (PEG 6000), at the following levels of osmotic potential: 0.0; -0.1; -0.2; -0.2; -0.4; and -0.5 MPa, and placed in chamber at constant temperatures of 25, 30 and 35 and alternating temperature of 20-30 °C, forming a 6 x 4 factorial. The seeds were submitted to the following evaluations: germination percentage, germination speed index, root length, shoot length, root dry matter, shoot dry matter. There was a significant interaction for all variables, with a negative effect as the osmotic potentials decreased. Thus, C. leprosum showed high sensitivity to low osmotic potentials, showing a steeper decrease from the potential of -0.2 MPa for all evaluated temperatures. Initial germination and development of C. leprosum seedlings was negatively affected by low osmotic potentials, with a tolerance limit of -0.4 MPa. Temperatures of 25 and 35 °C accentuate the negative effect of the low osmotic potential of water on the germination and early development of C. leprosum seedlings.

Andrographis paniculata has been widely used as a medicinal herb due to its enriched total andrographolide contents. Methyl jasmonate (MeJA), a natural plant signal-transducer molecule, is a potential elicitor in regulating secondary metabolites and alleviating drought stress. The objective of the present study was to assess the impacts of exogenously-applied foliar MeJA on morphological, physiological, and biochemical traits as well as total andrographolide contents of A. paniculata under water-deficit stress. The experiment consisted of four different foliar MeJA doses [0 (distilled water or control), 125, 250, and 500 μM] exogenously-applied at the pre-flowering stage (100 days after sowing) on uniform plants and two soil moisture regimes [well-watered (WW; 100% field capacity) and water-deficit (WD; 67.6% field capacity)]. Leaf osmotic potential of the WD plants was significantly declined by 25.43% over the WW plants, leading to chlorophyll degradation (SPAD value), diminution of photon yield of photosystem II (Φ PSII ), and reduction in net photosynthetic rate (P n ) and plant biomass. Foliar application of 250 μM MeJA alleviated the negative effects of water-deficit stress by improving leaf osmotic potential, SPAD value, Φ PSII , P n , and transpiration rate. Leaf biomass of A. paniculata was retained under MeJA treatments even in water-deficit conditions. An increase in neoandrographolide, 14-deoxyandrographolide, total andrographolide, and andrographolide yield per plant was observed when 125 μM MeJA was applied under water-deficit stress. Exogenous foliar application of MeJA at 250 μM alleviates water-deficit stress in A. paniculata and may provide an important tool to minimize the economic loss caused by dry conditions during the vegetative growth stage.

Arbuscular mycorrhizal fungi (AMF) are a consortium of symbiont fungi present in the root zone of plants, which provide phosphorus and enhance the soil water holding capacity, resulting in low-cost input for plant growth and development. The objective of this study was to promote growth and development of Indian pennywort (Centella asiatica (L.) Urb.) via arbuscular mycorrhizal fungi (AMF)-regulated water deficit tolerance. One-month-old stolon propagated stocks were cultivated under greenhouse conditions by following a regular irrigation schedule for a month. Two treatments of soil samples were prepared: i) sterilized soil—AMF and ii) sterilized soil + AMF. Three water regimes, (i) well-watering (control; 95% field capacity), (ii) moderately water deficit (73% field capacity) and (iii) severely water deficit (66% field capacity) for 14 days, were applied. Root colonization in + AMF plants was larger than—AMF, leading to the enhanced phosphorus content in the leaf tissues and better plant growth performances. Leaf temperature (Tleaf) (+ 0.92 °C) and crop water stress index (1.74 folds) were significantly increased, when subjected to severely water deficit. In contrast, leaf greenness was increased by 1.42 folds over the control and the maximum quantum yield of PSII and photon yield of PSII were retained. In the case of gas exchange parameters, net photosynthetic rate, and stomatal conductance were sensitive to severely water deficit. Under without AMF-inoculation, net photosynthetic rate was decreased by 52.2 and 79.1% when subjected to moderate and severe water deficit conditions, respectively. Increment of free proline and glucose in the water deficit stressed plants were evidently observed as major osmolytes to control the leaf osmotic potential, especially under without AMF-inoculation. Under AMF inoculation, free proline and glucose concentration in the leaf tissues was stable even subjected to moderate and severe water deficit. Madecassoside content in + AMF plants was the maximum at 120 mg g−1 dry weight, and it was retained under moderately water deficit at 118.9 mg g−1 dry weight, whereas it declined by 37.11% over the control when subjected to severely water deficit. Similarly, centellosides yield in + AMF plants under moderately water deficit was increased over the control (− AMF) and declined by 5 folds when subjected to severely water deficit. In the case of herbal yield traits, number of leaves, leaf area and plant biomass of AMF-inoculated plants were greater than those of without AMF inoculation and also retained even subjected to WD stress. In summary, AMF inoculation is an alternative way to promote madecassoside, high biomass yield and high centellosides content as well as alleviate moderate water deficit stress during the production of Indian pennywort.

Hydroponic culture containing 200 mM NaCl was used to induce oxidative stress in seedlings of cultivars initially primed with 1 mM SNP and 10 µM ABA. Exogenous application of sodium nitroprusside (SNP – a nitric oxide donor) and abscisic acid (ABA) was well sensitized more in cv. Swarna Sub1 than cv. Swarna and also reflected in different cellular responses. The major effects of salinity, irrespective of the cultivar, were lowering the water relation, including relative water content and osmotic potential, and decreasing the compatible solutes like alanine, gamma-aminobutyric acid, and glycine betaine. The accumulated polyamines were reduced more in cv. Swarna with a concomitant decrease in photosynthetic reserves. NADP-malic enzyme activity, sucrose accumulation, ascorbate peroxidase, and glutathione S-transferase activities gradually declined under NaCl stress and the catabolizing enzymes like invertase (both wall and cytosolic forms) also declined. On the contrary, plants suffered from oxidative stress through superoxide, hydrogen peroxide, and their biosynthetic enzymes like NADP(H) oxidase. Moderation of Na+/K+ by both SNP and ABA were correlated with other salt sensitivities in the plants. The maximum effects of SNP and ABA were found in the recovery of antioxidation pathways, osmotic tolerance, and carbohydrate metabolism. Findings predict the efficacy of SNP and ABA either independently or cumulatively in overcoming NaCl toxicity in rice.

The combined effects of deficit irrigation and crop load level on sweet cherry (Prunus avium L.) physiological and agronomic response were evaluated during the 2019 season in a commercial orchard located in southeastern Spain. Two irrigation treatments were imposed: (i) control treatment (CTL) irrigated above crop water requirements at 110% of crop evapotranspiration (ETC) and (ii) a deficit irrigation treatment (DI) irrigated at 70% ETC. Within each irrigation treatment, crop load was adjusted to three levels: 100% (natural crop load—high), 66% (medium crop load), and 33% (low crop load). The water relations results were more affected by the irrigation strategies applied than by the crop load management. The deficit irrigation strategy applied reduced soil water availability for DI trees, which led to a continuous decrease in their gas exchange and stem water potential. At harvest, the fruit water potential and osmotic potential of cherries from the DI treatment resulted in significantly lower values than those measured in cherries from CTL trees. On the other hand, both the irrigation strategies imposed and the crop load management used impacted fruit quality. Trees with the lowest level of crop load had fruits of greater size, regardless of the irrigation treatment assayed, and in the DI treatment, cherries from the trees with the lowest crop load were darker and more acidic than those from the trees with the highest crop load. Our results emphasize the different effects that rainfall before harvest has on mature cherries. Thus, cracked cherries at harvest represented 27.1% of the total yield of CTL trees while they were 8.3% of the total yield in DI trees. Cherries from CTL trees also showed a greater cracking index than those from DI trees. Moreover, a linear relationship between crop load and fruit cracked at harvest was observed, particularly for the CTL treatment; thus, the lower the crop load, the greater the proportion of cracked cherries.

Many studies have investigated the impact of a single calcium salt on plant physiology under heat-stress, but it is difficult to determine the effect of calcium from those of its counterions. To address this, we investigated calcium-mediated heat tolerance in tomato seedlings using foliar sprays of four different salt solutions: CaCl2, CaNO3, MgCl2 or KNO3. 24 h heat-The application of CaCl2 and CaNO3 improved the operating efficiency of photosystem II (PSII) in the light-adapted state (ΦPSII), maximum quantum efficiency of PSII in the dark-adapted state (Fv/Fm), and the CO2 assimilation rate under the heat-stress condition. In contrast, the application of MgCl2 and KNO3 had no significant effect on,those parameters. The application of CaCl2 and CaNO3 resulted in a lower production of hydrogen peroxide, superoxide, and cell death than the heat-stressed control plants. The application of MgCl2 and KNO3 also resulted in lower hydrogen peroxide and superoxide production, but to a lesser extent. Leaf osmotic potential values of seedlings treated with the salt solutions were lower than the control.