Irrigation Withholding Research Articles

Exploring drought mitigation options for improvement of physiology, yield and water use efficiency of aerobic rice (Oryza sativa)

An experiment was conducted during summer seasons of 2022 and 2023 in Wetland Farms at Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu to mitigate the ill effects of moisture stress during the flowering stage of rice (Oryza sativa L.) by moisture stress mitigating chemicals. The trial was laid out in split plot design (SPD) with 3 main plots and 4 sub-plots, and replicated thrice. In main plot, irrigation at IW/CPE ratio 1.0 from emergence to physiological maturity (M1); withholding irrigation (drought stress) for 8 days from heading stage (M2); and withholding irrigation (drought stress) for 12 days from heading stage (M3) and in sub-plot drought stress mitigating chemicals, viz. no spray (S1); salicylic acid spray @100 ppm (S2); sodium selenate @20 ppm (S3); and pink pigmented facultative methylotrophs (PPFM) @1% (S4) were tested. Results revealed that irrigation at IW/CPE 1.0 from crop emergence to physiological maturity along with foliar spray of selenium @20 ppm at heading stage had beneficial impact on growth, physiological parameters, yield attributes and yield. Drought stress given for 8 days from heading stage with selenium spray recorded lesser detrimental effect on growth characters, yield attributes and yield when compared to drought stress given for 12 days from heading stage in aerobic rice cultivation. The yield reduction in drought stress for 12 days from heading stage with selenium @20 ppm spray and drought stress for 8 days from heading stage with selenium @20 ppm spray were 23.6 and 16.5% respectively, when compared to irrigation at IW/ CPE ratio 1.0 from crop emergence to physiological maturity with selenium spray @20 ppm. Water use efficiency and water profitability also increased by the application of stress mitigating chemical of sodium @20 ppm. From this study, it is recommended that, in aerobic rice cultivation if there is any drought occurrence during heading stage of crop, the selenium application @20 ppm can withstand drought even up to 8 days from heading stage.

Leaf photosynthetic performance is not a key factor affecting grain yield in spring wheat subjected to heat and combined heat and drought stresses

AbstractThe yield traits and physiological responses of three wheat genotypes were studied when subjected to heat and combined heat and drought stress at anthesis under either aCO2 (400 ppm) or eCO2 (800 ppm) in a greenhouse. The heat treatment was 7‐days at day/night 35/28°C, and the combined heat and drought was withholding irrigation from the heat‐stressed plants until the photosynthetic rate reached <5 μmol m−2 s−1. The LM62 genotype had higher photosynthetic rate compared with LM19, though no significant difference in grain yield was found. eCO2 increased photosynthesis at 35°C and significantly lowered the electron transport rate at high intercellular CO2 concentrations. Maximum velocity of Rubisco carboxylation (Vcmax) and the maximum velocity of RuBP regeneration in leaves (Jmax) increased in 35°C compared with 25°C, though when normalized to 25°C both Vcmax and Jmax decreased in the heat‐stressed plants, indicating that an inhibition had occurred. The maximum photochemical efficiency of photosystem II (Fv/Fm) decreased under heat, which correlated with the yield loss caused by the stress. Fv/Fm also decreased under combined heat and drought, though it did not related to the declined yield. A small leaf area prolonged the drying period of Gladius, and it was the genotype with the lowest decrease in yield because of stress. It is concluded that the effects of heat and combined heat and drought stress on the gas exchange and photosynthetic capacity on leaf area basis are not directly linked to the yield performance among wheat genotypes, while the morphological characteristics of the plants are important determinants of grain yield in response to those abiotic stresses.

Effect of Different Cultural Treatments on Branching and Yield of Groundnut (Arachis hypogea L.)

The experiment was carried out at college of agriculture, karekere, hassan agricultural farm during year June 2022 to November 2022. The objective of this investigation was to study the effects of five different treatments nipping, passing empty drums, withhold of irrigation, nipping without irrigation and remaining cultural practices done at 20,20,30,30 and 30 days after sowing on the number of branches and yield of groundnut. A randomized complete block design with four replications was used in this experiment. The data was recorded based on different treatments on above mentioned days before and after sowing. The recorded results were observed as follows: no of branches recorded were nipping, passing of empty drums, withholding of irrigation, nipping without irrigation and following usually recommended practices were 19,21,15,21 and 15 respectively. The yield obtained in different treatment plots were 46.6, 53.9, 38.4, 58.5 (failure due to heavy rain) and 38.4 Q/ha, respectively. So, by observing the above results, we can conclude that the passing empty drums method showed high branches and high yield compared to other treatments. So, this cultural treatment can be recommended to farmers for increasing both yield and branches.

Salt and Water Stress Tolerance in Ipomoea purpurea and Ipomoea tricolor, Two Ornamentals with Invasive Potential

Invasive plants pose a significant threat to biodiversity, especially under the current unstable climatic conditions. This study aimed to test the salt and drought tolerance of two ornamental species of the genus Ipomoea during germination and vegetative growth. Germination tests were performed in the presence of increasing NaCl concentrations or iso-osmotic PEG concentrations—to mimic the osmotic stress caused by drought. Both species showed great invasive potential because of their high seed germination percentages and rapid germination under control (distilled water) and salt stress conditions, up to 200 mM NaCl. Germination and early seedling development were more affected in the presence of PEG. Subsequently, water stress (complete withholding of irrigation) and salt stress (watering with 100 mM and 200 mM NaCl) treatments were applied to young plants for three weeks, when all plants were harvested, to determine several morphological and biochemical parameters. Both species were sensitive to water deficit but relatively resistant to salt stress. Their salt stress responses were similar, based mainly on the inhibition of Na+ and the activation of K+ transport from roots to leaves and the uptake and accumulation of Ca2+; however, I. tricolor showed a slightly higher tolerance to salt stress than I. purpurea. Although I. tricolor has only been locally reported as invasive and is generally considered a ‘low-risk’ species, our results indicate that it may have an invasive potential even higher than I. purpurea, a recognised invasive weed, spread into areas with moderate salinity, affecting agricultural land or natural habitats of ecological interest.

Melatonin Decreases Negative Effects of Combined Drought and High Temperature Stresses through Enhanced Antioxidant Defense System in Tomato Leaves

In tomato (Lycopersicon esculentum L.), the effects of combined drought (D) and high temperature (HT) stress during the flowering stage had not been studied in detail. Therefore, this study was conducted with an objective of quantifying the effects of foliar spray of melatonin under individual and combined drought and HT stress. At flowering stage, D stress was imposed through withholding irrigation, while HT stress was imposed through exposing the plants to ambient temperature (AT) along with an increase of +5 °C. Under D + HT, plants were first subjected to drought followed by a + 5 °C increase in AT. The duration of individual or combined stress was ten days. At 80% available soil moisture, 100 µM melatonin was sprayed on D, HT, or D + HT treated plants. Among the stresses, D + HT stress increased the thylakoid membrane damage and decreased the photosynthetic rate and fruit yield more than D or HT stress. Foliar spray of 100 µM melatonin produced decreased thylakoid membrane damage [D: 31%, HT: 26%, and D + HT: 18%] and increased antioxidant enzyme, viz., superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, and glutathione reductase, activity over stress-control plants. The photosynthetic rate [D: 24%, HT: 22%, and D + HT: 19%] and fruit yield [D: 32%, HT: 23%, and D + HT: 16%] were increased over stress-control plants. Hence, it is evident that the increased photosynthetic rate and fruit yield in D + HT and 100 µM melatonin-sprayed plants may be associated with an increased antioxidant defense system. Melatonin as a novel biostimulator has a great potential in scavenging free radicals through increased antioxidant activity, which shields the photosynthetic membrane from damage and therefore helps in stress mitigation.

Evaluation of Drought Responses in Two Tropaeolum Species Used in Landscaping through Morphological and Biochemical Markers.

One of the most important challenges horticultural crops confront is drought, particularly in regions such as the Mediterranean basin, where water supplies are usually limited and will become even scarcer due to global warming. Therefore, the selection and diversification of stress-tolerant cultivars are becoming priorities of contemporary ornamental horticulture. This study explored the impact of water stress on two Tropaeolum species frequently used in landscaping. Young plants obtained by seed germination were exposed to moderate water stress (half the water used in the control treatments) and severe water stress (complete withholding of irrigation) for 30 days. Plant responses to these stress treatments were evaluated by determining several growth parameters and biochemical stress markers. The latter were analysed by spectrophotometric methods and, in some cases, by non-destructive measurements using an optical sensor. The statistical analysis of the results indicated that although the stress responses were similar in these two closely related species, T. minus performed better under control and intermediate water stress conditions but was more susceptible to severe water stress. On the other hand, T. majus had a stronger potential for adaptation to soil water scarcity, which may be associated with its reported expansion and naturalisation in different regions of the world. The variations in proline and malondialdehyde concentrations were the most reliable biochemical indicators of water stress effects. The present study also showed a close relationship between the patterns of variation of flavonoid and chlorophyll contents obtained by sensor-based and spectrophotometric methods.

Effect of Recurrent Salt and Drought Stress Treatments on the Endangered Halophyte Limonium angustebracteatum Erben

Limonium angustebracteatum is an endemic halophyte from the Spanish Mediterranean coastal salt marshes. To investigate this species' ability to cope with recurrent drought and salt stress, one-year-old plants were subjected to two salt stress treatments (watering with 0.5 and 1 M NaCl solutions), one water stress treatment (complete irrigation withholding), or watered with non-saline water for the control, across three phases: first stress (30 days), recovery from both stresses (15 days), and second stress (15 days). Growth and biochemical parameters were determined after each period. The plants showed high salt tolerance but were sensitive to water deficit, as shown by the decrease in leaf fresh weight and water content, root water content, and photosynthetic pigments levels in response to the first water stress; then, they were restored to the respective control values upon recovery. Salt tolerance was partly based on the accumulation of Na+, Cl- and Ca2+ in the roots and predominantly in the leaves; ion levels also decreased to control values during recovery. Organic osmolytes (proline and total soluble sugars), oxidative stress markers (malondialdehyde and H2O2), and antioxidant compounds (total phenolic compounds and flavonoids) increased by various degrees under the first salt and water stress treatments, and declined after recovery. The analysed variables increased again, but generally to a lesser extent, during the second stress phase, suggesting the occurrence of stress acclimation acquired by the activation of defence mechanisms during the first stress period.

Phenotyping Olive Cultivars for Drought Tolerance Using Leaf Macro-Characteristics

This work investigates the relationships between leaf traits and olive response to water stress through two complementary field experiments in order to screen genotypes for drought tolerance. The first experiment consisted of the phenotyping of 32 olive varieties for 11 leaf morpho-physiological traits during a fruit set phase under well-watered conditions. In the second experiment, the yield and vegetative responses of five representative varieties to the withholding of irrigation during the whole fruit growth period were assessed to identify leaf traits that are associated with olive resilience plasticity and that could be used as drought tolerance markers. The results highlighted large phenotypic variability for leaf area (LA, 2.9–9.5 cm2), petiole elasticity (8.0–36.0°), water loss in detached leaves (WLDL, 3.6–11.6%), stomatal density (222.6–470.1 no mm−2), stomatal length (11.4–18.7 µm), trichome density (120.5–204.4 no mm−2), trichome width (103.6–183.4 µm), leaf contents in cuticular wax (CWC, 44.7–606.2 µg cm−2), and soluble sugars (SSC, 15.8–536.9 mg gdw−1). Among these leaf traits, WLDL displayed a significant correlation with the yield stability index (r = −0.973) and water use efficiency (r = −0.939), suggesting its use as relevant drought tolerance phenotypic marker. Likewise, LA, SSC, and CWC were singled out as second-level drought tolerance markers, being strongly correlated with stability of leaf size and leafing intensity in response to water stress. Cluster analysis highlighted 12 distinct levels of drought tolerance within the studied olive collection. Based on the four identified phenotypic markers, “Lechin de Sevilla” alongside “Picholine Marocaine” were found to be the most drought-tolerant varieties, while Frantoio was the most sensitive. This study provides the first, unprecedented, insights into the usefulness of leaf phenotyping in olive drought tolerance screening, with a focus on structural and functional leaf traits.

Multivariate and Association Analyses of Quantitative Attributes Reveal Drought Tolerance Potential of Wheat (Triticum aestivum L.) Genotypes

ABSTRACT Drought is a major abiotic stress that limits wheat productivity around the globe. Therefore, a two-year (2019 and 2020) study was conducted in the experimental area of the Department of Plant Breeding and Genetics, Faculty of Agriculture & Environment, The Islamia University of Bahawalpur, Pakistan to estimate the association of quantitative attributes under normal and drought stress conditions. Twenty-five wheat genotypes from different research institutes of Pakistan were selected. Experiment was conducted in a randomized complete block design (RCBD) under field conditions with three replicates each. Two irrigation treatments were used, i.e., E1 with full irrigation and E2 with irrigation withheld at tillering and anthesis stages according to Zadoks growth stage scale. Significant differences were observed in studied wheat genotypes under both conditions for all the traits. Correlation analysis revealed highest positive association (r = 0.924**) between grain yield and flag leaf area followed by thousand grain weight (r = 0.754**) under normal conditions while biological yield was highly correlated with grain yield (r = 0.890**) under drought stress. PCA showed that out of the 12 PCs, only four were significant having eigenvalues >1; accounting for 83.33% and 79.12% of the total variation under normal and drought stress conditions, respectively. Furthermore cluster heat map divided the genotypes into four clusters and revealed that the most tolerant genotypes (Barani-17, Chakwal-50 and Johar-2016) were fallen into cluster 2 depicting their genetic relatedness. Based on tolerance indices, genotypes G11 (Barani-17), G12 (Ehsan-16), and G13 (Dharabi-11) were drought tolerant and G4 (Benazir-13), G20 (Punjab-2011) were drought-sensitive.

Recovery from Salinity and Drought Stress in the Perennial Sarcocornia fruticosa vs. the Annual Salicornia europaea and S. veneta.

Current agricultural problems, such as the decline of freshwater and fertile land, foster saline agriculture development. Salicornia and Sarcocornia species, with a long history of human consumption, are ideal models for developing halophyte crops. A greenhouse experiment was set up to compare the response of the perennial Sarcocornia fruticosa and the two annual Salicornia europaea and S. veneta to 30 days of salt stress (watering with 700 mM NaCl) and water deficit (complete withholding of irrigation) separate treatments, followed by 15 days of recovery. The three species showed high tolerance to salt stress, based on the accumulation of ions (Na+, Cl−, Ca2+) in the shoots and the synthesis of organic osmolytes. These defence mechanisms were partly constitutive, as active ion transport to the shoots and high levels of glycine betaine were also observed in non-stressed plants. The three halophytes were sensitive to water stress, albeit S. fruticosa to a lesser extent. In fact, S. fruticosa showed a lower reduction in shoot fresh weight than S. europaea or S. veneta, no degradation of photosynthetic pigments, a significant increase in glycine betaine contents, and full recovery after the water stress treatment. The observed differences could be due to a better adaptation of S. fruticosa to a drier natural habitat, as compared to the two Salicornia species. However, a more gradual stress-induced senescence in the perennial S. fruticosa may contribute to greater drought tolerance in this species.

Exogenously used boron and 24-epibrassinolide improved oil quality and mitigate late-season water deficit stress in camelina

The high oil content and quality of camelina [Camelina sativa (L.) Crantz] seed oil for various uses, including human nutrition and industry, has encouraged many countries to increase the cultivation of this oilseed crop. Due to the coincidence of initial irrigations of summer crops with the final stages of camelina growth, production of this crop in arid and semi-arid regions depends on tolerance to the late-season water deficit stress. Therefore this two years field experiment focused on boron (B) and 24-epibrassinolide (EBL) foliar spray effect on seed yield, oil content, oil yield and fatty acids profile (FAs) of camelina in a semi-arid area (Iran) during 2018−19 and 2019−20 growing season. Experimental treatments were arranged in a split-plot design based on randomized complete blocks with three replicates. Irrigation regimes based on withholding irrigation (WI): [full irrigation (FI) at 50 % of available soil water (ASW); withholding irrigation with 20 % of ASW from full flowering to silicle formation (WI1); withholding irrigation with 20 % of ASW from silicle formation to harvesting (WI2)] were considered as the main plots and ten levels of foliar spray (FS) consisted of control (non foliar spray), distilled water, B (0.5 and 1%) and EBL (0.5 and 1 μM) and their concomitant use (B 0.5 % + EBL 0.5μm, B 0.5 % + EBL 1μm, B 1% + EBL 0.5μm, and B 1% + EBL 1μm) were randomized to the subplot units. Seed and oil yield decreased by 6.7–8.4 % and 10–12 %, respectively in response to the water deficit during the flowering and silicle formation stages. The negative effect of drought stress on the quality of camelina oil was recorded as 3.3–5.3 % increment in erucic acid and significant decrease in the unsaturated fatty acids (UFAs) content, oleic acid (by 4.6–8.5 %), linoleic acid (by 3.5 %), linolenic acid (by 2.5 %) and 1.2–2.8 % for monounsaturated fatty acids (ΣMUFAs) content compared with the control treatment. While foliar spary of B and EBL increased oil content by ranged from 2 to 4% under-withholding irrigation treatments. Also ecosanoic acid and polyunsaturated fatty acids (ΣPUFAs) content significantly increased under combined application of B0.5 + EBL (0.5 and 1).

Inoculation with Bacillus amyloliquefaciens and mycorrhiza confers tolerance to drought stress and improve seed yield and quality of soybean plant.

The present study aimed to evaluate the effect of Bacillus amyloliquefaciens and/or Arbuscular Mycorrhizal Fungi (AMF) as natural biofertilizers on biomass, yield, and seed nutritive quality of soybean (Giza 111). The conditions investigated include a well-watered (WW) control and irrigation withholding at the seed development stage (R5, after 90 days from sowing) (DS). Co-inoculation with B. amyloliquefaciens and AMF, resulted in the highest plant biomass and yield under WW and DS conditions. The nuclear DNA content analysis suggested that co-inoculation with B. amyloliquefaciens and AMF decreased the inhibition of drought stress on both the size and granularity of seed cells, which were comparable to the normal level. The single or co-inoculation with B. amyloliquefaciens and AMF increased the primary metabolites content and alleviated the drought-induced reduction in soluble sugars, lipids, protein and oil contents. Plant inoculation induced the expression of genes involved in lipid and protein biosynthesis, whereas an opposite trend was observed for genes involved in lipid and protein degradation, supporting the observed increase in lipid and protein content. Plant inoculated with B. amyloliquefaciens showed the highest α-amylase and β-amylase activities, indicating improved osmolyte (soluble sugar) synthesis, particularly under drought. Interestingly, single or co-inoculation further strengthen the positive effect of drought on the antioxidant and osmoprotectant levels, i.e. phenol, flavonoid, glycine betaine contents, and glutathione-S-transferase (GST) activity. As a result of stress release, there was a decrease in the level of stress hormones (abscisic acid, ABA) and an increase in gibberellin (GA), trans-zeatin-riboside (ZR), and indole acetic acid (IAA) in the seeds of inoculated plants. Additionally, the ATP content, hydrolytic activities of plasma membrane H+ -ATPase, Ca2+ -ATPase, and Mg2+ -ATPase were also increased by the inoculation.

Effect of flower regulation on biotic and abiotic stress management in Pomegranate (Punica granatumL.) under hot arid climate

The present study was carried out for management of abiotic stresses (fruit cracking) and biotic stresses (mite and fungal spot) in pomegranate by flower regulation through water stress, pruning and ethrel application. The results revealed that horticultural interventions, chemical treatments and their interactions significantly minimized mite, fungal spot and fruit cracking incidence in pomegranate. In different combinations treatments of horticultural interventions and chemical, minimum mite incidence (4.80 and 4.65%) and fungal spot incidence (9.17 and 7.83%) were recorded in withholding irrigation during June + pruning + thinning with ethrel 2 ml/l treatment as compared to maximum mite (31.95 and 27.51%) and fungal spot (35.78 and 32.58%) recorded in control natural flowering without chemicals during the years 2017-18 and 2018-19, respectively. Lower fruit cracking incidence i.e. <2.0 kg/plant was observed in withholding of irrigation during June + pruning + thinning with ethrel applications in both years. The maximum fruit cracking (2.51 and 3.24 kg/plant) was recorded in withholding of irrigation during March without chemicals treatment during 2017-18 and 2018-19, respectively. Therefore, it can be concluded that withholding irrigation during June + pruning + thinning with ethrel 2 ml/l treatment reduced mite and fungal spot incidence and fruit cracking through induction of flowering and fruit growth during optimal climatic conditions and enhanced management.

Effects of Drought and Salinity on Two Commercial Varieties of Lavandula angustifolia Mill.

Global warming is not only affecting arid and semi-arid regions but also becoming a threat to agriculture in Central and Eastern European countries. The present study analyzes the responses to drought and salinity of two varieties of Lavandula angustifolia cultivated in Romania. Lavender seedlings were subjected to one month of salt stress (100, 200, and 300 mM NaCl) and water deficit (complete withholding of irrigation) treatments. To assess the effects of stress on the plants, several growth parameters and biochemical stress markers (photosynthetic pigments, mono and divalent ions, and different osmolytes) were determined in control and stressed plants after the treatments. Both stress conditions significantly inhibited the growth of the two varieties, but all plants survived the treatments, indicating a relative stress tolerance of the two varieties. The most relevant mechanisms of salt tolerance are based on the maintenance of foliar K+ levels and the accumulation of Ca2+ and proline as a functional osmolyte in parallel with increasing external salinities. Under water stress, significant increases of Na+ and K+ concentrations were detected in roots, indicating a possible role of these cations in osmotic adjustment, limiting root dehydration. No significant differences were found when comparing the stress tolerance and stress responses of the two selected lavender varieties.

Growth of Lonicera caerulea across Fertility and Moisture Conditions: Comparisons with Lonicera villosa and Invasive Congeners

Several species of honeysuckle from Europe and Asia have proved to be invasive in North America, with substantial impacts on native ecosystems. Although shrubby honeysuckles of Eurasian origin have appeared on banned plant lists in North America and other parts of the world, cultivars of the edible blue honeysuckle (Lonicera caerulea L.) derived from Eurasian germplasm and marketed as honeyberry, Haskap, or sweetberry honeysuckle have recently been widely developed for agricultural use in North America, with little scrutiny of invasive potential in North America despite its documented invasion of the Scandinavian Peninsula in northern Europe. To gain insight into differences in growth strategies among congeners, we compared the growth of Eurasian L. caerulea with that of a closely related congener in North America [Lonicera villosa (Michx.) R. &amp; S.] and two known invasive congeners from Eurasia (Lonicera tatarica L. and Lonicera xylosteum L.). In Expt. 1, L. villosa, L. caerulea, and L. tatarica were grown in #1 nursery containers after top-dressing with Osmocote Pro 17–5–11 4-month controlled-release fertilizer (CRF) at rates of 5, 10, 15, 20, and 25 g CRF/container. Across all fertilizer treatments, L. caerulea outperformed L. villosa by a factor of two for root and shoot dry weights, although L. tatarica produced more growth than either of the others and was more responsive to increasing CRF. However, L. caerulea more strongly resembled L. tatarica in form, producing leaves of greater individual size and producing significantly taller primary stems than L. villosa, evidence for prioritization of competitive growth. In Expt. 2, plants of the same taxa plus L. xylosteum were grown communally in #20 nursery containers, followed by a period in which each container was subjected to regular irrigation, withheld irrigation (dry treatment), or inundation (flooded treatment). Plant growth differed substantially among taxa, but moisture treatments did not affect growth significantly. As in Expt. 1, plants of L. caerulea in Expt. 2 produced greater dry biomass than plants of L. villosa and resembled the invasive Eurasian honeysuckles more strongly in size and form. We conclude Eurasian L. caerulea is distinct in growth rate and morphology from North American L. villosa. In light of these findings, the ecology and competitive ability of Eurasian L. caerulea may not be well predicted by ecological observations of its closely related North American congener.

Determining optimum period of withholding irrigation for inducing maturity of sugarcane (Saccharum spp. hybrid) in Southern Ethiopia

Withholding irrigation before harvesting is important for inducing maturity in sugarcane. The study was carried out to determine the optimum period of withholding irrigation for inducing maturity in sugarcane in southern Ethiopia. Field experiments were conducted on two sugarcane varieties, N Co 334 and B 52 298 by five treatments of withholding irrigation periods for 20, 30, 40 50 and 60 days in randomized complete block design at the crop age of 11.3 months during 2014-15. The data on soil moisture content, top to bottom ratio of Brix in cane juice by hand refractometer, Brix, pol, purity and reducing sugars percent juice, and recoverable sugar percent cane, estimated sugar yield were recorded. Error variances for all characters except top to bottom ratio of Brix and reducing sugars in canes in experiments of both varieties were homogeneous and thus the data were also analyzed in split-plot design with varieties as the main plot and withholding irrigation period (WIP) treatments as subplots. The soil moisture percent differed at different WIPs with lowest at WIP for 60 days. Quality characters, top to bottom ratio of Brix in juice, Brix, pol or sucrose, purity, and sugar recovery percent cane increased significantly with the increase in WIPs, being highest at 50 and 60 days. Reducing sugars percent juice declined significantly with lowest at WIPs for 60 days. Estimated sugar yield increased significantly with the maximum at WIP for 50 and 60 days. The optimum period for withholding irrigation was 50 to 60 days for inducing maturity in sugarcane if not offset by rains. It was, therefore, suggestive that the irrigation could be withheld to sugarcane crop of about 12 months for 50 to 60 days but the quality of sugarcane should be determined before harvesting for obtaining maximum sugar yield in southern Ethiopia

Physiological Beneficial Effect of Rhizophagus intraradices Inoculation on Tomato Plant Yield under Water Deficit Conditions

Increasing drought, under current climate change scenarios, will reduce the sustainability of tomato cultivation in the Mediterranean region. The present study evaluates the effect of Rhizophagus intraradices inoculation on tomato plant physiology and yield in response to progressive water deficit conditions. Two commercial products (Prod1 and Prod2) containing only R. intraradices were tested at two different concentrations (1% and 5% of the substrate volume) using three methods of inoculation: (a) mixed to substrate, (b) dissolved in water, (c) spread on seedlings root blocks before transplant. The highest mycorrhization of root fragments (F%) was found with Prod2 at 1% w/w at 40 days after sowing (DAS); this product was therefore used in a second experiment to inoculate tomato plants and test their physiological response to progressive water deficit induced withholding irrigation. Phenology, plant height, stem diameter, chlorophyll content and fluorescence, whole canopy gas exchange, biomass production and partitioning and phosphorus content were investigated in inoculated and not inoculated tomato plants under well-watered and water stressed conditions. Vegetative period and plant height were shorter in inoculated than in control plants; moreover, inoculation with R. intraradices increased fruit production by enhancing chlorophyll content under water stress condition, PS2 efficiency, ETR, Fv/Fm, net photosynthetic rate and whole canopy WUE.

Studies on flowering induction, sex ratio and fruit set improvement in pomegranate

The present study was conducted to induce flowering at the desired period with higher percentage of bisexual flowers and fruit set to improve yield and minimize fruit cracking through withholding of irrigation, pruning and ethrel application. Pooled data analysis revealed that horticultural interventions, chemical treatments and their interactions significantly affected sex ratio and fruit set. Among horticultural interventions, earliest defoliation (10.47 days), highest defoliation (81.25%), shortest flowering period (64.46 days), minimum male flowers (58.59%), maximum bisexual flowers (27.43%), maximum fruit set (25.84%) and fruit retention (82.23%) were recorded in withholding of irrigation during June + pruning and thinning as compared to control natural flowering. Among chemical treatments, earliest defoliation (7.59 days), highest defoliation (93.35%) and shortest flowering period (61.07 days) were recorded in ethrel 3 ml/l + DAP 5 g/l application while minimum male flowers (59.21%), maximum bisexual flowers (25.51%), maximum fruit set (25.16%) and fruit retention (80.74%) were recorded in ethrel 2 ml/l + DAP 5 g/l treatment as compared to control. Among interactions, earlier defoliation (6.78 days), highest defoliation (95.72%) and shortest flowering period (55.42 days) were observed in withholding of irrigation during June + pruning and thinning + ethrel 3 ml/l + DAP 5 g/l treatment. The minimum male flowers (57.78%), maximum bisexual flowers (28.22%), maximum fruit set (26.39%) and fruit retention (83.34%) were recorded in withholding of irrigation during June + pruning and thinning + ethrel 2 ml/l + DAP 5 g/l treatment as compared to maximum male flowers (66.36%), minimum bisexual flowers (22.03%), fruit set (22.19%) and fruit retention (75.28%) recorded in natural flowering without chemical treatment. Therefore, it can be concluded that withholding of irrigation during June + pruning and thinning + ethrel 2 ml/l + DAP 5 g/l treatment induced flowering during optimal climatic conditions and significantly improved sex ratio and fruit set of pomegranate.

Screening for Salt and Water Stress Tolerance in Fir (Abies alba) Populations

Drought periods are becoming more frequent and intense, due to the effects of climate change, threatening natural habitats worldwide, including European forests. Forest trees can also be affected by high soil salinity, because of the common practice of de-icing of mountain roads with NaCl in winter. We have evaluated the responses to salt and water stress of silver fir (Abies alba), an important forest species for which very limited information is available. One-year-old fir seedlings, with origin in seven different locations in Romania, were subjected to salt (watering with NaCl solutions of increasing concentrations) and water deficit (complete withholding of irrigation) treatments in the greenhouse. After one month, plant material was harvested and different morphological parameters were determined in the stressed and control plants. Both stress treatments inhibited growth of fir seedlings from all seven provenances, although quantitative differences in the responses to stress were observed between populations. Growth inhibition was established by the relative reduction – as compared to the non-stressed controls - in several parameters, such as stem elongation, root length, number of needles, or fresh weight and water content of roots and needles. Statistical multivariate analysis of the results suggested that seedlings from Valea Morii (population 6) were the most tolerant to both, water deficit and high (300 mM NaCl) salt concentrations. These results support the possibility to screen a large number of individuals from different populations, at the seedling stage, to select Abies alba genotypes with enhanced drought and/or salinity tolerance.&#x0D; &#x0D; *********&#x0D; In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue.&#x0D; *********

The effect of micronutrient foliar application on yield, seed quality and some biochemical traits of soybean cultivars under drought stress

This experiment carried out as split plot factorial based on a randomized complete block design with three replications during two consecutive years (2015–2016). The main plot consisted of drought stress: complete irrigation, irrigation withholding at R1 stage, irrigation withholding at R2 stage and subplots included foliar application of micronutrients: distilled water (control), zinc sulfate, manganese sulfate and zinc sulfate + manganese sulfate and cultivar as: Williams and Zan elite. The results showed that proline and linoleic acid were increased significantly, but chlorophyll a and b, seed yield, protein percentage, oleic and linolenic acids were decreased significantly by irrigation withholding. Also, the maximum values of chlorophyll b, protein percentage and linolenic acid were achieved by Williams. The significant increasing effect of zinc was found on the maximum root and stem proline, chlorophyll b, and oleic, linolenic and linoleic unsaturated fatty acids, meanwhile the maximum leaf proline was obtained by manganese sulfate.