Induction of Drought Tolerance in Maize (Zea mays L.) due to Exogenous Application of Trehalose: Growth,Photosynthesis, Water Relations and Oxidative Defence Mechanism

The present investigation was conducted to assess the ameliorative effects of foliar‐applied trehalose on growth, photosynthetic attributes, water relation parameters and oxidative defence mechanism in two maize cultivars under field water deficit conditions. Various components of the experiment comprised two maize cultivars (EV‐1098 and Agaiti‐2002), two water‐stress levels (irrigation after 2 weeks and irrigation after 3 weeks during the entire period of growth), and two levels of trehalose (0 and 30 mm ) and four replicates of each treatment. Water stress significantly reduced the plant biomass production, photosynthetic attributes and water relation parameters in both maize cultivars. In contrast, water stress considerably increased the leaf malondialdehyde (MDA) contents, the activities of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), and the levels of non‐enzymatic compounds such as ascorbic acid and tocopherols. In contrast, water stress caused a marked reduction in leaf phenolic contents. Foliar‐applied trehalose significantly increased plant biomass production, and improved some key photosynthetic attributes and plant–water relation parameters. The ameliorative effect of exogenously applied trehalose was also observed on the activities of some key antioxidant enzymes (POD and CAT) and non‐enzymatic compounds (tocopherols and phenolics). Overall, exogenously applied trehalose considerably improved drought tolerance of maize plants by up‐regulating photosynthetic and water relation attributes as well as antioxidant defence mechanism.     

Radiation‐Use Efficiency,Biomass Production,and Grain Yield in Two Maize Hybrids Differing in Drought Tolerance

Drought‐tolerant (DT) maize (Zea mays L.) hybrids have potential to increase yield under drought conditions. However, little information is known about the physiological determinations of yield in DT hybrids. Our objective was to assess radiation‐use efficiency (RUE), biomass production, and yield in two hybrids differing in drought tolerance. Field experiments were conducted in 2013 and 2014 with two hybrids, P1151HR (DT hybrid) and 33D49 (conventional hybrid) under well‐watered (I₁₀₀) and drought (I₅₀) conditions. I₁₀₀ and I₅₀ refer to 100 % and 50 % evapotranspiration requirement, respectively. On average, P1151HR yielded 11–27 % greater than 33D49 at I₁₀₀ and about 40 % greater at I₅₀, At I₁₀₀, greater yield in P1151HR was due to greater biomass at physiological maturity (BM_pm) resulting from greater post‐silking biomass accumulation (BM_post). At I₅₀, both hybrids had similar BM_pm but P1151HR showed a higher harvest index and greater BM_post. RUE differed significantly (P < 0.05) between the hybrids at I₁₀₀, but not at I₅₀. At I₁₀₀, the RUE values for P1151HR and 33D49 were 4.87 and 4.28 g MJ^?1 in 2013, and 3.71 and 3.48 g MJ^?1 in 2014. At I₅₀, the mean RUE was 3.89 g MJ^?1 in 2013 and 3.16 g MJ^?1 in 2014. Results indicate that BM_post is important for maintaining high yield in DT maize.     

Effect of Post-Anthesis Water Stress on Accumulation of Dry Matter, Carbon and Nitrogen and Their Partitioning in Wheat Varieties Differing in Drought Tolerance

In four wheat ( Triticum aestivum L.) cultivars of tall (C306 and Narmada) and dwarf (HD2329 and Kundan) type, post-anthesis water stress affected the dry matter accumulation in plant parts with respect to main shoot controls. HD2329 among the dwarf types and Narmada 112 among the tall types were more adversely affected by stress, with greater reductions in their biomass and grain yield. Of the tolerant types, C306 (tall) showed a marginal reduction while Kundan (dwarf) had no reduction in these parameters as a result of stress. The results also indicated a varietal response to carbon and nitrogen accumulation and their partitioning in the main shoot when subjected to post-anthesis stress. In the susceptible dwarf cultivar HD2329, and in the susceptible tall cultivar Narmada 112, carbon and nitrogen contents were reduced in the grains of stressed main shoots. Of the tolerant cultivars, the dwarf type Kundan was not affected by stress, while the tall type C306 registered an increase in carbon content and its partitioning to grain.     

Comparison of Drought Tolerance of Maize,Sweet Sorghum and Sorghum‐Sudangrass Hybrids

In drought‐prone environments, sweet sorghum and sorghum‐sudangrass hybrids are considered worthy alternatives to maize for biogas production. The biomass productivity of the three crops was compared by growing them side‐by‐side in a rain‐out shelter under different levels of plant available soil water (PASW) during the growing periods of 2008 to 2010 at Braunschweig, Germany. All crops were established under high levels of soil water. Thereafter, the crops either remained at the wet level (60–80 % PASW) or were subjected to moderate (40–50 % PASW) and severe drought stress (15–25 % PASW). While the above‐ground dry weight (ADW) of sweet sorghum and maize was insignificantly different under well‐watered conditions, sweet sorghum under severe drought stress produced 27 % more ADW than maize. The ADW of sorghum‐sudangrass hybrids significantly lagged behind sweet sorghum at all levels of water supply. The three crops differed markedly in their susceptibility to water shortage. Severe drought stress reduced the ADW of maize by 51 %, but only by 37 % for sweet sorghum and 35 % for sorghum‐sudangrass hybrids. The post‐harvest root dry weight (RDW) in the 0–100 cm soil layer for maize, sweet sorghum and sorghum‐sudangrass hybrids averaged 4.4, 6.1 and 2.9 t ha^?1 under wet and 1.9, 5.7 and 2.4 t ha^?1 under severe drought stress. Under these most dry conditions, the sorghum crops had relatively higher RDW and root length density (RLD) in the deeper soil layers than maize. The subsoil RDW proportion (20–100 vs. 0–20 cm) for maize, sweet sorghum and sorghum‐sudangrass hybrids amounted to 6 %, 10 % and 20 %. The higher ADM of sweet sorghum compared with maize under dry conditions is most likely attributable to the deep root penetration and high proportion of roots in the subsoil, which confers the sorghum crop a high water uptake capacity.     

Effect of Foliar Applications of Glycinebetaine on Stress Tolerance, Growth, and Yield of Spring Cereals and Summer Turnip Rape in Finland

Crop losses caused by environmental stresses might be reduced by applying osmoprotectans to crop canopies. Glycinebetaine is endogenously accumulated by some halophytes under stress conditions and represents such a compound. Glycinebetaine was applied exogenously to barley ( Hordeum vulgare L.), oat ( Avena sativa L.), spring wheat ( Triticum aestwum L.), and summer turnip rape ( Brassica rapa ssp. oleifera DC.) canopies and its optimal concentration was monitored in the greenhouse. In field experiments the response of crop plants to betaine applications was assessed by measuring accumulation of above ground biomass, leaf area index (LAI), leaf chlorophyll, and yield. The optimum betaine concentration producing advantageous effects on growth and crop physiology in turnip rape was close to 0.1 M and for wheat 0.3 M. Such concentrations promoted accumulation of betaine similar to that of halophytes under stress conditions [ca. 200 μmol (g DM)⁻¹]. In the 1993 field experiment peak LAIs were recorded in irrigated wheat and barley treated with 17.5 kg ha⁻¹ betaine applied at 300 1 ha⁻¹. Green leaf area was slightly more persistent in wheat treated twice with 1 kg ha⁻¹ betaine applied at 200 1 ha⁻¹ in 1994, although it was not associated with increased grain yield. Our results indicated that betaine has no actual potential in Finland for the principal grain crops but further studies are needed in stress prone environments to assess the potential of betaine treatments for preventing crop failures.     

Assimilation, Dissimilation and Accumulation of 14C in Two Maize (Zea mays L.) Hybrids of Different Drought Tolerance

The effects of exposure in the vegetative phase of growth to 5- or 10-day spells of soil drought (30% field water capacity) on assimilation, dissimilation and accumulation of ¹⁴C and on dry matter growth were studied in two maize hybrids, nos. 8344 and 8388 (Garst Seed Co.) of high and low drought tolerance. Under control water regime in soil there was no difference in ¹⁴CO₂ uptake and dry matter growth between hybrids. After five days of drought ¹⁴CO₂ assimilation dropped by about 75% referred to unit weight of dry matter in hybrid 8344 and by 56% in hybrid 8388. After 10 days of drought ¹⁴CO₂ assimilation rate was reduced by 75% in both hybrids. Soil drought increased the ¹⁴C dissimilation. There were no significant differences between hybrids in all treatments, with the exception of 5 days drought; after this treatment the dissimilation rate of hybrid 8344 was higher than that of 8388. Changes of translocation of ¹⁴C and its accumulation in particular organs occurred in drought treated plants; the amount of ¹⁴C accumulated in roots of plants of hybrid 8344 increased, while that of hybrid 8388 decreased. Changes of ¹⁴C accumulation in roots were positively correlated to changes of dry matter of those organs. One day after 10 days of drought assimilation and dissimilation rates in both hybrids were about 60% of controls.     

Comparative Effects of Salt and Water Stress on Seed Germination and Early Embryo Growth in Two Cultivars of Sweet Sorghum

In semiarid regions of the Mediterranean basin, water and salinity stresses restrict crop establishment. The effects of salt and water stress on seed germination and early embryo growth (radicle and shoot growth) were investigated in laboratory in two cultivars of sweet sorghum [Sorghum bicolor (L.) Moench] – cv. ‘90‐5‐2′ and cv. ‘Keller’ – to verify how these stresses may limit crop growth during the very early stages of growing season. Six water potentials (ψ) of the imbibition solution (from 0 to ?1.0 MPa) in NaCl or polyethylene glycol (PEG) for salt and water stress tests, respectively, were studied. Daily germination was recorded, and radicle and shoot lengths and dry weights (DWs) were measured 2 days after initial germination. Seed germination was reduced (8–30% lower than control) by water stress at ψ 相似文献   

Comparison of Salt and Drought‐Stress Effects on Maize Growth and Yield Formation with Regard to Acid Invertase Activity in the Kernels

The long‐term effects of salt stress (11 dS m^?1) and drought stress (35 % WHC) were investigated for two maize genotypes, focusing on the relation between metabolic changes around the time of pollination and the impact on yield determinants at maturity. The relatively salt‐resistant hybrid Pioneer 3906 and the relatively drought‐resistant hybrid Fabregas were compared. The experiments were conducted in large plastic containers in a vegetation hall in two consecutive years (2011 and 2012). Plant height and leaf area were significantly reduced under both stress conditions. The transpiration rate was only slightly reduced under drought stress; but under salt stress, a significant reduction occurred 40–53 days after sowing. As a significant increase in sucrose concentrations was observed in the salt‐treated maize kernels 2 days after pollination, the availability of assimilates was not limiting and the plants could afford to save water by reduced stomatal opening. Although under both stress conditions the soluble acid invertase activity was reduced 2 days after pollination, concomitantly, an increase in hexose concentrations was observed. Thus, in these experiments, the delivery of hexoses by acid invertase activity did not limit kernel development. Differences in grain yield at maturity between salt and drought stress were most likely caused by salt‐specific effects (Na⁺ toxicity), Fabregas being more affected than Pioneer 3906.     

Nitrogen Rates and Water Stress Effects on Production, Lipid Peroxidation and Antioxidative Enzyme Activities in Two Maize (Zea mays L.) Genotypes

Effects of nitrogen rates and water stress (WS) on production, lipid peroxidation and antioxidative enzyme activities in two maize (Zea mays L.) genotypes were assessed at different stages under two levels of water supply conditions. WS caused a significant decline in dry matter, grain yield and activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) whereas a marked rise in malondialdehyde (MDA) concentration was observed in leaves for the two genotypes. However, the responses of the two varieties to WS were different: significantly higher dry matter, grain yield and antioxidative enzyme activities and lower MDA content were observed for Shaandan 9 than Shaandan 911, therefore the former could be treated as a drought tolerance variety comparatively. A better correlation was obtained amongst dry matter, grain yield and physiological traits. The addition of nitrogen increased dry matter and grain yield as well as activities of SOD, POD and CAT to different levels and significantly decreased MDA content under WS. These effects were higher for Shaandan 911 than for Shaandan 9. Furthermore, a significant effect was found for Shaandan 911 between N rates for all traits unlike Shaandan 9. Hence, we suggest that nitrogen should be applied to a water‐sensitive variety to bring out its potential fully under drought.     

Effects of Soil Drought in the Generative Phase of Development of Field Bean (Vicia faba L. var. minor) on Leaf Water Status, Photosynthesis Rate and Biomass Growth

The effects of 10-day periods of soil drought during flowering (DI) or pod growth (DII) and during both these phases (DI + DII) on leaf water status, photosynthesis rate, plant growth and production of biomass was studied in pot experiments with field bean. Soil water content during drought spells were kept at 30% of field water capacity. Soil water deficiency DI and DII depressed the leaf water potential relatively to control by about 100 % and 140 % respectively, increased the water deficit by 100 % and 120 % and reduced photosynthesis rate by 80 % and 90 %. Rehydration of tissues completely abolished any decline of photosynthesis rate caused by drought DI, but after drought DII photosynthesis rate remained depressed by about 30 % even after rehydration. Drought periods DI and DII caused more rapid withering of leaves, a decline in the total leaf area and a temporary increase of root weight.
Drought occuring at flowering (DI) also activated the mechanism of plant adaptation to water deficiency during the pod formation phase (DII). Single or double periods of drought had not any significant influence on the number of pods and seeds, but decreased their weight.