Leaf Tissue Concentrations Research Articles

The SOS4 pyridoxal kinase is required for maintenance of vitamin B6-mediated processes in chloroplasts

Vitamin B(6) (pyridoxal 5'-phosphate and its vitamers) is an important cofactor in numerous enzymatic reactions. In spite of its importance, the consequences of altering vitamin B(6) content on plant growth and development are not well understood. This study compares two mutants for vitamin B(6)-metabolizing enzymes in Arabidopsis thaliana: a pdx1.3 mutant in the de novo synthesis pathway and a salvage pathway sos4 mutant that accumulates more vitamin B(6). We show that despite a difference in total B(6) content in leaf tissue, both mutants share similar phenotypes, including chlorosis, decreased size, altered chloroplast ultrastructure, and root sensitivity to sucrose. Assay of B(6) vitamer content from isolated chloroplasts showed that, despite differing B(6) vitamer content in whole leaf tissue, both mutants share a common deficiency in total and phosphorylated vitamers in chloroplasts. One of the splice variants of the SOS4 proteins was shown to be located in the chloroplast. Our data indicate that some of the phenotypic consequences shared between the pdx1.3 and sos4 mutants are due to B(6) deficiency in chloroplasts, and show that SOS4 is required for maintenance of phosphorylated B(6) vitamer concentrations in chloroplasts. Further, our data are consistent with a diffusion model for transport of vitamin B(6) into chloroplasts.

Wheat yield and physico-chemical properties of a sodic soil from semi-arid area of Iran as affected by applied gypsum

Irrigation by highly sodic water has been practiced only in recent years in Iran but has led to impaired productivity of thousands of hectares of agricultural lands. So, the present study was set out to evaluate the effectiveness of different rates and sizes of gypsum as an amendment which improves the physical and chemical properties of soil and crop productivity. A field experiment was conducted in a sodic soil at a farmer's field in Ramjerd, Fars. The treatments consisted of two gypsum granule sizes (1–10mm and <1mm), and two application methods (adding gypsum to the irrigation water and mixing it with soil) were employed at three soil-applied gypsum levels, i.e., 50%, 75% and 100% of gypsum requirement (GR). The findings of the study showed that the application of gypsum increased soil salinity and hydraulic conductivity but decreased sodium adsorption ratio (SAR) and pH. The increase of wheat yield in coarse gypsum was greater than that observed in fine gypsum but, concerning most soil and plant parameters, the difference between fine and coarse gypsum was not significant at all in terms of rates of GR. Drought condition was found to diminish the effect of gypsum on soil and plants as a 10% reduction in wheat yield was observed in a drought year as compared with a normal year. Plant density, fertile spikelets, and 1000-grain weight were improved as the soil-applied gypsum increased. Regarding chemical composition of leaf, plants grown on un-amended plots had higher Na and lower potassium (K) and calcium (Ca) concentrations in leaf tissue. The application of gypsum caused a significant increase in nitrogen (N), phosphorus (P), Ca, K, iron (Fe), and zinc (Zn) concentrations in wheat tissue but copper (Cu) and manganese (Mn) concentrations remained unchanged. It also increased Ca:Na and K:Na ratios in leaf tissue and had positive effects on crop yield. It was finally recommended that farmers reclaim sodic soil by applying coarse gypsum at the rate of 100% GR since it is a more cost-effective way of reclamation of sodic soil.

Silicon and Fungicide Effects on Anthracnose in Moderately Resistant and Susceptible Sorghum Lines

AbstractThis study aimed to evaluate the effect of silicon (Si) and its interaction with fungicide on the management of sorghum anthracnose. The experiments were carried out in Si‐deficient soil in the 2008/2009 and 2009/2010 growing seasons in a randomized, complete block, split‐split plot design with four replications. Calcium silicate (CS) and lime (L), at the rates of 6 and 5 ton/ha, respectively, were randomly assigned to the main plot. Two sorghum lines, BR‐008 (resistant) and BR‐009 (susceptible), were assigned to the split plots. The split‐split plots corresponded to with or without the fungicide Opera® (epoxiconazole + pyraclostrobin). The residual effect of CS and L from the 2008/2009 growing season was evaluated in the 2009/2010 growing season. For the 2008/2009 growing season, the area under anthracnose progress curve (AUAPC) was reduced by 39 and 42% for lines BR‐008 and BR‐009, respectively, with the application of CS. In the presence of the fungicide, the AUAPC was reduced by 35 and 42% for the CS and L treatments, respectively. Calcium silicate with and without fungicide contributed to decreasing the AUAPC by 44 and 37%, respectively. The fungicide spray decreased the AUAPC by 50 and 39% for lines BR‐008 and BR‐009, respectively. Without fungicide, the AUAPC decreased by 88% for line BR‐008 compared with line BR‐009; however, with fungicide, the reduction reached 90%. The Si leaf tissue concentration significantly increased with the CS application (5.9 g/kg) compared with the L application (0.3 g/kg), regardless of the sorghum line. The yield increased by 0.6 ton/ha with the CS compared to the L application. The fungicide increased yield by 0.48 ton/ha compared with the non‐fungicide spray treatment. The residual effect of CS in the soil increased Si leaf tissue concentration and yield as well as reduced the intensity of anthracnose in the 2009/2010 growing season.

Evaluation of zinc tolerance and accumulation potential of the coastal shrub Limoniastrum monopetalum (L.) Boiss.

The coastal shrub Limoniastrum monopetalum is capable of growth in soil containing extremely high concentrations of heavy metals. A greenhouse experiment was conducted in order to investigate the effects of a range of Zn concentrations (0–130mmoll−1) on growth and photosynthetic performance, by measuring relative growth rate, total leaf area, plant height, gas exchange, chlorophyll fluorescence parameters and photosynthetic pigment concentrations. We also determined the total zinc, nitrogen, phosphorus, sulphur, calcium, magnesium, sodium, potassium, iron and copper concentrations in the plant tissues. The study species demonstrated hypertolerance to Zn stress, since survival was recorded with leaf concentrations of up to 1700mgZnkg−1 dry mass when treated with 130mmolZnl−1. L. monopetalum exhibited little overall effects on photosynthetic function at Zn levels of up to 90mmoll−1. At greater external Zn concentration, plant growth was negatively affected, due in all probability to the recorded decline in net photosynthetic rate, which may be linked to the adverse effect of the metal on photosynthetic electron transport. Growth parameters were virtually unaffected by leaf tissue concentrations as high as 1400mgZnkg−1 dry mass thus indicating that this species could play an important role in the phytoremediation of Zn-polluted areas.

Treated sewage effluent: Agronomical and economical aspects on bermudagrass production

This study investigated the effects of irrigation using treated sewage effluent (TSE) combined with nitrogen (N) fertilization on the productivity and quality of bermudagrass, and on its economic feasibility under tropical conditions. The treatments employed were SI – no irrigation and no fertilization; A100 (control) – irrigation with potable water plus 520kgNha−1year−1 provided as NH4NO3; E0, E33, E66, and E100: irrigation with treated sewage effluent plus 0, 172, 343 and 520kgNha−1year−1 as NH4NO3, respectively. Chemical properties of TSE, shoot dry matter production, N concentration in bermudagrass were determined, and benefit–cost and economic viability analyses were carried out. Tree years of irrigation with TSE had agronomical benefits to bermudagrass such as: (i) saving 33% in N fertilizer by adding of 275kgNha−1year−1, increasing N accumulation in the soil; (ii) providing 70% of the N as NH4+, which is the form most quickly assimilated by the plants; (iii) building up dry matter production with 7Mgha−1year−1 and (iv) increasing leaf N concentration in leaf tissue. The main benefit of TSE irrigation occurs in drought seasons with the increase in N concentration in bermudagrass shoots. Higher N concentration in leaf tissue elevates the quality and the sales price for the grass harvested, thus optimizing the benefit–cost ratio for the producer. Therefore, TSE irrigation is a viable cost-effective alternative if the N concentration in the leaf tissue is considered in the sales price.

Impact of Nitrogen Source and Trinexapac-ethyl Application on Creeping Bentgrass (Agrostis stolonifera L.) Physiology under Neutral Shade, Deciduous Tree Shade, and Full Sunlit Conditions

Decreased light quantity or quality affects the growth of turfgrass plants. Shade causes thinning of turfgrass stands and loss in surface quality. Plant changes include increased chlorophyll levels, lower soluble sugars, and loss of canopy cover. The objective of this research was to investigate if applications of foliar nitrogen and trinexapac-ethyl [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (TE) would result in beneficial biochemical changes in creeping bentgrass (Agrostis stolonifera L. cv. Penncross) grown in different shaded environments. Foliar applications of three nitrogen treatments, (NH2)2CO, Ca(NO3)2, or (NH4)2SO4, were made weekly at 0.43 g N/m2. Growth regulator treatments consisted of an untreated control or TE applied biweekly at an a.i. rate of 0.057 kg·ha−1. Plots were established in full sun (FS), neutral shade (NS), and deciduous shade (DS). Chlorophyll content, soluble carbohydrates, flavonoids, clipping yield, and color were measured. Nitrogen treatments caused some variation in levels of soluble carbohydrates in shaded conditions. Chlorophyll (Chl) levels varied between TE treatments, with increased levels of chlorophyll b (Chl b) found in TE-treated plots under FS. Application of TE resulted in higher flavonoid concentrations in leaf tissue in shaded conditions. Repeated applications of (NH2)2CO significantly improved color (P = 0.05). Turfgrass managers maintaining creeping bentgrass in shade may benefit from applications of TE and (NH2)2CO.

Antioxidant Enzyme Activity and Gene Expression in Response to Lead Stress in Perennial Ryegrass

Lead pollution is an important issue in the world. Perennial ryegrass (Lolium perenne), as one of the widely used turfgrass and forage species, has a potential for bioremediation. The objective of this study was to investigate how antioxidant enzymes and their gene transcripts respond to Pb stress in perennial ryegrass. Ryegrass seedlings were subjected to 0, 0.5, and 3.2 mm of Pb(NO3)2 for 7 days in a hydroponic system maintained in a greenhouse. Both root and shoot growths were inhibited by Pb compared with the control. However, contents of chlorophyll (Chl) a and total Chl were unaffected by Pb treatment. Results from this study showed a substantial increase of malondialdehyde (MDA) content in leaf tissues when perennial ryegrass was exposed to Pb at 3.2 mm. The MDA content from plants in the 0.5 mm Pb treatment was lower than the control, indicating that an effective defense mechanism existed. Circumstantial evidence came also from the content of soluble protein in 0.5 mm Pb treatment, which was not different from the control. Furthermore, the activity of catalase (CAT) increased at 0.5 mm Pb compared with the control, indicating that CAT might play an important role in scavenging reactive oxygen species (ROS). The expression profiles of eight genes encoding antioxidative enzymes were upregulated within 24 hours of Pb treatment. In conclusion, antioxidant enzymes responded to Pb at an early stage of exposure and their gene expression profiles provided more details in time courses of the activation of those systems.

Effect of salinity on sodium and chloride uptake, proline and soluble carbohydrate contents in three alfalfa varieties

Salinity stress affected severely plant growth and production. Indeed, soil salinity represented one of the most important environmental stresses, which caused serious threats to agriculture and also results in the deterioration of environment. Accumulation of sodium, chloride, proline and soluble sugars was investigated in leaves, stems and roots of three alfalfa varieties (Hunterfield, Hyb.555 and Gabes) at the late bloom-early pod stage. The study was conducted in a greenhouse for 90 days of salt stress in whole-plants. Plants were irrigated with top water with four NaCl concentrations: (0 - 2.5 - 5 and 10g.l -1 ). Results showed that all varieties accumulated high Na + and Cl - contents in leaves and stems. Gabes variety differed from Hunterfield and Hyb.555 with Na + and Cl - contents significantly lower in leaves at the stressful treatments. Furthermore, Gabes proline content at 5 and 10g.l -1 NaCl in three organs was significantly higher than in the introduced varieties. Proline content in leaves, stems and roots increased with the rise of salt in pots, reaching a significantly higher level for Gabes at the stressful treatment (10g.l -1 ). Soluble sugar content in leaf tissue was higher in Gabes than those in the introduced varieties at the stressful treatments (5 and 10g.l -1 ). Contrary to the air parts (leaves and stems), soluble sugar contents in roots for Hunterfield and Hyb.555 are significantly higher, compared to Gabes variety, at the stressful treatment. This could be probably related to the difficulty in generating new leaves in Hunterfield and Hyb.555 varieties. Keyword: Alfalfa; chloride; proline; Salinity; sodium; soluble carbohydrate.

Tissue Specific Variation in Biochemical Compositions of Acorus calamus (L.) Leaves and Rhizomes

Sweet Flag (Acorus calamus L.) leaf and rhizome tissues were analyzed for biochemical compositions notably of carbohydrates and lipids. The glycolipid content measured in rhizome tissue was 62.3 mg%/FW almost double the glycolipid content (28.8 mg%/FW) in leaf tissues, whereas the sterol content in the leaf tissue (47.9 mg%/FW) was three times of the sterol content in rhizome tissues (15.5 mg%/FW). Carbohydrates content such as total sugar, reducing sugar, sucrose and fructose measured in leaf and rhizome tissues were more or less similar, with slightly higher values of total sugar (18.2 mg%/FW) in the leaf tissues. The study thus revealed variation in biochemical compositions in two different tissues leaf and rhizome of A. calamus.

Zinc tolerance and accumulation in the salt-marsh shrub Halimione portulacoides

The halophytic shrub Halimione portulacoides is known to be capable of growth in soils containing extremely high concentrations of Zn. This study evaluated in detail the tolerance and accumulation potential of H. portulacoides under moderate and high external Zn levels. A greenhouse experiment was conducted in order to investigate the effects of a range of Zn concentrations (0–130mmolL−1) on growth and photosynthetic performance by measuring relative growth rate, total leaf area, specific leaf area, gas exchange, chlorophyll fluorescence parameters and photosynthetic pigment concentrations. We also determined the total zinc, nitrogen, phosphorus, calcium, magnesium, sodium, potassium, iron and copper concentrations in the plant tissues. H. portulacoides demonstrated hypertolerance to Zn stress, since it survived with leaf concentrations of up to 2300mgZnkg−1dry mass, when treated with 130mmolZnL−1. Zinc concentrations greater than 70mmolL−1 in the nutrient solution negatively affected plant growth, in all probability due to the recorded decline in net photosynthesis rate. Our results indicate that the Zn-induced decline in the photosynthetic function of H. portulacoides may be attributed to the adverse effect of the high concentration of the metal on photosynthetic electron transport. Growth parameters were virtually unaffected by leaf tissue concentrations as high as 1500mgZnkg−1dry mass, demonstrating the strong capability of H. portulacoides to protect itself against toxic Zn concentrations. The results of our study indicate that this salt-marsh shrub may represent a valuable tool in the restoration of Zn-polluted areas.

Composted cattle and poultry manures provide excellent fertility and improved management of gray leaf spot in maize

Gray leaf spot incited by Cercospora zeae maydis, is an important disease of maize ( Zea mays L.) world-wide. The objective of this research was to evaluate the effect of composted poultry and cattle manures on development of gray leaf spot and yield of maize. The effects of composted manures were compared with those of different sources of inorganic synthetic nitrogen fertilizers in two cropping seasons. Composted manures and mineral fertilizers were tested to supply the recommended rate of 60 kg N ha −1 and at the highest rate of 90 kg N ha −1. Fertilizer treated maize plants were more diseased than non-fertilized (control). Higher disease severity was observed in plots receiving high levels of inorganic N fertilizers. The severity of gray leaf spot varied with fertilizer types ( P ≤ 0.05). Maize fertilized with composted cattle manure had the lowest levels of gray leaf spot, followed by composted poultry manure and urea (46%). Sulphate of ammonium (SA) (21%) and calcium ammonium nitrate (CAN) (27%) fertilized maize were more diseased and lower yielding. Overall grain yield across seasons in composted cattle manure, composted poultry manure and urea fertilization was 1.4 t ha −1, 0.9 t ha −1, 0.6 t ha −1 and 4.2 t ha −1, 3.7 t ha −1, 3.4 t ha −1 higher compared to CAN and non-fertilized (control) treatments respectively. Disease severity was also influenced by interactions between genotypes and fertilizers. The concentration of NH 4-N and NO 3-N in maize leaf tissues was associated with the degree of maize resistance to gray leaf spot. Maize fertilized with composted cattle or poultry manure and urea were more resistant to gray leaf spot with higher leaf tissue concentration of NH 4-N and lower concentration of NO 3-N. Plots fertilized with SA and CAN were heavily diseased with lower leaf tissue concentration of NH 4-N. It is concluded that organic composted poultry and cattle manures can provide a beneficial, renewable source of crop nutrients for small scale-maize farmers in Africa. Advantages over mineral fertilizers are that they are inexpensive, and may also provide management of gray leaf spot.

Flooding effects on phosphorus dynamics in an Amazonian mangrove forest, Northern Brazil

We examined porewater salinity, soil redox potential (Eh), soil extractable phosphate (extr.-P), leaf phosphorus (leaf-P) and plant growth in relation to inundation frequency (IF) and mangrove species distributions along a 600 m transect in the Braganca Peninsula, North Brazil. The forest species composition changed across the tidal zone with Avicennia germinans dominating (99.1%) the high intertidal (HI) zone where the IF was 41–67 d.y−1, Rhizophora mangle, Laguncularia racemosa and A. germinans co-occured in the mid intertidal (MI), and a mixed R. mangle (47.1%) - A, germinans (41.2%) stand occupied the low intertidal (LI) zone with an IF of 124–162 d.y−1. Low IF resulted in high Eh levels (200 mV) in the HI zone relative to the LI where Eh ranged from 0–100 mV. The IF showed a significant positive correlation with extr.-P (r = 0,89; p = 0.05) and a negative association with Eh (r = −0,75; p = 0.05). An ANCOVA confirmed that Eh and extr.P were influenced by flooding. Variations in these factors were reflected in patterns of P leaf tissue concentrations across the gradient; however, a MANCOVA showed that leaf-P was not related to tree height, tree volume or basal area. Water-logging conditions, porewater salinity, and P dynamics in the sediment appear to influence the forest structure. We suggest that P availability plays an important role in controling mangrove species distributions but not their growth.

Transgenic expression of phytase and acid phosphatase genes in alfalfa (Medicagosativa) leads to improved phosphate uptake in natural soils.

Alfalfa (Medicago sativa L.) is one of the most widely grown crops in the USA. Phosphate (P) deficiency is common in areas where forage crops are grown. To improve the use of organic phosphate by alfalfa, two Medicago truncatula genes, phytase (MtPHY1) and purple acid phosphatase (MtPAP1), were overexpressed in alfalfa under the control of the constitutive CaMV35S promoter or the root-specific MtPT1 promoter. Root enzyme activity analyses revealed that although both genes lead to similar levels of acid phosphatase activities, overexpression of the MtPHY1 gene usually results in a higher level of phytase activity than overexpression of the MtPAP1 gene. The MtPT1 promoter was more effective than the CaMV35S promoter in regulating gene expression and extracellular secretion under P-deficient conditions. Measurement of growth performance of the transgenic lines further proved that the best promoter–gene combination is the MtPHY1 gene driven by the MtPT1 promoter. Compared to the control, the plants with high levels of transgene expression showed improved growth. The biomass of several transgenic lines was three times that of the control when plants were grown in sand supplied with phytate as the sole P source. When the plants were grown in natural soils without additional P supplement, the best performing transgenic lines produced double the amount of biomass after 12 weeks (two cuts) of growth. Transgene effects were more obvious in soil with lower pH and lower natural P reserves than in soil with neutral pH and relatively higher P storage. The total P concentration in leaf tissues of the high-expressing transgenic lines was significantly higher than that of the control. The transgenes have great potential for improving plant P acquisition and biomass yield in P-deficient agricultural soils.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-011-9628-0) contains supplementary material, which is available to authorized users.

Effect of potassium silicate on epidemic components of powdery mildew on melon

The effects of silicon (Si) supplied in the form of potassium silicate (PS) were evaluated on epidemic components of powdery mildew of melon under greenhouse conditions. The PS was applied to the roots or to leaves. In the first experiment, epidemic components were evaluated after inoculation with Podosphaera xanthii. In the second experiment, the disease progress rate was evaluated on plants subjected to natural infection. The area under the disease progress curve was reduced by 65% and 73% in the foliar and root treatments, respectively, compared to control plants, as a consequence of reductions in infection efficiency, colony expansion rate, colony area, conidial production and disease progress rate. However, root application of PS was more effective than foliar application in reducing most of the epidemic components, except for infection efficiency. This can be explained by the high Si concentration in leaf tissues with root application, in contrast to the foliar treatment where Si was only deposited on the external leaf surfaces. The effects of PS reported in this study demonstrated that powdery mildew of melon can be controlled, and that the best results can be achieved when PS is supplied to the roots.

Increases in leaf artemisinin concentration in Artemisia annua in response to the application of phosphorus and boron

Malaria resurgence particularly in the third world is considerable and exacerbated by the development of multi-drug resistances to chemicals such as chloroquinone. Drug therapies, as recommended by WHO include the use of antimalarial compounds derived from Artemisia annua L., i.e. artemisinin-based therapies. This work aims to determine how A. annua plant dry matter can be enhanced while maximising artemisinin concentration from understanding the plant's mineral requirements for P and B. Experiments with differing of P, from 5 to 120 mg L −1 and B from 0.1 to 0.9 mg L −1 were undertaken. Mineral nutrients were supplied in irrigation water to potted plants and after a period of growth, dry matter production and leaf artemisinin concentration were determined. Increases in P application enhanced plant growth and total dry matter production. An optimal application rate, with respect to dry matter, was apparent around 30 mg P L −1. Despite increases in P application having no influence on leaf artemisinin concentration, optimal yields of artemisinin, on a per plant basis, were again achieved at supply rate around 30–60 mg L −1. Increasing B application rate had little influence on dry matter production despite increases in B leaf tissue concentration promoting the total amount of B per plant. Leaf artemisinin concentration significantly increased with B application rate up to 0.6 mg B L −1. The higher artemisinin concentrations when multiplied by total leaf dry matter at the higher B application rates produced an increase in total artemisinin production per plant. There was however no further significant effect on leaf artemisinin concentration when B supply concentrations increased further (0.9 mg L −1). Artemisinin production varied between the two experiments to a greater extent than plant dry matter production and the reasons for this are discussed in relation to growing environments and their possible impacts on artemisinin biosynthesis.

Irrigation of grapevines with saline water at different growth stages: Effects on leaf, wood and juice composition

Background and Aims: This study reports on the effects that timing of saline irrigation has on leaf and wood tissue concentrations of Na+ and Cl– and on juice composition. Methods and Results: Colombard vines on Ramsey rootstock were drip irrigated with saline water during any one of four annual growth stages: pre-flowering, berry formation, berry ripening and postharvest. At other times, vines were irrigated with non-saline water as was the control. Salts were annually flushed from the rootzone. Over six seasons, saline irrigation caused five- and sevenfold rises, respectively, in the leaf and juice Na+ concentrations and two- and fourfold rises in respective Cl- concentrations. Saline irrigation raised juice pH and this was associated with a rise in juice Na+. Normalising responses for inter-treatment differences in the seasonal salt load to isolate the effects of timing showed that juice Cl- concentration was most sensitive to saline irrigation during berry formation and juice malate concentration most sensitive to saline irrigation pre-flowering. Conclusion: Cl- uptake was greatest when saline irrigation was applied early in organ formation, whereas Na+ uptake reflected seasonal salt load in irrigation water. Significance of the Study: In vines on the chloride excluding rootstock Ramsey, yield loss under saline irrigation was associated with high concentrations of sodium in the leaf.

Potassium phosphite for control of downy mildew of soybean

Downy mildew of soybean, caused by Peronospora manshurica, is widely spread throughout Brazil. The objective of this study was to evaluate the use of potassium phosphite to control this disease. Field experiments were conducted during the growing season of 2006/2007 and 2007/2008 in the state of Parana in southern Brazil. The experimental design consisted of completely randomized blocks in a factorial arrangement (4 × 2) with four replications. Four rates of potassium phosphite (0, 375, 750 and 1500 g P 2O 5 + K 2O ha −1) were applied at two growth stages, V6 (fifth trifoliolate leaf) and R2 (full flowering), followed by one or two applications of pyraclostrobin and epoxiconazole (66.5 + 25 g a.i. ha −1) at R3 (pod development) or R2 and R5.1 (10% of pod filling), mainly for the control of Asian soybean rust ( Phakopsora pachyrhizi) and powdery mildew ( Microsphaera diffusa). Field experiments were conducted to quantify the severity of downy mildew on leaves, nutrient content in leaf tissue (N, P and K), leaf area index (LAI), yield and seed weight. The maximum severity of downy mildew was observed at a growth stage of R5.3 (50% of pods were ripe), with 14% and 46% of the leaf area affected in 2006/2007 and 2007/2008, respectively. Also it was detected some effect of phosphite on Asian rust control but it was mostly in the trial of 2007/08 when the epidemic was very low (9.7–21.8% of severity). There was a linear reduction in the severity of downy mildew and a significant improvement in the LAI with an increase in the rate of phosphite applied. During the 2006/2007 growing season, a significant yield improvement was observed due to the application of the highest rate of phosphite. Two fungicide applications following phosphite application significantly improved the control of Asian soybean rust and powdery mildew, yield and seed weight when compared to a single fungicide application.

Reduced Nitrogen, Phosphorus, and Potassium Rates for Intermediate-day Onion in Paddy Soil with Incorporated Rice Straw plus Manure

The effect of nitrogen (N), phosphorus (P), and potassium (K) supply on the growth and nutrient uptake of intermediate-day onions (Allium cepa L.) was investigated in a double cropping system of rice and onion in which rice straw had been annually applied. The experiment consisted of three sets of treatments: N (0, 120, 240, 360 kg·ha−1 N), P (0, 18, 35, 52 kg·ha−1), and K (0, 67, 133, 200 kg·ha−1) with the addition of 8.0 t·ha−1 of decomposed pig manure. The rice straw was incorporated with tillage after harvest. Foliage weight of the onion plant was affected by N rate on 21 Apr. and on 23 May. Bulb weight was also influenced by N rate on 23 May and at harvest. The only difference (P ≤ 0.05) in onion yield was observed between the zero N rate and all the other N levels. Soil pH was correlated with rate of N fertilization. Soil NO3-N for 240 and 360 kg·ha−1 N rates ranged from 36.6 to 113.7 and 49.9 to 148.6 mg·kg−1, respectively, which was at least twice as high as that at 120 kg·ha−1 N rate. The highest fertilizer use efficiency of nitrogen was 36.0% at 120 kg·ha−1 followed by 240 kg·ha−1 at 28.0% and 360 kg·ha−1 at 20.6%. There was no clear effect of P or K rates on P or K concentration in the onion bulbs. K concentration and uptake in the onion leaf tissue increased with higher K rates. In conclusion, compost and rice straw provided sufficient P and K to grow onions without additional P and K fertilizer, and under these conditions, the fertilizer level of 120 kg·ha−1 N produced as much onion bulb yield as higher N levels.

Effect of Putrescine and Paclobutrazol on Growth, Physiochemical Parameters, and Nutrient Acquisition of Salt-sensitive Citrus Rootstock Karna khatta (Citrus karna Raf.) under NaCl Stress

Salinity is a serious problem in arid and semiarid areas and citrus trees are classified as salt-sensitive. Because putrescine (Put) and paclobutrazol (PBZ) are known to act as plant protectants under environmental stresses, we examined the effect of Put and PBZ on the physiochemical parameters of the salt-susceptible citrus rootstock Karna khatta under NaCl stress. PBZ was applied at 0, 250, and 500 mg L−1 as a soil drench 1 week prior to salinization. A computed amount of NaCl salt to develop soil salinity of 3 dS m−1 (3 g NaCl kg−1 soil) and foliar spray of Put at 0 or 50 mg L−1 were applied. The electrical conductivity (EC) of the garden soil (0.35 dS m−1) was used as control. Application of PBZ and/or Put reduced the membrane injury index and increased relative water content, photosynthetic rate, and pigments content under saline conditions compared to what occurred in plants exposed to NaCl in the absence of PBZ or Put. Application of PBZ or Put alone or in combination also improved the activities of SOD and peroxidase and proline content under saline conditions. Application of PBZ and/or Put also increased K+ and reduced Na+ and Cl− concentrations in leaf tissues. It is proposed that PBZ and/or Put could improve the tolerance of salt-susceptible Karna khatta by regulating absorption and accumulation of ions and improving antioxidant enzyme activities.

Deficiency in Silicon Uptake Affects Cytological, Physiological, and Biochemical Events in the Rice–Bipolaris oryzae Interaction

This study investigated how a defect in the active uptake of silicon (Si) affects rice resistance to brown spot. Plants from a rice mutant (low silicon 1 [lsi1]) and its wild-type counterpart (cv. Oochikara), growing in hydroponic culture with (+Si; 2 mM) or without (-Si) Si, were inoculated with Bipolaris oryzae. Si concentration in leaf tissue of cv. Oochikara and the lsi1 mutant increased by 381 and 263%, respectively, for the +Si treatment compared with the -Si treatment. The incubation period was 6 h longer in the presence of Si. The area under brown spot progress curve for plants from cv. Oochikara and the lsi1 mutant was reduced 81 and 50%, respectively, in the presence of Si. The reduced number of brown epidermal cells on leaves from cv. Oochikara and the lsi1 mutant supplied with Si contributed to the lower lipid peroxidation and electrolyte leakage. The concentration of total soluble phenolics in cv. Oochikara supplied with Si (values of 4.2 to 15.4 μg g(-1) fresh weight) was greater compared with plants not supplied with Si (values of 1.9 to 11.5 μg g(-1) fresh weight). The concentration of lignin was also important to the resistance of cv. Oochikara and the lsi1 mutant. Polyphenoloxidase activity did not contribute to the resistance of cv. Oochikara and the lsi1 mutant to brown spot, regardless of Si supply. Peroxidase and chitinase activities were higher in cv. Oochikara and the lsi1 mutant supplied with Si. These results bring novel evidence of the involvement of Si in a more complex defense mechanism than simply the formation of a physical barrier to avoid or delay fungal penetration.