Distinguishing nitrogen deficiency and fungal infection of winter wheat by laser-induced fluorescence

One of the most important tasks in precision farming is the site-specific application of fertilisers and pesticides in heterogeneous large-area fields. For such site-specific crop management, effective remote sensing methods for the detection of crop diseases and nutrient deficiencies are required. The aim of the present work was to compare laser-induced fluorescence (LIF) parameters from nitrogen-deficient and pathogen (rust and mildew)-infected winter wheat (Triticum aestivum L.) plants and to assess the potential of LIF to detect and discriminate between these types of stress. Both long term nitrogen deficiency and pathogen infection resulted in an increase of the ratio of fluorescence at 686 and 740 nm (F686/F740) accompanied by a reduction of leaf chlorophyll content to approximately 35 μg cm⁻². A linear negative correlation between chlorophyll content and F686/F740 ratio (r² = 0.78) was found for leaves with chlorophyll content ranging between 17 and 52 μg cm⁻². Since chlorophyll breakdown appeared an unspecific symptom to both nitrogen deficiency and pathogen infection, it was not possible to discriminate between these types of stress only by means of the F686/F740 ratio. Specific for the pathogen-infected leaves was a large heterogeneity in the records of their spectral parameters caused by inhomogeneous, discrete lesions of fungi infection. Nitrogen-deficient plants with homogeneous reduction in chlorophyll content showed, in contrast, more uniform readings of the spectral parameters. Thus, mildew- and rust-infected plants, grown under sufficient nitrogen fertilisation could be distinguished from those grown under reduced nitrogen supply by the higher variance of their spectral readings. The simultaneous scanning multipoint mode measurements of LIF and laser light reflection characteristics with parallel estimation of their heterogeneity is proposed for the discrimination between nitrogen deficiency and pathogen infection under field conditions.     

Morphological Changes in Leaves of Mexican Lime Affected by Iron Chlorosis

Iron (Fe) chlorosis reduces the concentration of photosynthetic pigments, photosynthates, and crop yield. The effect of Fe chlorosis on leaf composition and cell structure was evaluated in Mexican lime (Citrus aurantifolia) with different degrees of Fe chlorosis. Iron chlorosis significantly reduced concentrations of chlorophylls a, b, and a + b, and caused thickening of leaves, due to the increase in palisade and spongy parenchyma cells. The chloroplasts of the chlorotic and albino leaves showed a disorganized ultrastructure; they had an elongated shape with disarrayed thylakoids, underdeveloped grana, scarce starch granules, and hole-like folds in the thylakoid membranes. The accumulation of calcium oxalate crystals in the upper and lower sides of the epidermis, crystal length, and total crystal content increased with Fe chlorosis severity. The green leaves, in contrast, had chloroplasts with typical ultrastructure. The degree of Fe chlorosis in the leaves significantly affected the concentrations of potassium (K); Fe, manganese (Mn), Fe²⁺, and the phosphorus (P)/Fe and K/calcium (Ca) ratios.     

Biochemical Responses to True and Bicarbonate-Induced Iron Deficiency in Grapevine Genotypes

ABSTRACT

Biochemical responses to direct or bicarbonate-induced iron (Fe) deficiency were compared in two Tunisian native grapevine varieties, Khamri (tolerant) and Balta4 (sensitive), and a tolerant rootstock, 140Ru. Woody cuttings of each genotype were irrigated with a nutrient solution containing one of the following: 20 μM Fe (control), 1 μM Fe (direct Fe-deficiency), or 20 μM Fe + 10 mM HCO₃ ^? (indirect bicarbonate-induced Fe-deficiency). Under direct Fe-deficient conditions, lower leaf chlorosis score and higher chlorophyll and leaf Fe contents were found in Khamri and 140Ru compared with Balta4. Moreover, indirect Fe deficiency caused similar effects on these parameters, which were more pronounced in Balta4. Both tolerant genotypes, Khamri and 140Ru, showed higher roots-acidification capacity and phenol release under the direct Fe deficiency compared with the bicarbonate-induced condition. In the sensitive variety, Balta4, no significant changes were found between the control and Fe-deficient plants. Root Fe(III)-reductase activity was strongly stimulated by both types of Fe deficiency in Khamri and 140Ru, and displayed no significant changes in Balta4. In the three genotypes, root and leaf activities of two Fe-containing enzymes, catalase and guaiacol peroxidase, were significantly affected under Fe deficiency (either direct or induced), though to a greater extent in the sensitive variety, Balta4. The latter also displayed higher leaf malonyldialdehyde (MDA) content, traducing an important membrane lipid peroxidation.     

Zinc Requirement of Maize Hybrids and Indigenous Varieties on Udic Haplustalf

ABSTRACT

A pot study was conducted on Gujranwala series (Udic Haplustalf) to compare zinc (Zn) requirement of maize hybrids (FHY- 456, FHY- 396, and FHY- 421) and indigenous varieties (EV-1089, Golden, and Soneri). Uniform rates of nitrogen:phosphorus:potassium (N:P:K) and four rates of Zn were applied in triplicate according to CRD. There was a significant (P < 0.05) main and interactive effect of maize genotypes and zinc application on shoot growth and Zn uptake. The three maize varieties uniformly produced maximum shoot dry weight at 3 mg Zn kg^?1 soil. The maize hybrids produced maximum shoot dry weight at 9 mg Zn applied kg^?1 soil. A 6.3 mg Zn kg^?1 plant tissue was optimum for FHY-421 (hybrid) and 9.5 mg Zn kg^?1 plant tissue was optimum for Soneri (variety). Hence, more pronounced response in maize hybrids than indigenous varieties require higher rates of Zn application. However, further verification of the results is warranted under field conditions.     

Nutritional Alleviation of Zinc-Induced Iron Deficiency in Indian Mustard and the Effects on Zinc Phytoremediation

ABSTRACT

Indian mustard (Brassica juncea Czern) is a promising species for the phytoextraction of zinc (Zn), but the effectiveness of this plant can be limited by iron (Fe) deficiency under Zn-contaminated conditions. Our objectives were to determine the effects of root-applied Fe and Zn on plant growth, accumulation of Zn in plant tissues, and development of nutrient deficiencies for B. juncea. In the experiment, B. juncea was supplied 6 levels of iron ethylenediamine dihydroxyphenylacetic acid (Fe-EDDHA; 0.625 to 10.0 mg L^?1) and two levels of Zn (2.0 and 4.0 mg L^?1) for 3 weeks in a solution-culture experiment. Nutrient solution pH decreased with decreasing supply of Fe and increasing supply of Zn in solution, indicating that B. juncea may be an Fe-efficient plant. If plants were supplied 2.0 mg Zn L^?1, plant growth was stimulated by increases in Fe supply, but plant growth was not influenced by Fe treatments if plants were supplied 4.0 mg Zn L^?1. Zinc concentration in roots and shoots was suppressed by increasing levels of Fe in solution. Leaf concentrations of Cu, Mn, and P were suppressed also as Fe supply in solutions increased. Iron additions to the nutrient solution were not effective at increasing the Zn-accumulation potential of B. juncea unless plants were supplied the higher level of Zn in solution culture. Even under these conditions, Fe additions were effective only if supplied at low levels in solution culture (1.25 mg Fe L^?1). Results suggest that Fe fertility has limited potential for enhancing Zn phytoextraction by B. juncea, even if plants suffer a suppression in growth from Fe deficiency.     

NUTRIENT DISORDER SYMPTOMOLOGY AND FOLIAR CONCENTRATIONS OF CLERODENDRUM THOMSONIAE

Clerodendrum thomsoniae plants were grown in silica sand culture to induce and photograph nutritional disorder symptoms. Plants were grown with a complete modified Hoagland's all nitrate solution. The nutrient deficiency treatments were induced with a complete nutrient formula minus one of the nutrients. Boron toxicity was also induced by increasing the element ten times higher than the complete nutrient formula. Reagent grade chemicals and deionized water of 18-mega ohms purity were used to formulate treatment solutions. The plants were automatically irrigated and the solution drained from the bottom of the pot and captured for reuse. The nutrient solutions were completely replaced weekly. Plants were monitored daily to document and photograph sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and critical tissue concentrations are presented. Plants were harvested for nutrient analysis when initial symptoms were expressed. Nutrient deficiency symptoms were described and foliar nutrient concentrations provided.     

STUDY ON THE EFFECTS OF NITROGEN DEFICIENCY ON GRAIN IRON AND ZINC CONCENTRATIONS OF LANDRACE AND BRED WHEAT VARIETIES IN CHINA

It has been reported that nitrogen (N) deficiency can significantly reduce grain iron (Fe) and zinc (Zn) concentrations in wheat. Here, we investigated the grain Fe (GFeC) and Zn (GZnC) concentrations of 42 Chinese wheat varieties grown in a field trial under low and high N conditions. Analysis of variance revealed that both GFeC and GZnC significantly differed among varieties and between N treatments, and significant interactions existed between variety and N treatment. The GFeC under the low N condition was 94.8% of that under high N condition, ranging from 79.4% to 112.7%; the GZnC under low N condition was 74.8% of that under high N condition, ranging from 59.5% to 102.5%. Wheat varieties with high GFeC and GZnC under both N conditions were identified, and this kind of varieties is desirable in breeding wheat with enriched Zn and Fe under a range of soil N conditions.     

IS CHLOROPHYLL FLUORESCENCE TECHNIQUE A USEFUL TOOL TO ASSESS MANGANESE DEFICIENCY AND TOXICITY STRESS IN OLIVE PLANTS?

A 130-day hydroponic experiment was carried out in a glasshouse to examine whether manganese (Mn) concentration in the nutrient solution affects the nutritional status of olive plants and to find out whether the chlorophyll fluorescence technique is suitable to assess Mn toxicity and/or deficiency stress in olive plants prior to the appearance of these two nutritional disorders. For this purpose, chlorophyll fluorescence parameters (F_v/F_m and F_v/F₀ ratios) were recorded every 40 days in the leaves of ‘Kothreiki’ and ‘FS-17’ olive cultivars, which were irrigated with Hoagland's nutrient solutions containing various Mn concentrations. In parallel the elongation of the main shoot of all experimental plants, as well as the concentrations of Mn, iron (Fe), zinc (Zn), boron (B), phosphorus (P), calcium (Ca), magnesium (Mg), and potassium (K) in their leaves were recorded. The following Mn treatments were applied: 0 μM Mn (to induce Mn deficiency), 40 μM Mn (to promote normal growth), and 640 μM Mn (to induce Mn toxicity). Our results indicated that not only the rate of shoot elongation but also the fluctuation with time of the leaf concentrations of all determined mineral elements (except for Mn) was not significantly affected by the Mn concentration in the nutrient solution, irrespectively of the cultivar. This was not observed with regard to the time variation of the F_v/F_m and F_v/F₀ ratios, where the values of these parameters were significantly reduced in the 640 μM Mn treatment at the 80th and 130th day of the experiment in both olive cultivars, compared to the relevant previous ones (those of the days 0 and 40th), something which did not happen in the other two Mn treatments (0 and 40 μM). However, in none of the two cultivars tested and in any of the three Mn treatments (0, 40 and 640μM) the F_v/F_m and F_v/F₀ ratios did not drop below the critical values of 0.8 and 4, respectively, even at the end of the experiment, where high Mn concentrations were found in the leaves of both cultivars treated with 640 μM Mn (616 μg g^?1 d.w. in ‘FS-17’ and 734 μg g^?1 d.w. in ‘Kothreiki’). Symptoms of Mn toxicity (curling and brown speckles) were observed in the top leaves of both cultivars, after the 90th day of the experiment. At the same time, the final leaf Mn concentrations (those of the 130th day of the experiment) in plants grown under 0 μM Mn were 23 μg g^?1 d.w. in ‘FS-17’ and 20 μg g^?1 d.w. in ‘Kothreiki’, i.e., a little above of the deficiency range (<20 μg g^?1 d.w.). At the 130th day, Mn concentration in nutrient solution, as well as Mn concentration in the leaves of both olive cultivars was negatively correlated with the leaf concentration of Fe and the values of the F_v/F_m and F_v/F₀ ratios, and positively with the concentrations of Zn and P in the leaves. Finally, the periodical measurement of the F_v/F_m and F_v/F₀ ratios was proved to be a non-reliable means to predict the appearance of the visible symptoms of Mn toxicity in olive leaves (although their values declined significantly at the 80th and 130th day of the experiment in both olive cultivars).     

CHANGES IN PHOSPHATE FRACTIONS,GROWTH RATE,NODULATION AND NITROGEN2 FIXATION OF PHOSPHORUS-STARVED SOYBEAN PLANTS

The objective of this study was to elucidate the effects of phosphorus (P) starvation on the internal P status expressed as P fractions (acid soluble P, sugarP, inorganic P, nucleotide P, and insolubleP) in different plant organs (leaves, roots and nodules), at different plant growth rates and dinitrogen(N₂) fixation rate of soybean plants. The symptoms of P starvation differed during early 10 days and late 28 days of starvation. There were close relationships between nodulation and N₂ fixation rate, and parameters of growth rate and internal P status. Although growth rate and N₂ fixation of P starved plants were reduced their nodules showed ability to accumulate more soluble P in comparison with the leaves. The decreased sugar-P and inorganic P accounted for accumulation of more soluble sugars and starch in the stressed leaves. In contrast, stressed nodules accumulated higher quantities of sugar P, inorganic P, and nucleotide P and had reduced quantities of starch and sucrose. The increased accumulation of phosphorylated sugars in the nodules was regarded as a manifestation of the mechanism of stress tolerance of soybean nodules to P limited nutrition.