Wheat (Triticum aestivum L.) production areas are expanding to soils low in available Mn in southern Georgia and to soils high in available Mn in northern Georgia. Useful data on Mn deficient and toxic levels in leaf tissue for top growth and physiological processes in wheat are needed to evaluate growth processes limiting wheat production. The objectives of this study were to correlate Mn deficiency and toxicity levels with top dry weight production, photosynthesis, chlorophyll concentration, and transpiration. Wheat plants were grown in 10 experimental concentrations ranging from 0.09 μM to 9.1 mM in nutrient solution. Photosynthesis and transpriration measurements were made on blade 1 of plants grown in the greanhouse. Total chlorophyll and Mn concentrations were determined on the experimental tissue after freeze‐drying. Foliar dry weights on a per pot (15 plants) basis were also determined. Severe Mn deficiency depressed top dry weight, photosynthesis, and total chlorophyll concentration, but transpiration was unaffected. Mild Mn toxicity reduced top dry weight but not photosynthesis, total chlorophyll concentration, or transpiration. Critical Mn deficiency levels for reducing top dry weight and apparent photosynthesis rates were similar, namely 0.23 and 0.30 mmol kg−1, repectively. Growth reduction from Mn deficiency is possibly due to reduced photosynthesis. Minimum Mn requirements for chlorophyll (0.14 mmol kg−1) is about one‐half of that for top production. The critical Mn deficiency level for transpiration could not be determined. The critical Mn toxicity level for top dry weight occurred at 7 mmol kg−1. Concentrations of 19, 19, and 24 mmol kg−1 were required for the depression of photosynthesis, total chlorophyll concentration, and transpiration, respectively. Maximum growth and yield are expected when the range of Mn concentration in blade 1 is 0.23 to 7 mmol kg−1. The critical levels are prelimilinary values to be used in evaluating Mn status of field‐grown wheat for possible deficiency and toxicity.
The lower and upper critical Mn levels in soybeans [Glycine max (L.) Merr.], which are not documented, were determined to provide guideline values for estimating the Mn status from deficiency through toxicity. Soybean (‘Bragg’) was grown in Hoagland nutrient solution with 14 Mn levels from 0 to 50,000 μg/liter. The plants were grown in the greenhouse for 33 days, harvested and analyzed for Mn. The lower critical levels where Mn is required at minimum concentration for maximum growth ranged from 9 to 11 μg/g in blade 1 (young) and blade 5 (old), respectively. Blade 3 was the most recently matured leaf and is suggested as the tissue to sample for plant analysis. The lower critical Mn level for blade 3 is 10 μg/g. The upper critical level where maximum Mn concentration in blade tissue can be tolerated for maximum growth ranged from 100 to 250 μg/g in blade 1 to 5, respectively. The upper critical Mn level for blade 3 was 160 μg/g. For the ‘Bragg’ cultivar maximum growth was attained from 10 to 160 μ/g Mn in blade 3. The distribution of Mn was low (3 to 7 μg/g) and uniform when plants were under Mn stress. With adequate Mn, the Mn concentration in blade increased with tissue age.
Wheat (Triticum aestivumL.) production areas have expanded to soils low in available Mn and to low pH soils with excess available Mn. The purpose of this study was to determine the effect of Mn deficiency and toxicity effects on ‘Stacy’ wheat growth components and to determine the Mn critical deficiency level (CDL) and critical toxicity level (CTL) in specific plant tissue in relation to top dry weight. The critical deficiency and toxicity values could be used as guidelines in tissue analysis to diagnose Mn deficiency and toxicity. Wheat plants were grown in nutrient solution containing 10 Mn rates from 0.09 μMto 9.1 mMin the greenhouse. Plants were harvested 26 days following treatment with Mn and tissue samples were analyzed for Mn and other elements in the wet ashed extract. Manganese deficiency and toxicity reduced top dry weight, root dry weight, plant height, and tiller number compared with plants supplied at adequate Mn levels. The CDL and CTL defined as the elemental concentration in the tissue associated with a 10% reduction in growth due to a deficiency or toxicity, respectively, were determined from the relationship of Mn concentrations in the tissue and top dry weight. The Mn CDL values for blades 1, 2, 3, and stem of Stacy wheat were 13,39,82, and 12 μg g‐1, respectively. Blade 1 is recommended for tissue sampling since the transition zone in the response curve is narrow and blade 1 is metabolically active and the most recently matured blade with a developed ligule. The Mn CTL values of the sampled tissues were 380, 900, 1100, and 200 μg g‐1for blades 1, 2, 3, and stem tissue, respectively. Maximum growth would be expected when tissue Mn concentrations are within the CDL and CTL of a specific plant tissue. The Mn concentration in tissues increased as Mn supply was increased. A reciprocal Fe/Mn and P/Mn concentrations existed in blade 1. Manganese deficiency and toxicity reduced K, Ca, and Mg concentrations.
Soybean [Glycine max (L.) Merr.] cultivars vary in plant growth response to Mn deficiency and toxicity. Cultivar selection for field studies to evaluate responses to Mn deficiency and toxicity is important. The objective of this study was to determine the differential sensitivity of cultivars to Mn deficiency and toxicity prior to regional field studies on the diagnosis and correction of Mn problems in the production of soybeans. For evaluating relative ranking of cultivars sensitive to Mn deficiency, seven soybean cultivars were grown in solution culture at severe (5 µg Mn/liter) and mild (50 µg Mn/liter) deficiency levels and compared with controls, (1,000 µg Mn/liter). For toxicity evaluations, seven cultivars were grown at severe (20 mg Mn/liter) and mild (10 mg Mn/liter) toxicity levels with controls at 0.5 mg Mn/liter. Cultivar sensitivity to Mn deficiency was partially dependent on the level of deficiency stress. ‘Davis’, ‘Lee 74’, ‘Bragg’, and ‘Pickett 71’ were the most sensitive under severe deficiency and Lee 74, Bragg and ‘Hutton’ were the most sensitive under mild deficiency. Davis, Lee 74, Pickett 71, Bragg, and ‘Ransom’ were the most sensitive to severe Mn toxicity at the severe Mn toxicity level. At mild toxicity, shoot weights as percent of control were similar for all cultivars. Visual symptom ratings and leaf blade Mn concentrations were significantly correlated with shoot dry weight as percent of control for Mn deficiency and toxicity stresses. The increased sensitivity to Mn toxicity by Lee 74 compared to that previously reported for the ‘Lee’ cultivar may be a result of genetic changes which occurred during the development of Lee 74.
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