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Joseph P. Albano and William B. Miller

Our objective was to determine the effects on plant growth and physiology that a photodegraded Fe-chelate containing lab-prepared nutrient solution would have when used in plant culture. Plants grown hydroponically in the irradiated Fe-DTPA containing nutrient solution had ferric reductase activity 2.2 times greater, foliar Fe level 0.77 times less, and foliar Mn level 1.9 times greater than in plants grown in an identical but non-irradiated solution, indicating that plants growing in the irradiated solution were responding to Fe deficiency stress with physiological reactions associated with Fe efficiency. The youngest leaves of plants that were grown in the irradiated solution had symptoms of Mn toxicity. Restoration of the irradiated solution by removing the precipitated Fe by centrifugation and adding fresh Fe-chelate resulted in plants that were, in general, not different from those grown in the non-irradiated solution (control).

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Joseph P. Albano and William B. Miller

Marigold (Tagetes erecta L.) grown hydroponically in an irradiated nutrient solution containing FeDTPA had root ferric reductase activity 120% greater, foliar Fe level 33% less, and foliar Mn level 90% greater than did plants grown in an identical, nonirradiated solution, indicating that the plants growing in the irradiated solution were responding to Fe-deficiency stress with physiological reactions associated with Fe efficiency. The youngest leaves of plants grown in the irradiated solution had symptoms of Mn toxicity (interveinal chlorosis, shiny-bronze necrotic spots, and leaf deformation). Plants grown in irradiated solution in which the precipitated Fe was replaced with fresh Fechelate were, in general, no different from those grown in the nonirradiated solution. Chemical name used: ferric diethylenetriaminepentaacetic acid (FeDTPA).

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David C. Ferree

The apple (Malus ×domestica Borkh.) cultivars Starkspur Supreme Delicious and Melrose were planted in 1987 on eight apomictic apple rootstock selections made in Germany by Dr. Hanna Schmidt and on M.7. Selections 2 [M. hupehensis (Pamp.) Rehd. parentage] and 8 [M. sieboldii (Regel) Rehd. parentage] were similar to M.7 in precocity, cumulative yield per tree, and yield efficiency, while the other selections with M. sargenti Rehd. in their parentage were slower to flower and had lower yields and yield efficiencies. Selections 2 and 8 tended to result in larger trees than M.7, while the selections with M. sargenti parentage were generally similar to M.7 in size. Except for trees on M.7 and selection 2, `Starkspur Supreme Delicious' developed more severe symptoms of internal bark necrosis (IBN) than did `Melrose', which normally does not show IBN. However, `Melrose' showed IBN symptoms on selections with M. sargenti parentage. IBN symptoms were positively correlated with leaf Mn concentrations. Influence of rootstocks on other nutrient elements, although significant, were small compared to the effect on Mn. A significant interaction occurred between cultivar and rootstock in their effects upon branch morphology, mostly because fewer flowering spurs and more vegetative spurs were observed on `Melrose' than on `Starkspur Supreme Delicious' when grafted on Selection 2. These apomictic selections offered no advantage over M.7 as rootstocks for apples.

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Joseph P. Albano, William B. Miller, and Mary C. Halbrooks

A specific physiological disorder, bronze speckle (J.P.A.'s nomenclature), was consistently induced in `First Lady' and `Voyager' marigold with Fe-DTPA concentrations greater than 0.018 mm Fe-DTPA (1 ppm) applied to a soilless medium. The disorder was characterized by specific symptomology distinguished visually by speckled patterns of chlorosis and necrosis, and downward curling and cupping of leaves. The percentage of total leaf dry weight affected with symptoms generally increased with increasing Fe-DTPA treatments. Symptomatic leaf tissue had a greater Fe concentration than corresponding asymptomatic leaf tissue. Leaf Mn concentrations in symptomatic and asymptomatic tissue were similar. In `First Lady', older leaf tissue accumulated more total Fe and was associated with more severe symptoms than younger tissue. Media leachate Fe concentrations increased over 6 weeks and were larger at greater Fe-DTPA treatments. Adjustment of nutrient solution pH to 4.0, 5.25, or 6.5 did not alter media pH, nor did it prevent disorder symptoms. Application of Fe-DTPA containing nutrient solution to a soilless medium resulted in leachate Fe levels 3 times greater than for FeSO4 treatments. Chemical names used: ferric diethylenetriaminepentaacetic acid, monosodium salt (Fe-DTPA).

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Theocharis Chatzistathis, Ioannis Therios, and Dimitrios Alifragis

root to shoot of the specific element, like for example happens with manganese (Mn) in Mn toxicity conditions. In that case, low transport of Mn from root to shoot, in many plant species, is the result of the oxidation of Mn 2+ to Mn 4+ ( El Jaoual

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Nguyen V. Hue and Yvonne Mai

Manganese (Mn) toxicity in crops is a serious problem in Hawaii, especially Kauai and Oahu, where most soils are highly weathered. To devise a management strategy to control Mn toxicity, a greenhouse experiment was conducted on an acid (pH 4.4) Oxisol (Wahiawa series) having 15g·kg-1 total Mn. Factorial combinations of lime (0, 2.0, and 4.0 g·kg-1 CaCO3) and two composts (made from chicken manure and from sewage sludge at 0, 5, and 10 g·kg-1) were applied to the soil, which was subsequently planted to watermelon (Citrullus lanatus Thunb. `Crimson Sweet'). Our preliminary results showed that: 1) liming reduced Mn extractability and phytoavailability, but the reduction in Mn per unit increase in pH was much less than predicted by theory; 2) for good watermelon growth, soluble Mn, as extracted by the saturated paste method, should be <2.0 mg·L-1 corresponding to a soil pH >5.7; 3) unlike the saturated-paste extractable Mn, the Mehlich3-extractable Mn varied less with pH in a given soil series than between soil series; 4) effects of composts on Mn toxicity varied with compost properties, especially their Ca content and pH altering capacity; and 5) the diagnostic criteria for Mn toxicity in watermelon are tentatively proposed as: leaf Mn >1000 mg·kg-1 and leaf Ca/Mn ratio (g·g-1) <25.

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Creighton Gupton and James Spiers

To determine whether manganese tolerance in rabbiteye blueberry (Vaccinium ashei Reade) is heritable, a 10-parent diallel cross was produced. A 250 ppm Mn solution (200 ml/plant) was applied to a sand culture, of the progeny daily. Visual ratings (1 - dead plant - 13 - no Mn toxicity symptom) were made after 6 weeks. Shoot weight and Mn content of leaves were determined. Narrow-sense heritability estimates (h2) were 0.45±0.28 for Mn content, 0.49±0.27 for visual ratings, and 0.37± 0.21 for shoot weight. The genetic correlation between neither shoot weight nor visual rating and Mn content (0.11 and -0.15, respectively) was very high; however, the correlation between shoot weight and visual ratings (1.00) was extremely high. This suggests that visual ratings provide an estimate of Mn effects on plans equal to objective measurements of shoot weight. Though h2 estimates for Mn content and visual ratings were similar, the lack of genetic correlation between the traits indicates that tolerance to Mn toxicity is independent of Mn content. The high h2 for visual ratings suggests mass selection as the method of choice for improving Mn tolerance in a rabbiteye blueberry population.

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Gail S. Lee and Tina G. Teague

In soils that can range in pH from the low 4's to 7, depending on the location and liming history, deficiency of Zn, B, and Mo coupled with the soil acidity complex of Mn toxicity had been previously identified as severe limiting factors in producing quality Brassica crops. Fertility studies on fall and spring planted Brassicas focused on the effect of including/not including micronutrients during various phases of growth when NPK preplant fertilizer was reduced. Differential responses to reduction in preplant NPK and applications of micronutrients was found to be dependent on planting time (fall or spring), species of Brassica planted and cultivar. Nutrient uptake in leaf blades and petioles was followed. In broccoli timing of micronutrient applications significantly affected the harvest period length. Broccoli final yields of the B, Zn and Mg treatments were found to contribute ≈75% to 80% of the final yield of a full range micronutrient solution.

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Desmond G. Mortley

Greenhouse studies were conducted to evaluate 5 levels of Mn (0.00025 to 0.1 g.L-1) on Mn toxicity or tolerance of sweetpotato [Ipomoea batatas (L.) Lam] grown in a modified half Hoagland's solution. The presence of oxidized Mn on the roots and leaves was demonstrated by the blue staining test with benzidene and the solubility and bleaching of oxidized Mn in the oxalic-sulfuric acid solution. Both storage root and foliage fresh and dry weights were highest at Mn concn of 0.00025 g.L-1 in the nutrient solution, while fibrous root dry weight was highest with 0.01 g.L-1 Mn in the solution. More Mn accumulated in foliage than in fibrous roots for all levels of Mn evaluated. N, P, and K concn in foliage was highest at a Mn concn of 0.1 g.L-1 Mn in the solution. Foliage dry weight was preserved up to a high Mn level of about 2700 ug. g-1 Mn in tissues, while taht for storage roots was preserved up to a high Mn level of about 1000 ug. g-1 in the tissues. Deposition of oxidized Mn was observed on fibrous roots particularly at the highest Mn levels in the nutrient solution.

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C.L. Gupton and J.M. Spiers

To determine if high Zn concentrations contribute to chlorosis in blueberry, plants of rabbiteye `Climax' and southern highbush `Bladen' were fertilized in sand culture with 30, 60, 90, and 120 ppm Zn solutions at 4, 4.5, 5, 5.5, 6, and 6.5 pH. Only Zn levels significantly affected the degree of chlorosis in plant leaves. No interaction among cultivars, pH, or Zn concentration was significant. The linear response to Zn levels was significant (P = 0.0001), but quadratic and cubic responses were not significant. Cultivars and Zn fertilization levels affected Zn and Mn accumulation; however, no difference in chlorosis rating was observed between cultivars. An inverse relationship existed between Zn fertilization levels and leaf Mn content so that the total concentration of the two minerals was about the same for each fertilization level, suggesting that Mn toxicity would not be expected at high levels of Zn fertilization. We concluded that high levels of Zn may induce chlorosis in rabbiteye and southern highbush blueberry.