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B. Castillo, M.A.L. Smith, D.L. Madhavi and U.L. Yadava

Interactions between irradiance levels (5–40 μmol·m-2·s-1) and iron chelate sources (FeEDTA and FeEDDHA) were observed for Carica papaya shoot tip cultures during both the establishment and proliferation stages of microculture. Reduced levels of irradiance (5 μmol·m-2·s-1) favored shoot tip establishment regardless of the source or level of iron. However, the highest percentage of successful explant establishment (100%), and significantly greater leaf length (1.16 cm; over double the size attained in any other treatment), resulted when a low concentration of FeEDTA alone was used at low irradiance. During the subsequent shoot proliferation stage, however, higher irradiance levels (30 and 40 μmol·m-2·s-1) were required, and FeEDTA failed to support culture growth when used as the sole iron source. The highest multiplication rates (3.6 shoots per explant) and leaf chlorophyll concentrations (0.22 mg/g fresh mass), and significantly improved shoot quality were achieved at 30 μmol·m-2·s-1 irradiance when both iron chelate formulations were combined (each at a 100 μM concentration) in the proliferation medium. Chemical names used: benzylamino purine (BA); ferric disodium ethylenediamine tetraacetate or FeNa2EDTA (FeEDTA); ferric monosodium ethylenediamine di(o-hydroxyphenylacetate), (FeNaEDDHA) or Sequestrene 138Fe (FeEDDHA); indoleacetic acid (IAA); 1-naphthaleneacetic acid (NAA).

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Joseph P. Albano and William B. Miller

We have shown previously that Fe-chelates incorporated into soluble fertilizers are vulnerable to photodegradation, and that such solutions can cause modifications in root reductase activity. The objective of this research was to determine the effects of Fe-chelate photodegradation under commercial production conditions. Marigolds were grown in a greenhouse and transplanted stepwise from #200 plug trays to 804 packs to 11.4-cm (4.5-inch) pots. Plants were harvested at the end of each stage, and treatments consisted of either irradiated (complete loss of soluble Fe) or non-irradiated fertilizer solutions ranging from 100-400 mg/L N (0.5–2 mg/L Fe). In the plug and pack stages, foliar Fe was significantly lower and Mn significantly higher in plants treated with the irradiated than nonirradiated fertilizer solutions, averaging 97 μg·g–1 and 115 μg·g–1 Fe, and 217 μg·g–1 and 176 μg·g–1 Mn, respectively. Fe(III)-DTPA reductase activity of roots of plugs treated with the irradiated fertilizer solution was 1.4-times greater than for roots treated with the non-irradiated fertilizer solution. Leaf dry weight in the plug and pack stages was not affected by treatment, and averaged 0.1 g and 1.2 g per plant, respectively.

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Gene E. Lester and Michael A. Grusak

Commercially grown honeydew fruit (Cucumis melo Inodorus group) and netted cantaloupe fruit (C. melo Reticulatus group) in low-humidity regions of the U.S. are typically field packed, eliminating the possibility for postharvest chelated-calcium dip treatments to extend fruit shelf life. In this study, calcium treatments were applied to orange-flesh honeydew fruit commercially grown in 2001 and 2002 in Sacramento Valley, Calif. and orange-fleshed netted cantaloupe fruit commercially grown in 2002 in Imperial Valley, Calif., and Rio Grande Valley, Texas. Aminoacid-chelated calcium and mannitol-complexed calcium compounds were applied to field-grown plants at the rate of 2.3 L·ha-1 (1 qt/acre) at 0, 1, 2, or 4 total applications during growth of honeydew and cantaloupe fruit. Applications were A) at female flowering, B) within 15 days (cantaloupe) or 20 days (honeydew) after flowering, C) within 30 days (cantaloupe) or 40 days (honeydew) after female flowering, and/or D) within 3 to 5 days before abscission. One application equaled (A) or (D), two applications equaled (A + B) or (C + D) and four applications equaled (A + B + C + D). Evaluations of fully abscised fruit were exterior and interior firmness, marketability, calcium concentrations, interior soluble solids concentration (sugars), and consumer preference (taste) following harvest and up to 3 weeks commercial/retail storage. Cantaloupe fruit at both locations did not appear to benefit from preharvest plant applications of calcium when compared to fruit from plants treated with water. Honeydew fruit, however, did and the benefit was observed both years. Honeydew fruit that received four preharvest plant applications of calcium, regardless of source, were generally superior in firmness, marketability, and had a higher calcium concentration than fruit from plants receiving water or one or two applications of calcium. Fruit sugars and taste were not affected by preharvest plant applications of calcium.

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Maritza Ojeda, Bruce Schaffer and Frederick S. Davies

Root ferric chelate reductase (FCR) activity in Annona glabra L. (pond apple), native to subtropical wetland habitats and Annona muricata L. (soursop), native to non-wetland tropical habitats, was determined under Fe-sufficient and Fe-deficient conditions. Four-month-old seedlings of each species were grown hydroponically in a complete nutrient solution containing 90 μm Fe or no Fe. The degree of tolerance of Fe deficiency was evaluated by measuring root FCR activity, chlorophyll and Fe concentration in recently matured leaves and plant growth. Root FCR activity was higher in soursop than in pond apple in the nutrient solution with Fe. However, there were no differences in root FCR activity between species under Fe-deficient conditions. Root FCR activity in pond apple and soursop was not induced in the absence of Fe. Leaf chlorophyll index and Fe concentration, and dry weights of pond apple were lower when plants were grown without Fe compared to plants grown with Fe. Leaves of pond apple grown without Fe became chlorotic within 3 weeks. Lack of Fe decreased the chlorophyll index and Fe concentration in young leaves less in soursop than in pond apple. In contrast, the Fe level in the nutrient solution had no effect on dry weights of soursop. The rapid development of leaf chlorosis and low FCR activity of pond apple may be due to its native origin in wetland areas where there is sufficient soluble Fe for plant growth and development.

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R.J. Cooper and L.A. Spokas

Supplemental Fe fertilization to improve turfgrass quality has become an increasingly common practice on many turfgrass areas. Field studies were conducted to evaluate the nutrient uptake, growth, and quality of Kentucky bluegrass (Pea pratensis L.) treated with chelated Fe sources. Iron sources were evaluated over 2 years at 1.5,3.0, and 6.0 kg Fe/ha applied in May, July, and September of each year. Turf treated with an iron orthophosphate citrate source (Fe-PC) exhibited more foliar growth than nontreated turf on seven of 11 sampling dates during the study. Iron citrate sources [Fe-C(EI) and Fe-C(T)] and Fe-DTPA applications resulted in similar growth rates, never stimulating growth more than the Fe-PC source and rarely increasing growth compared with nontreated turf. Increasing the Fe rate within source did not typically increase growth. Iron-treated turf exhibited quality superior to nontreated turf throughout the study with all sources performing comparably. Increasing Fe rate did not result in a corresponding increase in quality, due to greater phytotoxicity at higher rates. Although several sources produced notable phytotoxicity at 6.0 kg Fe/ha, repeated application did not decrease turfgrass density. Iron tissue content increased linearly with rate on four of five sampling dates during the study however, no source resulted in tissue Fe content significantly higher than other sources. Application of sources containing supplemental P and/or K did not increase tissue P or K content. Chemical names used: iron citrate (Fe-C); iron diethvlenetriamine pentaacetate (Fe-DTPA); iron orthophosphate citrate (Fe-PC).

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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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Gene E. Lester and Michael A. Grusak

Commercially grown honey dew fruit [Cucumis melo (Inodorus group)] typically are harvested before abscission because fruit cut unripe have a longer storage life than fully ripe fruit. However, because fully ripe fruit contain higher concentrations of soluble solids (predominantly as sugars), an attribute that increases their preference among consumers, methods are being explored to extend the storage life of fully ripe fruit. In this study, fully abscised honey dew fruit were evaluated for tissue attributes and consumer preference following postharvest dipping in either chelated or nonchelated calcium (Ca) solutions. Calcium sources were an amino acid-chelated Ca, ethylene-diamine tetraacetic acid (EDTA)-chelated Ca, or calcium chloride (CaCl2), with each provided at three different rates. Fruit were evaluated at harvest, and after 14 or 22 days commercial storage. Evaluations were peel surface changes (color and disorders), hypodermal-mesocarp tissue Ca concentration, flesh firmness, soluble solids concentration, and consumer preference of the edible flesh. Peel color became yellowed and lighter during storage for all fruit, with higher Ca rates resulting in more intensely yellowed fruit. Hypodermal-mesocarp tissue Ca concentration was 0.90 mg·g-1 of fresh weight (900 ppm) at harvest, and declined in all fruit by 22 days storage. Peel disorders (disease and spotting) were none to slight for all fruit by 14 days storage, but by 22 days storage disease incidence ranged from none to severe, depending on the Ca source and rate. Fruit firmness declined in all fruit throughout storage, with the smallest declines measured in fruit treated with the amino acid-chelated Ca. Soluble solids concentration of fully ripe fruit was 12.3% at harvest, and showed either no decline or slight declines with storage among the treatments. Consumer preference was highest for freshly harvested fruit, but fruit were desirable even after 22 days storage across all treatments. Postharvest application of Ca at ≤0.16 m Ca in an amino acid-chelated form, versus EDTA-chelated Ca or CaCl2, slowed honey dew melon senescence so that after 22 days of commercial and retail storage the fruit were of high marketable quality, and there was no detrimental effect on consumer preference for the edible flesh.

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Brandon R. Smith, Paul. R. Fisher and William R. Argo

The objective was to quantify the effect of substrate pH and micronutrient concentration on growth and pigment content for two floricultural crop species, Petunia ×hybrida `Priscilla' and Impatiens wallerana `Rosebud Purple Magic'. A 70% peat: 30% perlite medium was amended with dolomitic hydrated lime to achieve five substrate pH's ranging from pH 4.4 to 7.0. Plants were grown in 10-cm-diameter pots in a greenhouse for 4 weeks, and irrigated with a fertilizer containing (in mg·L-1) 210N-31P-235K-200Ca-49Mg. Micronutrients were applied using an EDTA (ethylenedinitrilotetraacetic acid) chelated micronutrient blend (C111), at 1×, 2×, and 4× concentrations (in mg·L-1) of 0.50Fe-0.25Mn-0.025Zn-0.04Cu-0.075B-0.01Mo. Petunia shoot dry mass and stem caliper decreased as substrate pH increased, whereas leaf length and width remained unchanged. The highest level of C111 resulted in higher dry mass and smaller leaf area compared with other C111 levels. Overall, substrate pH and C111 had little effect on plant size or mass for impatiens. For both species, increasing substrate pH above 5.3 resulted in a decline in chlorophyll, carotenoids, and the SPAD chlorophyll index (measured with a Minolta-502 SPAD meter) compared with the lowest three pH levels. Chlorosis was observed at pH 7 after 2 weeks of growth. Increasing C111 concentration had no effect on pigment content below pH 5.3, but increased pigment content at higher pH levels. The SPAD index was highly correlated with chlorophyll content. This research emphasizes that an acceptable range in substrate pH can vary depending on fertilizer practices, with higher micronutrient concentration compensating for lower solubility at high substrate pH.

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Brandon R. Smith, Paul. R. Fisher and William R. Argo

The objective was to quantify the effect of substrate pH and micronutrient concentration on tissue nutrient levels in Petunia ×hybrida Hort. Vilm.-Andr. and Impatiens wallerana Hook. F. Plants were grown in 10-cm-diameter pots for 4 weeks in a 70% peat: 30% perlite medium amended with five lime rates to achieve substrate pH values ranging from pH 4.4 to 7.0. Plants were irrigated with (in mg·L-1) 210N-31P-235K-200Ca-49Mg. Micronutrients were applied as an EDTA (ethylenedinitrilotetraacetic acid) chelated micronutrient blend (C111), at 1×, 2×, and 4× concentrations of 0.50Fe-0.25Mn-0.025Zn-0.04Cu-0.075B-0.01Mo. Patterns of tissue concentrations across substrate pH differed from nutrient solubility in the medium, particularly with regard to Mn. Foliar N content decreased slightly as substrate pH increased, whereas foliar Ca, Mg, and S increased. Although foliar P and K varied with pH, there was no consistent trend between species. Foliar total Fe, ferrous Fe, and Cu decreased as substrate pH increased, whereas foliar Zn increased. Foliar Mn content decreased for both species as pH rose to 6.0, and then increased from pH 6.0 to 7.0. In contrast, Mn level in the substrate, measured in a saturated medium extract using deionized water as the extractant, decreased as pH increased from pH 4.4 to 7.0. Chlorophyll content decreased when the ratio of tissue Fe to Mn was <0.57 (impatiens) or <0.71 (petunia), or Fe was <106 (impatiens) or 112 (petunia) μg·g-1. SPAD chlorophyll index also declined in petunia with foliar Mn >42 μg·g-1. Increasing C111 increased foliar Cu, total Fe and ferrous Fe in both species, and B for impatiens, and partly compensated for reduced nutrient solubility at high pH.

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Sunghee Guak, Lailiang Cheng, Leslie H. Fuchigami and Sunghee Guak

Bench-grafted `Fuji'/M.26 trees were sprayed with 1% CuEDTA on 31 Oct., defoliated manually on 12 Nov., or allowed to defoliate naturally. Foliar urea at 3% was applied at 14 days and 9 days before CuEDTA treatment. Plants were harvested after natural leaf fall and stored at 2 °C. One set of the plants were destructively sampled for reserve N (expressed as total Kjeldahl N or soluble protein concentration) analysis, and the remaining plants were transplanted into a N-free medium in the spring without any N supply for 40 days after budbreak. CuEDTA resulted in >80% defoliation within 5 days of application. Trees defoliated with CuEDTA had lower reserve N content than naturally defoliated controls, but had higher N than hand-defoliated controls. Foliar urea application before the CuEDTA treatment significantly increased reserve N level in all tree parts, without affecting the efficacy of CuEDTA on defoliation. The extent of spring regrowth was proportional to the reserve N level of the tree. Urea-treated plants, whether hand- or CuEDTA defoliated, had more growth in the spring than hand- or naturally defoliated controls. It is concluded that CuEDTA, as combined with foliar urea, can be used to effectively defoliate apple nursery trees, and increase reserve N level and improve regrowth performance during establishment.