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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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Desmond G. Mortley

The effects of 0.25, 1.0, 2.5, 10, and 100 mg Mn/liter on sweetpotato [Ipomoea batatas (L.) Lam] were evaluated in a greenhouse during 2 years using the nutrient film technique. Foliage and storage root dry weights declined linearly as Mn concentration increased in either whole plants or fibrous roots. Foliage and storage root dry weights were equally sensitive to Mn concentration in whole plants but 5 to 15 times more sensitive to increased Mn concentration in the fibrous roots. Foliar N, P, K, Ca, and Mg concentrations were adequate and did not appear to limit plant growth. Manganese concentrations in solution had very little effect on Fe, Zn, or B concentration. Manganese concentration was higher in the foliage than in fibrous roots. Plant roots showed browning at the higher (10 or 100 mg Mn/liter) concentrations in solution, which indicated the presence of oxidized Mn. Characteristic toxicity symptoms were observed in plants receiving 2.5 (moderate), 10, or 100 mg Mn/liter in solution.

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Desmond G. Mortley and Walter A. Hill

The influence of Azospirillum inoculation on sweetpotato Ipomoea batatas (L.) Lam.] was evaluated in combination with fertilizer N rates of 0, 40, and 80 kg·ha-1. Plants were inoculated with 5 ml of the inoculant at 2, 4, and 6 weeks after transplanting. Inoculation increased total and marketable yield by 12% and 17%, respectively, in 1984 and 5% and 22%, respectively in 1985. Higher storage root yields were accompanied by lower foliage yields, which suggested the inoculant may enhance storage root growth at the expense of foliage growth on soils with low to moderate N levels (40 to 80 kg·ha-1). Storage root N (1984 and 1985) and leaf N (1985) were higher for 40 kg N/ha with inoculation than with inoculation alone (treatments 4 vs. 2), which suggested that Azospirillum plus fertilizer N increased the N content of the plants.

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Pauline P. David, Audrey A. Trotman, and Desmond G. Mortley

One of the major objective of growth analysis data is to provide a basic understanding of some of the mechanisms that affect plant growth. This study was initiated to evaluate the effects on several growth parameters when plants are grown in an NFT system. Vine cuttings (15 cm length) of the sweetpotato cultivar ``Georgia Jet” was grown in a closed NFT system for a period of 120 days. Nutrient was supplied in a modified half-strength Hoagland's solution with a N:K ratio of 1:2.4. Destructive harvesting of plants occurred at 14 day intervals at which time plants were separated into their various component parts and analyzed for dry weight accumulation, leaf area index, crop growth rate, relative growth rate and net assimilation rate. Results showed dry weight distribution within the plant had a linear response for all component part evaluated. Greatest contributors to total plant dry weight was stem followed by leaves, fibrous roots, buds and flowers. However, once storage root production occurred it contributed the largest percentage to total plant dry weight. LAI was optimum at 80 days after planting (DAP) while CGR and RGR fluctuated throughout the growing season. Initially NAR was higher in foliage than storage roots but declined once storage root enlargement began, suggesting a translocation of assimilates to storage root.

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Lauren Lindsey, Raymon Shange, Ramble O. Ankumah, Desmond G. Mortley, and Sangita Karki

Organic fertilization techniques have become an attractive alternative to conventional techniques, but there remains interest in their impact on rhizosphere ecology. This study was aimed at assessing the impacts of various organic fertilizer amendments on storage root yield, chemical, biochemical, and microbial factors in the rhizosphere ecosystem and the bacterial community composition in the rhizosphere ecosystem. Four sweetpotato cultivars (J6/66, NCC-58, TU Purple, and Whatley/Loretan) and four organic fertilizer treatments [poultry litter, Megabloom (fish protein), NPK, and an untreated control] were used in the study. The experiments were conducted as a randomized complete block design with a 4 × 4 factorial treatment arrangement and three replications. Fertilizer treatments were split-applied at the rate of 134–67–67 kg·ha−1 NPK equivalent based on soil test recommendations 1 and 4 weeks after planting as single bands 15 cm from the plants and organic amendments were calculated based on total N content. Rhizosphere soil samples were collected at harvest and analyzed for soil pH, soil organic carbon (SOC), bacterial 16S rDNA, and selected soil enzymes. Organic amendments did not affect storage root yield or percent dry matter but enhanced both the mass and number of US#1 storage roots. Rhizosphere pH varied depending on cultivar and cultivar response varied with pH and ranged from 6.1 to 6.8, whereas SOC was similar regardless of the amendment. The impact of fertilizers was evident as Megabloom (fish protein) treatment suppressed the relative abundance (RA) of nitrifiers (Nitrosococcus and Nitrosomonadaceae). Also, the rhizosphere of ‘Whatley/Loretan’ seemed to have been a beneficial habitat for populations of common nitrogen-fixing bacteria Bradyrhizobium elkanii, and Rhodospirillaceae sp. as their RA increased significantly in the rhizosphere. That bacteria associated with carbon and nitrogen cycling under aerobic conditions were found to be ubiquitous in the rhizosphere of sweetpotato, suggesting that certain amendments positively impacted the populations of nitrogen-cycling bacteria, thus making them a viable alternative to NPK when considering increasing or sustaining yield while promoting long-term soil health.

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Desmond G. Mortley, Jun-Hyun Oh, Damicca S. Johnson, Conrad K. Bonsi, and Walter A. Hill

A greenhouse study was conducted to evaluate the influence of harvest intervals on biomass yield and omega fatty acids of ‘Golden purslane’ (Portulaca oleracea). Nutrients were supplied as a modified full-strength Hoagland solution two to three times weekly. Plants were harvested sequentially at 20, 40, and 60 days after transplanting (DAT) corresponding to 42, 63, and 84 days after sowing. Fatty acids were determined using a gas chromatography–mass spectrometry. Harvest intervals significantly influenced foliage fresh and dry weight, leaf number and plant height, and root length and fresh weight and were greatest at 60 DAT. Fatty acid analysis verified the presence of myristate, palmitate, linoleate, and linolenate at 20 DAT and in all three harvests, whereas stearate and oleate were detected only in the last two harvests (40 and 60 DAT). Linoleate, palminate, and linolenate were the most abundant fatty acids in purslane with levels in excess of 300 mg·kg−1. Those for myristate, stearate, and oleate were in excess of 200 mg·kg−1. The ratio of omega-6/omega-3 ranged from 0.44 for Harvest 1 to 1.1 for Harvest 3, whereas ratios for harvest intervals two and three were equal to or greater than the recommended daily human requirement. Results showed qualitative and quantitative differences of harvest intervals of purslane, suggesting that an optimal ratio of omega-6 to omega-3 fatty acids can be achieved ≈20 DAT.

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Philip A. Loretan, Fred A. Avicki, Desmond G. Mortley, and Wiletha Horton

A cooling system using the principles of heat transfer was designed to provide a temperature difference of 6C between root and shoot zones and to study the effect of this difference on growth, yield, and phenology of `TI-155' sweetpotato [Ipomoea batatas (L.) Lam.] grown using the nutrient film technique in a greenhouse. Treatments were temperature control (20C) and variable temperature (26C) in a randomized complete-block design with two replications. A modified half Hoagland's nutrient solution with a 1 N: 2.4 K ratio was used and was changed every 2 weeks. Nutrient solution pH was maintained between 5.5 and 6, and electrical conductivity, salinity, and solution temperature were monitored at regular intervals. Storage root fresh and dry weights (except for fibrous root dry weight) and foliage fresh and dry weights were not significantly influenced by root zone temperature. Leaf expansion rate and vine length were lower for root zone temperature control plants; stomatal conductance, transpiration, and leaf unfolding rates were similar for both treatments.

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Jennifer L. Seminara, Desmond G. Mortley, Philip A. Loretan, and Beverly Smith

Two trials were conducted to determine the effect of duration of storing vine cuttings on yield of sweetpotatoes grown under greenhouse conditions in nutrient film technique. TI-155 sweetpotato [Ipomoea batatas (L). Lam.] vine cuttings with leaves removed were stored at room temperature in an open basket for 0, 3, 5, and 7 days before planting in a complete randomized design with two replications. A modified half Hoagland's nutrient solution was used. Nutrient solution pH was maintained between 5.5 and 6.0 and changed every 2 weeks. Salinity, electrical conductivity, and solution temperature were monitored at regular intervals. Results show a trend toward increased percent dry matter as storage duration increased. Storing vine cuttings for 5 days produced the highest yield of storage root fresh and dry weights. Foliage fresh and dry weights were not influenced by preplanting treatments.

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Desmond G. Mortley, P.A. Loretan, C.K. Bonsi, and W.A. Hill

Growth chamber studies were conducted to evaluate the effect of four diurnal temperatures (24/18C, 26/20C, 28/22C, and 30/24C) on yield, leaf expansion and unfolding, and vine length of sweetpotatoes [Ipomoea batatas (L.) Lam]. Four vine cuttings (15 cm in length) of `TI-155' and `Georgia Jet' were grown for 120 days using a modified half-Hoagland nutrient solution with a 1:2.4 N:K ratio. Irradiance at canopy level averaged 600 μmol·m–2·s–1 at an 18/6 photoperiod, and RH of 70%. Storage root number/plant for both cultivars decreased with increased temperature. Storage root fresh and dry weights for both cultivars increased with temperatures up to 28/22C and declined at 30/24C. Foliage fresh and dry weights were not influenced by temperature for either cultivar. Leaf expansion rate and vine length were highest at 26/20C and lowest at 24/18C for both cultivars. Leaf unfolding rate was not affected by temperature foe either cultivar, but was more influenced by time of measurements.

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Desmond G. Mortley, Douglas R. Hileman, Conrad K. Bonsi, Walter A. Hill, and Carlton E. Morris

Two sweetpotato [Ipomoea batatas (L.) Lam] genotypes (TU-82-155 and NCC-58) were grown hydroponically and subjected to a temporary loss of lighting in the form of 14 days of prolonged darkness compared with a lighted control under standard daily light periods to determine the impact on growth responses and storage root yield. Vine cuttings of both genotypes were grown in rectangular channels. At 65 days after planting, lights were turned off in the treatment chambers and replaced by a single incandescent lamp, providing between 7 and 10 µmol·m−2·s−1 photosynthetic photon flux (PPF) for 18 hours, and the temperature lowered from 28/22 °C light/dark, to a constant 20 °C. Plants remained under these conditions for 14 days after which the original light level was restored. Growth chamber conditions predark included, a PPF mean provided by 400-W metal halide lamps, of 600 ± 25 µmol·m−2·s−1, an 18-hour light/6-hour dark cycle and a relative humidity of 70% ± 5%. The nutrient solution used was a modified half-Hoagland with pH and electrical conductivity (EC) maintained between 5.5–6.0 and 1000–1200 μS·cm−1, respectively, and was adjusted weekly. Storage root number and fresh weight were similar regardless of treatments. Plants exposed to prolonged darkness produced 10.5% and 25% lower fibrous root fresh and dry mass, respectively, but similar foliage yield and harvest index (HI). ‘NCC-58’ produced an average of 31% greater storage root yield than that of ‘TU-82-155’ but the number of storage roots as well as % dry matter (%DM) were similar. ‘NCC-58’ also produced 31% greater fibrous root dry weight, whereas ‘TU-82-155’ produced a 44% greater HI. The significant interaction between prolonged darkness and cultivars for %DM of the storage roots showed that DM for ‘TU-82-155’ was 18.4% under prolonged darkness and 17.9% in the light. That for ‘NCC-58’ was 16.4% under prolonged darkness compared with 19.4% (14.8% greater) for plants that were not subjected to prolonged darkness. The evidence that there were no adverse impacts on storage root yield following the exposure to prolonged darkness suggests that the detrimental effects were below the detectable limits for these cultivars in response to the short perturbation in the available light and that sweetpotatoes would be hardy under short-term failure situations.