Jonathan Egilla

Horticulture

Ph.D.
16.76

Publications

  • Jonathan N. Egilla, Rose Ogutu, Isabelle Nyirakabibi
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    ABSTRACT: With proper sanitation and growth rejuvenation, collards may be maintained in hydroponic culture for nine to twelve months for repeated leaf harvesting, thereby reducing the frequency of starting new crops from seed, and thus avoiding the longer lag time from seedling establishment to first harvest. Growth rejuvenation involves induction of adventitious roots on stems by carefully timed root pruning. Leaf growth and leaf macro- and micronutrient uptake of collards (Brassica oleracea var. Acephala ‘Champion’) was determined at 42 days after root pruning 77-day old seedling plants. Root pruned plants were established in Nutrient Film Technique (NFT) hydroponic culture with three sources of nutrient solution (15N-2.2P-12.5K [F1]; 15-7.0P-14.1K [F2]; and 20N-8.7P-16.6K [F3]). All nutrient sources supplied 200 mg nitrogen (N) per liter plus micronutrients. The ratios of nitrate (NO3–-N) to ammonium (NH4+-N) and Urea-N were 3.63:1, 1.54:1 and 0.43:1 for F1, F2, and F3; and the Urea-N content were 2.05, 2.60 and 10.10% of the total N supply, respectively. Whereas F1 contained 66.7 mg calcium (Ca) per liter, F2 and F3 had no Ca. The rate of adventitious root growth was highest with F1 and lowest with F3. Marketable yield of young fully expanded leaves (leaf– count [LC], fresh weight [LFW] were significantly affected by nutrient source (F1 > F3 > F2; p ≤ 0.002). With F1, leaf N and phosphorus (P) were within the sufficiency range for collards while potassium (K) and Ca were below the lower limit of the sufficiency range. Leaves have sufficient levels of magnesium (Mg) and sulfur (S), regardless of nutrient source. Leaf macronutrient content was highest with F1, which promoted higher leaf growth than either F2 or F3. With the exception of iron (Fe), leaf micronutrients were above the lower limit of the sufficiency range. Across nutrient source, LFW and LDW were positively correlated with N, P, K, Fe and manganese ([Mn]; R ≥ 0.5707, R2 ≥ 0.3141; p < 0.0001), but negatively correlated with leaf aluminum (Al) content (R = -0.5383, R2 = -0.5106; p < 0.0001). These observations suggests that leaf growth was limited by lower N, P, K, Ca and Fe in F2 and F3 plants, due to reduced growth of adventitious roots compared with F1. Subsequent experiments will further assess the effect of low Ca as well as high NH4+–N and Urea-N to NO3––N ratio on adventitious root growth of collards.
    2014 ASHS Annual Conference; 07/2014
  • Jonathan N. Egilla, Rose Ogutu, Isabelle Nyirakabibi
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    ABSTRACT: The growth and tissue mineral elemental content of lettuce [Lactuca sativa L. ‘Paris Island Cos’ (PIC) and 'Black Seeded Simpson' (BSS)] in response to nutrient solution source and concentration were evaluated in a Nutrient Film Technique (NFT) hydroponic culture system. Thirteen-day old seedlings were grown; and harvested 27 days after transfer into NFT hydroponic culture. Fertilizer sources for the two hydroponic solutions comprised of either 100%– or 50% Steiner's nutrient solution formulation, or a soluble fertilizer (15N–2.2P‐12K) at 200 mg·L-1 of N, plus micronutrients (CAMG). Mean nutrient solution pH was maintained between 6.0 and 6.7, while electrical conductivity (EC) ranged from 1.61 to 2.83. With the exception of copper (Cu), whole lettuce-head tissue analysis indicates no significant (P = 0.05) fertilizer × cultivar interaction for tissue elemental content, or growth parameters measured. Compared with 100% Steiner's and CAMG, average leaf count (LCNT) decreased at 50% Steiner's, in both BSS and PIC (P ≤ 0.002). In addition, head fresh- and dry weight (HFW, HDW) of PIC were reduced at 50% Steiner's (P ≤ 0.001), compared with the 100% level, despite increases in tissue content of nitrogen (N, 2.7–fold) and phosphorus (P, 13.4%). Similarly, 100% Steiner's significantly increased the HFW and HDW of PIC, compared with CAMG and 50% Steiner's (P ≤ 0.001). With BSS, there were no differences in HFW, HW, macro- and micronutrient content among the nutrient solution sources and concentration. Except for copper (Cu), zinc (Zn) and aluminum (Al), which increased at 100% Steiner's (P ≤ 0.0001) in PIC, tissue concentration of iron (Fe), manganese (Mn), boron (B), molybdenum (Mo), and sodium (Na) were highest at 50% Steiner's. Reductions in tissue elemental content at 100% Steiner's may have resulted from the 43% increase in EC (2.83 mS/cm) over the 50% level (1.61 mS/cm). The higher EC at 100% Steiner's caused root tip death and root stunting in seedlings, and delayed plant establishment by about two weeks compared to the latter. With both BSS and PIC, plants grown with CAMG had higher P and potassium (K) content than both levels of Steiner's, and higher N than 100% Steiner's nutrient solution. Similarly, with micronutrients, tissue Fe, Mn, B, and Mo content were higher with CAMG than at 100%, but not 50% Steiner's (P < 0.05).
    2013 ASHS Annual Conference; 07/2013
  • Jonathan N. Egilla, Rose Ogutu, Isabelle Nyirakabibi
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    ABSTRACT: The influence of nutrient solution renewal (RNWL) versus replenishment of depleted nutrients (RPLN), and seed propagation substrate (SBSTR) on leaf mineral nutrient content and yield of Swiss chard (Beta vulgaris L. ‘Lucullus’), were evaluated in a Nutrient Film Technique (NFT) hydroponic culture. Seedlings at the second true-leaf stage were transferred into NFT culture and grown with a soluble fertilizer solution (15N–2.2P–12K) at 200 mg·L-1 of N. The treatments comprised of two SMGMT techniques (RNWL and RPLN), and two seed propagation substrates (Oasis™ or Rockwool cubes). Laboratory leaf analysis at 63 days after transfer (DAT) into NFT culture indicates significant (P =0.05) SMGMT × SBSTR interaction for leaf nitrogen (N) and manganese (Mn) only. With RNWL, leaf N was higher in Rockwool than Oasis, whereas with RPLN N was highest in Oasis (P ≤0.05). Compared with Oasis, Rockwool increased leaf phosphorus (P), calcium (Ca) and magnesium (Mg) with RPLN (P ≤0.05), but not potassium (K) and sulfur (S). Besides N, SBSTR had no effect on leaf macronutrient content with RNWL. Across SBSTR, while leaf K was increased (P ≤0.01) by RPLN, leaf Ca was highest with RNWL (P ≤0.05); SMGMT did not affect the other macronutrients. Across SMGMT Rockwool increased leaf Mg (P ≤0.02) compared with Oasis, but no other macronutrient was affected by SBSTR. Of the micronutrients only leaf iron (Fe) content was affected by SBSTR within RNWL, being higher (P ≤0.05) in Rockwool than Oasis. Within RPLN Rockwool increased (P ≤0.02) the other micronutrients over Oasis, except copper (Cu) and molybdenum (Mo). With the exception of zinc (Zn) and Cu (RPLN > RNWL; P≤0.003), SMGMT had no effect (P ≤0.05) on the other micronutrients across SBSTR. Across SMGMT Rockwool increased leaf Fe, Mn, boron (B) and Al content over Oasis (P ≤0.02). Leaf growth and yield at 63-DAT indicates significant (P = 0.05) SMGMT × SBSTR interaction for leaf fresh- and dry weight (LFW, LDW [g]), but not leaf count (LC) and leaf area (LA; cm2) per plant. Within SMGMT LFW and LDW were higher in Rockwool than Oasis with either RNWL or RPLN (P≤0.01). Across SBSTR, RNWL increased LC and LA over RPLN (P≤0.01). Similarly, across SMGMT, LC and LA were higher in Rockwool than Oasis (P≤0.01). These observations suggests that RNWL with Rockwool substrate provided better growing conditions for optimum mineral nutrition and yield of Swiss chard in NFT hydroponic culture under the conditions of this experiment.
    2012 ASHS Annual Conference; 08/2012
  • Jonathan N. Egilla
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    ABSTRACT: The yield and leaf elemental concentration of beetroot was determined in a Nutrient Film Technique (NFT) hydroponic experiment. The nutrient solutions contained in mg L: 108 nitrogen (N) and 12.0 calcium (Ca) (N1Ca1), or 200 N and 66.7 Ca (N2Ca2), respectively. Edible root fresh weight (RFW [g/plant]), was significantly (P = 0.0308) increased with N2Ca2 over N1Ca1. The higher RFW yield of N2Ca2 grown beetroot corresponded with significantly (P = 0.05) higher leaf concentrations of Ca, magnesium (Mg), manganese (Mn), molybdenum (Mo), aluminum (Al) and sodium (Na), but not zinc (Zn). Lower tissue Ca and B concentration probably contributed to the reduced yield observed, and Na can be beneficial to the growth of beetroot in hydroponic culture. Adequate supply and enhanced uptake of Ca and B in balance with K, Mg and the other elements are essential in nutrient source selection and management during hydroponic culture of beetroot, and probably other members of Beta species.
    Journal of Plant Nutrition 01/2012; 35(2):203-214. DOI:10.1080/01904167.2012.636123 · 0.54 Impact Factor
  • Jonathan N. Egilla, Rose Ogutu, Isabelle Nyirakabibi
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    ABSTRACT: Growth and yield response of collards leaves to mineral nutrient stress was evaluated in NFT hydroponic culture over a 68-day cropping cycle. Seedlings of collards (Brassica oleracea, Acephala ‘Champion’) raised in 2.5 cm rockwool cubes were transferred into NFT culture at the second true-leaf stage and grown for 16 days in a conditioning nutrient solution prepared from a complete fertilizer (15N–2.2P–12.5K at 200 mg N liter-1 plus micronutrients [C1]). From days 17 to 68 after transfer (DAT) into NFT culture, three nutrient treatments were initiated by replacing the conditioning nutrient solution (C1) with either irrigation water from a well water source (C1–C0), a fresh C1 solution (C1–C1), or 15N–2.2P–12.5K at 300 mg N liter-1 (C1–C2). Water loss due to evapotranspiration was continuously replenished from the same source used to prepare the nutrient solution. At 37 days after initiation of nutrient treatment (DNT), nutrient stress (C1–C0) caused significant (p < 0.05) reduction in marketable yield (fresh weight of young, fully expanded leaves [LFW]), leaf dry weight (LDW), leaf area (LA) and leaf chlorophyll content (LCC) compared with C1–C1 and C1–C2. Specific leaf area (SLA) was significantly (p < 0.05) increased in C1–C0 compared with C1–C2, but not C1–C1; and leaf water content (LWC) was not affected by nutrition regime. By 68-DNT, all the above parameters were significantly lower in C1–C0 compared with C1–C1 and C1–C2. Whereas LDW decreased and LCC remained unchanged from 37 to 68-DNT; LFW, LWC, LA and SLA increased significantly (p < 0.05) in C1–C2. Both in C1–C0 and C1–C1, LFW, LDW and LA declined very significantly from 37 to 68-DAT, but LWC, LCC and SLA were not affected at C1–C1. Mineral nutrient stress significantly decreased leaf succulence, and consequently fresh weight yield of collards during a 68-day cropping cycle despite culture in liquid hydroponic system.
    2011 ASHS Annual Conference; 09/2011
  • Jonathan N. Egilla, Abua Ikem
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    ABSTRACT: Complete fertilizers formulated for fertigation and soil application are commonly used in hydroponic production. However, these are unsuitable for hydroponic culture of many crops because of imbalances in mineral nutrient composition. Currently, research information about the effect of nonhydroponic fertilizers and the confounding effects of crop type and culture condition on crop yield is limited. The influence of mineral nutrient source (FERT) and growing environment (two controlled environment hydroponic greenhouses; CEHG) with different temperature and relative humidity (RH) regimes on mineral elemental concentration and yield of cos lettuce (Lactuca sativa L. var. longifolia Lam.), cv. Cimmaron, were determined in a nutrient film technique (NFT) hydroponic culture. With the exception of calcium, both CEHG and FERT had a significant effect on the tissue concentration of all the macronutrients, and the concentration of micronutrients in lettuce tissue were optimum, regardless of FERT and CEHG, except for Fe (APHN and CAMG) and Mo (APHN). However, low tissue concentration of macronutrients may have contributed to reducing the marketable yield, which was also significantly affected by FERT.
    International Journal of Vegetable Science 01/2011; 17(1):83-103. DOI:10.1080/19315260.2011.536070
  • Jonathan N. Egilla, Rose Ogutu
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    ABSTRACT: Within the small-scale hydroponic industry, approaches to nutrient solution management in recirculating hydroponic culture are variable. Research information about the influence of nutrient solution management (SMGMT) on crop yield responses in commercial recirculating hydroponic culture is limited. The influence of nutrient solution renewal (RNWL) versus replenishment of depleted nutrients (RPLN), and propagation substrate (SBSTR) on leaf yield of Swiss chard (Beta vulgaris L. ‘Lucullus’), were evaluated in a commercial Nutrient Film Technique (NFT) hydroponic system. Two-week old seedlings of Swiss chard ‘Lucullus’ were transferred into NFT culture at the second true-leaf stage and grown under controlled environment greenhouse conditions with a soluble fertilizer solution (15N-2.2P-12K) at 200 mg N liter-1. The treatments comprised of two nutrient management techniques (RNWL and RPLN), and two propagation substrates (Oasis™ or Rockwool cubes). At 63 days after transfer (DAT) into NFT culture, RNWL significantly (p≤ 0.001) increased mean per plant leaf count (LC), leaf fresh weight (LFW), leaf dry weight (LDW) and leaf area (LA). Across SBSTR, these parameters were respectively, 18%, 82%, 45%, and 48% higher with RNWL than RPLN. Similarly, mean LC, LFW, LDW and LA were significantly (p≤ 0.01), higher in Rockwool than Oasis™ cubes. Across SMGMT, these parameters were respectively, 14%, 56%, 58% and 25% higher in Rockwool than Oasis™ cubes. However, with RNWL, SBSTR had no significant (p=0.05) effect on LC. Interaction between SMGMT and SBSTR was not significant (p=0.05). Within SMGMT only LFW and LA were significantly (p≤0.05) higher in Rockwool than Oasis cubes with RNWL, whereas mean LC, LFW, LDW and LA were highest in Rockwool cubes with RPLN (p≤0.01). These observations suggests that RNWL with Rockwool substrate provided better growing conditions for optimum yield of Swiss chard in NFT culture under the conditions of this experiment.
    2010 ASHS Annual Conference; 08/2010
  • Jonathan N. Egilla, Rose Ogutu, Isabelle Nyirakabibi
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    ABSTRACT: Small-scale hydroponic growers commonly utilize non-hydroponic soluble fertilizers for crop production. Currently, there is limited research information about appropriate nutrient solution concentrations and their interactions with various cultural practices on crop yield responses in commercial hydroponic culture. The influence of nutrient solution concentration (NCONC), and propagation substrate (SBSTR) on the growth, and marketable leaf yield of Swiss chard (Beta vulgaris L. ‘Lucullus’), were evaluated in a commercial Nutrient Film Technique (NFT) hydroponic system. Two-week old seedlings of Swiss chard ‘Lucullus’ were transferred into a commercial NFT hydroponic system under controlled environment greenhouse conditions at the second true-leaf stage. The NFT system comprised of rows (28 cm apart) of PVC Hydro-Troughs (5.1 × 10.2 cm × 3.7 m) with 4.45 cm diameter holes spaced 20 cm apart (along the trough). The treatments comprised of two propagation substrates (Oasis™ or Rockwool cubes), and two concentrations of a soluble fertilizer (15N–2.2P–12.5K), prepared at 150 and 200 mg N liter–1 (C1and C2, respectively). At 63 days after transfer (DAT) into NFT culture, mean per plant leaf count (LC), leaf fresh weight (LFW), leaf dry weight (LDW) and leaf area (LA) were significantly (p≤0.01) higher at C2 than C1 with Oasis™ cubes. However, with Rockwool only LFW was significantly (p<0.05) increased at C2. Mean per plant LC, LFW, LDW and LA across SBSTR were respectively, 14%, 64%, 46%, and 54% higher at C2 than C1. Similarly, LFW, LDW and LA were significantly (p≤0.05) higher in Rockwool, regardless of CONC. However, LC was not affected by SBSTR and NCOC × SBSTR interaction was nonsignificant (p=0.05). Mean LC, LFW, LDW and LA across NCONC were respectively, 10%, 52%, 54%, and 31% higher in Rockwool than Oasis™ cubes. These observations suggests that Rockwool substrate provided a better root environment for optimum yield of Swiss chard in NFT culture at both nutrient solution concentrations under the conditions of this experiment.
    2010 ASHS Annual Conference; 08/2010
  • Jonathan N. Egilla, Rose Ogutu
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    ABSTRACT: The effect of three commercial fertilizers on leaf yield of Collards (Brassica oleracea, Acephala group ‘Champion’) was evaluated in a closed, nutrient recirculating ‘Nutrient Film Technique’ (NFT) hydroponic system. Seedlings raised in 1-inch rockwool cubes were transferred into rows (28 cm apart) of PVC Hydro-Troughs with 4.45 cm diameter holes at 20 cm spacing (along the row) at the first true-leaf stage. Seedlings were grown until harvesting, either with Peters Excel-CAL-MAG® (CAL-MAG), Peters Peat-Lite Special® (PLTE), or Peters General-Purpose Soluble Fertilizer® (P-GP) containing 15-5-15, 15-16-17 and 20-20-20, respectively, as percent N-P2O5-K2O. Nutrient solution from each fertilizer source was prepared to supply nitrogen (N) at 200 mg/liter. At 64 days after transfer to NFT culture, the 77-day old Collards plants were root-pruned, and the fertilizer solutions renewed. Forty-two days after root pruning, marketable leaf yield (young, fully expanded leaves) from the fertilizer treatments were compared. Significant differences were observed in leaf count, leaf fresh and dry weight (CAL-MAG > [PLTE = P-GP]) and leaf dry weight ratio (CAL-MAG > PLTE > P-GP) (P = 0.01). Differences in petiole sap nutrient content was significant for NO3–-N (PLTE > CAL-MAG [P = 0.01]; and P-GP > CAL-MAG [P = 0.05]), and potassium (CAL-MAG > [PLTE = P-GP]) (P = 0.01). Petiole sap sodium content also varied significantly with fertilizer treatment (CAL-MAG > P-GP > PLTE) (P = 0.05), and (CAL-MAG > [P-GP = PLTE]) (P = 0.01). Petiole NO3––N concentration indicates that N supply in nutrient solution was not the yield-limiting factor in this study. CAL-MAG, the only calcium (Ca)–supplying fertilizer of the three (38.3 mg Ca/liter), promoted greater marketable leaf yield than either PLTE or P-GP. Magnesium supply from CAL-MAG was 1.7 and 4-fold the amount from PLTE and P-GP, respectively.
    2009 ASHS Annual Conference; 07/2009
  • Jonathan Egilla
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    ABSTRACT: Interaction Between Nutrient Source and Growing Substrate on the Yield of Beetroot in NFT Hydroponic Culture Jonathan N. Egilla Lincoln University Cooperative Research Program, 904 Chestnut St., Jefferson City, MO 65102-0029. Abstract. The effect of mineral nutrient (fertilizer) and growing substrate source on the yield of beetroot (Beta vulgaris ‘Bulls Blood’) was evaluated in a closed, nutrient recirculating ‘Nutrient Film Technique’ (NFT) hydroponic system. Seedlings raised in 1-inch oasis or rockwool cubes were transferred into rows (28 cm apart) of PVC Hydro-Troughs with 4.45 cm diameter holes at 20 cm spacing (along the row) at the one true-leaf stage. Seedlings were grown until harvesting, either with Peters Excel-CAL-MAG® (CAL-MAG; J. R. Peters, Inc., Allentown, PA), or All-Purpose Hydroponic Nutrient® (APHN; Hollister's Hydroponics, Grand Junction, CO), consisting of 15-5-15, and 9-4-15, respectively as percent N-P2O5-K2O. Nitrogen (N) concentration in nutrient solution was 200 mg/liter with CAL-MAG, and at manufacturer's recommended concentration (1 lb fertilizer/100 gallon of water [108 mg N/liter]) with APHN. CAL-MAG increased fresh and dry weight yield of beetroot 2-3 fold compared with APHN. Fertilizer × substrate interaction was significant (P ≤ 0.05) for all the yield parameters measured except root dry weight (RDW) and root:leaf ratio (RLR). With CAL-MAG, components of yield (except RDW and RLR) were increased significantly (P ≤ 0.0003) in rockwool compared with oasis cube. However, with APHN, only leaf fresh weight was significantly higher (P = 0.0492) in rockwool than oasis cube. While fertilizer had no effect on leaf total N and potassium, CAL-MAG significantly increased the concentration of calcium (Ca), magnesium, and sulfur (P <0.0001; P = 0.0069 and P = 0.0246, respectively) over APHN, but phosphorus was significantly higher (P = 0.0403) with APHN. Of the micronutrients, leaf boron (B) and molybdenum (Mo) (P < 0.0001), as well as aluminum (Al; P = 0.0403) concentration varied significantly with fertilizer, and fertilizer × substrate interaction was significant (P ≤ 0.05) for B and Al. With the exception of Ca and B (respectively, 66–75% and 52–72% below the sufficiency range), leaf concentration of essential nutrients were sufficient for beetroot, regardless of fertilizer. These trends suggest that tissue Ca and B concentration contributed to the observed yield response of beetroot in this study.
    2009 ASHS Annual Conference; 07/2009
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    Abua Ikem, Jonathan Egilla
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    ABSTRACT: Trace element content of fish feed and bluegill sunfish muscles (Lepomis macrochirus) from aquaculture and natural pond in Missouri were determined using the inductively coupled-plasma optical emission spectrometer (ICP-OES) and the direct mercury analyzer (DMA). Dietary intake rates of trace elements were estimated. Dogfish muscle (DORM-2) and lobster hepatopancreas (TORT-2) reference standards were used in trace element recovery and method validations. The average elemental concentrations (mg/kg diet, dry wt.) of fish feed were: As 1.81, Cd 2.37, Co 0.10, Cr 1.42, Cu 8.0, Fe 404, Mn 35.9, Ni 0.51, Pb 9.16, Se 1.71, Sn 20.7, V 0.09, Zn 118 and Hg 0.07. The mean elemental concentrations (μg/kg wet wt.) in bluegill muscles from both aquaculture and wild (in parenthesis) sources were: As 0.36 (0.06), Cd 0.28 (0.01), Co 0.0 (0.0), Cr 0.52 (0.05), Cu 0.38 (0.18), Fe 17.5 (2.43), Mn 0.18 (0.24), Ni 0.18 (0.04), Pb 1.03 (0.04), Se 0.34 (0.30), Sn 0.66 (0.42), V 0.02 (0.01), Zn 6.97 (9.13) and Hg 0.06 (0.24). Kruskal-Wallis chi square indicated significant differences in As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Sn, V, Zn and Hg (P<0.001), Se (P<0.01) and Mn (P<0.05) across the sampling locations. Dietary intake rates, estimated from weekly consumption of 228g of aquaculture and wild bluegills, posed no health risks for approximately 85% of all samples. Copyright © 2008 Elsevier Ltd. All rights reserved.
    Food Chemistry 09/2008; 110(2-110):301-309. DOI:10.1016/j.foodchem.2008.02.003 · 3.26 Impact Factor
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    J. N. Egilla, F. T. Davies, T. W. Boutton
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    ABSTRACT: The influence of drought stress (DS) upon whole-plant water content, water relations, photosynthesis, and water-use efficiency of Hibiscus rosa-sinensis cv. Leprechaun (Hibiscus) plants at three levels of potassium (K) nutritional status were determined after a 21-d gradually imposed DS treatment. Compared to K-deficient plants, adequate K supply improved the leaf water content (LWC) and leaf water relations of Hibiscus by decreasing the , and generally sustained rates of net photosynthesis (P N) and transpiration (E), and stomatal conductance (g s), both in DS and non-DS plants. In K-deficient Hibiscus, LWC, turgor potential ( P), and P N, E, and g s as well as instantaneous water-use efficiency, WUE (P N/E) were consistently lower, compared to K-sufficient plants. Carbon isotope discrimination () was lower (i.e. longterm WUE was greatest) in DS than non-DS plants, but K had no effect on during the 21-d drought treatment period under glasshouse conditions. However, the trend in the value of DS plants suggests that could be a useful index of the response of Hibiscus to DS under glasshouse growing conditions. Thus the incorporation of a properly controlled fertilization regime involving sufficient levels of K can improve the acclimation of P N to low leaf, increase P N/E of Hibiscus, and may have potential benefit for other woody plants species.
    Photosynthetica 01/2005; 43(1):135-140. DOI:10.1007/s11099-005-5140-2 · 1.01 Impact Factor
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    ABSTRACT: As a potential phytoremediation system for phytoextraction of chromium (Cr), we evaluated the influence of the arbuscular mycorrhizal fungus Glomus intraradices on leaf tissue elemen-tal composition, growth and gas exchange of sunflower (Helianthus annuus L.). Sunflower seedlings were either inocu-lated with mycorrhizal fungi (AM) or non-inoculated (Non-AM) and then exposed to two Cr species: {12 mmol of trivalent cation (Cr þ3) [Cr(III)] or 0.1 mmol of divalent dichromate anion (Cr 2 O 7 À) [Cr(VI)]}. Both Cr species depressed plant growth, decreased stomatal conductance (g s) and net photosynthesis (A).
    Journal of Plant Nutrition 09/2002; 25(11). DOI:10.1081/PLN-120014702 · 0.54 Impact Factor
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    ABSTRACT: Chromium (Cr) is a heavy metal risk to human health, and a contaminant found in agricultural soils and industrial sites. Phytoremediation, which relies on phytoextraction of Cr with biological organisms, is an important alternative to costly physical and chemical methods of treating contaminated sites. The ability of the arbuscular mycorrhizal fungus (AM), Glomus intraradices, to enhance Cr uptake and plant tolerance was tested on the growth and gas exchange of sunflower (Helianthus annuus L.). Mycorrhizal-colonized (AM) and non-inoculated (Non-AM) sunflower plants were subjected to two Cr species [trivalent cation (Cr3+) {Cr(III)}, and divalent dichromate anion (Cr2O7-) {Cr(VI)}]. Both Cr species depressed plant growth, decreased net photosynthesis (A) and increased the vapor pressure difference; however, Cr(VI) was more toxic. Chromium accumulation was greatest in roots, intermediate in stems and leaves, and lowest in flowers. Greater Cr accumulation occurred with Cr(VI) than Cr(III). AM enhanced the ability of sunflower plants to tolerate and hyperaccumulate Cr. At higher Cr levels greater mycorrhizal dependency occurred, as indicated by proportionally greater growth, higher A and reduced visual symptoms of stress, compared to Non-AM plants. AM plants had greater Cr-accumulating ability than Non-AM plants at the highest concentrations of Cr(III) and Cr(VI), as indicated by the greater Cr phytoextraction coefficient. Mycorrhizal colonization (arbuscule, vesicle, and hyphae formation) was more adversely affected by Cr(VI) than Cr(III), however high levels of colonization still occurred at even the most toxic levels. Arbuscules, which play an important role in mineral ion exchange in root cortical cells, had the greatest sensitivity to Cr toxicity. Higher levels of both Cr species reduced leaf tissue phosphorus (P). While tissue P was higher in AM plants at the highest Cr(III) level, tissue P did not account for mycorrhizal benefits observed with Cr(VI) plants.
    Journal of Plant Physiology 06/2001; 158(6). DOI:10.1078/0176-1617-00311 · 2.77 Impact Factor
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    ABSTRACT: Little is known about physiological changes that occur with micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plantlets during acclimatization. Plantlets were transferred to ex vitro conditions to study selected physiological changes and growth performance during acclimatization and post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry matter (DM). Chile pepper plantlets became acclimatized within 6 days after transplantation. During this period, physiological adjustments occurred, which were critical for plantlet survival. After initial ex vitro transplanting, plantlets experienced water deficit [leaf wilting and reduced relative water content (RWC)], which corresponded with reduced stomatal conductance (g s) and transpiration (E), and an increase in stomatal resistance (r s). Thus, leaf stomata that developed in vitro were functional ex vitro. Because of this stomatal control, plantlets minimized transplant shock, recovered and survived. Prior to transplanting, plantlets were photomixotrophic, as indicated by low photosynthetic rates (A). During acclimatization, RWC, g s, E, and A were significantly lower two days after transplanting. However, within 6 days after transplanting, plantlets recovered and became photoautotrophic – attaining high A, g s, and E. Water use efficiency was initially low during the first days after transplanting, but increased dramatically at the end of the acclimatization period in part due to increased A. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with increased plantlet growth.
    Plant Cell Tissue and Organ Culture 01/2001; 66(1):17-24. DOI:10.1023/A:1010606430060 · 2.61 Impact Factor
  • J.N. Egilla, F.T. Davies Jr, M.C. Drew
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    ABSTRACT: As competition for the limited water supply available for irrigation of horticultural crops increases, research into crop management practices that enhance drought resistance, plant water-use efficiency and plant growth when water supply is limited has become increasingly essential. This experiment was conducted to determine the effect of potassium (K) nutritional status on the drought resistance of Hibiscus rosa-sinensis L. cv. Leprechaun (Hibiscus). All the treatments were fertilized with Hoagland's nutrient solution, modified to supply K as K_2SO_4, at 0 mM K (K_0), 2.5 mM K (K_2.5), and 10 mM K (K_10), under two irrigation regimes (drought stressed [DS] and non-drought stressed [non-DS]). Regular irrigation and fertigation were adopted for 54 days, and drought stress treatment (initiated on day 55) lasted for 21 days; while non-DS control plants continued to receive regular irrigation and fertigation. Following the 21-day drought stress period, plants were labeled with ^86Rb^+ to determine the percentage of post-drought stress live roots. Both K deficiency (K_0) and drought stress reduced shoot growth, but drought stress increased root growth and thus the root:shoot ratio. At K_0, plants were K-deficient and had the lowest leaf K, Fe, Mn, Zn, Cu, B, Mo and Al, and highest Ca concentrations. Although the percentage of live roots was decreased by drought stress, K_2.5 and K_10 plants (with similar percent live roots) had greater root survival ratio after drought treatment than the K-deficient plants. These observations indicate that adequate K nutrition can improve drought resistance and root longevity in Hibiscus rosa-sinensis.
    Plant and Soil 01/2001; 229(2). DOI:10.1023/A:1004883032383 · 3.24 Impact Factor
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    Andres A. Estrada-Luna, Fred T. Davies, Jonathan N. Egilla
    HortScience: a publication of the American Society for Horticultural Science 06/2000; 35(3). · 0.86 Impact Factor
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    ABSTRACT: L.) plantlets was determined during acclimatization and plant establishment. Guava plantlets were asexually propagated through tissue culture and grown in a glasshouse for 18 weeks. Half of the plantlets were inoculated with a mixed endomycorrhiza isolate from Mexico, ZAC-19, containing Glomus diaphanum, G. albidum and G. claroides. Plantlets were fertilized with modified Long Ashton nutrient solution that supplied 11 μg P ml−1. Gas exchange measurements were taken at 2, 4, 8, and 18 weeks after inoculation using a portable photosynthesis system. All micropropagated guava plantlets survived transplant shock. After 6 weeks, mycorrhizal plantlets had greater shoot growth rates and leaf production than non-mycorrhizal plantlets. This also corresponded with increased photosynthetic rates and stomatal conductance of mycorrhizal plants. By 18 weeks, mycorrhizal plantlets had greater shoot length, leaf area, leaf, stem, and root dry mass. However, gas exchange was comparable among treatments, in part because the container size was restricting growth of the larger mycorrhizal plantlets. Non-mycorrhizal plantlets had greater leaf area ratios and specific leaf areas than mycorrhizal plantlets. Increased leaf tissue mineral levels of P, Mg, Cu, and Mo also occurred with mycorrhizal plantlets. Roots of inoculated guava plantlets were heavily colonized with arbuscules, vesicles and endospores. Guava plantlets were highly mycotrophic with a mycorrhizal dependency index of 103%.
    Mycorrhiza 01/2000; 10(1):1-8. DOI:10.1007/s005720050280 · 2.99 Impact Factor
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    ABSTRACT: Crinum lilies (Crinum spp. L.) are tropical and sub-tropical bulbous plants with excellent potential for southern US landscapes. Unfortunately, the more desirable crinum cultivars are slow and expensive to propagate by traditional offsets. The objective of this research was to develop reliable procedures for multiplying Crinum `Ellen Bosanquet' by tissue culture. A sterilization procedure for cleaning explants was developed in which bulb chips containing a basal plate were submersed and agitated in 0.525% hypochlorite for 1h. For shoot formation, tri-scales (three scales attached to a section of the basal plate) were used as the explant source and grown on MS-based media containing five levels of benzyladenine (BA) (0–22.2μM) and five levels of naphthaleneacetic acid (NAA) (0–5.3μM). The greatest shoot formation was obtained from the highest level of BA (22.2μM) without NAA. In a subsequent experiment, explants were cultured for 4 months on media containing 35.5–88.8μM BA, and then transferred to hormone-free media for 3 months. BA at 35.5μM stimulated optimal shoot (8.4) and bulblet (2.8) formation. Plantlets were successfully acclimatized and rooted ex vitro.
    Scientia Horticulturae 12/1999; 82(1):95-102. DOI:10.1016/S0304-4238(99)00037-0 · 1.50 Impact Factor

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