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  • Author or Editor: R.J. McAvoy x
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R.J. McAvoy and H.W. Janes

Tomato seedlings (Lycopersicon esculentum Mill. cv. Laura) were grown in an environmental chamber. In two separate experiments, plant growth from emergence to anthesis was divided into three equivalent segments based on either the actual number of days or the stage of plant development. In both experiments, plants were exposed to a high PPF (300 μmol·s-1·m-2)2) treatment (H) for one segment and a lower PPF (150 μmol· s-1·m-2) treatment (L), for the other two segments, resulting in three light treatment combinations (i.e., HLL, LHL, and LLH). Total dry weight and dry weight per unit of leaf area increased significantly in response to high PPF during all three treatment periods. Final plant weights and plant heights differed significantly between treatments, resulting in distinct plant growth characteristics. Plants from the HLL treatment began to flower 1 day before the LHL treatment and 2 days before the LLH treatment. The HLL plants initiated fewer leaves before initiation of the floral axis than the LHL and LLH plants. The light environment following the initial segment of seedling development most influenced final truss position at anthesis.

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Usha R. Palaniswamy and Richard J. McAvoy

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M.T. Kelley, G.C. Elliott and R.J. McAvoy

Four different granulated rockwool (RW) aggregates were combined with peat at 15, 30, or 45 percent (v/v) RW resulting in twelve different peat:RW media. The RW aggregates used were either fine or coarse textured and absorbent or repellent to water. A soil based medium was used as a control. Bulk volume, bulk density, total porosity, water porosity (WP), and aeration porosity (AP) were determined for all media. Hybrid lily, cvs. `Enchantment' and `Jamboree', growth in these media were compared by measuring the dates of visible bud and anthesis, flower number, leaf number and area, plant height and dry weight of stems, leaves, and flowers. Physical properties of the RW media varied significantly from the soil based medium. Increasing the volume percent RW had a negative linear effect on WP but a positive linear effect on AP for all RW aggregates. Lily growth in the soil based medium was statistically similar to all RW media. The dates of visible bud and anthesis, as well as leaf number and area decreased linearly as the volume percent repellent coarse RW increased.

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Richard J. McAvoy, Bernard B. Bible and Michael R. Evans

The early onset of bract necrosis in poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) is characterized by small dark-stained spots that precede the development of enlarged necrotic lesions. Electron micrographs of adaxial epidermal and subepidermal tissues with early symptoms of necrosis revealed large, electron-dense deposits in cell vacuoles. These spherical bodies resembled condensed tannins observed in the epidermal tissues of peach and apple fruit. Chemical analysis of bract tissues confirmed the presence of condensed tannins. Furthermore, there were higher concentrations of condensed tannin in bract samples with 2-mm-diameter lesions than in samples with lesions <0.5 mm (equivalent to catechin concentrations of 59 and 13 mg·g-1 fresh mass, respectively). No tannin bodies were observed in parallel samples of healthy-appearing bracts in which only trace concentrations of condensed tannins were measured (0.2 mg·g-1 fresh mass). The evidence suggests an association between condensed tannin accumulation in localized areas of the bract and the early appearance of bract necrosis symptoms.

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Usha R. Palaniswamy, Richard J. McAvoy and Bernard B. Bible

Purslane (Portulaca oleracea L.) is an excellent source of the essential fatty acid α-linolenic acid (LNA) but little is known of the effects of cultural conditions on LNA concentration. Purslane seedlings were grown under an instantaneous photosynthetic photon flux [PPF (400 to 700 nm)] of 299 or 455 μmol·m-2·s-1 for a daily duration of either 8, 12, 16, or 20 hours. Thus, plants were exposed to a daily PPF of 8.6, 12.9, 17.2, or 21.5 mol·m-2·d-1 in the low PPF treatment (299 μmol.m-2.s-1) and 13.1, 19.7, 26.2, or 32.8 mol·m-2·d-1 in the high PPF treatment (455 μmol·m-2·s-1). Plants in all treatments received a 20-hour photoperiod by providing ≈5 μmol·m-2·s-1 from incandescent lamps starting at the end of the photosynthetic light period. At low PPF, purslane grown under a 16 hour PPF duration produced the highest concentrations of total fatty acids (TFA) and LNA per unit leaf dry weight (DW), but at high PPF, concentrations of these compounds were highest under 8 and 12 hour PPF duration. Trend analysis indicated that maximum TFA and LNA concentrations occurred with a daily PPF of 14.1 and 17.2 mol·m-2·d-1, respectively; and in the thylakoids, protein, chlorophyll, and LNA concentrations peaked at a PPF of 21.8, 19.9, and 16.1 mol·m-2·d-1, respectively. LNA as a percentage of TFA was unaffected by treatment. Shoot DW increased with PPF up to the highest PPF exposure of 32.8 mol·m-2·d-1.

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G.C. Elliott, R.J. McAvoy and M. Abbott

Seedlings of Catharanthus roseus “Grape Cooler” was transplanted to cell packs of media: peat-vermiculite-perlite (MM220), peat-hydrophilic rockwool (ABS), and peat-hydrophobic rockwool (REP) and grown in subirrigation trays using 20N-4.4P-17K fertilizer at 50, 150 or 250 ppm N applied at each irrigation. Shoots of four plants in each of two replications were harvested 2, 3, 4 and 5 after transplant. Leaf samples from the third harvest were analyzed for essential elements. Electrical conductivity (EC) was measured in saturated media extracts at each harvest. Significant media by fertilizer interactions were obtained for fresh weight and leaf area at the final harvest. Greatest growth was obtained with 50 ppm N in ABS, but with 150 ppm N in MM 220 and REP. In tehse, growth was similar at 50 and 150 ppm N, but less growth REP than MM220 at 250 ppm. More growth was produced with ABS at 50 ppm N, but less at 150 or 250 ppm N. Leaf tissue N increased 38.5 to 54.5 mg g-1 dry wt. as fertilized increased 50 to 150 ppm, while other nutrients were not significantly affected. Media EC increased with time and fertilizer concentration, with EC in all media fertilized with 250 ppm N exceeding 4.5 dS m-1 at the final harvest.