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  • Author or Editor: Jonathan N. Egilla x
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Four-week-old seedlings of Scarlet eggplant (Solanum integrifolium Poir.), a short-day fruiting vegetable, were grown for 20 weeks in a greenhouse (G/H) from 14 Mar. to 2 Aug. 2005. Mean daily photosynthetic photon flux in the G/H was about 480, 349 and 71 μmol·m–2·s–1 above-, within canopy; and at pot level, respectively in July. Seedlings were grown either in Turface® (fritted clay) or fine sand. Fertilizer treatment consisted of 5 g Osmocote® (18% N-6% P2O5-12% K2O) per pot, plus 100 mL of Peat-lite® (15% N-16% P2O5-17% K2O) solution at 200 mg·L-1 of N twice weekly, or Peat-lite only. Seedling growth (plant height, leaf number) during the first 12 weeks in both growing media was similar regardless of fertilizer treatment. The number of lateral shoots (not fruit number, FRN) increased from early fruit set (week 14) until termination (week 20), but there were no significant (P = 0.05) growing media or fertilizer treatment effects. While root dry mass was similar in both growing media, shoot dry mass was significantly (P < 0.0001) increased in fritted clay. Conversely, FRN and fruit dry mass (FDM) were, respectively, 8- and 11-fold greater in sand compared with fritted clay. Fertilizer treatment had no significant (P = 0.05) effect on both FRN and FDM either in fritted clay or sand. These trends indicate that S. integrifolium can produce limited amounts of fruit under the long daylength conditions of the summer at reduced irradiance, but factors determining shoot growth may have significant influence on fruit yield under this condition.

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Two-week-old seedlings of cos lettuce (Lactuca sativa L. var. longifolia) `Cimmaron' were transferred into NFT hydroponic troughs in July and Sept. 2005. The crop was grown either in a polyethylene or polycarbonate greenhouse. Mean July temperature and maximum relative humidity (RH) in the two greenhouses were 30.5 and 27.7 °C ± 0.32 °C; 81.3% and 84.7%, respectively. In September, the mean temperature and RH in the same greenhouses were 22.6 °C and 21.9 °C ± 0.30 °C; 95.6% and 99.2%, respectively. Lettuce crop grown with Peters Excel® [15N–5P2O5–15K2O; (Excel)], had higher fresh mass (FM) and dry mass (DM) compared with either Peat-lite®; [15N-16P2O5-17K2O; (Peat-lite)] or All-Purpose Hydroponic Fertilizer® [9N-4P2O5-15 K2O; (All-Purpose)], but lower DM/FM. At harvest, the crop had good market quality, regardless of mineral nutrient source (MNS). MNS significantly (P ≤ 0.05) influenced yield (FM and DM) in September, regardless of greenhouse type. However, in July only Peat-lite caused significant (P < 0.0252) increase in DM, under the higher temperature condition of greenhouse I. This trend suggests that good quality lettuce and sustained yield can be obtained with the soluble fertilizers Excel and Peat-lite, which are not formulated for hydroponic crop production. Furthermore, `Cimmaron' can produce satisfactory yield under relatively high temperature conditions. However, taste panel evaluation and nutrient content analysis of lettuce produced with these various fertilizers are necessary to determine consumer satisfaction.

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Micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plants were transferred to ex vitro conditions to study plantlet performance and selected physiological changes that occur 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 mass. Measurements were taken at 0, 1, 2, 3, 6, 12, and 24 days after transplanting. After initial transplanting ex vitro to liner pots with soilless media, plantlet wilting was observed that correlated with reduced leaf relative water content (RWC). Water stress was partially alleviated by a reduction in stomatal conductance (gs), confirming that the in vitro formed stomata were functional and able to regulate transpiration (E) to minimize desiccation losses. Because of this stomatal control, plantlets had minimal transplant shock, recovered, and survived. Prior to transplanting, micropropagated plantlets showed heterotrophic/mixotrophic characteristics as indicated by low photosynthesis [(A) 4.74 μmol·m2·s-1]. During acclimatization, RWC, gs, E, and A were significantly lower 2 days after transplanting. However, within 6 days after transplanting, plantlets recovered and became autotrophic, attaining high A (16.3 μmol·m-2·s-1), gs, and E. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with dramatic increases in plantlet growth.

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The role of mycorrhiza fungi during acclimatization and post-acclimatization of micropropagated chile ancho plantlets was characterized through physiological and plantlet development changes. Regardless of mycorrhizal colonization, the pepper plantlets had initially low photosynthetic rates and poor growth following transplanting ex vitro. During the first days of acclimatization, water deficits occurred as evidenced by drastic reductions in relative water content. Consequently, transpiration rates and stomatal conductance (gs) declined, confirming that in vitro formed stomata were functional, thus avoiding excessive leaf dehydration and plant death. Mycorrhiza had a positive effect on gas exchange as early as day 7 and 8, as indicated by increasing photosynthesis (A) and gs. Mycorrhizal plantlets had reduced levels of abscisic acid (ABA) during peak stress (6 days after transplanting ex vitro), which corresponded with subsequent increases in gs and A. During acclimatization, A increased in both non-colonized and colonized plantlets, with greater rates observed in mycorrhizal plantlets. During post-acclimatization, mycorrhiza colonized 45% of the roots of pepper plantlets and enhanced plant growth by increasing leaf area, leaf dry mass, and fruit number. Mycorrhiza also enhanced total leaf chlorophyll content, A, and nutrient uptake of pepper plantlets, particularly N, P, and K. Early mycorrhizal colonization produced important benefits, which helped ex vitro transplanted plantlets recover during acclimatization and enhance physiological performance and growth during post-acclimatization.

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Rooted cuttings of Hibiscus rosa sinensis L. cv. Leprechaun were irrigated with full strength Hoaglands solution containing 0, 2.5, or 10 mM K+. Half of the plants at each K+ level were subjected to a 21-day slowly developing drought stress cycle (DS) followed by a recovery period (day 22), while the other half were non-drought stressed (NDS). Midday leaf water potential (Ψleaf) at day 21 were -1.5 to -1.6 MPa for DS and -0.5 MPa for NDS plants. Photosynthesis (A) was lowest during early stress and recovery of 0 mM K+ plants. Transpiration (E), stomatal conductance (g), and instantaneous water use efficiency (A/E), were generally lowest in 0 mM K+ plants. During peak stress, A was highest in the 2.5 mM K+ plants, whereas E was lowest and A/E highest in 10 mM K+ plants. Ψleaf did not differ among K+ treatments during peak stress and recovery, but osmotic potential was highest (least negative) and turgor potential lowest in 0 mM K+ plants. DS plants had lower carbon isotope discrimination (Δ) compared to NDS plants at all K+ levels, suggesting higher A/E for DS plants. Although there was no significant K+ effect, there was a trend at peak drought stress of Δ lower A and higher A at the 2.5 mM K+ level.

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Rooted cuttings of Hibiscus rosa sinensis L. cv. Leprechaun were grown in fine sand and irrigated with full strength Hoaglands solution containing 0, 2.5, or 10 mM K+. Half of the plants at each K+ level were subjected to a 21-day slowly developing drought stress cycle (DS) and the other half were non-drought stressed (NDS), which yielded a midday leaf water potential (Ψleaf) at day 21 of -1.5 to -1.6 MPa and -0.5 MPa, respectively. Drought stress reduced leaf area (LA), leaf area ratio (LAR), shoot, root, leaf and total dry weights of 2.5 and 10 mM plants and increased the root:shoot ratio of all K+ treatments. Increasing K+, increased all growth parameters measured in both DS and NDS plants, except for LAR, which was greatest at 0 mM K+. At 0 mM K+, drought stress did not affect LA, LAR, shoot, root and total dry weights. Neither drought nor K+ treatments affected specific leaf area (SLA). In NDS plants, K+ had no effect on percent live root ratio (PLR) as indicated by translocation of 86Rb+ from leaves into living roots, determined by autoradiography. Although drought stress reduced PLR at all K+ levels, PLR was greatest at the higher K+ levels.

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Pawpaw (Asimina triloba) is an under-exploited small tree with commercial potential as a fruit crop, ornamental tree, and source of secondary products with insecticidal and medicinal properties. It is most often propagated from seeds that are recalcitrant and must be stored moist at a chilling temperature. Seeds display combinational (morphophysiological) dormancy. Endogenous, physiological dormancy is broken by about 100 days of chilling stratification followed by a period of warm moist conditions where the small embryo develops prior to seedling emergence about 45 days after the warm period begins. Pawpaw cultivars with superior fruit characteristics are propagated by grafting onto seedling understocks. The most common practice is chip budding. Other methods of clonal propagation have proven problematic. Pawpaw can be propagated from cuttings, but only in very young seedling stock plants. Micropropagation from mature sources is not yet possible, but shoot proliferation has been accomplished from seedling explants and explants rejuvenated by induction of shoots from root cuttings of mature plants. However, rooting of microcuttings and subsequent acclimatization has not been successful.

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