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- Author or Editor: N. Suzanne Lang x
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Protea neriifolia R. Br., P. susannae E.P. Phillips × compacta R. Br., and P. eximia (Salis. ex Knight) Fourcade cut flower stems were examined to determine the relationship between postharvest leaf blackening rate and preharvest carbohydrate status. Postharvest leaf blackening was highest (83% by day 4) in P. eximia floral stems, which had the lowest preharvest sucrose concentrations. In contrast, P. susannae × compacta had <5% leaf blackening by day 4 and the highest preharvest leaf sucrose concentrations. Starch concentrations were highest in P. neriifolia; however, leaf blackening was intermediate between P. susannae × compacta and P. eximia and reached 52% at day 4. Preharvest carbon-exchange rate and stomatal conductance in all three species were extremely low, despite high photosynthetically active radiation and apparent lack of water stress. Comparing preharvest carbohydrate profiles in vegetative and floral stems suggests that vegetative stems may have a sink-to-source transition zone between the second and third divisions, while most leaves on floral stems may have transferred carbohydates to source leaves at harvest. While preharvest floral stem sucrose concentrations can be linked to leaf blackening rate, the high starch reserves in P. neriifolia reduced leaf blackening little in this species. We conclude that leaf blackening may be related more to inflorescence sink demand after harvest and oxidative substrate availability than preharvest reserve carbohydrate concentrations in each species.
A major postharvest problem of Protea neriifolia is premature leaf blackening. Carbohydrate stress, due to floral sink demand, may lead to cellular disorganization and leaf blackening. Leaf blackening, nonstructural carbohydrates, ethylene, carbon exchange rates, stomatal conductance and lipid peroxidation were measured on leaves of vegetative and floral stems preharvest, and during a 7 day dark postharvest period. Postharvest treatments were: 0 or 0.5% sucrose in the vase solution, 20% sucrose pulse, or floral decapitation. Leaf blackening was significantly reduced in vegetative stems and floral stems in the 20% pulse treatment, in comparison to all other treatments. Ethylene production and lipid peroxidation were not associated with leaf blackening in any treatment and leaf respiration rates declined for all treatments over time. The magnitude and rate of leaf blackening was inversely related to leaf starch concentrations, with greatest carbohydrate depletion occurring within 24 h of harvest (by 75-85%). Leaf starch from the 20% pulse treatment increased by 300%, in contrast to declining starch concentrations in all other treatments. The data suggest that the flowerhead functions as the major sink for carbohydrate depletion leading to subsequent leaf blackening.
Shaded environments present major obstacles for establishing high quality, persistent, and resistant turfs. Exogenous fructose applications are being examined as a potential method to counteract the effects of shade on turf. This work examines the effectiveness of fructose applications under different light levels on two fine leaf fescue cultivars: chewings fescue (Festucarubra var. commutata) `SR5100' and creeping red fescue (Festucarubra var. rubra) `Dawson'. The experiment was conducted at Michigan State University, East Lansing, inside a simulated dome environment. The experiment was a randomized complete-block design that began 21 Oct. 2004 with two main factors: light and fructose. There were three light treatments: ambient light (shaded); supplemental high light; and supplemental low light. Fructose (0% or 1.25% weight/volume), dissolved in water with an organosilicone adjuvant, was applied once per week. Quality and color ratings, clippings, core samples, density, and leaf reflectance were recorded. In addition, light response curves (LRC) were taken inside an Econoair®
growth chamber using a LI-COR-6400® on the fine fescues, kentucky bluegrass (Poa pratensis) `Cynthia', and bermudagrass (Cyondon dactylon) `Princess'. Preliminary results show that fructose had no significant effect in each light treatment for turf quality and color. However, fructose had a significant impact on clipping weights and density. The LRC specified the required and potential carbon needs as well as indicated the threshold levels, respectively, by species. The impact of fructose alone and in combination with supplemental light on photosynthesis efficiency will be presented.
This study investigated the influence of plant size, as determined by plant density, and fruit load variation on the production and quality of bell pepper (Capsicum annuum L.) seeds. Six-week-old `Resistant Giant no. 4' bell pepper seedlings were transplanted 15, 30, 45, and 60 cm apart. Plants spaced 45 cm apart were not thinned or were thinned to one or three fruit per plant. Pepper plants grown at low plant densities produced larger fruit and seeds that germinated faster and at higher percentages than plants grown at higher densities. Assimilate export rate (AER) increased linearly with plant spacing. At harvest, C exchange rate (CER) and AER of plants with nonthinned fruit loads were ≈ 300% and 500% higher, respectively, than those of plants with one or three fruit. Fruit thinning decreased CER and AER; however, seeds produced by plants with one or three fruit had significantly higher germination percentages than plants with full fruit loads. These observations suggest that the high CERS of smaller plants with nonthinned fruit loads may have been insufficient to compensate completely for the higher sink demands. Therefore, crop cultural practices that increase the ratio of pepper plant size to total fruit count may increase the quality of seeds produced by those plants.
Commercially-produced, endodormant `Gloria' azaleas were placed into temperature × duration dormancy-breaking treatments at 2 month intervals to characterize seasonal variation in floricultural performance. Given the standard industry practice to break bud dormancy is 6 weeks at 3.5 to 7.2 C, three temperatures (3.5, 7.5, 11.5 C) and four durations (2, 4, 6, 8 weeks), plus a non-chilled control, were used to examine the contribution of each dormancy-breaking factor to subsequent floricultural quality. Treatment-Induced leaf abscission and flowering were quantitated, including days to Initial flowering and 50% flowering. Flowering response of dormant-budded azaleas produced during late spring and early summer (chilled during summer and early fall, respectively) was primarily and positively related to chilling duration, with only a minor influence of chilling temperature. In contrast, flowering of fall-produced endodormant plants (chilled during late fall) was best at 3.5 C, regardless of duration. Across all intervals, control plants averaged a leaf loss rate of 3 to 4 per day, suggesting a steady-state turnover rate. While leaf abscission was higher in all chilling-treated plants, those produced during fall and given the standard (or longer) chilling treatment exhibited about twice the total abscission (averaging as much as 20 leaves per day) as plants produced at other times, resulting in a clear reduction in plant foliar quality.
Year-round production of the florist azalea cv. Gloria is limited by non-uniform flowering in fall-produced, endodormant-budded plants. To examine the effects of the standard dormancy-breaking chilling treatment (six weeks at 3.5 C) on carbohydrate metabolism, single-cutting plants were chilled in low light (10 μmol·m-2s-1) or in continuous dark Treatment effects were studied by destructively harvesting canopy organs for dry weight and carbohydrate analysis at two week intervals during treatment and at five day intervals during greenhouse forcing. Flowering performance was also evaluated. No differences were found between the low light or continuous dark chilling treatments for canopy organ dry weights, days to initial flowering, or days to 50% flowering. Leaf dry weight decreased 22% during chilling, and did not recover to pre-treatment levels through 15 days of forcing. Stem dry weights did not change during treatment or forcing. Floral bud dry weights were maintained during treatment and increased during forcing. Analysis of soluble carbohydrates indicated that the low light treatment influenced carbohydrate metabolism, resulting in Increased concentrations of sucrose, fructose, and glucose in all canopy organs compared to the dark treatment Maltose concentrations were higher in the light for leaves and stems, but not buds. The potential significance of these changes, with respect to dormancy-breaking treatments and uniform flowering performance, will be discussed.
Some day-neutral herbaceous perennial species can be difficult to manage as vegetative stock plants because they initiate floral buds under most environmental conditions. Although flowering of many long-day plants can be inhibited by maintaining plants under short days, extension growth is often suppressed, which makes cuttings difficult to harvest. Ethephon (2-chloroethylphosphonic acid) is an ethylene-releasing chemical used to abort flowers, inhibit internode elongation, and promote branching of floriculture crops. The objective of this research was to determine whether ethephon is effective at maintaining vegetative growth and increasing the number of cuttings harvested for three popular perennial species that are difficult to maintain as vegetative plants. Spray applications of ethephon were applied for 10 weeks biweekly (every 2 weeks) or weekly at 0, 400, 600, or 800 mg·L−1. Biweekly applications at 600 mg·L−1 or weekly applications at 400 mg·L−1 increased branching and the number of vegetative cuttings in Coreopsis verticillata L. ‘Moonbeam’ and Veronica longifolia L. ‘Sunny Border Blue’, respectively. Ethephon application increased branching in Dianthus caryophyllus L. ‘Cinnamon Red Hots’, inhibited leaf expansion and stem extension, but did not abort flowers, and induced marginal leaf necrosis at all concentrations tested. Therefore, ethephon application has potential to maintain vegetative stock plants of C. verticillata ‘Moonbeam’ and V. longifolia ‘Sunny Border Blue’ but not D. caryophyllus ‘Cinnamon Red Hots’.
Dye transport through vascular pathways was examined in tissues surrounding the graft union of second-leaf, field-grown trees of `Lapins'/Gisela 5 (`Gi 5') (dwarfing) and `Lapins'/'Colt' (nondwarfing). Excavated, intact trees were allowed to take up xylemmobile dye via transpiration for 6 h before sectioning the tree into scion, graft union, and rootstock tissue. `Lapins'/'Gi 5' had a significantly larger stem cross-sectional area in the central graft union than did `Lapins'/'Colt'. Per unit cross section, dye transport of both `Lapins'/'Gi 5' and `Lapins'/'Colt' was significantly less in the graft union than in rootstock sections, with still less transported to scion tissues in `Lapins'/'Gi 5'. `Lapins'/'Gi 5' had a tendency to produce vascular elements oriented obliquely to the longitudinal axis of the tree. Dye was distributed more uniformly axially and radially across the graft union in `Lapins'/'Colt' than in `Lapins'/'Gi 5', with an apparent accumulation of dye in `Lapins'/'Gi 5' graft union. Xylem vessel diameters and vessel hydraulic diameters (VDh) were smaller overall in `Lapins'/'Gi 5' than in `Lapins'/'Colt'; however, graft unions in both had smaller VDh than did rootstock sections. These observations suggest reduced transport efficiency of xylem vessels in the graft union in `Lapins'/'Gi 5' may be due to smaller vessels, vascular abnormalities and/or increased amounts of callus and parenchyma tissue.
Dwarfing rootstocks in sweet cherry (Prunus avium L.) have been planted worldwide. No single theory has emerged to answer why scion dwarfing occurs in fruit trees. This research examines the vascular pathway in a dwarfing cherry system to determine if physical limitations alter water transport as a possible dwarfing mechanism. Second-leaf `Lapins' trees grafted onto Gisela 5 (Gi5; dwarfing) and Colt (vigorous) rootstocks were field-grown in East Lansing, Mich. During maximum shoot elongation, trees were dug, placed into containers with safranin dye solution (0.1% w/v) for 6 hours and then removed for division (3-5 cm in length) based on location in scion, graft union, and rootstock tissue. Tissues were sectioned using a sliding microtome (120 μm) for examination with a laser confocal microscope (Zeiss LSM Pascal). Mean stem area and vessel diameter were measured; and mean hydraulic diameter was calculated for vessels in the area of dye translocation. Overall, Lapins/Gi5 stem area in the graft union was larger compared to Lapins/Colt; however dye translocation in Lapins/Gi5 was reduced compared to other tissues in the tree. Confocal microscopy indicated dye uptake through the grafted region was more uniformly distributed in Lapins/Colt than in Lapins/Gi5, with dye accumulation in areas of maximum translocation. Vessel diameter did not differ in these areas of translocation. However, in both combinations there was a reduction in mean hydraulic diameter of graft union sections, suggesting a reduction in vessel efficiency to translocate water in this region. Vascular system anomalies were more frequent in Lapins/Gi5, disrupting acropetal dye translocation. This suggests the greatest reduction in vascular transport is in Lapins/Gi5.