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Chenping Xu and Beiquan Mou

of each plant to measure RWC, SLA, succulence, and chlorophyll content. The SLA was calculated as SLA = leaf area/DW ( Evans, 1972 ). Leaf RWC was calculated as RWC (%) = 100 × [(FW − DW)/(TW − DW)], where TW is turgid weight after being soaked in

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Corrie Cotton and Gregory E. Welbaum

Maturity at harvest determines seed viability and vigor. However, separating seeds from different stages of development can be difficult using existing seed sorting technologies. New technology non-destructively sorts seeds based on their chlorophyll fluorescence (CF), so seeds with the same dry weight but with different physiological maturates can be separated. We determined whether chlorophyll content of muskmelon (Cucumis melo L. cv. Top Mark) seeds changes during development and whether those changes were related to viability and vigor. Seed viability and vigor were determined using an Association of Official Seed Analysts wet paper towel germination test. `Top Mark' seeds from nine stages of development were run through the SeedMaster Analyzer (Satake USA Inc., Houston, Texas), which calculated the chlorophyll content of each seed. The CF signal was fed into a computer to obtain a frequency histogram. Forty, 45, and 55 days after anthesis (DAA) seeds had germination percentages of 96%, 98%, and 100%, respectively, the highest in the study. Fifty-five DAA had greater seed vigor and viability and contained the lowest CF values; 207 on the 1000-value scale. The less-mature seeds contained higher chlorophyll content and had the lowest seed vigor and viability. Seed vigor and chlorophyll content were negatively correlated in this study. All seeds with high CF values had low vigor, but not all seeds with low CF values have high vigor. Seed aging during storage can reduce viability and vigor independent of chlorophyll content. Based on chlorophyll content, the SeedMaster Analyzer can non-destructively remove immature, low-vigor seeds that have the same physical characteristics and weight as more mature seeds. Chlorophyll fluorescence technology may allow the seed industry to further improve seed quality and maximize vigor.

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G.E. Bell, B.M. Howell, G.V. Johnson, W.R. Raun, J.B. Solie and M.L. Stone

Differences in soil microenvironment affect the availability of N in small areas of large turfgrass stands. Optical sensing may provide a method for assessing plant N needs among these small areas and could help improve turfgrass uniformity. The purpose of this study was to determine if optical sensing was useful for measuring turfgrass responses stimulated by N fertilization. Areas of `U3' bermudagrass [Cynodon dactylon (L.) Pers.], `Midfield' bermudagrass [C. dactylon (L.) Pers. × C. transvaalensis Burtt-Davy], and `SR1020' creeping bentgrass (Agrostis palustris Huds.) were divided into randomized complete blocks and fertilized with different N rates. A spectrometer was used to measure energy reflected from the turfgrass within the experimental units at 350 to1100 nm wavelengths. This spectral information was used to calculate normalized difference vegetation index (NDVI) and green normalized difference vegetation index (GNDVI). These spectral indices were regressed with tissue N and chlorophyll content determined from turfgrass clippings collected immediately following optical sensing. The coefficients of determination for NDVI and GNDVI regressed with tissue N averaged r 2 = 0.76 and r2 = 0.81, respectively. The coefficients of determination for NDVI and GNDVI regressed with chlorophyll averaged r 2 = 0.70 and r 2 = 0.75, respectively. Optical sensing was equally effective for estimating turfgrass responses to N fertilization as more commonly used evaluations such as shoot growth rate (SGR regressed with tissue N; r 2 = 0.81) and visual color evaluation (color regressed with chlorophyll; r 2 = 0.64).

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John E. Erwin and Gerald Pierson

Lypcopersicum esculentum cv `Money Maker' seeds were germinated at constant 20C. Three days after germination seedlings were randomly divided into 3 groups and placed into 3 growth chambers maintained at 23/17, 20/20, or 17/23C (day/night temperature) (DT/NT). Irradiance and photoperiod were maintained at 250 μmol s-1 m-2 and 12 hrs, respectively. At the 2 leaf stage, plants in each chamber were divided into 3 groups of 3 plants each to receive a growth regulator treatment. Growth regulator treatments consisted of spray applications of either ancymidol (52ppm), GA3 (12ppm), or water applied every 3 days for 21 days. Measurements were taken on internode length and chlorophyll content after 21 days. Internode length increased as the difference (DIF) between DT and NT increased (DT-NT). Exogenous applications of GA3 overcame inhibition of stem elongation resulting from a -DIF environment. Application of ancymidol did not significantly decrease stem elongation in a -DIF environment. Temperature regime had a significant impact on chlorophyll content per mg dry weight. In contrast, growth regulator applications had a significant impact on chlorophyll content cm-2. There was no significant impact of either temperature regime or growth regulator treatment on the chlorophyll a/b ratio.

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Hong Wang and Robert C. Herner

A study of the ultrastructure of leaf tissues of Chinese mustard shows that there is a progressive degeneration of the membrane structure of the grana of the chloroplast accompanied with the appearance of globules of lipid material and loss of chlorophyll during leaf senescence. A controlled atmosphere of 5% CO2 plus 3% O2 maintained chloroplast grana membrane structure for up to 4 weeks storage at 10°C. Both 5% CO2 (in air) and 5% CO2 plus 3% O2 maintained the highest chlorophyll content compared to 3% O2 alone or in air (control).

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Wayne F. Whitehead and Bharat P. Singh

The effect of in-row plant densities on gas exchange, chlorophyll content and leaf area index of okra (Abelmoschus esculentus (L.) Moench) was studied. The six in-row plant densities ranged from 8 cm to 48 cm (D1 - D6). On 11 and 27 July 1990, the photosynthetically active radiation (PAR), transpiration (E), net photosynthesis (Pn) and chlorophyll content (Chl) at top- and mid-canopy levels and leaf area index (LAI) were measured. Mid-canopy PAR was 86 ± 6% less than that of the top-canopy and E, Pn and Chl at mid-canopy were respectively 55, 90 and 10% lower than those of the top-canopy. The interaction of plant density with canopy position was significant for E and Pn. The highest E and Pn, (12.28 mmol m-2 s-1 and 22.01 μmol CO2 m-2 s-1, respectively) were recorded at the D5 top-canopy. In-contrast, the lowest E and Pn, (4.17 mmol m-2 s-l and 1.23 μmol CO2 m-2 s-1, respectively) at the D6 mid-canopy were recorded. The LAI also exhibited significant variation among plant densities with a range of 4.65 to 4.97 for D5 and D3, respectively. These results indicate that 40 cm in-row density was the most suited for gas exchange of okra.

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Mark H. Brand

The effect of shading during nursery production on the growth, foliage color, and foliar chlorophyll content of container-grown Kalmia latifolia cultivars was investigated. Five cultivars were grown under 40% shade, 60% shade, or full sunlight for a 2-year production cycle. During the first year of production, there were no significant differences in measured growth characteristics for most cultivars in response to light treatment. Shade improved foliar color by decreasing lightness (L*), decreasing chroma, and changing hue angle from a yellow-green to a darker green. Foliar chlorophyll concentration increased under shade. In the second year of the production cycle, the response of foliar color and chlorophyll concentration to shade was similar to that observed in year 1. Plant size, number of branches, leaf area, leaf dry mass, and stem dry mass decreased linearly with increasing shade in year 2. Although shading improves foliar color, it probably should not be employed for container production of Kalmia latifolia in cool, northern production areas due to reduced plant growth during year 2. Shade may be useful in the first year of production to enhance foliar color without reducing shoot growth.

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Cary A. Mitchell, Tina Leakakos and Tameria L. Ford

This study evaluated the potential of high photosynthetic photon flux (PPF) from high-pressure sodium (HPS) lamps, alone or in combination with metal halide (MH) plus quartz iodide (QI) incandescent lamps, to support lettuce growth, with or without N supplementation. Varying exposures to radiation from combined HPS, MH, and QI lamps influenced dry weight gain and photosynthetic pigment content of hydroponically grown `Black-Seeded Simpson' lettuce (Lactuca sativa L.) seedlings. Cumulative leaf dry weight declined with increasing exposure, up to 20 hours per day, to 660 μmol·m-2·s-1 of photosynthetically active radiation (PAR) from HPS lamps concomitant with constant 20 hours per day of 400 m mol·m-2·s-1 from MH + QI lamps. Leaves progressively yellowed with increasing exposure to radiation from the three-lamp combination, corresponding to lower specific chlorophyll content but not to specific carotenoid content. Lettuce grown under 20-hour photoperiods of 400, 473, or 668 μmolm·m-2·s-1 from HPS radiation alone had the highest leaf dry weight at a PPF of 473 μmol·m-2·s-1. Chlorophyll, but not carotenoid specific content, decreased with each incremental increase in PPF from HPS lamps. Doubling the level of N in nutrient solution and supplying it as a combination of NH4 + and NO3 - partially ameliorated adverse effects of high PPF on growth and pigment content relative to treatments using single-strength N as NO3 .

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Harry G. Simmons, Alisara Menakanit, Surawit Wannakrairoj and Poonpipope Kasemsap

Bamboo has increasingly become a popular exterior ornamental plant because of its durability, versatility, and evergreen qualities in conditions of extreme temperature and moisture variations. Use as an interior foliage plant has been limited due to the difficulty of finding species adaptable to lower light levels. Nineteen species from seven genera (Bambusa, Cephalostachyum, Dendrocalamus, Gigantochloa, Schizostachyum, Thyrsostachys, and Vietnamosasa) were evaluated. Fifteen plants from each species were potted in like conditions (50% leaf mold; 50% topsoil; 5 g of 14–14–14 controlled-release fertilizer) and grown under a maximum daily photosynthetic photon flux density (PPFD) range between 1200 to 2000 μmol·m-2·s-1 for 6 weeks. Chlorophyll content of leaves was measured. The commercial quality of leaves, culms, and general appearance was also recorded. Light was then limited to a maximum PPFD of 150 to 300 μmol m-2s-1 for 6 weeks and all measurements were again recorded. Five species had significant increases in chlorophyll content after the 6-week period of reduced light levels. Species with a larger maturity size had a greater mortality percentage as well as lower quality leaf and overall appearance when grown under reduced light levels. Culm quality remained constant in 18 of the 19 species after the 6-week period. Vietnamosasa ciliata showed the greatest increase in chlorophyll levels as well as highest commercial quality of leaf and overall appearance.

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Glenn C. Wright, Kim D. Patten and Malcolm C. Drew

`Tifblue' rabbiteye blueberry (Vaccinium ashei Reade) and `Sharpblue' southern highbush blueberry (primarily V. corymbosum) were treated with 0, 25, or 100 Mm Na+ as Na2SO4 or NaC1, and 0, 1, 3, or 10 Mm supplemental Ca2+ in sand culture in the greenhouse. Greatest stomatal conductance (gs) and net assimilation (A) occurred in unsalinized `Tifblue' plants not given additional Ca2+. Stomatal conductance, A, transpiration (E), and xylem water potential(Ψ)of `Tifblue' and `Sharpblue' plants were all lowered as salinity increased, and these effects were more pronounced with NaCl than with Na2SO4. After 63 days, for plants given 100 Mm Na+ as NaCl, gs and net assimilation rate were reduced to only 10% of the unsalinized controls, while for plants salinized with 100 mm Na+ as Na2SO4, gs and A were 35% and 43%, respectively, of unsalinized controls. Leaf necrosis was more extensive on `Sharpblue' plants given NaCl than on `Tifblue' plants. Neither Ca2+ nor Na+ treatments led to severe chlorosis; reductions in leaf chlorophyll content were mainly due to necrosis. The Na+- induced reduction in gas exchange was associated with negative Ψw Ca2+ deficiency, or a combination of these factors. Additional factors leading to inhibition of gas exchange in NaCl- stressed plants include Cl- toxicity and leaf necrosis. Calcium supplements were unable to ameliorate NaCl damage in `Tifblue' or `Sharpblue' plants, possibly because of the inability of Ca2+ to counter Cl- entry and toxicity. In contrast, additional Ca2+ improved gs, A, Ψw, and leaf chlorophyll content of `Tifblue' plants that received Na2SO4. For plants treated with 25 mm Na+ as Na2SO4 and 1 mm Ca2+, gs was 1.5 to 2.5 times higher than in plants without added Ca2+. Low (1 mm) concentrations of Ca2+ were more effective in ameliorating the effects of 100 mm Na+ as Na2SO4. than were 3 or 10 mm Ca2+ supplements, possibly because higher Ca2+ concentrations damaged the metabolism of the calcifuge blueberry.