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Yin-Tung Wang

objectives of this study were to determine the long-term effects of harvesting leaves to various degrees, supplemental feeding of mineral nutrients, and the application of powdered sulfur on the rate of leaf initiation, leaf growth, and harvestable leaf yield

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K.S. Yourstone and D.H. Wallace

This study was undertaken to determine whether plastochron index (PI), a mathematical construct that quantifies shoot development, can be applied to indeterminate bean (Phaseolus vulgaris L.) genotypes. Length measurements of the middle trifoliate leaflet were the basis of the PI calculation. The expansion of each middle trifoliate leaflet at every node on each plant tested was measured over time to determine whether the growth pattern of each leaflet fits the assumptions of the PI construct. Plants from five indeterminate bean genotypes were grown in two controlled environments: A constant 29C with 12-hr of daylength, and a constant 23C with 12-hr daylength extended to 14 hr with low light intensity. Early leaflet expansion was exponential for all five genotypes in both environments. Expansion rates of successive leaflets were also similar, although a few leaflets in three of the 10 genotype-environment combinations differed in their rates of expansion. Exponential and equal rates of expansion validate the calculation of the fractional component of the PI. In both environments, all genotypes exhibited an increasing rate of leaf initiation with time, which precludes the use of a simple linear slope in estimating rate of development.

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K.S. Yourstone and D.H. Wallace

The plastochron index was used to compare the effects by daylength, mean temperature, and diurnal temperature fluctuation, on the rate of node development of five indeterminate common bean (Phaseolas vulgaris L.) genotypes grown in eight growth chamber environments. Regression analysis described temporal trends in the plastochron index. Regression curves for the various genotype—environment combinations were compared using canonical variates analysis. At a constant 17C, extending daylength from 12 to 14 or 16 hr had no effect on rate of node development. The rate of node development increased at a constant 23C when daylength was lengthened from 12 to 14 or 16 hr. The increase in rate of node development was more pronounced in genotypes with higher photoperiod sensitivity, as measured by delay of flowering. Temperature rise from 17 to 23 to 29C also increased the rate of node development, with genotypes again exhibiting differential response. Diurnal fluctuation of 6C about a mean of 23C had the same node development rate as a constant 23C.

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Neil O. Anderson and Peter D. Ascher

Commercial chrysanthemums are short day (SD) plants. Recently, several day neutral (DN) garden genotypes have been identified. Both glasshouse and garden cultivars vary in heat delay insensitivity (HDI). This research analyzed yield components (seed set, germination, yield potential) and tested a DN/HDI ideotype for its effectiveness. Progeny from a 6 × 6 diallel were embryo rescued, clonal ramats were grown in two environments (glasshouse—long days; field—long to short days) and evaluated for flowering, early flowering response groups, thermozero temperature response, low long day leaf number (LDLN), high leaf initiation rates, and low mean stem lengths of the terminal shoot. Self seed set ranged from 0% to 8% while outcross seed set was 0% to 92%. General and specific combining ability were highly significant for seed set, the reciprocals, and their interactions. Germination averaged 67%, while yield potential was 44%. Cotyledon pigmentation in embryo rescued seedlings was 7% albinos, 15% anthocyanin (transposable elements), and 78% normal (green). SD parents did not flower in either photoperiod although PPSL-10 carried alleles for DN. SD x DN crosses produced some DN progeny and fit a 1:3 chi square ratio (DN:SD), indicating DN to be recessive. However, DN x DN crosses also fit a 3:1 chi square ratio, due to HDI. No progeny flowered within the 3 to 6 week ideotype; visible bud date had a heritability of h 2 = 0.50. Most progeny were within the LDLN range (h 2 = 0.72). Several leaf initiation rates exceeded the ideotype (h 2 = 0.003); plant height also matched the ideotype (h 2 = 0.66). Both visible bud and flowering dates require significant improvement before progeny match the DN/HDI ideotype.

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Michael D. Berg and Preston K. Andrews

An aeroponic growth chamber is a system for growing plants in air with water and nutrients supplied by intermittent mist. This type of plant growth system is especially useful for experiments where root accessibility is desired. Tomatoes (Lycopersicon esculentum L. `Bonnie Best') were used to test the performance of an aeroponic growth chamber. A nutrient solution mist was applied through spray nozzles suspended below roots of supported seedlings. Mist application was regulated by electric timers, so that mist was applied for 50 sec. every 5 min. during the 16-hr light period, which was supplemented with a high-pressure sodium lamp. Root and stem lengths, leaf number and leaf lengths were measured weekly. Plastochron index (PI) was used to measure rate of leaf initiation. PI increased linearly, indicating uniform initiation of leaf primordia and absence of environmental stresses. Stem and root lengths increased consistently throughout the growing period. Each plant was harvested, separated into leaves, shoots and roots, oven dried, and dry weights measured.

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Donald T. Krizek

Roots exposed to drying soil have been shown to generate non-hydraulic signals which can be communicated to the shoot. Such `root signals' can cause an inhibitory effect on leaf growth without causing detectable water deficits in the shoots. Plants grown in restricted root zone volumes also typically show a reduction in leaf and shoot growth. Although water stress and root restriction both impair growth, their effects on photosynthesis, leaf initiation, and C, N, and P metabolism may be quite different. Abscisic acid (ABA) has been shown to be produced in the roots after only mild dehydration and to play a major role in signal transduction from the roots to the shoots. Whether root-restricted plants are capable of generating `root signals' such as ABA or other plant hormones, which can be communicated to the shoot, remains to be determined. The application of new tools, such as gas chromatography/mass spectrography for hormone analysis, nuclear magnetic resonance imaging, and photoacoustic spectroscopy, should help to identify the nature of `root signals' generated during root restriction and clarify their regulatory role in shoot behavior.

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J.D. Everard and W.H. Loescher

In celery (Apium graveolens L.), up to 50% of newly assimilated carbon may be partitioned into mannitol in mature leaves. Mannitol biosynthesis involves three unique enzymatic steps, and mannose 6-phosphate reductase (M6PR) is the critical regulatory step in the pathway. We measured M6PR enzyme activities, M6PR protein levels (using an immunological method) and M6PR transcript levels (by Northern blotting) to assess effects of leaf development on mannitol biosynthesis. M6PR was limited to green tissues and was under tight transcriptional regulation during leaf initiation, expansion, and maturation. M6PR expression was also closely correlated with the capacity of leaves to partition newly fixed carbon into mannitol (measured by 14C pulse/chase on intact leaves). Previous studies have also shown salt stress to lead to mannitol accumulation in celery. Using the methods outlined above we also investigated the combined effects of salt stress and leaf development on M6PR expression and the capacity of leaves to partition C to mannitol. Under salt stress M6PR expression and the capacity to synthesize mannitol occurred in younger leaves than in control plants. Thus, the increase in mannitol pool size in salt-stressed celery plants is due, in part, to enhanced de novo synthesis in young leaves. The data also confirmed the relationship between development of photosynthetic capacity, mannitol synthesis and M6PR activity. Supported by USDA-NRI grant # 940-1439.

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N. Bernstein, A. Meiri, and M. Zilberstaine

In most crop species, growth of the shoot is more sensitive to salt stress than root growth. Avocado [Persea americana Mill.] is very sensitive to NaCl stress. Even low concentrations of salt (15 mm) inhibit tree growth and decrease productivity. Observations in experimental orchards have suggested that root growth in avocado might be more restricted by salinity than shoot growth. In the present study, we evaluated quantitatively the inhibitory effects of salt stress on growth of the avocado root in comparison to the shoot. Seedling plants of the West-Indian rootstock `Degania 117' were grown in complete nutrient solution containing 1, 5, 15, or 25 mm NaCl. The threshold NaCl concentration causing root and shoot growth reduction occurred between 5 and 15 mm. At all concentrations, root growth was much more sensitive to salinity than shoot growth. A concentration of 15 mm NaCl, which did not affect the rate of leaf emergence on the plant and decreased leaf biomass production only 10%, induced a 43% reduction in the rate of root elongation and decreased root volumetric growth rate by 33%. Under 25 mm NaCl, leaf biomass production, leaf initiation rate and leaf elongation rate were reduced 19.5%, 12%, and 5%, respectively, while root volumetric growth and root elongation rate were reduced 65% and 75%, respectively. This strong root growth inhibition is expected to influence the whole plant and therefore root growth under salinity should be considered as an important criterion for rootstocks' tolerance to NaCl.

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R. Bruce Carle and J. Brent Loy

The morphology, growth rate and anatomy of the fused vein trait were characterized in Cucurbita pepo using the inbreds NH2405 (fused vein), NH7210 (moderately fused vein), and NH614 (normal). Morphological analysis showed that the trait is characterized by a partial fusion of the five primary leaf veins. Fusion begins at the distal point of the petiole and extends along the central vein. Branching of the veins is delayed and there is a reduction of the interveinal leaf blade. Consequently, the upper leaf surface appears puckered or wrinkled. Depending on genetic background, the onset of fused vein leaf production starts at the fourth to tenth leaf stage and continues throughout vegetative growth. The extent of fusion increases with leaf number but stabilizes by the twentieth leaf stage maximum extent of vein fusion also varies with genetic background (5-20 cm). Though fused vein and normal inbreds differed in the rate and pattern of leaf growth, examination of F2 and BC populations revealed no significant effect of the fused vein trait on leaf number, leaf size, and rate of leaf initiation. Anatomical examination revealed different vascular patterns in the transition zone between petiole and leaf blade for normal and fused vein leaves. In normal leaves, the vascular bundles of the petiole enlarge and coalesce to form a vascular crescent. The crescent reorganizes and diverges as large vascular columns and pairs of smaller flanking vascular bundles into each vein. In contrast, two cycles of enlargement, coalescence, and dispersal occur in fused vein leaves.

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Jo-Ann Bentz and Alden M. Townsend

The suitability of container-grown clones of red maple, Acer rubrum L., as a host to the potato leafhopper, Empoasca fabae Harris (Homoptera: Cicadellidae), under different fertilization regimes was determined, and compared to different freeman maple cultivars (A. ×freemanii E. Murray). Three clonal selections of red maple (USNA numbers 56026, 59904, and 55410), and three freeman maple cultivars (55892 `Indian Summer', 67256 `Jeffersred' [trademark Autumn Blaze], and 55890 `Armstrong') were potted in 7.6-L containers, fertilized with either 0, 3.3, or 6.6 g/pot of calcium nitrate and used in experiments. When given a choice, female leafhoppers laid more eggs on leaves of red maple clone 56026 than on leaves of clone 59904, with oviposition linearly increasing on both clones with increases in the fertilization level applied to the trees. Yet, when female leafhoppers were confined to leaves using organza sleeve cages, oviposition increased linearly as fertilizer level increased, without a significant clonal effect. Oviposition did not differ among freeman maple cultivars, nor was it influenced by the fertilizer level applied to the freeman maple trees. Nymphs had the lowest odds of surviving to adulthood when reared on the freeman maple `Jeffersred', but highest when reared on red maple 59904. Red maple 59904 had the fastest growth rate while red maple 55410 had the slowest. Leaf initiation and expansion in red maple 56026 was significantly slower than in the other selections. Leaf development of these three red maple clones was significantly accelerated by the application of fertilizer, regardless of level. The maple selections differed in their mean amounts of foliar macronutrients and micronutrients, which related to the fertilizer level applied to trees. Unfertilized trees had the highest C to N ratio, which decreased as fertilizer level applied to trees was increased. This study showed that fertilization improved the performance of the potato leafhopper on previously nonpreferred maple selections, and that the foliar nutrient content and C to N ratio could be used as indicators of tree susceptibility to insect attack under different growing conditions.