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Kil Sun Yoo, Leonard M. Pike, and B. Greg Cobb

Inner scales excised from dormant bulbs of the short-day `Texas Grano 1015Y' onion (Allium cepa L.) were cultured in vitro and leaf growth was examined. Light promoted leaf growth, but no differences in leaf growth were observed for media pH between 4 and 7. Leaf growth rate in darkness was highest at 24C, reduced at 15C, and greatly reduced at SC. Kinetin promoted leaf growth at 1, 10, and 100 μm. IAA was effective at 1 and 10 μM, but not at 0.1 and 100 μm. GA3 promoted growth at 0.1 μM. No inhibitory effects of ABA on leaf growth could be detected. Chemical names used: 1-H-indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellic acid (GA3), 6-furfurylaminopurine (Kinetin).

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Stan D. Wullschleger and Derrick M. Oosterhuis

Growth-chamber studies were conducted to examine the ability of seven vegetable crops-`Blue Lake' bean (Phaseolus vulgaris L.), `Detroit Dark Red' beet (Beta vulgaris L.), `Burgundy' okra (Abelmoschus esculentus (Moench), `Little Marvel' pea (Pisum sativum L.), `California Wonder' bell pepper (Capsicum annuum L.), `New Zealand' spinach (Spinacia oleracea L.), and `Beefsteak' tomato (Lycopersicon esculentum Mill.)–to adjust osmotically in response to water-deficit stress. Water stress was imposed by withholding water for 3 days, and the adjustment of leaf and root osmotic potentials upon relief of the stress and rehydration were monitored with thermocouple psychrometers. Despite similar reductions in leaf water potential and stomata1 conductance among the species studied, crop-specific differences were observed in leaf and root osmotic adjustment. Leaf osmotic adjustment was observed for bean, pepper, and tomato following water-deficit stress. Root osmotic adjustment was significant in bean, okra, pea, and tomato. Furthermore, differences in leaf and root osmotic adjustment were also observed among five tomato cultivars. Leaf osmotic adjustment was not associated with the maintenance of leaf growth following water-deficit stress, since leaf expansion of water-stressed bean and pepper, two species capable of osmotic adjustment, was similar to that of spinach, which exhibited no leaf osmotic adjustment.

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Richard J. Heerema*, Ted M. De Jong, and Steven A. Weinbaum

Spurs are the primary bearing unit in mature `Nonpareil' almond (Prunus dulcis (Mill.) D.A. Webb) trees. Our objective was to determine whether almond spurs behave autonomously with respect to various biological activities throughout the season. If autonomous, a spur's carbohydrate demands are met primarily by its own leaves and, therefore, the sink to source ratio of the spur itself is expected to be closely linked to its growth and development. In these experiments almond spurs differing in leaf area and/or fruit number were monitored for leaf development, fruit set, floral initiation, spur survival and carbohydrate storage. Previous-season spur leaf area had no relation to the number of leaves preformed within the dormant vegetative bud or final spur leaf area in the current season, but spurs which fruited in the previous season began spring leaf expansion later and current-season spur fruiting was associated with lower spur leaf area. There was little or no relationship between final percentage fruit set at the spur level and spur leaf area in either the current or previous seasons. Current-season spur leaf area was positively related to both spur flower bud number and spur winter survival. Carbohydrate storage in dormant spurs increased with increasing previous-season spur leaf area. These data are consistent with the concept of spur autonomy especially with regards to spur activities late in the season. The relationships of some of these same spur parameters to spur light exposure are currently being investigated.

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Chao-Yi Lin and Der-Ming Yeh

Guzmania lingulata (L.) Mez. ‘Cherry’ plants were grown in coconut husk chips. All plants were given 8 mm nitrogen (N), 2 mm phosphorus (P), 4 mm calcium (Ca), and 1 mm magnesium (Mg) at each irrigation with potassium (K) concentration at 0, 2, 4, or 6 mm. After 9 months, K concentration did not alter the number of new leaves, and shoot and root dry weights. Increasing K concentration did not affect the length but increased the width of the most recently fully expanded leaves (the sixth leaves). Plants under 0 K exhibited yellow spots and irregular chlorosis on old leaves being more severe at the middle of the blade and leaf tip. Numbers of leaves with yellow spots or chlorosis decreased with increasing K concentration. Chlorenchyma thickness was unaffected by K concentration, whereas water storage tissue and total leaf thickness increased with increasing K concentration. Leaf N concentration in the sixth or 10th leaf was unaffected by solution K concentration. However, plants at 0 mm K had higher N concentration in the 14th leaf than those in sixth and 10th leaves. Leaf P, Ca, and Mg concentrations decreased with increasing solution K concentration. K concentrations were higher in the sixth leaf than the 14th leaf in plants at 0, 2, or 4 mm K, whereas leaf K concentration was 15 g·kg−1 on dry weight basis in the sixth, 10th, or 14th leaves in plants treated with 6 mm K.

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G.R. Panta and D.S. NeSmith

Eight muskmelon (Cucumis melo reticulatus L.) cultivars were selected to test whether a model could be developed to estimate leaf area across cultivars. Regression analyses of leaf area vs. leaf width and length revealed several models that could be used for estimating the area of individual muskmelon leaves. A linear model using leaf width squared was the best overall, yielding the equation A = 3.3 + 0.63 (W2), where A is area of an individual leaf lamina (square centimeter) and W is leaf width (centimeter) at the widest point perpendicular to the leaf midrib. Forcing the intercept through the origin did not significantly alter prediction capability and resulted in a simple model of the form A = 0.64 (W2) that was applicable to all eight cultivars.

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Jeffrey Melkonian and David W. Wolfe

Cucumber (Cucumis sativus L. cv. Marketmore 80) plants were exposed to a soil water deficit and subsequently rewatered. Maximum stress intensity was -1.5 MPa midday leaf water potential compared to -0.6 to -0.8 MPa in the well watered control, eight days after withholding water. Midday stomatal conductance {ks), leaf turgor potential and water potential decreased in the stress treatment compared to the control beginning at the first sampling, two days after withholding water. The decrease in all three was approximately linear with time over the stress. Decreased leaf elongation was observed at the second sampling, three days after the initial decline in ks and five days after withholding water. At similar relative water content {RWC), osmotic potentials of the stress and control treatments were the same throughout most of the stress. Further, there was no difference in osmotic potential, at the same RWC, between the stress and control treatments 12 - 16 hours after rewatering. Split-root experiments were also conducted to examine a possible role of a non-hydraulic signal from roots in drying soil in the regulation of ks and leaf elongation in cucumber. No conclusive evidence of a signal was found despite significant decreases in soil water potential of one-half of the root system of the stress plants. However, fluctuating vapor pressure gradients (vpg) may have obscured evidence of a signal.

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Jingwei Dai and Robert E. Paull

The growth and development of Anthurium andraeanum Andre cv. Kaumana flower before and after emergence from the subtending leaf base was studied. Eighty days before emergence, the anthurium flower was =0.3 cm long, enclosed by two tightly rolled stipules at the base of the subtending leaf petiole. During the rapid elongation stage of the leaf petiole, the flower (0.8 to 1.0 cm long) entered a period of slow growth 40 to 60 days before flower emergence. After the subtending leaf blade unfurled and had a positive photosynthetic rate, flower growth resumed. Spathe color development started =28 days before emergence when the flower was =50% of the emergence flower length (4.5 cm). At flower emergence, the spathe, excluding the lobes, was =75% red. The lobes did not develop full redness until 7 to 10 days after emergence. Peduncle growth was sigmoidal with the maximum growth rate 21 days after emergence. Spathe growth is characterized by a double sigmoid curve. The young, growing, subtending leaf blade had a negative net photosynthetic rate. Removal of this leaf blade advanced flower emergence by 18 days. The soft green leaf (25 to 30 days after leaf emergence) had a slightly positive measured net photosynthetic rate, and the removal of this leaf resulted in flower emergence 11 days earlier. A mature subtending leaf had the highest measured net photosynthetic rate, and its removal had little effect on flower emergence. The subtending leaf acted as a source of nutrients required for the developing flower. Altering the source-sink relationship by leaf removal accelerated flower emergence, probably by reducing the slow growth phase of the flower.

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Junhuo Cai, Junjun Fan, Xuying Wei, and Lu Zhang

surface), 2) vigorous leaf growth (i.e., rapid leaf extension), 3) leaf maturity (i.e., the leaf stops growing), 4) flower bud predifferentiation (i.e., the leaf tip begins to turn yellow), 5) flower bud differentiation (i.e., the leaf withers), 6

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Robert M. Pyne, Adolfina R. Koroch, Christian A. Wyenandt, and James E. Simon

effective when it is demonstrated that mature plants maintain or increase disease tolerance relative to younger growth stages ( Wang et al., 2000 ). The relationship between cotyledon and true leaf growth stages in response to downy mildew has been explored