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Abstract

Horticultural instruction in secondary schools is not new. In fact, it dates back to the middle ages in Western Germany (2). Some of the earlier high school horticultural programs in the United States are found in Los Angeles, 1908 (1), Cleveland, 1911 (1), and Boston 1918 (11). However, only since 1963, has horticultural instruction in secondary schools become widespread in the United States. Loewen (4) conducted a survey of the 50 states in 1968 and found 31 of the 43 states responding had such horticultural programs.

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Abstract

The direct formation of adventitious buds from leaf tissue of African violet (Saintpaulia ionantha Wendl.) resulted in the maintenance of the parent chimera pattern. Low cytokinin levels contributed to the formation of a single, symmetrical rosette.

Open Access

Vegetative 6-cm Euphorbia pulcherrima `Freedom' cuttings were placed in black 200-ml bottles containing humic acid solutions, nutrient solutions, or deionized water. Humic acid solutions were prepared using Enersol SC (American Colloid, Arlington Heights, Ill.). Concentrations of 500, 750, and 1000 mg/L humic acid were compared to solutions containing mineral element concentrations equivalent to those contained in humic acid solutions. After 4 weeks, 88%, 75%, and 88% of cuttings had rooted in the 500, 750, and 1000 mg/L humic acid solutions, respectively. Cuttings placed in nutrient controls or deionized water failed to form roots after 4 weeks. Average root fresh mass was 175, 80, and 72 mg for cuttings placed in 500, 750, and 1000 mg/L humic acid solution, respectively. Average number of roots formed per cutting ranged from 21 in the 500-mg/L solution to 6 in the 1000-mg/L solution. Average lengths ranged from 26 mm in the 500-mg/L to 12 in the 1000-mg/L solution. As humic acid concentration increased, average root fresh mass, average number of roots, and the length of the longest root significantly decreased.

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Various cultivars of strawberry (Fragaria ×ananassa Duch.) were stored for 42 h under an atmosphere of 15% CO2 to determine whether their firmness would be enhanced. Compared to initial samples and stored control samples, enhanced firmness was found in 21 of the 25 cultivars evaluated. The CO2 had no effect on color, as measured by Hunter `L', `a' and `b', or on soluble solids concentration (SSC) or pH. There were significant differences among cultivars in firmness; Hunter color `L', `a', and `b'; SSC; and pH.

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A 10-year field experiment was conducted on 20-year-old apple trees (Malus domestica Borkh.) inoculated with Phytophthora cactorum (Leb. & Cohn) Schroet. to study the influence of the scion cultivar on rootstock susceptibility. The rootstock MM.111 was less susceptible to P. cactorum than M.7 when `Golden Delicious' was the scion, but there were no differences when `Delicious', `Haroldred Delicious', or `McIntosh' were the scions. Similarly, the rootstock M.26 was less susceptible than M.7 when `McIntosh' was the scion, but there were no differences when `Delicious', `Haroldred Delicious', or `Golden Delicious' were the scions. These results suggest that the influence of scions on rootstock susceptibility to P. cactorum crown rot is variable.

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Legume ground covers in pecan orchards can reduce nitrogen inputs and increase beneficial insects. Preliminary data indicate that certain legumes can supply over 100 kg·ha-1 N. Additionally, certain legumes have high aphid populations which attract beneficial insects. When aphid populations on the legumes crash, beneficial insects seek alternative food sources in the pecan trees, thus reducing the necessity for pesticide applications. Preliminary studies suggest that a mixture of 'Dixie' crimson clover and hairy vetch produces high populations of beneficial insects and over 100 kg·ha-1 N. Treatments were established at four pecan orchard sites in Oklahoma, each with 5 ha of a crimson clover/vetch mixture and 5 ha of native grass sod. Additions of 0-200 kg·ha-1 N were added to the sod plots but no supplemental N was added to the legume plots. Nitrogen and biomass production by the legumes, and leaf N concentration of pecans were determined. In addition, both aphid and beneficial insect populations were monitored in the legume and grass treatments, and in the pecan trees. Results will be discussed in the presentation.

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Abstract

The relationship between net CO2 assimilation rate (A) and nitrogen (N) content during leaf senescence was determined on field grown Vitis vinifera L. ‘Thompson Seedless’ leaves. Measurements commenced subsequent to fruit harvest and were made at weekly intervals until leaf fall. Maximum A was greater than 2.0 nmoles CO2 cm-2s-1 when leaf N content was greater than 3.0%. There was a linear relationship between A and percent N content regardless of whether A was expressed on an area or dry weight basis. However, the correlation between A on a dry weight basis and percent leaf N was greater than that between A on an area basis and percent leaf N. The percent N content and net CO2 assimilation rate decreased as weight per unit leaf area (W) increased. There was no effect on leaf N content on stomatal conductance (gs) when N content was greater than 2%. The results suggest that leaf N content could be used an as indicator of a grapevine's leaf photosynthetic capacity subsequent to fruit harvest.

Open Access

‘Concord’ grapevines (Vitis labruscana Bailey) are susceptible to lime-induced chlorosis, which decreases growth and productivity. In two separate experiments, we grew own-rooted vines in a peat–perlite medium adjusted to different pHs with CaCO3 to characterize how lime-induced Fe deficiency affects root and leaf ferric chelate reductase (FCR) and key enzymes and metabolites involved with glycolysis and the tricarboxylic acid (TCA) cycle in leaves. In addition, we measured the pH of the xylem sap as well as Fe, citrate, and malate concentrations. For both experiments, foliar levels of total Fe, active Fe (extracted in 0.1N HCl), and chlorophyll decreased as lime rate increased. An increase in root-medium pH from 5.8 to 7.5 resulted in a 10-fold increase in root FCR activity, whereas leaf FCR activity decreased 10-fold. An increase in root-medium pH did not raise xylem sap pH but decreased Fe and citrate to some extent. Xylem malate was highest at pH 6.6 and decreased both above and below this pH. Foliar data were evaluated in relation to active Fe content, because it is a better indicator of Fe nutritional status. Lower active Fe decreased midday CO2 assimilation and PSII quantum efficiency as well as night respiration. As active Fe decreased, aconitase activity decreased linearly, whereas the activity of glucose-6-phosphate dehydrogenase, NAD(P)-isocitrate dehydrogenase, NAD(P)-malic enzyme, malate dehydrogenase, phosphoenolpyruvate (PEP) carboxylase, PEP phosphatase, and pyruvate kinase increased curvilinearly. Glucose-6-phosphate, fructose-6-phosphate, and 3-phosphoglycerate content decreased curvilinearly as active Fe decreased. Malate content increased as active Fe increased to 1.0 mg·m−2 and then decreased above this level. Citrate increased linearly as active Fe decreased and was an order of magnitude lower than malate content. Our results suggest that leaf FCR activity may limit Fe assimilation to a greater extent than root FCR activity. The decreased leaf aconitase activity under Fe deficiency is the most likely cause of the increase in citrate levels. Greater activity of the other glycolytic and TCA enzymes under Fe deficiency may help to funnel carbon into the mitochondria and enhance NAD(P) reduction. Citrate levels (and the citrate:malate ratios) in the xylem exudate and leaf were much lower when compared with other species and may be linked to Fe inefficiency of ‘Concord’.

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Plants grown on calcareous soils often exhibit symptoms of Fe-deficiency induced chlorosis despite a high content of total Fe in the leaf tissue. Iron is transported in the xylem primarily as the ferric citrate (Fe-Citr) chelate, and changes in pH, HCO - 3, and Citr can lead to the formation of different Fe-Citr species. Understanding how Fe dissociates from these chelates may help explain why Fe is immobilized in the leaves. The goal was to quantify Fe mobilization (Fe-Mob) from Fe-Citr in an assay system buffered at pH 5, 6, or 7 when: 1) the molar ratio of HCO - 3 to Fe increased in a 1 Fe: 1 Citr system; 2) the molar ratio of Citr increased in a 1 Fe: 3 HCO - 3 system; and 3) solutions were photoreduced (PR) or left in the dark. For non-PR solutions, Fe-Mob from Fe-Citr using 500 μmol NADH was the greatest at the 1 Fe: 0 HCO - 3-level, and decreased as HCO - 3 increased. Fe-Mob also decreased as buffer pH increased from 5 to 7. Increasing the Citr ratio was effective in increasing Fe-Mob, but the effect decreased as buffer pH increased from 5 to 7. PR solutions behaved quite differently. In the 1 Fe: 1 Citr system, little to no Fe-Mob was detected at any buffer pH. However, there were already large pools of Fe2+ in solution, which decreased as HCO - 3 increased, irrespective of buffer pH. Increasing the Citr ratio greatly increased Fe-Mob in the 1 Fe: 3 HCO - 3 system, and mobilization decreased as buffer pH increased. Increasing Citr did not increase the amount of Fe2+ in solution. This work illustrates that increasing the HCO - 3: Fe ratio can lead to an immobilization of Fe, and that increasing the Citr ratio can aid in Fe-Mob from Fe-Citr when the HCO - 3: Fe ratio is high. Increasing the Citr ratio, however, does not increase the amount of PR Fe2+.

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`Concord' grapevines (Vitis labruscana Bailey) can readily develop iron deficiency-induced leaf chlorosis when grown on calcareous or high pH soils. Iron (Fe) chelates are often applied to the soil to remedy chlorosis but can vary in their stability and effectiveness at high pH. We transplanted own-rooted 1-year-old `Concord' grapevines into a peat-based medium adjusted to pH 7.5 and fertigated them with 0, 0.5, 1.0, 2.0, or 4mg·L–1 Fe from Fe-EDDHA [ferric ethylenediamine di (o-hydroxyphenylacetic) acid] to determine the effectiveness of this Fe chelate for alleviating Fe deficiency-induced chlorosis at high pH. Vines were sampled midseason for iron, chlorophyll, CO2 assimilation, and photosystem II quantum efficiency (PSII) and at the end of the season for leaf area, dry weight, and cane length. We found that leaf total Fe concentration was similar across all treatments, but active Fe (extracted with 0.1 n HCl) concentration increased as the rate of Fe-EDDHA increased. Chlorophyll concentration increased curvilinearly as applied Fe increased and was highly correlated with active Fe concentration. CO2 assimilation, stomatal conductance, and PSII were very low without any supplemental Fe and increased rapidly in response to Fe application. Total leaf area, foliar dry weight, and cane length all increased as Fe application increased to 1 mg·L–1 Fe, but above this rate, a further increase in Fe did not significantly increase growth. Our results demonstrate that Fe-EDDHA is very effective in alleviating Fe deficiency-induced leaf chlorosis in `Concord' grapevines grown at high pH, which provides a foundation for continuing research related to the optimum rate and timing of application of Fe-EDDHA in `Concord' vineyards on calcareous soils. Compared with total Fe, leaf “active Fe” better indicates the actual Fe status of `Concord' vines.

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