Ursula K. Schuch

Water relations of host trees and resistance to the phloem-boring beetle Phoracantha semipunctata F. (Coleoptera: Cerambycidae).

Abstract Environmental stresses, particularly water deficit, predispose eucalypt trees to attack by the eucalyptus longhorned borer, Phoracantha semipunctata F. (Coleoptera: Cerambycidae). Our experiments with potted eucalypts revealed that reduced tree water potential was associated with lower resistance to colonization by neonate P. semipunctata, but the linear relationship between water potential and colonization success was reversed at higher larval densities. There was no indication that the bark exudate “kino” served to defend trees from borer attack. Larvae were not able to colonize the cambium of eucalypt logs with high bark moisture, and survival was low under high moisture conditions in artificial hosts composed of pure cellulose. In trees and cut logs with moist bark, larvae failed to reach the cambium, feeding instead in poorer-quality tissues just beneath the bark surface. Our findings suggest that variation in resistance of eucalypts to attack by the borer is associated with moisture content of the bark.

Melon aphid performance on chrysanthemum as mediated by cultivar, and differential levels of fertilization and irrigation

Population parameters of the melon aphid, Aphis gossypii Glover, were compared for insects grown on six cultivars of chrysanthemum, Dendranthema grandiflora Tzvelev (‘Fontana’, ‘Iridon’, ‘Pink Lady’, ‘Splendor’, ‘White Diamond’, and ‘White View Time’) fertilized with 3 different levels of nitrogen (80, 160 and 240 mg N/l) and 2 levels of irrigation (high 300 ml and low 210 ml every other day). Fecundity, longevity, and survivorship of aphids were significantly affected by the cultivar treatment, but were not affected by irrigation or fertilizer treatments or by any combination of interactions among cultivar, fertilizer and irrigation. Significantly fewer aphids survived on the cultivar ‘Pink Lady’ (populations reduced by 20.8%) than any other cultivar examined. Intrinsic rates of increase (rm), finite rates of increase (R0), and population doubling times (DT) for aphids were different among fertilizer levels and cultivars, but were not different among irrigation levels. There were no significant fertilizer by irrigation interaction effects upon rm, R0, or DT. The highest rate of fertilizer applied (240 mg N/liter) adversely affected the intrinsic rate of increase of melon aphids; however, aphid intrinsic rate of increase was weakly correlated with foliar soluble protein levels (r= 0.989, P = 0.0954). Foliar soluble protein levels were not associated with fertilization treatment. Melon aphids perform consistently better on the cultivars ‘White Diamond’, ‘Fontana’, and ‘Splendor’, relative to those aphids growing on ‘Iridon’, ‘Pink Lady’, or ‘White View Time’. In general, melon aphids performed best on ‘White Diamond’ and poorest on ‘Pink Lady’.

Exposure of Petunia seedlings to ethylene decreased apical dominance by reducing the ratio of auxin to cytokinin

Seedlings of Petunia x hybrida ‘Orchid’ treated with the ethylene-releasing compound ethephon at 0.9, 1.7, and 3.5 mM evolved ethylene at a higher rate as the concentration of ethephon increased. Regardless of the concentration of ethephon applied, ethylene evolution peaked 6 to 8 h following application. Evidence that ethephon application decreased apical dominance included an increase in the number of new nodes on the main stem and a sustained increase in the length of new and existing lateral shoots compared to the control (no ethephon). Plants treated with 3.5 mM ethephon developed mild chlorosis, whereas a concentration of 1.7 mM ethephon decreased apical dominance without phytotoxic effects. The auxin/cytokinin ratio decreased in the apical shoot section as early as 1 h after ethephon treatment. In contrast, a decrease in the ratio in the subapical shoot section was not detected until 24 h after ethephon application. Reduction in auxin/cytokinin ratio was a result of a decrease in indole-3-acetic acid (IAA) and an increase of zeatin riboside (ZR), but not isopentenyladenosine (iPA). These results suggest that exposing ‘Orchid’ petunia seedlings to ethylene via ethephon lowers the auxin/cytokinin ratio, thereby promoting the outgrowth of lateral shoots.

Gibberellic acid causes earlier flowering and synchronizes fruit ripening of coffee.

The effect of 100 mgl−1 gibberellic acid (GA3) on flowering and fruit ripening synchrony, fruit set, fruit fresh weight, and vegetative growth were studied for different size classes of coffee (Coffea arabica L. cv. Guatemalan) flower buds. Flower buds that were > 4 mm, but not developed to the candle stage at the time of GA3 treatment, reached anthesis 20 days earlier than the controls, and their development was independent of precipitation, unlike the controls. Fruit from buds that were treated with GA3 at the candle stage showed earlier and more synchronous ripening than the control, although no differences in flowering were found during anthesis. Buds that were smaller than 4 mm at the time of treatment did not respond to GA3 applications. Treatment with GA3 did not affect fruit set, fresh weight of fruits, or vegetative shoot growth.

Endogenous IAA levels and development of coffee flower buds from dormancy to anthesis

Dormant coffee (Coffea arabica L.) flower buds require water stress to stimulate regrowth. A xylem specific water-soluble dye, azosulfamide, was used to quantify water uptake of buds after their release from dormancy by water stress. In non-stressed flower buds, the rate of water uptake was generally slower and variable compared to stressed flower buds, where the rate of uptake tripled from 1 to 3 days after rewatering and preceded the doubling of fresh and dry weight of buds. Free, ester and amide IAA levels of developing flower buds were measured by gas chromatography-mass spectrometry-selective ion monitoring using an isotope dilution technique with [13C6]IAA as an internal standard. Throughout development, the majority of IAA was present as amide IAA. The proportions of amide and free IAA increased one day after plants were released from water stress, and preceded the doubling of fresh and dry weight. Free and conjugated IAA content per bud remained stable during the period of rapid flower growth until one day before anthesis.

Response of chrysanthemum to uniconazole and daminozide applied as dip to cuttings or as foliar spray

Uniconazole and daminozide were used as dip on unrooted cuttings or as foliar spray on pinched Dendranthema grandiflora Tzvelev. ‘Dalvina’ to control height. Stem elongation was determined on cuttings dipped in solutions of 0, 1.25, 2.5, 5, or 10 mg/L uniconazole or cuttings were dipped and later treated with foliar sprays in concentrations of 1.25/5, 1.25/10, 2.5/10, and 5/5 mg/L uniconazole, respectively. Other plants were sprayed once or twice with uniconazole at 10 mg/L. Daminozide treatments included a pre-plant dip/foliar spray application of 1000/2000 mg/L, respectively, or two foliar sprays of 2,000 mg/L. Uniconazole dip alone retarded stem elongation linearly up to 8 weeks after propagation, 5 weeks after pinching, but was not discernible from the control treatment 8 weeks after pinching. Uniconazole at 2.5/10 and 5/5 mg/L as a dip/spray combination resulted in plants 33% shorter than the control at the end of the production. Doubling uniconazole dip or spray treatments from 5 to 10 mg/L provided no additional reduction of stem elongation. The single uniconazole spray and both daminozide treatments had no effect on final height, although daminozide treatments reduced stem dry weight compared to the control. Stem dry weight was reduced by uniconazole dip/spray combinations compared to dip treatments alone. Similarly, inflorescence and root dry weights were also reduced by the highest uniconazole concentrations. Higher concentrations of uniconazole reduced transpiration on a per leaf area basis up to 47% compared to the control at the end of production. In contrast to previous work, leaf area and leaf thickness increased with some uniconazole treatments, while time to anthesis was not affected by any of the treatments.

Crop Coefficients for Arizona Landscape Trees

Water use of many landscape plants is not only a factor of how much water a plant needs, but rather how much it receives. Previous research has found that desert-adapted trees such as live oak, once thought to be a low water user, will readily consume several times the quantity of water considered necessary for such a plant. Knowing the actual amount of water a particular tree species needs to survive or to grow to mature size will be helpful in applying irrigation water more judiciously. This information will help landscape managers and managers of water to increase the water use efficiency. In times of water shortage, the actual minimum, rather than the estimated minimum water requirements can be applied to maintain functionality of established landscape trees. Applying less irrigation water than required to achieve maximum growth can also be helpful in reducing plant maintenance such as pruning. The objectives of this project were to determine how nine species of commonly grown trees in southwestern semi-arid landscapes perform regarding growth and quality when irrigated to allow 30%, 50% or 70% depletion of available water in the soil. Results from this study will help to determine safe levels of soil water depletion to ensure growth and functionality. Data was collected on soil moisture and when combined with local weather data, resulted in the development of crop coefficients for three species of trees considered high, medium, or low water use.