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Cheryl R. Hampson and Anita N. Azarenko

Self-incompatibility, a genetic mechanism enforcing out crossing, is most commonly controlled by a single, multi-allelic gene, designated the S-gene. Sporophytic self-incompatibility (SSI), a form of incompatibility determined by the parent plant rather than the gametes, is present in the Brassicaceae, Compositae and other families, and also in hazelnut (Corylus avellana L.). Little is known about the molecular basis of SSI in plants other than crucifers. An S-gene cloned from Brassica oleracea (donated by Dr. June Nasrallah, Cornell University) was used to probe genomic DNA obtained from seven hazelnut genotypes. DNA hybridization was observed in cultivars `Hall's Giant' and `Willamette'. Gene similarity was estimated to be 70-80%.

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Elzbieta Z. Krzesinska, Anita N. Azarenko, and Dennis C. Gross

The syrB gene required by Pseudomonas syringae pv. syringae van Hall to produce the phytotoxin syringomycin is activated by plant signal molecules. Extracts from twigs of 12 cherry (Prunus) genotypes were tested for their ability to induce syrB::lacZ fusion in P. syringae pv. syringae strain B3AR132 to determine whether signal activity is correlated with susceptibility to bacterial canker. One-year-old twigs of `Napoleon', `Corum', and 12 cherry rootstocks (F12/1, `Colt', M×M2, M×M39, M×M60, Gi 148-1, Gi 148-9, Gi 154-2, Gi 154-5, Gi 169-15, Gi 172-9, and Gi 173-9) were tested at concentrations of 0.2, 1.0, and 2.0 mg twig dry weight/ml solution for their ability to induce syrB::lacZ fusion, as measured by β -galactosidase activity. Extracts from all cherry genotypes induced syrB::lacZ fusion, but to varying degrees. The highest β -galactosidase activity was observed in `Napoleon' and `Corum'-the most susceptible genotypes; activities were two to four times higher than that of F12/1, a disease-resistant genotype. Activities higher than that of F12/1 were induced at the lowest extract concentration by rootstocks M×M60, Gi 148-1, Gi 148-9, and Gi 154-5, whereas rootstocks M×M2, M×M39, Gi 154-2, Gi 172-9, Gi 173-9, and `Colt' were not significantly different from F12/1. At the two highest extract concentrations tested, only `Napoleon' and `Corum' consistently had higher induct&m activity than F12/1. At high extract concentrations, interfering substances seemed to suppress or antagonize the induction of syrB::lacZ fusion. These results suggest that susceptible genotypes contain higher signal activities than resistant genotypes.

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Habib Khemira, P.B. Lombard, David Sugar, and Anita N. Azarenko

Mature hedgerows of `Anjou' pear (Pyrus communis L.) trees, planted north(N)-south (S) or east (E)-west (W), were used to study the effect of hedgerow orientation on fruiting and canopy exposure. In 1990, flower bud density tended to be lower on the E-W rows, especially on their N sides. Fruit set (FS) was highest on the S side of E-W rows and lowest on the N side, while the E and W sides of the N-S rows were intermediate. Crop density (CD) had a similar pattern as FS, with more fruit on the S than on the N side of the E-W rows. CD was more evenly distributed between the sides on the N-S hedgerows. Differences in FS and CD between sides were related to different levels of sunlight interception. Light exposure was lowest on the N sides of the E-W rows and highest on the S sides throughout the growing season and especially toward the equinoxes. Increased exposure to the sun on the S and W sides late in the season led to more fruit with solar injury. Fruit from E–W rows were larger and less firm. Accumulated yields over 11 years showed a 21.4% increase in the N-S rows over those of the E-W rows.

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Cheryl R. Hampson, Anita N. Azarenko, Rebecca McCluskey, and Jeffery Olsen

Many deciduous tree fruit species have a light requirement for floral induction. Floral induction of hazelnut has been reported to occur through the end of May into July. At the end of May, less than 5% full sun reaches the base of the canopy in a mature hazelnut orchard. Leaf area density was estimated to be 7.6. Six levels of shade (0, 30, 47, 63, 73, or 92%) were imposed on caged 7-year-old hazelnut trees (Corylus avellana L. cv. Ennis) to determine effects of shade on yield and nut quality. Shading reduced yield of nuts per tree from 3.43 kg in 0% shade to 0.62 kg in 92% shade and yield efficiency from 70.2 g/cm2 in full sun to 18.3 g/cm2 in 92% shade. Yield and yield efficiency decreased substantially in 30% shade. When shade exceeded 47%, nut and kernel size decreased sharply, but % kernel increased slightly. In comparison to trees in full sun, shaded trees had a higher incidence of moldy or shrivelled kernels and a lower incidence of blanks.

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Habib Khemira, Timothy L. Righetti, and Anita N. Azarenko

Fruit tree responses to foliar urea sprays are variable. We hypothesized that such variability is a function of leaf age-related changes in urea-N mobility after urea is absorbed. Two experiments were conducted to study the distribution of urea-derived N in shoots and branches of apple (Malus ×domestica Borkh.) trees. Urea labeled with 15N was applied to young expanding leaves in spring and to senescing spur leaves in fall. At the low concentrations used [0.5%, 1%, and 2% (w/v)], very little spring-applied 15N was found in tissues other than the treated leaf. Fall-applied urea-15N, however, was detected in high concentrations in dormant buds and bark of the spurs to which the treated leaves were attached. Almost no N was exported to neighboring tissues. The following spring, there was some redistribution of labeled N to adjacent buds. Foliar urea sprays applied immediately after harvest contributed most to bud N; less urea-N was exported to the buds following later fall applications.

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David R. Sandrock, Anita N. Azarenko, and Timothy L. Righetti

Nitrogen accumulation patterns were established for Weigela florida (Bunge.) A. DC. `Red Prince' (fast growth rate) and Euonymus alatus (Thunb.) Sieb. `Compactus' (slow growth rate). From these, daily and biweekly N delivery schedules were designed to match N supply with N accumulation patterns of each taxon. Delivery schedules were sliding scales in that total N applied was controlled by independent increases (or decreases) of N concentration and solution volume. Daily and biweekly N delivery schedules were tested against a constant N rate (200 mg·L-1) and Osmocote 18N-2.6P-9.9K (The Scotts Co., Marysville, Ohio). Plants were grown in 3.8-L containers in 7 douglas fir bark: 2 sphagnum peatmoss: 1 silica sand (0.65 mm; by volume) outdoors in full sun on a gravel pad for 142 d. Within each taxon, Weigela and Euonymus grown with sliding-scale N fertilization schedules had similar total dry weights, leaf areas, and total plant N contents to plants grown with a constant N rate (200 mg·L-1) or Osmocote 18N-2.6P-9.9K. Sliding-scale liquid fertilization based on plant N requirements introduced less total N to the production cycle and resulted in higher N uptake efficiency than fertilization with a constant N rate of 200 mg·L-1. In general, liquid N fertilizer treatments resulted in plants with higher shoot to root ratios than plants treated with Osmocote 18N-2.6P-9.9K. Weigela and Euonymus treated with biweekly schedules were similar to plants treated with daily schedules (same total amount of N delivered with each treatment).

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Cheryl R. Hampson, Anita N. Azarenko, and John R. Potter

In hazelnut (Corylus avellana L.), vigorous vegetative growth and traditional orchard practices that include little or no pruning combine to produce a dense, shady canopy. A study designed to quantify the effect of shade on reproduction and photosynthetic rate in this shade-tolerant species was undertaken to assess whether some degree of pruning might improve productivity. Shade cloth was used to exclude 30%, 47%, 63%, 73%, or 92% of ambient sunlight from whole `Ennis' and `Barcelona' trees from mid-May until harvest. Photosynthetic light response curves were obtained for leaves that had developed in full sunlight, deep inside the canopy of unshaded trees, or in 92% shade. Light-saturated net photosynthetic rates were 12.0, 6.1, and 9.3 μmol·m-2·s-1 of CO2 and dark respiration rates were 2.0, 1.1, and 0.7 μmol·m-2·s-1 of CO2, respectively, for the three light regimes. Light-saturated photosynthetic rates of leaves from 30% or 63% shade differed little from the control (0% shade). Area per leaf increased by 49% and chlorophyll concentration (dry weight basis) by 157% as shading increased from 0% to 92%. Shading to 92% reduced specific leaf weight (68%), stomatal density (30%), light compensation point (69%), and dark respiration rate (63%) compared to controls. Female inflorescence density declined by about one-third and male inflorescence density by 64% to 74% in the most heavily shaded trees of both cultivars compared to controls. Shade was more detrimental to yield than flowering: yield per tree dropped by >80%, from 2.9 to 3.4 kg in full sun to 0.6 to 0.9 kg in 92% shade. Shade reduced yield primarily by decreasing nut number and secondarily by decreasing nut size. The incidence of several kernel defects increased as shade increased. Therefore, hazelnut leaves showed considerable capacity to adapt structurally and functionally to shade, but improving light penetration into the canopy would probably increase orchard productivity.

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Habib Khemira, Timothy L. Righetti, and Anita N. Azarenko

Young bearing spur (Red-Spur Delicious) and standard (Top-Red Delicious) type apple trees were given one of the following treatments: 120g N applied to the ground in spring (SG), 120g N applied to the ground one month before harvest (PG), 60g N sprayed on the foliage after harvest (FF), 60g N SG and 60g N PG, or 60g N SG and 60g N FE Urea and NH4NO3 depleted in 15N (0.01 atom percentage 15N) were used for foliar and ground applications, respectively. Very little labeled N was present in leaves and fruit with PG applications, but roots, bark, and buds contained substantial amounts of it. Nitrogen from the FF sprays was effectively translocated to buds and bark. Percentage of N from the fertilizer in Sept leaves from spur-type trees that had only 60 g of N in spring was 56% higher than that found in standard-type trees. This figure rose to 180% with 120 g N spring application. Mature fruit showed the same trend. Spur-type trees appeared more responsive to N management practices. In contrast to the above ground structure, small roots of standard-type trees showed more label than those of spur-type trees. The difference was bigger with SG applications. Partitioning of N in the roots was apparently affected by the scion.

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David R. Sandrock, Ray D. William, and Anita N. Azarenko

Nitrogen (N) management in container nurseries is part of a complex system. Working within this system, nursery owners, managers and employees routinely make N management decisions that have consequences for the immediate nursery environment (e.g., plant growth, yield, disease susceptibility, water quality) as well as areas beyond nursery boundaries (e.g., surface and groundwater quality, public perception). Research approaches often address parts of the system associated with the immediate nursery environment and purpose. As a result, best management practices that contribute to greater N use efficiency have been developed. Research approaches that consider the whole system reveal novel relationships and patterns that identify areas for future research and may direct future management decisions. To investigate N management from a whole system perspective, a group of nursery managers from Oregon and scientists from Oregon State University met three times between 2001 and 2003. Growers drew their N management systems and identified components, relationships and feedback loops using an ActionGram technique. From this information, researchers developed Group-based On-site Active Learning (GOAL). GOAL combines Action-Grams and the Adaptive Cycle at container nursery sites. In this case, N flow and management in container production systems served as the topic of active learning. Managers and employees from four wholesale container nurseries evaluated the GOAL exercise. After completing GOAL, 94% of participants indicated that they learned a new idea or concept about N cycling in their container nursery. Of those, 100% gained new ideas and concepts from peers and colleagues present at the meeting. In addition, 60% gained new ideas and concepts from researchers and 60% developed their own ideas and concepts. GOAL is a learning tool that provides a simple, convenient, interactive format for investigating complex systems.

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David R. Sandrock, Timothy L. Righetti, and Anita N. Azarenko

Cornus sericea L., Weigela florida (Bunge) A. DC., and Euonymus alatus (Thunb.) Sieb were grown outside in 3.8-L plastic containers for 345 days (1 Apr. 2001 to 11 Mar. 2002). Nitrogen (N) was applied at rates (NAR) of 25, 50, 100, 200, and 300 mg·L–1 and delivered as aqueous double-labeled 15N depleted NH4NO3 (min 99.95% atom 14N). In all species, root, shoot, and total plant dry weight increased with increasing NARs while root to shoot ratios decreased. Similarly, root, shoot, and total plant N increased with NAR for each species, and at each NAR more N was stored in the roots than in the shoots. Estimation of fertilizer N uptake determined by the total N method was higher for all species and at each NAR than estimation of N uptake determined by the fertilizer 15N tracer method. Fertilizer N uptake efficiency determined by the total N method was highest at 25 mg·L–1 and decreased as NARs increased. In contrast fertilizer N uptake efficiency determined by the fertilizer 15N tracer method was lowest at 25 mg·L–1 and increased or remained relatively constant as NARs increased. Differences in N uptake and N uptake efficiency can be attributed to overestimation by the total N method due to the inclusion of nonfertilizer N and underestimation by the fertilizer 15N tracer method due to pool substitution. Corrected N uptake efficiency values can be calculated by adjusting the original data (total N or 15N uptake) by the distance between the origin and the y intercept of the regression line representing the data.