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M.E. Scott and T.E. Michaels

Effective genetic resistance to common bacterial blight [Xanthomonas campestris pv. phaseoli (Smith) Dye] is not present in common bean (Phaseolus vulgaris L.) cultivars grown in Ontario. Foliar symptoms and seed yield of white pea bean breeding lines from a P. vulgaris/P. acutifolius interspecific cross in the presence and absence of common blight were evaluated. In inoculated plots, seven of the 20 breeding lines did not differ significantly in severity of foliar symptoms from the most resistant controls, XAN 159 and XAN 161. The most susceptible lines tended to have the highest yield when grown under disease-free conditions (r = 0.61 and 0.49 at two locations). However, the susceptible lines showed an average yield loss of 25% when disease-free and inoculated plots were compared, while resistant lines had little or no yield loss. The most severely infected lines tended to have the greatest loss in yield (r = 0.72 and 0.53 at two locations). A resistant breeding line from this study is available as OAC 88-1.

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Michael E. Reinert and Dan T. Stearns

ePortfolios are gaining popularity in academic communities worldwide. Purposes of ePortfolios include: converting student work from paper to digital format, thereby allowing it to be centrally organized, searchable, and transportable throughout their academic lives and careers; promoting student centered learning and reflection; improving advising; and career planning and resume building. Pennsylvania State University is investing in the use of ePortfolios in course work throughout the university system. To facilitate these efforts, the university provides all students and faculty with 500 MB of hosted web space to create and share their portfolios. One of the courses using ePortfolios is Horticulture 120, Computer Applications for Landscape Contracting, in the Landscape Contracting program. Outcomes of implementing ePortfolios include increased availability of student work to potential employers, enhanced recruiting through displays of student work, and enabled reflection on completed work. Students showed improved quality in project work because their projects would be publicly available through the Internet to potential employers, faculty, family, and other students.

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Martina T.V. Adeleke, Michael Pillay, and Bosa E. Okoli

Meiotic studies in Musa L. have been hampered by: 1) time-consuming efforts required to find the correct stages of cell division; 2) rigidity of the microsporocyte cell wall that makes preparation of smears difficult; and 3) poor staining of prophase chromosomes. This study describes an improved technique to examine meiosis in Musa. The procedure involves dissection of microsporocytes from the anthers, centrifugation to obtain large number of microsporocytes, enzymatic digestion of cell walls and treatment of cells with acetic-alcohol that results in spontaneous bursting of the protoplasts and release of chromosomes. Previous meiotic studies in Musa used acetocarmine that stained only highly condensed metaphase and anaphase chromosomes easily but not the relaxed prophase stages. In this study, we found that silver nitrate, Giemsa and Leishmans' stain were also effective for staining Musa chromosomes. Silver staining was most effective for the less contracted prophase chromosomes. By providing an improved procedure to examine all the meiotic stages in Musa, this technique will be useful to develop pachytene karyotypes, characterize new hybrids and identify nuclear restitution mechanisms that are important in breeding schemes.

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Dennis T. Ray, Joy J. Winzerling, and Michael E. Staten

Feedback from employers, internship supervisors, and graduate schools tells us that we are doing a good job of teaching students academically/technically, but our graduates require greater training in communications, critical thinking/problem solving, and leadership/management. Because of their long-term importance to our graduates, we call these “career skills.” To address this issue a task force was established, and over a 2-year period, this group defined the College of Agriculture and Life Sciences [CALS (University of Arizona, Tucson)] Students Career Skills Competencies and vetted them through college faculty and more than 50 companies. We divided the CALS Student Career Skills Competencies into three categories: 1) communication skills, 2) critical thinking/problem solving skills, and 3) leadership/management skills. We are currently asking each degree-granting unit in the college how they do, or will, incorporate these competencies into their curricula, with the idea of incorporating the competencies into existing courses first, to avoid increasing the number of required credit hours for graduation and time to degree. Our goal is that by graduation, each student should have had multiple opportunities to hone each of these competencies.

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Thomas J. Tworkoski, Michael E. Engle, and Peter T. Kujawski

A polypropylene fabric containing control-release pellets of the herbicide, trifluralin, can be oriented in the soil to regulate the distribution of plant roots. In 1990, trenches were dug near 10-year-old red oak (Quercus rubra L.) and 10-year-old yellow poplar (Liriodendron tulipifera L.) and fabric containing trifluralin control-release pellets and polypropylene fabric alone were installed vertically to redirect root growth. Roots grew alongside trifluralin fabric and fabric alone and did not penetrate either fabric 38 months after installation. Shoot growth of yellow poplar was reduced about 47% each year by the trifluralin fabric treatment compared to control. Red oak shoot growth was not affected by trifluralin fabric. Leaf water potential was not affected by treatment in either species. Trifluralin residues in trifluralin fabric decreased from 23.3% to 22.0% from July 1990 to October 1993. During this time, trifluralin levels increased from 0.4 to 3.6 mg·kg-1 in soil sampled 0 to 15 cm below trifluralin fabric. These results suggest that controlled-release trifluralin will provide persistent inhibition of root and shoot growth of some species and will not migrate significantly in the soil. Chemical names used: α,α,α-trifluoro-2,6-dinitro-N-N-dipropyl-p-toluidine (trifluralin).

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Haofeng Chen, Vanessa E.T.M. Ashworth, Shizhong Xu, and Michael T. Clegg

The authors report a quantitative genetic analysis of avocado (Persea americana Mill.) growth rate, flower abundance, and fruit set. The data are based on a total of 204 different genotypes of progeny of ‘Gwen’ avocado. Each was replicated four times, with two replicates planted in each of two locations in southern California (Irvine and Riverside). Data were collected over 4 years (consecutive) on tree height, canopy diameter, and trunk diameter, representing three distinct measures of growth rate. Growth data were found to fit a linear regression over years, so the slope (growth rate) was used in the analyses. In addition, 2 years of data on flower abundance and 1 year on fruit set were also collected. Quantitative genetic analyses of these data showed that broad-sense heritability (H) was 35.5%, 30.3%, and 26.6% for tree height, canopy diameter, and trunk diameter respectively; and 33.8% and 23.0% for flowering abundance and fruit set respectively. No genotype-by-location effect was noted for growth rate; however, flower abundance and fruit set showed a relatively weak genotype-by-location effect (21.9% and 17.1% respectively). The H estimates are low, probably as a result of sources of uncontrolled environmental error associated with variation in initial planting dates, but fall within the range that should permit quantitative trait locus analyses. The authors also found a moderate positive correlation between tree growth rates and fruit set, but none between growth rates and flower abundance. Different pollen parents have significantly different impacts on tree growth rates, flower abundance, and fruit set.

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Lauren C. Garner, Vanessa E.T.M. Ashworth, Michael T. Clegg, and Carol J. Lovatt

‘Hass’ avocado (Persea americana Mill.) is characterized by excessive flower and fruit abscission, resulting in extremely low fruit set. Low outcrossing rates might be a factor contributing to low yields. It is hypothesized that self-fertilized flowers and resulting fruit abscise at a much higher rate than fruit that are the product of outcrossing. However, significant relationships between outcrossing rates and yields have only been established in a few avocado studies. The objective of this research was to investigate the importance of outcrossing to yield in a commercial ‘Hass’ orchard containing ‘Bacon’, an effective pollinizer of ‘Hass’. Microsatellite markers were used to determine the rate of outcrossing of fruit persisting to harvest on ‘Hass’ trees. Experiments were conducted during sequential on- and off-crop years. During both years, outcrossing rates were not related to yield or alternate bearing. These results indicate that outcrossing was not the primary factor affecting flower and fruit persistence and ultimately yield in this orchard for the two sequential years of this research.

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T. Gregory McCollum, Hamed Doostdar, Michael Burkhart, Randall Neidz, Richard T. Mayer, and Roy E. McDonald

Inhibition of the growth of fungal pathogens has been related to levels of a β-1,3-endoglucanase (EC 3.2.1.39) (GLU) in citrus as well as other plant species. Our long-term objective is to transform Citrus spp. to express enhanced levels of GLU with the aim of increasing resistance to fungal pathogens. We have purified a β-1,3-endoglucanase from nonembryogenic Citrus sinensis (L.) Osbeck cv. Valencia callus to electrophoretic homogeneity by means of pH precipitation and ion exchange chromatography. The protein has an apparent M r of 32.5 and a pI > 10. The enzyme hydrolyzes laminarin (Laminaria digitata) optimally at pH 5 and 50°C. The enzyme will hydrolyze any glucan polymer with a β-1,3 linkage whether soluble or insoluble and the rate of hydrolysis is proportional to the relative abundance of β-1,3 linkages. The enzyme does not hydrolyze cellulose or starch. Product characterization by thin-layer chromatography indicates that the enzyme is an endohydrolase. Initial attempts to sequence the protein indicated that it was N-terminally blocked. Therefore the protein was hydrolyzed using AspN, the fragments separated by SDS-PAGE, blotted onto nitrocellulose, and one of the fragments was sequenced. Amino acid sequence analysis indicated that the protein shared homology with a number of β-1,3-endoglucanases. Antibody to the purified protein was raised in rabbits and used to screen an amplified cDNA library prepared from Citrus sinensis (L.) Osbeck cv. Valencia callus. One of the positive clones was selected and sequence analysis indicated that the clone was homologous with other β-1,3-endoglucanases.

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Carlos Calderón-Vázquez, Mary L. Durbin, Vanessa E.T.M. Ashworth, Livia Tommasini, Kapua K.T. Meyer, and Michael T. Clegg

Avocado (Persea americana) is a subtropical tree prized for its large and nutritious fruit. Although native to Mesoamerica, avocado is now grown in tropical and subtropical regions around the world, and consumer demand for avocado continues to grow at a considerable rate. Despite the appeal of avocado, its genetic improvement has been slow owing to substantial land and labor requirements combined with the fact that young trees do not produce fruit for several years and a pollination system that makes it difficult to produce genetic crosses. Molecular markers promise to accelerate the rate of breeding progress, especially for simple traits of high heritability. One of the distinguishing features of the avocado fruit is the presence of a number of compounds that have been linked to human health. As a prelude to the use of molecular markers for the improvement of nutritional traits, this article reports estimates of the heritability of carotenoids, β-sitosterol, and α-tocopherol content (the most biologically active form of vitamin E) in ripe avocado fruit. Each of these three compounds has been linked to beneficial health outcomes, and each is shown to have a sufficiently high heritability to predict successful marker-assisted selection.

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Sadanand A. Dhekney, Zhijian T. Li, Michael E. Compton, and Dennis J. Gray

Stamens and pistils from mature grapevines and leaves from in vitro micropropagation cultures were used to optimize parameters influencing somatic embryogenesis in Vitis. Embryogenic competence was dependent on species/variety, explant type and developmental stage, medium composition, and growth regulator concentration. Of varieties evaluated, a greater number produced embryogenic cultures from stamens and pistils (26) compared with leaves (six). Among the different stamen and pistil stages, Stage II and III explants produced the maximum embryogenic response regardless of genotype and medium composition. Of seven culture media tested, the highest embryogenic response was recorded from varieties cultured on MSI (18) and PIV (16) media. Experiments annually repeated over 3 to 10 years demonstrated reproducible results. Highly reliable protocols for somatic embryogenesis were obtained for 29 Vitis species and varieties, including 18 Vitis vinifera varieties, Vitis riparia, Vitis rupestris, Vitis champinii, and eight Vitis hybrids. Embryogenic cultures were maintained on X6 medium for a period of 6 months to 2 years depending on the variety and used in studies involving genetic transformation and transgenic plant regeneration.