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J. L. Green, J. Matylonek, A. Duncan, and E. Liss

HortBase, a global electronic information system for classroom, distance education, lifelong learning and Extension, incorporates three innovative concepts: 1) Three-dimensional team-creation of the electronic information files (subject, communications, and information science authors working together from start to finish to create the file). Team-creation respects, uses, and develops the professional strengths of each of the three team members. 2) National peer review by each file creator's professional society (ASHS, ACE, and ASIS, respectively) not only enhances information quality and continued professional development of the authors, but also creates wider acceptance and use of the information. 3) Nationwide, or even worldwide, distribution of the workload and costs of creation, review, revision, and distribution of the electronic information, rather than individual efforts-expenditures within each state, will minimize redundancy and will enable us to do more as a group and to specialize individually. Capabilities of electronic information systems facilitate, indeed require, this new approach to information development and delivery.

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Edwin J. Reidel, Patrick H. Brown, Roger A. Duncan, and Steven A. Weinbaum

Almond [Prunus dulcis (Mill.) D.A. Webb] yields have increased substantially since the 1961 publication of the Univ. of California (UC) guidelines for leaf potassium (K). Numerous growers and reputable analytical laboratories are concerned that the recommendations for leaf K are inadequate. A highly productive almond orchard with low leaf K was selected to reassess the leaf K critical value of 1.1% to1.4% and determine the relative sensitivity of various yield determinants to inadequate K availability. Baseline yields for 100 individual trees were measured in 1998 and four rates of potassium sulfate were applied under drip irrigation emitters to establish a range of July leaf K concentrations between 0.5% and 2.1%. No relationship was observed between leaf K and post-treatment yield measurements made in 1999. We also monitored individual limb units on trees from the treatment extremes for effects of low K availability on flower number, percentage fruit set, fruit size, spur mortality, and vegetative growth (potential fruiting sites in subsequent years). Those measurements indicated that although current-year yield determinants (percentage fruit set and fruit size) were not influenced by K deficiency, components of future yield were impacted negatively by low K availability: mortality of existing fruiting spurs was increased by K deficiency and growth of fruiting wood was reduced.

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J.L. Green, D. Hannaway, J. Matylonek, A. Duncan, E. Liss, and K.J. Starr

HortBase, a global electronic information system to support horticultural decisions in classroom, distance education, life-long learning, and Extension, incorporates three innovative concepts: 1) Three-dimensional-team creation of individual electronic information files (subject, communications, and information science authors collaborating from start-to-fi nish to create the file). Team-creation respects, utilizes and develops professional strengths and resources of each team member. 2) Nation-wide, or even world-wide, distribution of the workload and costs of creation, review, revision, and distribution of the individual electronic information files, rather than redundant individual efforts and expenditures, enables us to do more as a group and to specialize individually. And, 3) National peer review by each file creators' professional society (ASHS, ACE, and ASIS respectively) enhances information quality, continued professional development of the authors, and wider acceptance and use of the information. Capabilities of electronic information systems facilitate, indeed require, this new approach to information development and delivery. For additional information, http://forages.css.orst.edu/HortBase/.

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Jason A. Ferrell, Timothy R. Murphy, Ron R. Duncan, and William K. Vencill

The usage of seashore paspalum (Paspalum vaginatum Swartz) as a recreational turf has increased in recent years. On similar species, such as bermudagrass (Cynodon ssp.), plant growth regulators (PGRs) are used to decrease mowing frequency. However, no data currently exists for the use of PGRs on seashore paspalum. Therefore, field experiments were conducted over 2 years to determine the effects of trinexapac-ethyl and paclobutrazol on seashore paspalum. Paclobutrazol was non-injurious to turf when applied sequentially, 4 weeks apart, at rates as high as 0.56 kg·ha-1 of a.i. However, these same treatments failed to reduce vegetative growth. Conversely, trinexapac-ethyl treatments produced unacceptable injury (>15%) when applied sequentially, 4 weeks apart, at rates higher than 0.19 kg·ha-1 of a.i. As trinexapac-ethyl rates were reduced to ≤0.14 kg·ha-1 of a.i., injury was reduced to ≤ 12% while vegetative growth was suppressed to ≥59%, relative to nontreated seashore paspalum. Therefore, trinexapac-ethyl can serve as an effective option for those managing seashore paspalum turf areas. Chemical names used: 4-(Cyclopropyl-α-hydroxymethylene)-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl); (+/-)-R *,R *-β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazol-1-ethanol (paclobutrazol).

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T.J.K. Radovich*, R.C. Pratt, L.A. Duncan, N. Welty, and M.D. Kleinhenz

Cucurbita maxima and C. pepo are difficult to hybridize, and it was our objective to generate F1 hybrids between ornamental cultivars of the two species. C. maxima `Lakota' and C. pepo `Jack O'Lantern'; and `OZ'; were selected as parents. `Lakota' (L) is an heirloom, hubbard-type cultivar producing pear-shaped, red-orange fruit with dark green mottling, `Jack O'Lantern'; (J) is an open-pollinated Halloween-type pumpkin cultivar and `OZ' is a Halloween-type hybrid. Sixteen plants of each cultivar were greenhouse-grown in a CRB design during the period July-Sept. 2003. Interspecific crosses were made in both directions, with intraspecific crosses (J × O) and selfs (L) serving as controls. Fruits were harvested about 20 d after pollination. Embryos were excised under aseptic conditions and grown on either full strength Murashige and Skoog (MS) media with 6% sucrose (S6), full strength MS media with 6% maltose (M6), or half strength MS media with 3% sucrose (S3). Fruit set was generally greater in the intraspecific crosses (33%) and selfs (67%) than in the interspecific crosses (15 %), with the notable exception of the interspecific combination L × J (85% fruit set). Embryos of interspecific and control crosses were about 1.5mm and >1cm long, respectively. Hypocotyl and root growth 10 d after plating was better on S3 (3.2 and 1.7 cm) than on S6 (1.6 and 0.25 cm) or M6 (0.35 and 0 cm), and a greater number of functional hybrids were obtained from embryos grown on S3 (6 plants) than on S6 (2 plants) or M6 (2 plants). The interspecific plants were backcrossed to one of the parents and novel combinations of shape, color and variegation in hybrid fruit were observed.

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Kendra Baumgartner, Phillip Fujiyoshi, Craig Ledbetter, Roger Duncan, and Daniel A. Kluepfel

Prunus dulcis (almond) is one of the most susceptible horticultural crops to Armillaria root disease. Resistance to Armillaria mellea and Armillaria tabescens, the geographically isolated causal fungi that attack almond and closely related Prunus persica (peach), has been evaluated in studies of almond, peach, and other Prunus rootstocks, but not in one comprehensive study. We evaluated the relative resistance to A. mellea and A. tabescens of six clonally propagated almond and peach rootstocks (Bright’s 5, Empyrean 1, Hansen 536, Krymsk 1, Krymsk 86, and Lovell) in comparison with that of clonally propagated Marianna 2624 rootstock (resistant control) and clonally propagated Nemaguard rootstock (susceptible control). Replicate clones used in the growth chamber assay were micropropagated and rooted in vitro before inoculating the culture medium with Armillaria spp. At 2 months, the most resistant and susceptible rootstocks were Krymsk 86 and Hansen 536, respectively, with 27% vs. 89% mortality. This finding was consistent among two isolates of A. mellea and one isolate of A. tabescens in three replicate experiments. Our finding of low mortality among Krymsk 86, Krymsk 1, and Marianna 2624, which all share Prunus cerasifera (Myrobalan plum) parentage, is consistent with past reports of resistance in the field to A. mellea, but conflicts with reports of susceptibility to A. tabescens. Resistance to A. tabescens of genotypes with Myrobalan plum parentage in our assay may reflect the simplified rooting environment of tissue culture medium, which does not perfectly mimic a field trial, in which biotic and abiotic factors may affect host resistance. Nonetheless, our growth chamber assay may provide a more rapid alternative to identify sources of resistance for breeding and to screen progeny of such crosses.

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Bridget M. Lamp, Joseph H. Connell, Roger A. Duncan, Mario Viveros, and Vito S. Polito

Scanning electron microscopy was used to examine almond [Prunus dulcis (Mill.) D.A. Webb (syn. Prunus amygdalus Batsch, Amygdalus communis L.)] flower bud development for three cultivars (Nonpareil, Carmel, and Butte) from four California locations (which span the range of almond production in California) for 2 years, and for `Nonpareil' in a single location for a third year. The objectives were to document timing of floral developmental events and to better understand the extent of variation that exists within and among cultivars, locations, and years. Results indicated that the time of floral initiation relative to hull split varied among cultivars. Median time for floral initiation in `Nonpareil' was more than 3 weeks after the onset of hull split. For `Butte' and `Carmel', median time of floral initiation preceded the onset of hull split. Extensive variation in the timing of bud development events within a cultivar was apparent. Timing of developmental events varied among locations, but no patterns emerged consistent with the north to south range which spanned 4°15' latitude and 520 km. Among years, development occurred earliest in 1997, a relatively warm year, and was delayed in 1998 and 1999, relatively cool years. Results indicate an earlier onset of floral initiation than reported in the classical literature on the subject.

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T. Auxt Baugher, J. Schupp, K. Ellis, J. Remcheck, E. Winzeler, R. Duncan, S. Johnson, K. Lewis, G. Reighard, G. Henderson, M. Norton, A. Dhaddey, and P. Heinemann

Hand thinning is a necessary and costly management practice in peach (Prunus persica) production. Stone fruit producers are finding it increasingly difficult to find a workforce to manually thin fruit crops, and the cost of farm labor is increasing. A new “hybrid” string thinner prototype designed to adjust crop load in vase or angled tree canopies was evaluated in processing and fresh fruit plantings in varying production systems in four U.S. growing regions in 2009. Data were uniformly collected across regions to determine blossom removal rate, fruit set, labor required for follow-up green fruit hand thinning, fruit size distribution at harvest, yield, and economic impact. String thinner trials with the variable tree forms demonstrated reduced labor costs compared with hand-thinned controls and increased crop value due to a larger distribution of fruit in marketable and higher market value sizes. Blossom removal ranged from 17% to 56%, hand thinning requirement was reduced by 19% to 100%, and fruit yield and size distribution improved in at least one string-thinning treatment per experiment. Net economic impact at optimum tractor and spindle speeds was $462 to $1490 and $264 to $934 per acre for processing and fresh market peaches, respectively. Case study interviews of growers who thinned a total of 154 acres indicated that commercial adoption of string-thinning technology would likely have positive impacts on the work place environment.