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Curt R. Rom

Shoot growth `Starkspur Supreme Delirious' on 10 different rootstock was measured on 3-, 4- and 6-year-old trees at weekly intervals from budbreak until terminal bud formation. Spur density, spur development, and extension shoot leaf area development were measured in September. Growth rate was analyzed by regression against chronological time and accumulated growing degree days using linear and nonlinear statistics.

Rootstock affected shoot length, leaf number, leaf area, leaf size, leaf dry weight/leaf area and internode length. Trees on M.4, M.7 EMLA, P-1 and seedling had the longest shoots and highest shoot growth rate. Trees on P16 had least leaves and leaf area per shoot and smallest shoot leaves. Leaf dry wt./area were negatively correlated to leaf size. Typically, trees with shortest shoot length and smallest internode length had greatest spur density. Rootstock affected both rate and duration of shoot growth. Shoots on trees with P22 and P2 rootstocks grew for the shortest duration while trees on M.4 and M.7 EMLA grew for the longest period.

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Curt R. Rom

To enhance the opportunities for students to access information and the instructors of a large, general plant science class, “Virtual Classroom” concepts using computers resources were implemented. The Virtual Classroom uses three computer resources: 1) a closed subscription LISTSERV for the extramural class discussions, 2) electronic mail for homework assignment and submission, and 3) a World Wide Web Internet homepage for the course. In a large, introductory-level class, student–teacher interaction can be limited. The size of the class and the content may inhibit questioning and discussion among the class participants. The LISTSERV allowed for questions to be posed by students at their leisure and facilitated discussion among students and the instructor outside of the confines of the class meeting. The LISTSERV also allowed instructors to to respond to the students by referring questions to “experts” on a particular subject. Using e-mail for homework assignment and submission was useful for tracking when student read assignments and submitted completed assignments. Electronic assignment grading and returning was paperless and easy for instructors to maintain. The homepage provided students with a permanent syllabus, lecture outlines, homework assignment descriptions, and study aids. Additionally, from the homepage students were able to send e-mail to instructors and search library databases and other electronic databases. Experiences from the instructors using these computer resources will be presented and discussed.

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Curt R. Rom

Current practices of fertilizer management, potential problems, and paths for fertilizer management research were discussed. Apple nutrition management in the humid southern regions of the U.S. is typically challenged by several factors such as inherently low soil pH, variable soil chemistry, and irregular precipitation. Some literature and personal experiences with orchard replant conditions and fumigation, fertigation, fertilizer delivery system, and time of fertilizer application were reviewed. On replant sites, fumigation and liming significantly improved tree survival and growth in the first 5 years. Fertigation with ammonium nitrate significantly lowered soil pH in the root zone compared to top dress applications. Using calcium nitrate resulted in less pH reduction. Results of studies of autumn application of N fertilizers have been mixed, with reports of no, decreased, or increased effects on fruit set, yield, and growth. Studies with size-controlling rootstocks indicate additional need to study the uptake of Mn and related Mn toxicity. Precocious rootstocks with high early yields have resulted in foliar K levels approaching deficiency within the first 10 years of production. Indications are that high-density orchards may have additional requirements for K fertilizers.

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Jason McAfee and Curt Rom

Pesticides and alternative fruit thinners are needed for certified organic fruit growers. Transient reductions in photosynthesis (Pn) have proven an effective technique for fruit thinning. Pesticides can be detrimental to plant growth by Pn reduction. This study was developed to measure plant response to foliar applications of essential oils at 2% concentrations. Treatments were applied to vegetative apple trees grown under controlled environment conditions to study photosynthetic effects. There was no significant effect on Pn for treatments; however, clove oil was very phytotoxic and defoliated all trees in this study. Cinnamon oil and cedarwood oil significantly decreased evapotranspiration and stomotal conductance 1 day after treatment. Differences in plant growth were not significantly different for all treatments excluding clove oil. Studies on concentration effects may determine horticultural usefulness of these compounds.

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Curt R. Rom

As part of the NC-140 rootstock evaluation trials, `Starkspur Supreme Delicious' on 18 rootstocks planted in 1984 were evaluated for growth and pruning requirement. After 9 seasons, trees on the P.22 produced the smallest trees, 1.1 m width and 1.7 m height. The stocks P.16, P.2 and Bud.9 produced trees 2.0-2.2 m wide and 2.1-2.6 m tall. Trees on MAC.39, C.6, MAC 1, M.26 EMLA P.1, BUD.490, M.7 EMLA, CG.24, and domestic seedling were 2.9-3.4 m wide and 3.7-4.3 m tall. The largest trees were on P.18 and M.4; 3.6 m wide and 4.2 m tall. Dormant pruning time in two seasons significantly increased at an exponential rate with increasing tree width and height. An asymptote for maximum pruning time had an x-axis intersection at approximately 2.7 m tree height. Pruning time per tree significantly increased in a linear manner with increasing trunk cross section. When pruning time was calculated on a per hectare basis, trees planted at 1460 to 2000 trees/ha required less pruning time than when planted at ≤ 750 tr/ha or ≥ 4000 tr/ha. Trees on P.16, P.2, Bud.9 and C.6 required the least pruning per unit of fruit production.

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Curt R. Rom*

In a required introductory horticulture course during a 5-year period, students received early progress grades 1/3rd of the way through the course reflecting 20% of the possible points to be awarded in the class. It was thought that student knowledge of their grade performance may result in changes in behavior and class performance. The early progress and final grades both had a bell-shaped distribution with 45% and 48% of students receiving grades better than “C” for early progress and final grades, respectively. There was a significant although low correlation between early progress grades and final grades for the course (r 2 = 0.58). About 50% of the students received a final grade equal to the early progress grades, and 27% received grades higher than the early progress grades. The greatest change in performance were students who received a “D” early progress grade; 60% of those students improved their final grade. Nearly 25% of the students received final grades lower than the early progress grades. Of students receiving failing early progress grades (12%), nearly 60% withdrew from the course and only 10% received passing final grades.

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Renae E. Moran and Curt Rom.

Greenhouse grown `Lawspur Rome'/M.111 trained to single shoots were given the following shade (73%) treatments: 1) sun-all-day (control), 2) shade in the morning (am-shade), 3) shade in the afternoon (pm-shade) and 4) shade-all-day. All shade treatments increased shoot length and decreased dry weight/leaf area (DW/LA). Shade-all-day increased leaf no., LA/leaf and shoot dia. DW partitioning to leaves in shade-all-day was 19% greater than control and to roots was 34% less than control. Pn of am-shade did not increase in the afternoon when PFD was maximal. Saturated net photosynthesis (Pn) was 72% of control in am-shade, 84% of control in pm-shade and 62% in shade-all-day. Shade reduced Pn by 40% of control.

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Curt R. Rom and Bruce Barritt

The role of spur leaves in bud and fruit development on two spur-type `Delicious' apple strains (Malus domestica Borkh.) and factors affecting spur development were studied. Reducing spur leaf area on vegetative spurs in August reduced the number of spurs that flowered the following year but did not affect flower size. On spurs that did flower, leaf area reduction the previous year did not influence leaf number or area, but the bourse shoot leaf area was reduced. Spur bud diameter, leaf area, size, specific leaf weight (SLW), and leaf dry weight were larger on 2-year-old vegetative spurs than on 1- or 3-year-old spurs. Within each age section of a limb, spur leaf number, area, size, SLW, and bud diameter decreased from the apical to basal positions on the limb. Flower number did not vary within a limb section, but fruit set was lower on the most apical and basal spurs compared to midshoot spurs. Fruit size was largest at the apical end of each limb section and was smallest at basal positions. These relationships were not affected by strain, tree age, or orchard location. Summer pruning at 30 days after bloom tended to increase leaf number, area, size, and spur length compared to unpruned trees or pruning later in the season but did not influence spur bud diameter.