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Warren E. Shafer, Gregory Clarke, Robert Fritts Jr., and Derek Woolard

ReTain™ is an organic, water-soluble formulation that contains 15% (w/w) of aminoethoxy-vinylglycine (AVG). AVG, a naturally occurring plant growth regulator, competitively inhibits ACC (1-aminocyclopropane-1-carboxylic acid) synthase, the enzyme responsible for the conversion of S-adenosylmethionine (SAM) to ACC, the immediate precursor of ethylene in plants. ReTain has been under commercial development for the past 6 years, which includes U.S. EPA-approved Experimental Use Permit (EUP) programs in 1995 (Shafer et al., 1996, Proc 23rd Annu. PGRSA Mtg., p. 233–234) and 1996. Under the 1996 EUP, ReTain was tested on nearly 4000 acres of apples in 18 states. When used according to label directions (i.e., 50 g AVG/acre applied 4 weeks before anticipated harvest) with a nonionic surfactant, ReTain effectively reduced preharvest drop and generally resulted in fruit of higher quality than untreated (control) or naphthaleneacetic acid (NAA) -treated fruit. ReTain can delay fruit maturity (as indexed by starch conversion) by ≈7 to 10 days. ReTain-treated fruit were typically firmer (by 0.5 to 1.0 lb), produced significantly less ethylene, and maintained notably greater firmness through storage. The incidence and severity of watercore in `Delicious' was significantly reduced by ReTain, as was the frequency of fruit cracking in `Fuji' and `Gala' in several trials. Based on this benefit profile, ReTain can be an effective harvest management tool for apple growers. U.S. EPA approval for the commercial registration of ReTain is anticipated prior to the 1997 use season.

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Derek D. Woolard*, Judy Fugiel, F. Paul Silverman, and Peter D. Petracek

Tables, graphs, and photographs can effectively convey detailed results of a PGR experiment. However, we have observed that demonstrating PGR treatment effects by time-lapse video creates a strong impact on both scientists and non-technical audiences. Time-lapse video also provides a method for obtaining a continuous visual record that can be used to establish the precise chronology of a slow process. Recent advances in notebook computers, inexpensive digital cameras (e.g. 3Com HomeConnect™), and time-lapse software (e.g. Picture WorkLive™) allow scientists and teachers to inexpensively prepare time-lapse videos. Important considerations for the production of quality time-lapse videos include: 1. treatment effects should be substantial, consistent, and visible, 2. digital camera images should be clear, 3. lighting should be constant and provide adequate brightness and proper color, 4. camera movement such as those due to vibrations should be minimal, 5. camera placement should simplify composition. Time-lapse videos of PGR treatment effects will be shown, and methods of production will be discussed.

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Steven J. McArtney, Suzanne R. Abrams, Derek D. Woolard, and Peter D. Petracek

Fruit set of apple can be reduced by cloudy weather, short-term shade treatments, or application of photosynthetic inhibitors when the young fruit are ≈8 to 15 mm in diameter, indicating that fruit are sensitive to a transient carbohydrate stress during this period. We investigated the potential for S-abscisic acid (ABA) and an ABA analog [(+)-8′-acetylene ABA] to chemically thin apple fruit by causing a stomatal limitation of photosynthesis. Stomatal conductance (g S) of ‘Imperial Gala’/M.7 was reduced by 60% 3 h after application of 250 mg·L−1 ABA or 25 mg·L−1 (+)-8′-acetylene ABA. Stomatal conductance began to recover 4 days after application but did not return to control levels until 19 days after treatment. Application of 250 mg·L−1 ABA combined with 100 mg·L−1 6-benzyladenine (6-BA) when mean fruit diameter was ≈10 mm reduced fruit set of ‘Gala’/M.7 but not ‘Pink Lady™’/M.7 or ‘Morganspur Delicious’/MM.111. Fruit set of ‘Pink Lady™’/M.7 was reduced by application of 20 mg·L−1 (+)-8′-acetylene ABA + 100 mg·L−1 6-BA at full bloom or 10 mg·L−1 (+)-8′-acetylene ABA + 100 mg·L−1 6-BA at the 10-mm fruit diameter stage. Fruit set of ‘Morganspur Delicious’/MM.111 was reduced by application of 25 mg·L−1 (+)-8′-acetylene ABA, either alone or in combination with 75 mg·L−1 6-BA, at the 10-mm fruit diameter stage. ABA and (+)-8′-acetylene ABA triggered leaf abscission at rates above 250 mg·L−1 and 25 mg·L−1, respectively. Fruit set and g S data from the present studies indicate the biological activity of (+)-8′-acetylene ABA is 10-fold higher than ABA. These results suggest that ABA and (+)-8′-acetylene ABA reduced fruit set by causing a stomatal limitation in photosynthesis that resulted in a transient carbohydrate stress. Thinning responses to ABA and (+)-8′-acetylene ABA at the concentrations used in these experiments were reduced compared with standard concentrations of currently available chemical thinning agents. However, increasing the concentration of ABA or (+)-8′-acetylene ABA to levels that would achieve comparable thinning are also likely to result in unacceptable leaf abscission.

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Warren E. Shafer, Gregory Clarke, Robert Fritts Jr., Ricardo Menendez, and Derek Woolard

Aminoethoxyvinylglycine (AVG) is a naturally occurring plant growth regulator that was first patented in 1973 (US patent #3,751,459). AVG has been shown to competitively inhibit ACC (1-aminocyclopropane-1-carboxylic acid) synthase (Yu et al., 1979, Arch. Biochem. Biophys. 198:280–286), which is the enzyme responsible for the conversion of S-adenosylmethionine (SAM) to ACC, the immediate precursor of ethylene in plants. Because of this unique mode of action, AVG has been tested over the years on a wide array of plant tissues. Studies on plants of horticultural interest have included cut flowers (e.g., Baker et al., 1977 HortScience 12:38–39), greenhouse crops (e.g., Saltveit and Larson, 1981, J. Amer. Soc. Hort. Sci. 106:156–159), and tree fruits (e.g., Bangerth, 1978, J. Amer. Soc. Hort. Sci. 103:401–403). AVG is currently being developed by Abbott Laboratories for use on apples (e.g., Shafer et al., 1995, Proc. 22nd Annu. PGRSA Mtg, pg 11–15). This presentation: a) briefly reviews prior literature regarding the effects of AVG on apples, b) provides an update on Abbott's commercial development program, and c) outlines some near-term research objectives for the use of AVG on apples.