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Robert Fritts Jr. and Daniel L. Ward

Release LC (Abbott Laboratories), a commercial formulation of gibberellins, was applied to apricot, cling peach, freestone peach, nectarine, and plum varieties. Application was by commercial airblast sprayer. Fruit firmness was increased in the season of application in all crops. Meta analysis of the data indicated a maximum response for each crop differed over the rate range of 16 to 48 g a.i./acre. Changes in fruit soluble solids were slight. No differences in fruit color were observed. Reduction in flower bud density (thinning) was observed the following season. The reduction in bud density reduced the time required to hand-thin to a commercially acceptable level. A difference in thinning sensitivity to gibberellin was evident between crops.

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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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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.