"Gibberellin Inhibits Fruit Abscission Following Seed Abortion in Peach"
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J. AMER. Soc. HORT. SCI. 115(1):107-110. 1990. Gibberellin Inhibits Fruit Abscission Following Seed Abortion in Peach G.W. Stutte and J. Gage Department of Horticulture, University of Maryland, College Park, MD 20742 Additional index words. fruit set, GA3, GA4+7 , fruit development, parthenocarpy, Prunus persica Abstract. Seed coats of developing fruit of peach [Prunus persica (L.) Batsch CVS. Redkist, Redskin, and Loring] were punctured at 31, 33, and 38 days after full bloom (DAFB), respectively. Injections of water, 390 mg GA3/liter, or 390 mg GA4+7/liter were made immediately following seed puncture. Seed puncture and water injection following puncture resulted in abscission of all fruit. Injection of GA3 and GA4+7 delayed abscission of ‘Redkist’ and ‘Redskin’ fruits of punctured seeds by 6 to 10 days. Both GA treatments resulted in normal growth into Stage II and increased fruit retention through Stage III in ‘Loring’. About 100 µl of 250, 500, or 1000 mg GA3/liter was injected into the locule of ‘Loring’ fruits following seed puncture at 30, 40, or 50 DAFB. GA treatments at 30 DAFB resulted in 75% fruit set in comparison to seeded control fruit, while fruit treated at 40 and 50 DAFB abscised by the end of Stage II. Increasing GA concentration from 250 to 1000 mg·liter-1 had no additional effect. Movement of the GA was 3 examined by injecting H-GA1 into the locule following the puncture treatment. More than 97% remained in the fruit after 96 hours. The percentage of 3H recovered in the seed cavity decreased over time, whereas recovered label increased in both endocarp and mesocarp. The results suggest a potential regulatory role for seed-produced gibber- ellins during early Stage I of development. We have identified an apparent change in tissue sensitivity to gibberellin induction of seedless fruit development between 30 and 40 DAFB in ‘Loring’ peach. Peach fruit development is recognized to have three stages of II by rapid development of the embryo and hardening of the development (Connors, 1919). Stage I is characterized by rapid endocarp, and Stage III by rapid mesocarp expansion (final swell). growth of the pericarp and limited embryonic development, Stage Cultivars differ in the length of each phase, with early and late- season cultivars differing chiefly in the duration of Stage II (Tukey, 1936). Extensive physiological, biochemical, and mor- Received for publication 26 Apr. 1988. Scientific Article no. A-4792. Contri- phological changes occur during early seed development (Stage bution no. 7813 of the Maryland Agricultural Experiment Station, College Park. I) (Thorne, 1985; Zucconi, 1983). The role of growth sub- We thank the Fruit Laboratory, USDA, Beltsville, Md., for the use of plant stances in fruit set and development of peach has been reviewed material and Chic Nishijima, Dept. of Pomology, Univ. of California, Davis, 3 by, among others, Nitsch (1953), Powell and Pratt (1966), for the gift of H-(3,4) gibberellin A1. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this Luckwill et al. (1969), Crane (1969), and Zucconi (1983). paper therefore must be hereby marked advertisement solely to indicate this Small, parthenocarpic fruit generally abscise by late Stage I fact. J. Amer. Soc. Hort. Sci. 115(1):107-110. 1990. 107 (Crane, 1963). Abscission of some fruit (“June drop”) occurs DAFB). Regression analysis was performed following log (x– 1) at the onset of Stage II. Tukey (1936) found that killing the transformation of the percent set data. 3 embryo during early Stage II, but not during late Stage II or Transport of H-(3, 4) gibberellin A1. At 38 DAFB, fruiting Stage III, caused fruit abscission of several peach and cherry shoots of ‘Loring’ were excised and brought into the laboratory cultivars. He concluded that fruit set and development are de- and the bases were recut and placed into water. About 0.5 µCi 3 -1 pendent on a viable ovule. of H-(3,4) gibberellin Al (30 Ci·mmol ; 1 Ci = 37 GBq) Parthenocarpic peaches can be induced to set and develop if was injected into the fruit following the puncturing of the em- sprays of GA3 >250 ppm are applied from 50% full bloom to bryo, as described above. GA1 was chosen as the tracer because 7 days after full bloom (DAFB)(Crane, 1963). Stutte (1985) it is the active gibberellin in various model systems (MacMillan found a 15% increase in fruit set over seeded fruit when GA3 and Phinney, 1987). A single fruit was removed from each of was injected into the ovule following embryo abortion 23 DAFB three single-shoot replicates at 48 and 96 hr and separated into in ‘Biscoe’ peach. seed, pericarp, petiole, and stem tissues. To minimize cross- We sought to further examine the role of the seed in early contamination of tissue samples with 3H during excision, the peach fruit development. We hypothesized that gibberellins will tissue at the point of injection was discarded and the scalpel substitute for a Stage I seed and permit normal fruit set and rinsed three times in 100% methanol before excising a different development. Our objectives were to test the effect of time of tissue. GA application and concentration, the response of cultivars to Tissues were homogenized in 80% methanol (MeOH) using GA under orchard conditions, and determine the movement of a mortar and pestle and centrifuged at 17,000 × g for 20 min, GA following application. and the supernatant saved. The pellet was resuspended two more times in 80% MeOH, then centrifuged, and the supernatants were combined. The remaining pellet was resuspended in a scin- Materials and Methods tillation vial with a minimal volume of 100% methanol. After Seed abortion. Six-year-old trees of the mid- to late-season the samples were taken to dryness a centrifugal rotary evapo- ‘Loring’, ‘Redskin’, and ‘Redkist’ peaches growing in the or- rator (Savant Speed-Vac, Farmingdale, N.J.), 10-ml scintilla- chards of the USDA/ARS, Beltsville, Md., were used in these tion cocktail (PCS, Amersham, Arlington Heights, Ill.) was experiments in 1986. A randomized block design consisting of added, and then the samples were counted in an Intertechnique three replicates of five trees per replicate was used for each SL30 scintillation counter. Quench correction was obtained using cultivar, for a total of 15 trees per cultivar. Uniform branches the external standard method. (> 3 cm at basal end) around each tree were selected for each treatment, and fruits were thinned to three per shoot; the middle Results fruit on each shoot was tagged for treatment. Five treatments Seed abortion. All puncture and injection treatments resulted were applied on 8 May 1986, a date that corresponded to 31 in fruit abscission of ‘Redskin’ and ‘Redkist’ by the end of Stage DAFB for ‘Redskin’, 33 DAFB for ‘Redkist’, and 38 DAFB II (Fig. 1 a and b). Injection of water had little effect, whereas for ‘Loring’. The treatments were a seeded control, seed punc- both GA treatments delayed the onset of abscission by several ture, and seed puncture with injection of GA3 or GA4+7, both days. In ‘Loring’, fruit abscission was not affected by injection at 390 mg·liter –1 or of water (100 µl each). Each treatment of water, but both GA treatments inhibited fruit abscission through was repeated three times on each tree for a total of 45 sample Stage I; 68% of the GA3-treated and 42% of the GA4+7-treated fruit per treatment. fruit being retained 5 weeks after treatment. The injections were made with a 1.27-cm 25-gauge needle. Although not obvious from Figs. 1 or 2, a decrease in growth The seed coat was ruptured by an initial puncture made through rate of ‘Loring’ fruit was observed within 4 days of seed punc- the basal end into the locule, while injection of 100 µl of GA ture unless GA was injected. Periodic sectioning of a population or water was made at the apical end with a second puncture into of seeded fruit indicated that the decline in rate of growth in the locule. The initial puncture reduced pressure build-up as- non-abscising fruits corresponded to the onset of Stage II (Fig. sociated with the injections and acted as a channel of escape for 2). Abscission of fruit was unrelated to initial fruit size. Thirty- the 50 to 100 µl of liquid endosperm that was forced from the seven percent of the GA-treated fruits developed to maturity endocarp by the injection. It is assumed that the 100 µl of GA and ripened 2 weeks before seeded controls. These fruits ap- was injected into the locule. Vernier calipers were used to mea- peared slightly elongated during Stage I and Stage II, but were sure the cheek diameter of all non-abscising fruit every 3 days similar in shape to seeded fruit at harvest. through Stage II, and weekly thereafter. The date of abscission GA3 partially counteracted the effect of seed puncture on of each tagged fruit was recorded. abscission when injected at 30 DAFB (Fig. 3). By the end of Experiments were conducted in 1987 at the Wye Research Stage II (64 DAFB), all the embryo-aborted fruit not treated and Education Center, Queenstown, Md. on 4-year-old ‘Loring’ with GA had abscised, irrespective of treatment date. Gibber- peach trees. To determine the effect of timing and GA concen- ellin application at 30 DAFB resulted in 75% fruit retention, tration effects, fruit were injected at 30, 40, or 50 DAFB with relative to seeded controls. The GA injections at 40 and 50 100 µl of 0, 250,500 or 1000 mg GA3/liter, as described above.