Controlling Cropping in `Loadel' Cling Peach Using Gibberellin: Effects on Flower Density, Fruit Distribution, Fruit Firmness, Fruit Thinning, and Yield

Abstract

<jats:p>Whole-tree sprays of Release LC [predominantly gibberellic acid] (GA,) were applied in a commercial peach <jats:italic>[Prunus perisca</jats:italic> (L.) Batsch.] orchard in the California Central Valley on three dates from mid-June (about 90 days after full bloom = 28 days before harvest) to late July (14 days postharvest) 1993 at 50, 75, 100, and 120 mg·liter<jats:sup>-1</jats:sup>. Gibberellin (GA) reduced the number of flowers differentiated in 1993, thereby reducing fruit density in 1994, when sprays were applied by early July 1993. Sprays in late July did not reduce flowering and fruiting density in the following year. In 1994, there were fewer fruit located on the proximal third of the shoot after GA sprays of 75,100, and 120 mg-liter' applied on 15 June compared to hand-thinned controls, and reduction was linear with increase in GA rate. Fruit numbers in the middle and distal sections of shoots were reduced by all 15 June and some 9 July GA sprays, with fewer fruit as concentration increased. However, the distribution of fruit within shoot sections, after GA treatments during floral differentiation, expressed as a percentage of the total number of fruit along fruiting shoots, showed even fruiting compared with hand thinning. Due to reduced flowering in response to GA treatments in June and early July 1993, the hand-thinning requirement was significantly reduced, with no thinning required in 1994 from 15 June 1993 GA sprays. All sprays applied in early July resulted in 40% to 60% fewer fruit removed during thinning than the nontreated controls. Sprays in late July were ineffective. Sprays of GA applied in mid-June at 50,75, 100, and 120 mg·liter and sprays of 120 mg·liter<jats:sup>-1</jats:sup> GA applied in early July (4 days preharvest) increased the firmness of `Loadel' cling peach (about 26% improvement in June sprays) in 1993. The salable yield of fruit (after removal of the undersized fruit) was the same on hand thinned and on non-hand thinned trees treated with GA on 15 June at 50 mg·liter<jats:sup>-1</jats:sup>. The salable yield of fruit was increased by GA sprays of 50 and 75 mg·liter applied on 9 July 1993 compared to controls. There were no differences in fruit size (by weight or diameter) among the aforementioned treatments and hand thinning. GA sprays of 75,100, and 120 mg-liter' applied on 15 June 1993 tended to reduce salable yield, but fruit size increased with decreased yield. Based on the results obtained in 1993 and 1994, we believe that Release LC has good potential for chemically thinning peaches in California.</jats:p>

Effects of gibberellic acid treatments on fruit thinning and fruit quality in Japanese plum (Prunus salicina Lindl.)

“…GA 3 treatments applied 7 WAA were reported to have moderate effects on fruit setting, while those applied 10 WAA were less effective; however, treatments conducted 13 WAA had the greatest effect, reducing fruit set by two-to threefold in comparison to that of control plants (Coneva and Cline, 2006). Hand-thinning requirements in the year after treatment were reported to be significantly reduced by the application of GA 3 sprays at 13 and 16 WAA, but thinning was not required at all for peach trees treated with GA 3 at anthesis (Southwick et al, 1995b). The present study demonstrated that as the concentration of GA 3 increased, the number of fruits in the following year's harvest decreased.…”

“…Gibberellins are thought to move from the fruit toward the nearest internode, thereby inhibiting the formation of fresh fruit buds 6-8 weeks after fruit setting (Webster and Spencer, 2000). Gibberellic acid treatment has been applied in apples (McArtney andLi, 1998), avocados (Salazar-García and, mangoes (Turnbull et al, 1996), citrus fruits (El-Otmani et al, 2000), apricots (Southwick et al, 1995a(Southwick et al, , 1997Southwick and Yeager, 1993), loquat (Reig et al, 2011), peaches and nectarines (Taylor and Geisler-Taylor, 1998;García-Pallas et al, 2001;Coneva and Cline, 2006;González-Rossia et al, 2007;Stern and Ben-Arie, 2009;Southwick et al, 1995b) and Japanese plums (González-Rossia et al, 2006).…”

GA3inhibits flowering, reduces hand-thinning, and increases fruit size in peach and nectarine

“…However, since fruit thinning with chemical thinners in stone fruit is not as commercially efficient as in pome fruit (Byers et al, 2003), it became necessary to examine different concepts for fruit thinning at a much earlier stage of development, for example when flowering was initiated. Southwick et al (1995) found that GA 3 sprays on 'Loadel' cling peach trees at 90 DAFB reduced fruit yield in the following year. Gonzalez-Rossia et al (2007) also found similar trends in some Spanish peach and nectarine cultivars, although, like Southwick et al (1995), they had to use a high rate of GA 3 (≤ 100 mg l -1 GA 3 ) for good results.…”

“…However, hand-thinning is costly, and generally requires between 100 -500 h ha -1 , depending on tree vigour, age, size, flower production, thinning intensity, cultivar, and season (Southwick et al, 1995;1996). Alternative thinning techniques, such as mechanical approaches, chemical thinners (Byers et al, 1990;2003;Moran and Southwick, 2000;Fallahi et al, 2006), and inhibitors of photosynthesis (Byers et al, 1984), have been examined as substitutes for handthinning, but the thinning results were variable in stone fruit (Byers et al, 2003).…”

“…Reducing flower initiation has been proposed as an alternative strategy to hand-thinning in stone fruit such as apricot (Southwick et al, 1997), Japanese plum (Gonzalez-Rossia et al, 2006), and peach (Southwick et al, 1995;GonzalezRossia et al, 2007). All of these studies showed that the concentration and timing of GA 3 application affected the efficiency of GA 3 in inhibiting flower formation in stone fruit.…”