Peach and apple thinning by shading and photosynthetic inhibition

Induction and Characterization of Fruit Abscission during Early Physiological Fruit Drop in Citrus

“…Many tree treatments, such as defoliation, shading, and girdling, have been applied to investigate the mechanism of fruit abscission. Defoliation (Mehouachi et al, 1995) and shading (Byers et al, 1990) decreased photosynthetic activity, whereas girdling blocked photoassimilate transport from leaves to roots, thus increasing carbohydrate availability to the growing fruits (Yamanishi, 1995). Sucrose supplementation increased citrus fruit set (Iglesias et al, 2003).…”

“…Defoliation reduces the number of leaves (Mehouachi et al, 1995) and shading induces a reduction in photosynthetic activity (Byers et al, 1990), resulting in increased fruit abscission. Girdling treatment reduces fruit abscission by blocking photoassimilate transport from leaves to roots, thus increasing carbohydrate availability for the growing fruits (Yamanishi, 1995).…”

Fruit thinning with specific reference to citrus species : A review

“…Cultivars differ in the length of each phase,with early and late cultivars differing mainly in the duration of each stage or phase.Early and late season cultivars differ in the duration of stage II (Stuttle and Goge,1990).A lot of physiological ,biochemical and morphological changes occur during early seed development(stage I) (Zuchini,1983).Abscission of peach varies from late stageI (Crane,1963),"June drop"fruits(stage(onset of stageII) (Turkey,1936) cited by Stuttle and Goge,1990 who observed that the killing of embryo during early stage II or III caused fruit abscission in several peach cultivars.Some practices also affect fruit abscission.Shading the fruit trees cause abscission Byers et al(1990) investigated the effect of different levels of shading on red delicious apple trees for 10 day periods from 10 to 20,15 to 25,20 to 30 and 25 to 35days after full bloom.He reported that this interval caused greater fruit abscission than shading from 5 to 15,30 to 40,35 to 45 to 57 days after full bloom.Fruits of diameter 8 to 33mm in diameter(10 to 30 days after full bloom) were very sensitive to 10 days of shade but fruit sizes of 6 to 12mm are usually the most sensitive to chemical thinners.Shading fruit tree limbs by spraying trees with chemical photosynthetic inhibitors can induce abortion as has been reported in apple and apple (Byers et al ,1984(Byers et al , ,1985.The explanations of these findings are that a brief period after bloom when the fruits are extremely sensitive to the application of a photosynthetic inhibitor or light limitation by shading treatment.Similarly,it has been reported that shading whole trees is more effective than shading limbs on old trees (Byers et al,1985) Chemical thinners also cause fruit abscission which causes thinning.Similarly,photosynthetic inhibitors can also be applied as thinners. Byers et al,1990).Apple fruit abscission after fertilization and during June drop is considered to be caused by the competition for essential metabolites among individual fruitlets and vegetative shoots. (Quinlan and Preston,1971) It has been reported that NAA thinning sprays reduced the amount of reducing sugars in young apple fruitlets (Schneider and Lasheen,1973) .This is apparently due to reduced level of photosynthates reaching the developing fruit.Further reports have indicated that the most sensitive period for NAA( Naphthalene Acetic Acid) induced abscission in apples is 10 to 20 days after full bloom.It has been observed that chemical photosynthetic inhibitor activity and natural June drop are initiated at about the same critical period as hormone spray thinning.…”

“…(Ouma,2010).Shade thinning is apparently effective for a longer period than chemical thinners.The mechanism causing June drop or NAA,Carbaryl or ethylene induced abscission may be similar to that caused by photosynthetic inhibitors though age of the leaves may limit their effect later in the season. ( Byers et al,1990) Time of Application of Chemical Thinners: Timing of application of chemical thinners can be affected by many factors including species or cultivars.Application can be timed by calendar reference to a particular stage of blossoms.But this method is not recommended because it does not consider year-to-year variation nor any side effect on fruitlet growth and the role that this may have in response to a chemical thinner. (Knight,1987).Another method used is by timing according to size which is also not possible practically because fruit bloom over an extended period and sprays cannot be applied when fruits are of a certain size.…”

“…The force causes the heavier fruits and those closer to the point of impact to separate from the spurs. (Byers, 1990, cited by Valenzuela, 1992) Blossoms or fruits can be thinned. In practice early fruit thinning (from bloom upto about 2 weeks before pit hardening) can reduce the percentage of small peach fruit at harvest (Farley, 1923;Shoemaker, 1933),iIncrease total yields (Havis, 1962) and advance maturity.…”