Organ Loss and Yield Impacts of ‘Valencia’ Sweet Orange in Response to Fruit Abscission Agents

Abstract

<jats:p>To successfully use abscission agents for ‘Valencia’ sweet orange mechanical harvesting throughout the harvest season, unwanted flower, fruitlet, and leaf drop must be assessed and minimized. Ethephon (400 mg·L<jats:sup>−1</jats:sup>), 1-methylcyclopropene (1-MCP; 5 m<jats:sc>m</jats:sc>), ethephon + 1-MCP, 5-chloro-3-methyl-4-nitro-1<jats:italic>H</jats:italic>-pyrazole (CMNP; 200 mg·L<jats:sup>−1</jats:sup>), and a kinetic adjuvant control [0.15% (v/v)] were applied to ‘Valencia’ branches at various times from full bloom in Mar. 2006 to the end of full bloom in Mar. 2008. Effects of these treatments on fruit detachment force (FDF) and abscission of developing and mature fruit, flowers, and leaves were recorded. Three separate response periods to abscission agent applications were observed: the first spanned the first 100 days after bloom (DAB) and was characterized by high initial response followed by decreasing sensitivity; the second spanned between 100 and 225 DAB and was characterized by little to no response; and the third spanned from 225 DAB to harvest and was characterized by a gain in sensitivity. Young fruitlets in the first response period were highly sensitive to ethephon but were less sensitive to CMNP or ethephon + 1-MCP. Mature fruit in the third response period were highly sensitive to CMNP and less sensitive to ethephon or ethephon + 1-MCP. The application of ethephon resulted in high leaf abscission and showed no clear sensitivity pattern throughout both cropping years. CMNP or ethephon + 1-MCP application caused minimal leaf abscission. The same abscission agent treatments were applied on whole tree canopies 6 and 28 DAB in Mar. 2007. Application date had no significant effect on the measured parameters. Although ethephon application induced high initial leaf drop, leaf area indices determined 7 months after any compound application were not significantly different. However, subsequent 2008 yield in trees sprayed with ethephon in 2007 was significantly less, whereas 2008 flower number was higher. The results indicate a complex interaction of fruitlet abscission and leaf loss during the first response period contributed to yield reduction and increased flower number in ethephon-treated trees.</jats:p>

Gene expression in Citrus sinensis fruit tissues harvested from huanglongbing-infected trees: comparison with girdled fruit

“…Bark was removed on PCR-negative ‘Hamlin’ trees grafted on ‘Swingle’ rootstock in groves located in Lake Alfred, FL near the end of stage II fruit growth ( Pozo and Burns, 2009 ) in July 2010. Twigs with a single subtending fruit were selected for girdling.…”

Allometric Models for Estimating Carbon Fixation in Citrus Trees

“…In the laboratory, the leaf area was quantified in 100 leaf subsamples from each replicate tree with a LiCor 2000 leaf area meter. The LAI was then calculated as the leaf area divided by the ground surface area under the canopy (Pozo and Burns, 2009). The root total biomass ratio (RTB) was calculated as the ratio of total root biomass (coarse and fibrous roots) and biomass of the whole tree.…”

Anatomical and histological changes in the fruit abscission zone of water dropwort (Oenanthe stolonifera DC.)

“…As a result, a variety of chemicals and plant hormones have been used to control fruit abscission (Pozo and Jacqueline, 2009). The fruit abscission zone (AZ) can differ according to internal conditions such as cultivar, fruit maturation, and carbohydrate content (Castillio-Llanque and Rapoport, 2009;Iglesias et al, 2006;Taghizadeh et al, 2009).…”