Citrus abscission

Several inferences can be drawn from these data that may suggest the impacts to be expected at the consumer and decomposer levels. Accelerated leaf drop may influence the development of pests—namely, aphids, scale insects, and red citrus mites. Pest populations might be increased if injured leaves had higher concentrations of amino acids or free sugars before abscission (see Chapter 11) or diminished if leaves fell too rapidly. Leaf and fruit drop would provide a larger substrate for populations of decomposer organisms at the soil surface. 

An active abscission research program for citrus has been underway for a number of years in Florida by the Florida State Citrus Commission in collaboration with a number of chemical companies. This program was initiated originally because of a shortage of labor for handpicking citrus. Chemicals to speed up the removal of fruit by mechanical harvesters and to increase... 

The preharvest drop of citrus fruit can be reduced or prevented with 2,4-dichlorophenoxyacetic acid, which delays development in the abscission zone of the fruit stem, thus allowing the fruit to remain on the tree longer. Because of 2,4-D s herbicidal properties, however, care must be taken in spraying to prevent the chemical from damaging other crops, as well as the target crop... 

With the exception of 2,4-D and gibberellic acid treatments of a variety of citrus crops, where improved fruit set, reduced fruit drop, and the ability to delay harvesting without loss of fruit quality are recognized benefits, few applications have been developed for the use of hormone-type regulators in tropical fruits. Recent work has shown that gibberellic acid will delay postharvest ripenining and improve the quality of bananas and that napthaleneacetic acid treatment of oil palm to delay fruit abscission has increased both yield and oil content. 

Several materials have commercial use as abscission agents (6). In cotton, the products Accelerate (endothall), Folex (merphos) and DEF (oxidized form of merphos) have been identified as defoliants. Amid-thin continues to be used to thin fruit set. 3-CPA and Peach-thin 322, formerly used as peach thinners, serve as reminders of the disadvantages of highly specialized markets. RELEASE and PIK-OFF are under development as citrus abscission agents. 

Over the past several years, we have included within the scope of agricultural R and D efforts the search for abscission agents with prime emphasis on citrus abscission. My comments in part will be drawn from factors which have effected the development of the potential abscission agent RELEASE by Abbott Laboratories. Examples relative to the general concerns and obstacles in the development of a plant growth regulator will also be discussed. 

In the case of citrus abscission, screening has involved several approaches (9)... 

With such cooperation, mutual support and obviously some "luck" (23), plant growth regulators, including abscission agents, may still be expected to be developed (24, 25) not only to enhance quality and yields of major crops e.g., cotton, corn, tobacco, but also important fruit crops e.g., apples, oranges (citrus), grapes, cherries, etc. 

Anatomy of the abscission zone at the base of mature fruits has been investigated in apples (10), cherries (11), citrus (12), and olives (13) and has been discussed as related to mechanical fruit removal (2, 14), The histochemistry of the separation layer of mature fruit is very similar to that of leaves of citrus (15) and bean (16,17), The actual separation occurs through one or more processes in the separation zone (a) a weakening of the cementing ability of the middle lamella between cells, and (b) a softening of the entire cells (17), In some plants, the abscission zone is structurally differentiated as a layer of compact cells or as a zone of localized cell division in other species, abscission may occur across a transect of cells which show little or no visible diflFerentiation (18). Thus, major components of the separation process involve the dissolution of middle lamella and lysis of cell walls or entire cells in the separation zone, but this is not necessarily associated with distinctive morphological characteristics (19). 

Cycloheximide (CHI), when applied directly to separation zones, will inhibit abscission of citrus fruit explants 24) as it does bean petiole explants (29). By application to citrus fruit surfaces, the rind is injured, evidenced as small pitted areas, and ethylene is produced in quantities that accelerate the abscission processes (41). Apparently, CHI applied to the fruit wall enhances the senescence processes, including ethylene production, thereby stimulating citrus fruit abscission via ethylene production and not by action directly on the tissues in the separation zone (41). Cycloheximide has also been used for harvest of olives (80, 103) and apples (104). 

Use Nutrition, color fixing, flavoring and preservative in meats and other foods, oxidant in bread doughs, abscission of citrus fruit in harvesting, reducing agent in analytical chemistry. The iron, calcium, and sodium salts are available for biochemical research. 

Use Organic synthesis, abscission of citrus fruit in harvesting. 

Recently brassinolide was found to retard the abscission of leaf explants of Calamondin (6). Thus, the present experiments were also included to observe the effects of brassinolide on the fruit set of Morita navel oranges (Citrus sinensis), a cultivar derived from Washington navel. 

As a treatment for abscission in citrus plants, the tendency for a plant to lose its leaves, flowers, and fruits. 

Ben-Yehoshua, S., Biggs, R.M., 1970. Effects of iron and copper ions in promotion of selective abscission and ethylene production by citrus fruit and the inactivation of indoleacetic acid. Plant Physiol. 45, 604-607. 

Abscission, the dropping of leaves and other plant parts, is correlated with diminished production of auxin in those parts. By treating evergreen holly (Ilex aquifolium) with auxin, leaf and berry drop during shipment is minimized. Auxins also prevents preharvest drop of citrus fruits. 

Ethylene glycol dimethacrylate abscission aid, citrus fruit harvesting Cycloheximide absorbent... 

Although these data call into question ethylene s present position as the do it in almost all plant hormone, there is no denying the manifold effects of applied ethylene in plant growth and development. For many years ethylene itself has been used commercially to elicit some of these effects, for example, fruit ripening. Compounds which initiate ethylene responses by inducing the plant to produce its own ethylene (a wound response) have been used in the field. Cycloheximide application, for example, stimulates abscission of citrus by stimulating ethylene production at the button [15]. The possibilities for harnessing ethylene responses in... 

Hu AS, Jiang BF, Guan YL, Mou H (1990) Effects of epi-brassinolide on abscissirai of young fruit explants and cellulose activity in abscission zone citrus. Plant Physiol Commun 5 24-26... 

Extracts from citrus orange Citrus sinensis) pedicles contained cellulase activity. The effects of pH, ionic strength, and ethylene on the extraction of cellulase from the abscission zones of citrus-leaf Citrus sinensis) explants have been studied. Prior treatment of the explants with ethylene increased the solubility of the enzyme in phosphate buffers, regardless of pH,... 

---