Fruit Setting and Development

Cytokinins probably play a role in sex expression. It may be that in certain monecious species cytokinins are below a critical level for differentiation of perfect flowers. Topical applications of cytokinin to a known staminate flowered grapevine 3 weeks before anthesis induced the plant to produce perfect flowers (Negi and Olmo 1966). An additional example is to be found in the production of male flowers by Mercurialis annua following treatment with cytokinins (Durand 1969). Furthermore, soaking of Luff a acutangula seed in a N-benzyladenine solution promoted early pistillate flower production (Bose and Nitsch 1970). In this connection it may be important to note that cytokinins have been reported to induce ethylene formation in plant tissues (Fuchs and Lieberman 1968). 

While little more than inferences can be made at this time, it appears that in the development of floral organs auxins, gibberellins, cytokinins, morphactins and ethylene play significant but, as yet, undefined roles preceding the development of tissues giving rise to fruits. 

In nature, the fruit-setting period is accompanied by a high degree of uncertainty. Climatic factors such as late frosts or a very wet or a hot, dry period during a brief pollination period may practically eliminate fruit and seed production for a crop year. Because of the importance of the pollination-fertilization-fruit development phase in the life cycle of angiosperms, a great deal of attention has been devoted to it. Many internal and external factors impinge upon it. 

Ordinarily fruit growth is relatively rapid. Mobilization of food in the growing fruit is often faster than it can be supplied by photosynthesis. Thus physiological balances in other parts of the plant may be drastically altered. Although 

Chloroform extracts of pollen can replace many of the initial effects of pollen on ovary growth. Whatever the factor(s) may be, they are nonspecific, for they will cause fruit set in unrelated genera and even unrelated families (Gustafson 1937). Once beyond the critical period following pollination and fertilization, many fruits seem to be self-sufficient for plant hormones. 

---

The results show that the role of gibberellin in fruit set and development must be thoroughly investigated. It has long been the viewpoint that auxins produced in the seeds control fruit set and development. 

Itoo S (1986) Persimmon. In Monselise SP (ed) CRC handbook of fruit set and development. CRC Press, Boca Raton, pp 355-370... 

Garner WW, Allard HA (1923) Further studies in photoperiodism the response of the plant to relative length of day and night. J Agric Res 23 871-920 Gil GF, Martin GC, Griggs WH (1972) Fruit set and development in the pear Extractable endogenous hormones in parthenocarpic and seeded fruits. J Am Soc Hortic Sci... 

Weaver RJ (1972) Plant growth substances in agriculture. Freeman, San Francisco Weaver RJ, Van Overbeek J, Pool RM (1966) Effect of kinins on fruit set and development in Vitis vinifera. Hilgardia 37 181-201... 

Endogenous auxins are involved in fruit set and growth. Normally, fruit will not develop if the flower is not pollinated and fertilization occurs. In some plants, fertilization of one egg cell is sufficient but in others, such as melons and apples, several seeds must be fertilized. By treating the female flower parts with auxin it is possible to produce parthenocarpic fruit (fruit produced without fertilization) such as seedless tomatoes and cucumbers (30). 

Modification of sex expression Control of fruit set and fruit development... 

The quality of extracted citrus juices depends on enzyme reactions that occur not only in the fruit during the development period, but also in the juice during processing. When juice is extracted from citrus fruit, enzymes are released from their normal restraint in the cell. Several of these enzymes catalyze reactions that adversely affect taste and appearance of the juice. Unless the reactions are controlled, the juice products will not meet the standards of quality set up by the USDA Food Safety and Quality Service. The two reactions of commercial importance are the hydrolysis of pectin to pectic acid, which clarifies juice, and the lactonization of limonoic acid A-ring lactone to the bitter compound, limonin. Research efforts to identify and characterize the reactions, to isolate and purify the enzymes, and to develop methods to control the reactions are described in this review. 

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. 

Fruit with small, brown, sunken spots that turn dark and are raised. Cause Melanose. This fungal disease usually attacks trees more than 10 years old and is worst in wet springs. As rain washes spores over fruit, a tear-streaked pattern of infection develops. Copper spray applied just once at fruit set controls this disease, but since fruit damage is only cosmetic, spraying isn t really necessary. Keep melanose in check by pruning out dead wood, which may harbor the disease. 

---