Charles W. Coggins

Plant Growth Regulators in Citriculture: World Current Uses

ABSTRACT Plant growth regulators (PGRs), both naturally occurring and synthetic, are used extensively in citriculture not only to help growers solve production problems, but also to increase the market value of the crop and to improve grower returns. Yield increases are obtained via an improvement in fruit set, particularly for shybearing cultivars, and/or fruit size, especially for the “small-fruit” group of mandarins. Increased fruit number per tree is achieved indirectly through an increase in flower number as a result of better flower initiation or by a direct effect on fruit set. Improved fruit size is brought about directly by stimulating the growth of fruit tissues or indirectly by reducing fruit number by partial inhibition of flower initiation or by subsequent fruit removal. PGRs are also used to hasten maturity, to delay harvest, and to maintain fruit quality postharvest, resulting in greater profits to the grower. This article provides an overview of current uses of PGRs in citriculture. The re...

Growth regulator effects on retention of quality of stored citrus fruits

Abstract A 3-year study was initiated to determine the possible effects of two growth regulators, 2,4-dichlorophenoxy acetic acid (2,4-D) and gibberellic acid (GA3) on the quality of on-tree-stored and cold-stored fruits of cultivar ‘Clementine’ mandarin (Citrus reticulata Blanco) and cultivar ‘Washington’ navel orange (Citrus sinensis (L.) Osbeck). Treatments were applied at fruit color break as whole tree sprays, and fruits were either analyzed immediately after harvest or stored at 4°C and 85% relative humidity and analyzed at 4 and 8 weeks of storage. Regardless of the cultivar, GA3 alone or in combination with 2,4-D significantly slowed the rate of rind color change and the rate of rind softening, both on the tree and post-harvest. However, the rate of change in color and firmness of the rind on the tree and post-harvest was variety dependent. When used alone, 2,4-D had no effect on these factors. No growth regulator effects were noted on weight loss, extractable juice, juice titratable acidity (TA) and total soluble solids (TSS), or the ratio TSS/TA. It is concluded that the delayed senescence obtained from GA3 is primarily at the rind level.

The efficacy of five forms of 2,4-D in controlling preharvest fruit drop in citrus

Over a period of three seasons, five forms of 2,4-dichlorophenoxyacetic acid (2,4-D) were evaluated for efficacy in preharvest fruit drop control in California (CA) citrus at three navel orange and three grapefruit sites. The forms of 2,4-D evaluated were: isopropyl ester, isooctyl ester, butoxyethyl ester, dimethylamine salt and acid. In 17 of the 18 trials, fruit drop was reduced by a statistically significant level for the season by an application of 2,4-D regardless of form. Seven out of these 17 trials showed no statistically significant difference in efficacy among the forms used. Of the 10 sites that showed statistically significant form effects, no one form was consistently superior and differences between the forms were minor. All forms of 2,4-D evaluated in these trials provided excellent control of preharvest fruit drop. The practical value of the fruit holding ability among the forms is probably slight. On an acid equivalent basis, it appears that the form of 2,4-D applied to citrus trees has little influence on preharvest fruit drop control.

Pre-harvest rindstain of Valencia orange : histochemical and developmental characterization

Abstract Pre-harvest rindstain of California cultivar ‘Valencia’ orange has economic significance since fresh fruit marketability is reduced. Quantification of the incidence of rindstain as related to tree quadrant has allowed us to designate quadrants where rindstain was most likely to occur (upper outside SW) or least likely (lower inside NE) to occur. Growth and development characteristics of fruit from the two quadrants were measured throughout fruit development. Significant differences in percent weight loss between fruit from the SW and NE quadrants occurred at color break and at commercial maturity. Structural and histochemical changes in flavedo tissue of fruit from SW or NE tree quadrants were monitored over the course of fruit development and maturation. First evidence of periderm formation occurred in October, coincident with observed changes in histochemical staining for lipids. These differences were increasingly evident as the fruit approached horticultural maturity and visual symptoms of rindstain developed. The development of a pronounced periderm in affected fruit suggests that rindstain is due to a physical trauma, although we do not believe it is caused by wind.

Identification of Age Anomalous Components of Food Commodities by Radiocarbon (14C) Analyses

“Post-maximum-bomb” 14C activities (1964 to the present) provide a natural isotopic signature to obtain information on biomass source age in contemporary food preparations. An analysis of the 14C content in frozen orange juice-containing products purchased in 1996 suggested, in one case, an inferred growth period between 1992 and 1994 for oranges used in the preparation of this commodity. In another case, the 14C analysis indicated an inferred average growth period of 1988−90 for the organics in a “frozen concentrated enriched citrus beverage”. The presence of significant amounts of chemical additives obtained or synthesized from fossil carbon sources can also be documented by measuring 14C content. Keywords: Radiocarbon; carbon isotopes; orange juice; component age