Grape Fruit Quality Research Articles

Growth regulator and low-volume irrigation effects on grapefruit quality and fruit-drop

‘Marsh’ ( Citrus paradisi Macf.) grapefruit trees on rough lemon ( C. jambhiri Lush.) rootstock received irrigated and unirrigated treatments. Half of each irrigation treatment received a GA 3 + 2,4-D spray at color break. Pre-harvest sprays of GA 3 and 2,4-D extended the grapefruit harvest season by increasing fruit removal and rind puncture force, delaying development of mature color and decreasing late-season and post-freeze fruit-drop. Although soil moisture content in the top 0.9 m of unirrigated blocks was reduced by approximately 40%, xylem pressure potentials of these trees and performance of GA 3 + 2,4-D were unaffected. Soil moisture content was not an accurate indicator of tree water status for large grapefruit trees.

Redblush Grapefruit Quality as Affected by Controlled Artificial Climates1

Abstract ‘Redblush’ grapefruit borne on young fruiting trees and grafted on sour orange seedlings were exposed to natural and artificial climates. Fruit exposed to artificially controlled and naturally occurring minimum night temperatures above 70°F, combined with high day temperatures, had high Brix contents, low acid, and thin but green peels. Fruit exposed to minimum night temperatures below 60°, combined with moderate to cool day temperatures had both high Brix and acid and thicker but better colored peels. Cool temperatures in the late fall after hot summer and early fall conditions aided in thickening and coloring of peels of fruit which had already attained high Brix and early maturity.

Effects of 2,4-D and related substances on fruit-drop, yield, size, and quality of grapefruit

From 1947 to 1950, 34 field experiments were conducted to study the effects of applications of 2,4-D and related substances on fruit-drop, yield, size, and quality of grapefruit in California. It was found that water sprays of 8 ppm 2,4-D reduced mature fruit-drop an average of 44 per cent, as compared with nonsprayed trees, and that this response to 2,4-D occurred under a wide range of climatic and environmental conditions. This spray was more effective in reducing fruit-drop when applied in May than when applied in July, and annual applications of 2,4-D for three years have shown no accumulative detrimental effects. The differences in fruit-drop resulting from the use of various forms of 2,4-D were not great. Thus far, 2,4-D has not proved incompatible with any agricultural spray chemicals, and has been effective in reducing mature fruit-drop when applied in conjunction with other spray treatments. The 2,4-D sprays had no undesirable effects on the quality of fruit which was mature, or nearly mature, at the time of spraying. Trees sprayed with 2,400 ppm 2,4-D as a kerosene “aeromist” at less than 10 gallons per acre showed a reduction in mature fruit-drop, as compared with nonsprayed trees, but this method cannot yet be recommended for commercial use. A water spray of 8 ppm 2,4,5-T was as effective as an 8 ppm 2,4-D spray in reducing mature fruit-drop. A spray of 25 ppm naphthalene-acetic acid was not effective, and a spray of 25 ppm naphthoxyacetic acid was only slightly effective. Application of 8 ppm 2,4-D to trees with young, expanding leaves induced a curling and deformation of the leaves. Subsequent leaf growth was normal. Application of the spray between leaf growth flushes minimized the distortion. No influence on yield or fruit quality was noted as a result of the leaf curl. There was an increase in fruit size of commercial value if the correct concentration of 2,4-D was sprayed on trees bearing fruit less than 16 weeks old. However, the fruit quality was lowered when trees bearing young fruit (less than 16 weeks) were sprayed with 2,4-D at too high a concentration in relation to the stage of fruit growth. A lowering in quality as a result of an 8 ppm 2,4-D spray was observed in only one experiment, where the application was made on trees in full bloom.