DIPHENYL has been used extensively in the citrus industry to control blue mold, green mold, and stem-end rot. It is a crystalline substance, which may be dissolved in various solvents and impregnated into paper wraps, pads, or box liners used to enclose packed commodities. Diphenyl vapors are slowly released from such materials and reduce the action of decay organisms. A storage test conducted in Palestine showed that oranges wrapped in diphenyl wraps and stored for 18 weeks had only 2 percent of decay, while those in untreated wraps were a total loss. Research workers found that diphenyl controlled decay of lemons in Texas and both oranges and grapefruit in Florida.

G. B. Ramsey, M. A. Smith, and B. C. Heiberg, of the Department of Agriculture Market Disease Laboratory in Chicago, learned that diphenyl vapor inhibits vegetative growth and prevents the production and germination of spores of certain citrus decay fungi. The fumigant thus aids in preventing spread of the molds from decayed fruit to healthy fruit by contact and also by inoculation with spores. The degree of inhibition of growth varied with specific fungi. The most common citrus decay organisms are quite sensitive to diphenyl vapor. The vapor does not kill them, however, for they resume growth when the fumigant is removed.

Many commodities are adversely effected by diphenyl vapor. J. M. Rattray found that South African grapes developed an off-flavor and and turned brown in the presence of ortho-phenyl-phenol, a derivative of diphenyl. W. T. Pentzer and W. R. Barger obtained similar results with Emperor grapes in California. Di-phenyl cannot be used with apples, pears, bananas, tomatoes, and cucumbers, because they take up the odor of the chemical. Citrus takes up small amounts of diphenyl in the rind but the flesh is not affected.

IODINE, like diphenyl, is applied to wraps or liners used in packaging and acts as a volatile inhibitor of decay organisms. The packaging material is dipped in an alcoholic solution of iodine and potassium iodide of the desired concentration, dried, and stored in airtight containers until used.

R. G. Tomkins, in England, found that iodine wraps reduced decay of oranges caused by Penicillium digitatum. He found, however, that iodine was so volatile that it lost its fungicidal effect rather rapidly. It stains the packaging materials an unsightly brown and injures some varieties of fruit.

DuPlessis learned that iodized wraps were effective in reducing the gray mold of grapes. After 10 days in storage treated grapes showed 19.9 percent infection of Botrytis, while untreated grapes showed 42 percent. Wraps treated with I percent iodine and 2 percent potassium iodide reduced Botrytis infection to 1-41-7-04 percent, compared with 12.27 percent in the check. The treatment did not impair the flavor.

In California iodized wraps reduced decay to one-fourth that of untreated grapes. The treatment caused no injury to the fruit, but the control was inferior to that obtained with sulfur dioxide.

MODIFICATION OF ATMOSPHERES in storage rooms by increasing the amount of carbon dioxide (CO₂) and reducing the oxygen content slows down the respiration of the commodity being treated and (sometimes) the organisms of decay. Carbon dioxide does not act as a fumigant. It does not kill disease organisms but only inhibits them. After removal from such modified atmospheres the organisms resume normal growth.

Carbon dioxide has been used with considerable success as a supplement to refrigeration of commodities that are subject to physiologic disturbances at near freezing temperatures. An outstanding example is the storage of New York-grown McIntosh apples at 40 in atmospheres of 5 percent carbon dioxide and 2 percent oxygen. Control of decay comparable to that obtained at lower temperatures is achieved by this treatment without undesirable browning of the flesh.

Charles Brooks and others in the Bureau of Plant Industry, Soils, and Agricultural Engineering found that peaches, apricots, strawberries, and red raspberries were quite sensitive to injury by carbon dioxide. Only slight injury was observed when plums, cherries, blackberries, blueberries, black raspberries, currants, pears, apples, and oranges were treated. Grapes, peas, sweet corn, and carrots were especially resistant to injury by carbon dioxide. Injury from excessive exposure to carbon dioxide was evidenced by a loss of aroma and flavor or even by the development of fermentation.

Carbon dioxide also has been used to treat fruits and vegetables in loaded refrigerator cars. Applied immediately after loading, the gas is as effective in controlling decay as is rapid cooling to 32 . To obtain the desired results, 800 to 1,000 pounds of solid carbon dioxide are used initially. Carbon dioxide is particularly effective in controlling decay of cherries caused by species of Rhizopus, Monilia, and Penicillium. At 45 , an atmosphere containing 25 percent carbon dioxide controls fungus decay of sweet cherries and also has a favorable effect on the firmness, brightness, and freshness of the fruit. Bing and Lambert cherries tolerate concentrations up to 40 percent when stored for 12 days at 60 or 20 days at 45 .

Carbon dioxide may be introduced into storage room atmospheres in several ways. Simply sealing the room will cause carbon dioxide to accumulate as a result of respiration by the stored commodity. It may be released from cylinders of the compressed gas. It may be obtained by the "melting" of solid carbon dioxide (dry ice). The use of the gas is limited because many storage rooms and refrigerator cars are not sufficiently airtight to retain the gas over extended periods.

JOHN M. HARVEY is a plant pathologist in the Bureau of Plant Industry, Soils, and Agricultural Engineering at Fresno, Calif. After receiving his doctor's degree at the University of California in 1950, he joined the field laboratory of the Department at Fresno, Calif., where he specializes in the plant diseases associated with the handling, transportation, and storage of horticultural crops.

W. T. PENTZER joined the Department of Agriculture as a junior marketing specialist in 1926. From 1929 to 1949 he was in charge of the field laboratory at Fresno, where much of the research on sulfur dioxide fumigation of grapes was conducted. Since 1949 he has been head of the division of handling, transportation, and storage of horticultural crops at Beltsville, Md.