After Harvest

Market Diseases Caused by Fungi

G. B. Ramsey, M. A. Smith.

The diseases of the fresh fruits and vegetables caused by fungi during the various phases of the marketing process are due either to contamination and infection that occur during the growing season or to infections through Injuries incidental to harvesting, processing, packing, and transporting the Produce.

Like all living things, fruits and vegetables are subject to disease and death when invaded by certain kinds of organisms. Of the thousands of fungi found everywhere in the air, soil, and water and on living and dead plants, some invade normal tissues and cause decay, some cause trouble only when injuries open the way for them to enter, and some do not cause damage under any circumstances.

More than too fungus diseases may cause decay and blemishes in commercial shipments of fruit. More than 150 cause serious losses in vegetable shipments during transit and marketing. Some crops have as many as 40 different diseases that might cause serious, costly damage by the time the produce reaches the consumer.

The amount of damage and loss from disease varies greatly with the commodity, the kind of disease, the growing conditions, and the handling conditions.

Because the cost of harvesting, grading, packing, and shipping most fruits and vegetables exceeds the value of the commodity itself at the shipping point, it behooves all hands to have all fresh fruits and vegetables graded, packed, and handled carefully and shipped by approved methods so they bring a suitable price and the loss of valuable food during the marketing process is reduced.

BLACK ROT of banana is caused by the fungus Endoconidiophora paradoxa. It is present wherever bananas are grown. It enters the bunches through the tips and butts of the stalks when the fruit is harvested. Severe infection may cause 10 to 25 percent of the fruit to drop from the bunches during ripening and marketing.

The evidence of infection on green fruit is the small black areas at the end of the fruit near the point of attachment to the cushion. The cushions and the main stalk may also show similar discolorations, but little or no growth of the fungus occurs on the surface of the fruit.

The green fruit on arrival at the terminal markets is placed in ripening rooms, where temperatures of 60 to 70 F. and a high relative humidity are maintained conditions ideal for the development of black rot. When the yellow color begins to develop in the fruit, the infected areas become brown. They have slightly water-soaked borders. A fine growth of the fungus appears over infected fruits and stalks. As the fungus continues to invade the peel of the fruit from the point of attachment to the cushion, the peel turns brown or black. The fungus usually does not invade the edible part of the fruit, but the discoloration of the peel may lower its salability.

Control of black rot depends mainly on the prevention of infection of butts and tips of stalks at harvesttime.

BLUE MOLD ROT, caused by the fungus Penicillium expansum, destroys many apples in transit, storage, and market. It occurs on all varieties of apples in all parts of the country.

Blue mold is not important as an orchard disease but when rainfall is abundant and humidity is high, the fungus may be present on fallen fruits and on mashed or overripe fruit in the packing house. The spores on them infect fruit in storage and in the packing shed.

The fungus enters the fruits through skin breaks or lenticels. The decay first appears as soft, watery, light brown or yellow spots, which vary in size and may occur on any part of the fruit. The spots are shallow at first but quickly go deeper. Eventually the decay may involve a third or more of the fruit. Within a few days after decay develops, a white surface growth of the fungus appears. It later becomes bluish green when large numbers of spores are produced. Affected fruit has a musty odor when decay is well advanced and spore production is heavy. The decayed flesh has a musty taste.

Important factors in the control of blue mold are careful handling during picking and packing, packing house sanitation, precooling, and prompt storage at 30 to 32 F. Temperatures in transit should not exceed 45 .

BROWN ROT, caused by the fungus Monilinia fructicola, attacks peaches, plums, apricots, and cherries in transit, storage, and market. In the orchard the disease may occur on leaves, blossoms, fruits, twigs, and limbs.

On peaches, plums, and apricots, brown rot first appears as small, circular, light-brown spots, which may enlarge so rapidly as to bring about extensive decay in 24 hours if the temperature is between 60 and 70 and the humidity is high. In its early stages on cherries the decayed areas are light brown, but as the disease progresses the margin of the decayed area fades into the normal flesh color, leaving no distinct line separating diseased from healthy tissue. The skin covering the rotted spot remains firmly attached to the tissue beneath. The decayed areas at no stage are sunken, and the flesh remains fairly firm.

As the decay progresses, yellowish-gray masses of the fungus may develop on the surface. They contain millions of spores, which can start the disease On other fruits. Later the skin turns dark brown or black, and the decay extends to the seed.

Peaches harvested from orchards in which brown rot is present are usually contaminated with the spores. When temperature and humidity are favorable, spores may germinate and penetrate the uninjured skin of the fruit or enter through mechanical injuries that occurred in the orchard or during packing operations. Once infection is established, the disease may spread from one fruit to another by contact.

Usually moisture is sufficient in carloads of peaches for spores of the brown rot fungus to germinate and for the fungus to grow in already infected fruit. New infections are almost entirely prevented by temperatures that are below 50 . The maintenance of proper temperatures in refrigeration is therefore important in retarding development of brown rot.

Fruit with a temperature of 85 loaded into a refrigerator car iced to capacity may take 36 to 48 hours to be cooled below 50 . That is enough time for decay to become established. Precooling peaches for 4 to 6 hours to reduce the temperature to 50 is a good way to retard decay in transit.

In standard refrigerator cars brown rot often is more prevalent at the top of the load than at the bottom because the higher temperatures at the top hasten its development. Usually that is not true in modern refrigerator cars equipped with fans that provide forced air circulation and keep the temperature more uniform throughout the load. The fans, built under the floor racks near the ice bunkers in the ends of the cars, draw the warm air from the body of the car into the bottom of the bunker and force the cold air from the bunkers over the top of the load.

Sprays or dusts containing sulfur are commonly used to control brown rot in the orchard. Large peach-packing centers commonly apply sulfur dust during the grading operation. Other fungicides have been used for postharvest treatments of peaches, but further research is needed to determine their effectiveness in reducing brown rot in transit and on the market.

BULL'S-EYE ROT is a form of decay found in apples and pears from the Pacific Northwest and British Columbia. Six different rots have the bull's-eye appearance.

The most common bull's-eye rots on both apples and pears in the market are caused by the fungi Neofabraea perennans and N. malicorticis. From the cankers that the fungi make on twigs and branches, spores may be washed by rain to the apples or pears below. Infection of fruit occurs through lenticels. The diseases develop slowly in the fruit and do not become apparent until after it has been in storage several months. Apparently the fungi cannot spread from one fruit to another.

The decay caused by Neofabraea perennans usually is centered around lenticels. It is moderately firm, cream-or tan-colored, slightly sunken, and round. It has brown borders. The surface of the rotten place often is covered with creamy-white spore masses.

Careful spraying with bordeaux mixture is the best way to control the diseases in the orchard. Removing diseased limbs and cankers is another effective control measure.

The rot caused by the fungus Phialophora malorum is sometimes grouped with the bull's-eye rots. It occurs in the Pacific Northwest and has been found on fruit in the Midwest and East. The rot is fairly firm and usually occurs around the lenticels as small, shallow, roundish, light-brown spots. Infected places on the fruits may join into large spots. There is usually no evidence of fungus growth or spores on infected fruit. The disease does not spread from one fruit to another.

No satisfactory measures for its control have been developed.

GRAY MOLD, caused by the fungus Botrytis cinerea, is a serious disease of pears in storage. The fungus, widely distributed, is found on discarded fruit and other debris in orchards and packing houses. The decay it causes is fairly firm. In advanced stages the fruit often has a sour odor.

Infection occurs most often at the stem end but may take place through skin breaks on any part of the fruit. The skin of affected fruits is at first slate gray, and usually there is a sharp line of demarcation between the diseased and healthy tissue. As the decay progresses the fungus may grow on the surface of the fruit. Later many spores are produced that can germinate and cause new infections.