134 Modern Food Microbiology
Fungal Agents
A synopsis of some of the common spoilage conditions of vegetables and fruits is presented in
Table 6–8. Some of these spoilage conditions are initiated preharvest and others postharvest. Among
the former, Botrytis invades the flower of strawberries to cause gray mold rot, Colletotrichum invades
the epidermis of bananas to initiate banana anthracnose, and Gloeosporium invades the lenticels of
apples to initiate lenticel rot.
13 The largest number of market fruit and vegetable spoilage conditions
occur after harvesting, and although the fungi most often invade bruised and damaged products, some
enter specific areas. For example, Thielaviopsis invades the fruit stem of pineapples to cause black rot
of this fruit, and Colletotrichum invades the crown cushion of bananas to cause banana crown rot.
13
Black rot of sweet potatoes is caused by Ceratocystis, neck rot of onions by Botrytis allii, and downey
mildew of lettuce by Bremia spp.
9 Some of the spoilage conditions listed in Table 6–8 are discussed
below.
Gray mold rot. This condition is caused by Botrytis cinerea, which produces a gray mycelium. This
type of spoilage is favored by high humidity and warm temperatures. Among the vegetables affected
are asparagus, onions, garlic, beans (green, lima, and wax), carrots, parsnips, celery, tomatoes, endives,
globe artichokes, lettuce, rhubarb, cabbage, Brussels sprouts, cauliflower, broccoli, radish, rutabagas,
turnips, cucumbers, pumpkin, squash, peppers, and sweet potatoes. In this disease, the causal fungus
grows on decayed areas in the form of a prominent gray mold. It can enter fruits and vegetables through
the unbroken skin or through cuts and cracks.
Sour rot (oospora rot, watery soft rot). This condition of vegetables is caused by Geotrichum
candidum and other organisms. Among the vegetables affected are asparagus, onions, garlic, beans
(green, lima, and wax), carrots, parsnips, parsley, endives, globe artichokes, lettuce, cabbage, Brussels
sprouts, cauliflower, broccoli, radishes, rutabagas, turnips, and tomatoes. The causal fungus is widely
distributed in soils and on decaying fruits and vegetables. Drosophila melanogaster (fruit fly) carries
spores and mycelial fragments on its body from decaying fruits and vegetables to growth cracks and
wounds in healthy fruits and vegetables. Because the fungus cannot enter through the unbroken skin,
infections usually start in openings of one type or another.
27
Rhizopus soft rot. This condition is caused by Rhizopus stolonifer and other species that make
vegetables soft and mushy. Cottony growth of the mold with small black dots of sporangia often
covers the vegetables. Among those affected are beans (green, lima, and wax), carrots, sweet potatoes,
potatoes, cabbage, Brussels sprouts, cauliflower, broccoli, radish, rutabagas, turnips, cucumbers, cantaloupes, pumpkins, squash, watermelons, and tomatoes. This fungus is spread by D. melanogaster,
which lays its eggs in the growth cracks on various fruits and vegetables. The fungus is widespread
and is disseminated by other means also. Entry usually occurs through wounds and other skin breaks.
Phytophthora rot. This market condition, caused by Phytophthora spp., occurs largely in the field
as a blight and fruit rot of market vegetables. It appears to be more variable than some other market
“diseases” and affects different plants in different ways. Among the vegetables affected are asparagus,
onions, garlic, cantaloupes, watermelons, tomatoes, eggplants, and peppers.
Anthracnose. This plant disease is characterized by spotting of leaves, fruit, or seed pods. It is caused
by Colletotrichum coccodes and other species. These fungi are considered weak plant pathogens. They
live from season to season on plant debris in the soil and on the seed of various plants such as the
tomato. Their spread is favored by warm, wet, weather. Among the vegetables affected are beans,
cucumbers, watermelons, pumpkins, squash, tomatoes, and peppers.
Blue mold rot is a post-harvest disease of apples and pears that is caused by Penicillium expansum
while gray mold rot is caused by Botrytis cinerea. In an attempt to control these fungi on apples
and pears, two biocontrol agents have been tested—Candida sake and Pantoea agglomerans.
32 When
Fungal Agents
A synopsis of some of the common spoilage conditions of vegetables and fruits is presented in
Table 6–8. Some of these spoilage conditions are initiated preharvest and others postharvest. Among
the former, Botrytis invades the flower of strawberries to cause gray mold rot, Colletotrichum invades
the epidermis of bananas to initiate banana anthracnose, and Gloeosporium invades the lenticels of
apples to initiate lenticel rot.
13 The largest number of market fruit and vegetable spoilage conditions
occur after harvesting, and although the fungi most often invade bruised and damaged products, some
enter specific areas. For example, Thielaviopsis invades the fruit stem of pineapples to cause black rot
of this fruit, and Colletotrichum invades the crown cushion of bananas to cause banana crown rot.
13
Black rot of sweet potatoes is caused by Ceratocystis, neck rot of onions by Botrytis allii, and downey
mildew of lettuce by Bremia spp.
9 Some of the spoilage conditions listed in Table 6–8 are discussed
below.
Gray mold rot. This condition is caused by Botrytis cinerea, which produces a gray mycelium. This
type of spoilage is favored by high humidity and warm temperatures. Among the vegetables affected
are asparagus, onions, garlic, beans (green, lima, and wax), carrots, parsnips, celery, tomatoes, endives,
globe artichokes, lettuce, rhubarb, cabbage, Brussels sprouts, cauliflower, broccoli, radish, rutabagas,
turnips, cucumbers, pumpkin, squash, peppers, and sweet potatoes. In this disease, the causal fungus
grows on decayed areas in the form of a prominent gray mold. It can enter fruits and vegetables through
the unbroken skin or through cuts and cracks.
Sour rot (oospora rot, watery soft rot). This condition of vegetables is caused by Geotrichum
candidum and other organisms. Among the vegetables affected are asparagus, onions, garlic, beans
(green, lima, and wax), carrots, parsnips, parsley, endives, globe artichokes, lettuce, cabbage, Brussels
sprouts, cauliflower, broccoli, radishes, rutabagas, turnips, and tomatoes. The causal fungus is widely
distributed in soils and on decaying fruits and vegetables. Drosophila melanogaster (fruit fly) carries
spores and mycelial fragments on its body from decaying fruits and vegetables to growth cracks and
wounds in healthy fruits and vegetables. Because the fungus cannot enter through the unbroken skin,
infections usually start in openings of one type or another.
27
Rhizopus soft rot. This condition is caused by Rhizopus stolonifer and other species that make
vegetables soft and mushy. Cottony growth of the mold with small black dots of sporangia often
covers the vegetables. Among those affected are beans (green, lima, and wax), carrots, sweet potatoes,
potatoes, cabbage, Brussels sprouts, cauliflower, broccoli, radish, rutabagas, turnips, cucumbers, cantaloupes, pumpkins, squash, watermelons, and tomatoes. This fungus is spread by D. melanogaster,
which lays its eggs in the growth cracks on various fruits and vegetables. The fungus is widespread
and is disseminated by other means also. Entry usually occurs through wounds and other skin breaks.
Phytophthora rot. This market condition, caused by Phytophthora spp., occurs largely in the field
as a blight and fruit rot of market vegetables. It appears to be more variable than some other market
“diseases” and affects different plants in different ways. Among the vegetables affected are asparagus,
onions, garlic, cantaloupes, watermelons, tomatoes, eggplants, and peppers.
Anthracnose. This plant disease is characterized by spotting of leaves, fruit, or seed pods. It is caused
by Colletotrichum coccodes and other species. These fungi are considered weak plant pathogens. They
live from season to season on plant debris in the soil and on the seed of various plants such as the
tomato. Their spread is favored by warm, wet, weather. Among the vegetables affected are beans,
cucumbers, watermelons, pumpkins, squash, tomatoes, and peppers.
Blue mold rot is a post-harvest disease of apples and pears that is caused by Penicillium expansum
while gray mold rot is caused by Botrytis cinerea. In an attempt to control these fungi on apples
and pears, two biocontrol agents have been tested—Candida sake and Pantoea agglomerans.
32 When