STONEFRUIT DISEASES Plant parts attacked and damage symptoms
Brown rot(Monilinia sp)
Typical symptoms in the field are blossom and twig blight or brown rot on fruit. Fruit infections may occur in the field or may occur in the packinghouse. Quiescent infections may occur in the field and only rapidly develop when the fruit ripens. Water soaked lesions appear on infected fruit and these lesions can expand quickly. Brown mats of conidiophores and conidia are produced on the lesions of infected fruits.
Rhizopus rot(Rhizopus sp)
This postharvest disease is characterized by production of a mass white mycelium, with long mycelial stolons extending to and infecting adjacent fruit. Black sporangia generally are produced. Fungal enzymes in juice leaking from decayed tissues cause brown streaks on the epidermis of adjacent healthy fruit. Infected fruit becomes soft and watery.
Blue mold(Penicillium italicum)
Infected fruit become soft, watery, and slightly discolored and are easily punctured. A white, powdery growth of mycelium develops on the surface of the lesion and soon a mass of blue spore forms, leaving only a narrow white fringe on the outer edge of the lesion.
Green mold(Penicillium digitatum)
Green mold infections look almost identical to blue mold infections early on. However, the spore mass that develops is green in color and does not extend to the outer edge of the lesion as the blue mold does. Both green and blue mold develop most rapidly at 24° C. Blue mold can also grow at temperatures below 10° C whereas green mold does not.
Plant parts attacked and damage symptoms
Blue mold (Penicillium sp)
Blue mold is the most important postharvest disease of apples and is also important or pears. Blue mold may originate from wounds, stem-end invasions, or core rots. Infection can also occur through lenticels. There are at least 11 species of blue mold that attack pomefruits but P. expansum is the most predominate species. Penicillium spp. are readily isolated from orchard soils. Blue mold is rare in the fields except where fruit have fallen to the ground. Most fruit infections occur when airborne or waterborne conidia enter wounds incurred during harvest or handling. Conidia populations can quite high from sporulating fruit in packinghouse bins. A good diagnostic for blue mold is the characteristic earthy, musty order associated with the decay. Infected fruit flesh is soft and watery and separates easily from healthy tissue. A clear diagnostic is the development of blue-green spores either around or within fruit wounds.
Gray mold (Botrytis cinerea)
Gray mold is the most important postharvest disease of pears and the second most important postharvest disease of apples. Gray mold lesions first appear as pale tan areas without sharp margins. Infections may originate from wounds, stem punctures, or the stem or calyx end of the fruit. As the decay enlarges, the older portions of the decay may turn darker brown, but the edges often remain a paler color. Distinct gray colored conidia develop on the infected fruit.
Moldy core(Alternaria alternata)
Alternaria rot is characterized by round, brown to black, dry, firm, shallow lesions around skin breaks or at the calyx or stem depression. Advanced rots become spongy and the affected flesh is streaked with black. Under moist conditions, dark-colored mycelium may develop in the surface of the lesions.
Bull's eye rot(Pezicula malacorticis)
Lesions are circular, flat to slightly sunken, and most often brown with a lightly brown of tan center. Fungal signs are not evident in young lesions but acervuli are often present in older lesions. Rotted tissue is firm and does not readily separate from healthy tissue. Lesions develop most frequently at lenticels, but they can also occur at wounds or around the stem or calyx.
Mucor rot(Mucor piriformis)
Mucor rot develops at the stem or calyx end of the fruit or at a puncture wound in the skin. Infected tissue is soft, watery, and light brown. Sporangiophores baring sporangia protrude from cracks in the skin. Infected fruit in cold storage will eventually decay, releasing copious amounts of juice containing sporangia that can infect other fruits.
Plant parts attacked and damage symptoms
Green mold (Penicillium digitatum)
The fungus survives from season to season primarily as conidia in the orchard. Infection is initiated by air borne spores that enter the rind through wounds. After infection, a soft water soaked, slightly discolored spot appears. White mycelium appears on the surface of the rind and after it reaches approximately 2.5 cm in diameter, olive green spores are produced. Sporulation and re-infection can occur in the field or in the packinghouse. Spore populations can become quite large if sanitary efforts are not well utilized in the packinghouse.
Blue mold (Penicillium italicum)
Symptoms of early blue mold infections look almost identical to green mold or sour rot infections. Disease tissue becomes soft, watery, and slightly discolored. A white powdery growth of mycelium develops on the surface of the lesion and eventually a blue spore mass forms leaving only a narrow white fringe of mycelium surrounding the lesion.
Symptoms associated with bruised or injured rind are brown to black spots, 1.5cm or more in diameter. The decay may appear firm and dry or, if sufficiently deep-seated, may cause the fruit to become soft. Under high humidity masses of pink or salmon-colored spores develop on the lesion surface. Under drier conditions these spores appear brown or black.
Sour rot(Geotrichum candidum)
Initial symptoms are identical to those of green mold and blue mold. Lesions appear as water soaked, light to dark yellow, slightly raised spots. Extra cellular enzymes produced by the fungus degrade the rind, segment walls and juice vesicles, causing the fruit to disintegrate into a slimy, watery mass. Under high humidity the lesion may become covered with a yeasty, sometimes wrinkled layer of white or cream-colored mycelium.
Diplodia Fruit rot(Diplodia natalensis)
Infections occur most frequently at the stem end of the fruit but occasionally can occur via injuries on the side or stylar end of the fruit. The fungus grows rapidly through the spongy central axis of the fruit. It grows unevenly through the rind, which produces finger-like projections of brown tissue on the infected fruit.