Photo by Melody

Definition of brown rot

Categorized under "General"

Definition as written by paulgrow:

A common and destructive disease of stone fruits (e.g., peach, plum, nectarine, apricot, and cherry.)

The fungus may attack blossoms, fruit, spurs and small branches. Under certain conditions, the entire crop can be completely rotted on the tree. Fruit not kept in cool storage may be rotted in two to three days by the fungus.

Symptoms first appear in the spring as the blossoms open. Diseased flowers wilt, turn brown, and may become covered with masses of brownish-gray spores. The diseased flowers usually remain attached into the summer.

Young fruits are normally resistant, but may become infected through wounds. As fruits mature they become more susceptible to attack, even without wounds. Fruit infections appear as soft brown spots which rapidly expand and produce a tan powdery mass of conidia.

The entire fruit rots rapidly, then dries and shrinks into a wrinkled mummy - rotted fruit and mummies may remain on the tree or fall to the ground. Fruit infection may spread rapidly, especially if environmental conditions are favorable and fruits are touching one another.

The fungus may move from diseased blossoms or fruit into the spurs. The fungus may then invade and cause diseased areas (cankers) on the twigs below. Succulent shoots are sometimes infected by direct penetration near their tip. A canker may form encircling the twig, causing death of the twig beyond the canker (twig blight).

Brown rot is caused by the fungus, Monilinia fructicola. It survives the winter in mummified fruits and in twig and branch cankers produced the preceding year. Both sources may produce spores that can infect blossoms and young shoots. At blossom time, a mummified fruit that has fallen on the ground produces up to 20 or more small, tan, cup-like structures on slender stalks that are called apothecia. As an apothecium matures, it becomes thicker and the cup opens to a bowl-like disc l/8 to l/2 inch in diameter across the top. The inner surface of each bowl is lined with thousands of spore-containing sacs (asci). At this stage, the slightest disturbance of air movement will cause an apothecium to forcibly discharge millions of spores.

These spores (ascospores) are carried by wind to the open or unopened blossoms and young shoots. If a film of water (either from dew or rain) is present for 5 hours or longer, the spores can germinate and penetrate the plant. If the infected blossom does not drop off, the fungus soon grows through the pedicel to the twig and forms a canker.


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