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Verticillium rot of fruit

Other names for Verticillium rot of fruit are nucleated fruit trees “Verticillium black brain”, “Verticillium vascular wilt” and “Vascular wilt”. The disease is generally found on apricot, peach, plum, cherry, sour cherry and Nectarine. Also, the bases used for these trees are also susceptible to wilt. The bases include plum “myrobalan” and cherry “mahaleb”. In Iran the verticillium rot disease has been reported on apricots in Shahroud, Khoy, Kerman and Semnan provinces, on almond in Neyshabour, Kerman province, Semnan and Chaharmahal va Bakhtiari; on Cherry and sour cherry in Kerman province, on plum and apricots in Gorgan and Mazandaran province . The damage caused by this disease in Shahroud apricot orchards is significant. Verticillium wilt is the most important cause of drying of fruit trees, especially apricots in Kerman and Semnan provinces.

Symptoms

Apricot and almond trees

In apricot and almond trees, the first sign of Verticillium rot disease is sudden wilting of leaves of one or more branches at the beginning of summer. The leaves are first darkened and quickly wrinkled. Most wrinkled leaves remain on the branches and look like flags. Symptoms of the disease usually appear on the leaves in the branches of the branches, progressing rapidly upwards. Younger trees affected by the disease may fall, but the older shoots may still grow next year. Repeated wilting of the leaves of the affected branches over several years usually results in stopping of terminal growth, low branching or death of the branches. According to two researchers, “the symptoms of Verticillium rot disease in apricots first start with wilting, then with yellowing and leaf falling of several branches, eventually leading to the affected branches drying up and spreading to other branches.” “In the transverse sections of the trunk and branches, the wooden pots turn brown.”

Cherry trees

Symptoms of verticillium rot  and wilting in cherries first appear as wrinkles on the leaves of one or more thorns on the one-year-old shoot. Cherry trees with this disease stop growing; their leaves darken, their growth stops, and their fruits grow abnormally small. Unlike other nucleated fruit trees, older cherry trees are also susceptible to wilting and are likely to lose their resistance to the disease.

Peach trees
Verticillium rot and wilt is a very dangerous disease for peach trees, but the good news is that these trees are less susceptible to this disease than other groups. Brown to dark veins are visible on the woody branches of the diseased branches. This browning is not obvious in the cherry tree but is quite evident in the plum and sloe trees.

Cause of disease
There is still controversy over the species of fungus that causes vascular wilt on nucleated fruit trees and other perennial plants. But nowadays it is accepted that Verticillium dahlia kleb is the causative agent of Verticillium rot. Formerly known as V. albo-atrum, this species produced resistant black mycelium in culture after 10 days but did not produce starch. Also V. dahlia can grow at 30 ° C but V. albo-atrum cannot grow at this temperature.

Verticillium caries disease cycle and epidemiology
Verticillium dahlia is a soil fungus and can live up to 90 cm below the soil surface, but its sklerotes are usually found in 15 to 30 cm of soil. At temperatures above 25 degrees Celsius, the fungus cannot continue to live continuously. Also, soil moisture conditions are detrimental to this microorganism and reduce its biological viability. If soil moisture conditions are appropriate, microsklerotes can survive for several months to a year, even at high temperatures such as temperatures above 30 degrees.

Verticillium transport routes
Entering infected plants into the soil that can infect healthy plants. Transmission of Verticillium rot of fruit agent by wind-polluted soil particles and a knife used for transplantation. When this microorganism enters the new environment, it usually stagnates in the soil as it sleeps or attacks its host plants and weeds and produces more microbes in the soil. In fallow soils that are sandy and clayey, the inoculum of Verticillium is reduced, but a small amount of it remains alive under harsh conditions.
The severity of Verticillium rot of fruit trees is increased in wet soils. Most disease development is at 21 to 27 degrees Celsius, and the best is 24 degrees Celsius. Soil acidity in the range of 4.4 to 6.7 did not have a specific effect on disease development. Many food deficiencies in some plants can exacerbate the disease.
Verticillium rot fruit usually appears on trees in mid-summer and increases in severity in late summer. Tree roots are where Verticillium can survive in the winter and continue to grow the following year

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