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Phytophthora rot of crown, collar and root of fruit trees

Phytophthora rot of crown, collar and root of fruit trees
Phytophthora rot of crown, collar and root are present in all countries where apples are grown, and damage is greater in areas that use apple shortening stands to plant these trees. The fungus has several varieties that generally cause three types of caries in the tree:
۱- collar rot
Phytophthora rot of collar is related to the transplanted parts. In this caries, the lower parts of the trunk show symptoms on the surface or above the soil (crown). This type of caries is most often caused by phytophthora in trees that their inplantations area is closer to the soil surface.
۲- Crown rot
Phytophthora rot of crown disease is related to the base part of the tree. In this case, the collar skin tissues (root and trunk junction) and the roots of the root of the plant invade and cause caries.
۳- root rot
Phytophthora rot of root involves the root system and parts farther from the collar, and usually occurs with the caries of the collar, although it can appear on its own. In Iran, this rot (crown and collar rot) is not common and does not cause much damage. It has been reported only in Shiraz, Miandoab, Karaj and Shahriar on apple tree.
Symptoms
Phytophthora rots are divided into two groups. The first batch of nonspecific symptoms develop on the diseased shoots. This means that the number of shoots this year will be slow, followed by a decrease in the number of shoots. The leaves are pale and appear purple in early autumn. Fruits sometimes shrink and color before they reach maturity. Therefore, the trees with the disease become weak and dry for a few years, but they can suddenly dry up.
The second type are specific symptoms, which include phytophthora rot, crown, collar and root. These symptoms are often not visible. To see the signs of crown and collar, you need to cut and remove the outer layers of skin to the root surface. In this case, the texture of the wood will be red rather than white, with the color orange to brown.
In Phytophthora rot, if you cut the brown textures of the crown in the inner part of the drainage vessels and in the surface layer of the wooden textures with a knife, a zebra or marble ribbon is seen. Occasionally you will see canker and collar rot and grime-like discharges, which is well visible in the ‘Cox Elbow Pain’ apple variety. In Phytophthora rot disease there is a clear boundary between the infected and the healthy area, and it is interesting to know that most of the fungal activity is at the same boundary, so you can sample the phytophoric caries of the fruit trees to isolate the fungus. In root rot, the roots turn brown and rot, after which saprophytic fungi attack them.
Disease agent (Click to buy disease agent)
Various species of Phytophthora have been recognized worldwide as the causative agent of crown, collar and root phytophthora rot, including P. cactorum globally. syringae in Europe and Canada, P.megasperma in Australia and the United States, P. cambivora in Australia, Japan and the United States, P.cryptogea in Australia and the United States, P. dreshslera and P. citricola in the United States. Be. In Iran, only P. cactorum species have been isolated from apple tree, which we have discussed in the following.
The mycelium of Phytophthora rot of fruit trees agent is colorless with no transverse walls. Older mycelia can be strapped. The asexual reproductive organs are zoospores. The zoospore is formed in sporangia. The sexual reproductive organs are called espore, which is caused by anthracite and eugenics fertilization.
P. cactorum is a hematological fungus. The sporangia are papillae and are sporadic in that they form sympodial on the sporangiophore. It has a parametric antride. In the solid medium, sporangia, eugenes and its spores are well formed. The appropriate temperature for the growth of this species is 26 degrees Celsius and the maximum temperature is 32 degrees Celsius.
Life Cycle and Epidemiology
P. cactorum, like other phytophthora rot of trees, has a wide range of hosts and attacks many crops. The fungus is an earthy species so it can be present in the area before planting. Phytophthora raw material can be introduced into the ground by seedlings or irrigated from the garden to remote gardens. Phytophthora survives after being transferred to the soil around the root of the tree as mycelium or ash in the infected tissues of the host plant or ash in the residues of organic matter or soil. According to the researchers, the main factor in the survival of the fungus in the absence of the plant is that it can also live on fallen fruits on the ground. The most important source of infection in phytophthora rot is zoospores. The optimum temperature for the formation of zoospore within the sporange is about a few degrees lower than the temperature appropriate for mycelial growth. The higher the number of sporangia that cause phytophoric rot in grain trees when the soil moisture is saturated or close to it, so the places where water accumulates for a long time provide conditions for the outflow of zoospores and their propagation elsewhere. Earth provides. According to research, the cause of the movement of zoospores to the roots and crowns may be a chemical phenomenon.

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