Thursday, May 1, 2014

Diseases of Apple: White Root Rot

This is in continution of my previous post on Diseases of Apple: Collar Rot Management. By now you know about the collar rot symptoms and its managment practices. But a small description about white root rot here will help you distinguish between the two.  White root rot is taking heavy toll in wet temperate zone of Himachal Pradesh, besides fallacy in the diagnose is further making the situation worse. It is important to understand the disease symptoms and how to distinguish the intermingling symptoms. The description on white root rot is given below


White root rot as name indicates the white fluffy growth of mycelium can be seen on roots during monsson months this mycelial mat can be seen on soil level. The disease caused by Dematophora necatrix, a polyphagus fungus that can infect more than 173 plant species. The fungus has been increasingly imposing problem and resulting in the death of plants. Further, death of a tree, due to root rot in an orchard does not mean the end of losses, instead the incitant being soil borne also spread to neighbouring sites. The economic losses, therefore, are likely to multiply in compound manner within and outside the infected orchards.

The fungus first invades feeder roots and disease symptoms can be ascertained on lateral roots, which turn into dark brown colour and become infested with white flocculent fungus during monsoon months. The earliest above ground manifestation of the disease is bronzing of the leaves, stunted growth and size. There is progressive decline in foliage and twig growth. White root rot affected trees are usually associated with a heavy weak blossom and fruiting next year, however in succeeding years, few leaves emerge and much of the immature fruits induce early colouration and fail to reach maturity. Severity in years leads to die-back/drying of twigs and branches. Fibrous roots are completely devoured in advance stage, and the tree dies as cortical and phloem cells are ruptured, which disrupt the translocatory system. Infected trees often persist for 2-3 years depending upon the infestation of the fungus and young trees if infested may die quickly with necrotic leaves still on the dead plant is a characteristic symptom.

In coming post I shall be dealing with the predisposing factors of the disease.