The Relationship Between Time of Cortical Senescence and Foliar Symptom Development of Phymatotrichum Root Rot of Cotton

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Abstract
Borescopic observations revealed that Phymatotrichum omnivorum is capable of attacking roots of cotton seedlings 5 days after emergence. Roots in contact with the fungus became water-soaked and discolored. The fungus colonized the root and new strands originated from the colonized region. Disease symptoms were restricted to the root; no foliar symptoms appeared until the root cortex sloughed. Cortex sloughing occurred 18-25 days and plant death 27-50 days after seedling emergence, regardless of the age at which cotton plants were exposed to sclerotial inoculum of P. omnivorum. The expression of phymatotrichum root rot symptoms on cotton is intimately associated with cortical senscence.