Observations on Root Decay in Coconuts, its Cause and its Relation to the Foliar Symptoms of Disease in the Disease Belt of Travancore-Cochin
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1955
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The common foliar symptoms of disease met with in the disease belt of Travancore-Cochin have been classified into four categories, viz., wilt, tapering stem, yellowing of outer leaves accompanied by nut-fall and general chlorosis. The symptoms in each category are described. A comparative study of the root systems of healthy trees and those exhibiting different types of foliar symptoms, showed that only tapering stem symptoms were consistently associated with a high percentage of root decay. Some of the healthy trees had a high percentage of decayed roots, while a few palms in early stages of wilt (root) disease were free from root decay. There was no significant difference in the extent and frequency of root decay, between healthy trees and those in early stages of wilt (root) disease; it is therefore suggested that the name wilt is more appropriate for this disease (category 'A'). Root rotting observed in the middle and advanced stages of wilt disease, and in the other two categoric (yellowing of outer leaves, and general chlorosis) might be a secondary effect of disease. In the infection experiments with isolates of three fungi, R. solani, R. bataticola and B. theobromae, only one isolate of R. solani parasitised coconut roots causing a brown rot of tissues. There was a difference in pathogenicity between isolates of R. solani. The isolates of the other two fungi that were tried, were not pathogenic. Nematodes associated with a soft rot of roots could not infect living coconut roots and are probably saprophytic. Observations have indicated that biting insects might also contribute towards death of coconut roots and that a persistent high water table or a hard soil pan might pave the way for root decay.
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Indian Coconut Journal, April-June 1955