PHYTOPHTHORA DISEASES OF PLANTATION CROPS IN INDIA

Abstract

The genus Phytophthora began with type species P. infestans de Bary. At present, the genus contains 50 morphological species. The species of phytophthora are unique and can be distinguished from other fungi by their special characters such as vegetative diploidy, presence of cellulose in the cell walls instead of chitin, heterokont flagella in zoospores and resistance to polyene antibiotics such as pimaricin. The genus Phytophthora belongs to the family pythiaceae of the order peronosporales within Oomycetes under kingdom Mycetae;most of them are serious plant pathogens causing wide range of disease on food. Vegetable, forage, fruit,ornamental,plantation crops and forest trees. They attack roots, stem bases, growing points, fruits and foliage of plants. Aithough a large number of taxonomic keys are available, the identification of phytophthora is still seems to be difficult due to limited morphological criteria based on which species are being identified and a large amount of variability and overlapping exits within species. The biochemical and molecular evidences such as protein patterns, isozyme profile, mt DNA-RFLP and rDNA sequence data have shown that phytophthora taxonomic keys based on morphological criteria have limitations as exemolified by P.megasperma species complex and P. cryptogea and P. drechsleri. Revised classification schemes involving a combination of both morphological and molecular criteria may be needed. Studies on host-pathogen interactions indicated that phytophthora species do not possess unique specialized machinery for colonizing their respective hosts. Structural features of the hosts, performed chemical inhibitors,induced structural barriers, hypersensitive reaction and phytoalexins have been reported to provide resistance against phytophthora. However, host resistance in all the crops is either inadequate or totally absent.Though integrated disease management is the stategy, fixed schedules of prophylactic copper fungicidal applications still hold good for coconut, arecanut, cocoa and rubber. The systemic fungicides like metalaxyl, fosetyl-AI and potassium phosphonate were also found equally effective in checking phytophthora on coconut, arecanut, black pepper and cardamom. Even though copper fungicides are effective, Phytosanitation coupled with eco-friendly bio-control methods through soil application of Trichoderma and Gliocladium, VAM and fluorescent pseudomonads have been found to be highly promising for management of soil borne problems like capsule rot of cardamom and foot rot of black pepper . Biocontrol options are less attractive for other crops because of the target infections are aerial parts. Innovative methods like disease guards have been highly cost effective in managing arecanut Phytophthora.