Phytophthora: a Genus of Interest.

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Species Diversity in Genus Phytophthora

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S.K. Chile, V.V. Mishra and R.M. Anadeo* Department of Botany Govt. Post Graduate College, Seoni (M.P.) India * Retired Principal Govt. P.G. College, Chhindwara (M.P.) India

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The genus Phytophthora has attracted the attention of both mycologists and plant pathologists on account of its interesting biology. As fungi the systematic position of Oomycetes to which this genus belongs, has always been the crux of discussion amongst biologists. Its status as a member of fungi kingdom has also been questioned (Alexopoulos, et. al., 1996).

Systematic position and Taxonomy of Phytophthora : 

Systematic position and Taxonomy of Phytophthora The old Phycomycetes has been split to induct many independent classes, one of them is Oomycetes. Sparrow (1976) questioned the validity of the term ‘Oomycetes. Kreisel (1969) and Shaffer (1975) have excluded them from the kingdom fungi. Because of their closeness to the algae especially Xanthophyceae these fungi are some times called ‘Algal fungi’.

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The Oomycetes have been treated in several ways in groupings of heterokont organisms such as the; subdivision Peudofungi, phylum Heterokonta of the Kingdom Chromista (Cavalier-Smith, 1986, 1987) or sudivition Heterokontimycotina of the kingdom Heterokonta (Dick, 1976, 1990). Margulis et. al., (1989) have made another approach to include them in Protoctista.

Alexopoulos, et. al. (1996) in the fourth edition of ‘Introductory Mycology’ classified the genus, Phytophthora, : 

Alexopoulos, et. al. (1996) in the fourth edition of ‘Introductory Mycology’ classified the genus, Phytophthora, Kingdom Stramenopila, Phylum Oomycota, Class Oomycetes, Order Perenosporales, and Family Pythiaceae.

Phytophthora is fungus-like, is commonly referred to as a fungus and is studied by mycologists. There are a number of features which set Phytophthora apart from 'true fungi' including. : 

Phytophthora is fungus-like, is commonly referred to as a fungus and is studied by mycologists. There are a number of features which set Phytophthora apart from 'true fungi' including. Asexual reproduction by means of biflagellate zoospores with a longer tinsel flagellum directed forward and a shorter whiplash flagellum directed backward. Various features of zoospore ultrastructure. aseptate hyphae

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Cell walls composed primarily of Œ-glucans but also containing hydroxyproline as well as small amounts of cellulose rather than chitin Diploid thallus in which meiosis occurs in the developing gametangia. Oogamous reproduction by gametangial contact that results in the production of the thick walled sexual spores termed as oospores. Mitochondria with tubular critae. Various biochemical and molecular characteristics.

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As against single-cycle pathogens, Phytophthora has a devastating potential because it is multi-cyclic and can produce inoculum continuously after the initial infection, as long as conditions remain favorable. some species may live saprophytically as water-moulds, the majorities of pathogenic forms have no prolonged free-living saprophytic existence, but survive in the soil in the form of oospores, chlamydospores, or within diseased host tissue. Dynamic nature; by the continuous appearance of new pathogenic races in the field and by frequent sectoring of colonies in the laboratory

Species Diversity in Phytophthora : 

Species Diversity in Phytophthora Waterhouse (1963) presented a key for the identification of the species of Phytophthora in which he included 38 species validly published till 1963. Ho (1981) incorporated 52 species of Phytophthora. Erwin and Ribeiro (1996) described 64 species of Phytophthora.

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Variability in some species of the genus also permits the recognition of few varieties and formae speciales (Brasier, 1991). The morphological differentiations of the major species of Phytophthora do not necessarily represent genetic differences among the species. Isolates with divergent sporangial characters, temperature requirements, and hosts have sequence homology in their ITS DNA.

The molecular methods will provide useful and rapid tools for identification of species : 

The molecular methods will provide useful and rapid tools for identification of species Protein electrophoresis, Isoenzymes, DNA polymorphisms, Karyotype analysis, and Chromosome electrophoresis PCR Amplification of DNA A web-based molecular identification tool

Molecular Genetics of Phytophthora : 

Molecular Genetics of Phytophthora Genome size. Genome organization Genome instability Gene structure Genetic maps. Genomic resources. The elicitor-receptor model in Phytophthora Biochemistry of Phytophthora infected plants.

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Mechanisms of infection by Phytophthora Adhesion, penetration, and colonization of host tissue. Biochemistry of Phytophthora infected plants. Suppression of host defense responses. Induction of defense responses and disease-like symptoms. Phytophthora vs. Antibiotics Symptomology of Phytophthora Diseases

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Symptomology of Phytophthora Diseases The following figure shows the range of symptoms caused by different species of Phytophthora Crown Rot Collar Rot Trunk Canker Butt Rot Stem Canker Bud Rot Fruit Rot Pod Rot Foliar Blight Root Rot Tuber Rot Phytophthora capsici Phytophthora infestans Phytophthora phaseoli Phytophthora capsici Phytophthora citricola Phytophthora citrophthora Phytophthora megasperma Phytophthora nicotianae Phytophthora cinnamomi Phytophthora erythroseptica Phytophthora infestans Phytophthora fragariae Phytophthora sojae

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Thank you