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Etiology

Flagellate Protozoon Associated with Poor Development of the Root System of Cassava in the Espirito Santo State, Brazil. E. W. Kitajima, Professor, Departamento de Biologia Celular, Universidade de Brasilia, 70910 Brasilia, DF; Marilene H. Vainstein(2), and J. S. M. Silveira(3). (2)Graduate student, Departamento de Biologia Celular, Universidade de Brasilia, 70910 Brasilia, DF; (3)Researcher, Estação Experimental de Linhares, Empresa Capixaba de Pesquisa Agropecuaria, C. Postal 62, 29900 Linhares, ES, Brazil. Phytopathology 76:638-642. Accepted for publication 16 October 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-638.

'Chochamento das raizes' (empty roots) is a problem of increasing importance in cassava (Manihot esculenta) culture in the northern Espirito Santo state, Brazil. It affects particularly the cultivar Unha, the most cultivated in this region, and is characterized by poor development of the root system and general chlorosis of the aerial parts. A flagellate protozoon (Phytomonas sp.) was found associated with the diseased plants, living in the lacticifer ducts. The protozoon is easily detected by light microscopy in the smears of latex exuded from cut wounds. Under the electron microscope, the flagellates show the typical subpellicular layer of microtubules, single flagellum with 9+2 axial complex and paraxial structure, basal body, and kinetoplast. Field surveys showed that about 50% of the chlorotic Unha cassava plants contained the flagellate in the latex, whereas none was found in symptomless plants. Under greenhouse conditions, the flagellate was transmitted only by grafting. Attempts to transmit the protozoon by injecting or pricking latex suspensions into healthy plants or using a Tingidae hemiptera (Vastiga sp.) as vector have been unsuccessful.