FLAGELLATE PROTOZOAN ASSOCIATED WITH POOR DEVELOPMENT OF THE ROOT-SYSTEM OF CASSAVA IN THE ESPIRITO-SANTO STATE, BRAZIL

"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 protozoan (Phytomonas sp.) was found associated with the diseased plants, living in the lacticifer ducts. The protozoan 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 protozoan by injecting or pricking latex suspensions into healthy plants or usign a Tingidae hemiptera (Vastiga sp.) as vector have been unsuccessful.