Septoria tritici . [Descriptions of Fungi and Bacteria

Abstract

Abstract A description is provided for Septoria tritici [Mycosphaerella graminicola] . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Triticum aestivum and other Triticum spp., as well as Secale vulgare (Sprague, 1950). DISEASE: Leaf spot (or speckled leaf blotch) of wheat. Occurs chiefly on leaves forming light green to yellow spots between the veins. A speckled appearance is later produced when the pycnidia develop in the leaf and sheath lesions which are various shades of brown, elongated, linear to elliptical, sometimes vein-limited, with a diffuse margin, variable in size but not normally exceeding 1 cm in length. Where infection is severe, shrivelling of leaves, defoliation and invasion of the crown tissues may result in weakened or dead plants. Seedlings may also be killed. GEOGRAPHICAL DISTRIBUTION: Africa (Algeria, Ethiopia, Kenya, Morocco, South Africa, Tanzania); Asia (Afghanistan, China, India, Iran, Iraq, Israei, Japan, Korea, Pakistan, Turkey, U.S.S.R.); Australasia (Australia, New Zealand, Tasmania); Europe (Austria, Belgium, Bulgaria, Czechoslovakia, Cyprus, Denmark, France, Germany, Great Britain, Greece, Italy, Netherlands, Norway, Poland, Portugal, Rumania, Spain, Sweden, Switzerland, Turkey, U.S.S.R., Yugoslavia); North America (Canada, U.S.A.); Central America (Guatemala); South America (Argentina, Bolivia, Brazil, Chile, Uruguay). (CMI Map 397, 1963.) TRANSMISSION: By seed which may be contaminated with infected chaff and plant debris (Noble et al. , 1958). The fungus has been intercepted in the United States on stem and leaf fragments in shiploads of wheat grain from Australia (24: 308). Fragments of infected leaves maybe wind dispersed and seed sown with infected leaf debris transmits the disease in the field (38: 687; 42: 11). Spores produced on infected plant residues lose their viability after burial for 1 month in soil (Bilu & Bever, 1957). Pycnidia survive the summer in volunteer wheat plants or in leaves and leaf sheaths lying on the ground, and there are records of conidia from stacked wheat remaining viable for 5-18 months according to the amount of exposure to rain (Weber, 1922; Bilu & Bever, 1957; 36: 389; 38: 657).