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Factors Determining the Development of Wheat Spindle Streak Mosaic Caused by a Soil-Borne Virus in Ontario. J. T. Slykhuis, Cell Biology Research Institute, Research Branch, Canada Department of Agriculture, Ottawa, Ontario. Phytopathology 60:319-331. Accepted for publication 15 September 1969. DOI: 10.1094/Phyto-60-319.

Wheat spindle streak mosaic, characterized by light green to yellow spindle-shaped dashes and short streaks on the younger leaves, and mosaic and necrosis on the older leaves of winter wheat in May and June, has been widespread most years since 1957 in fields in Ontario, where wheat is frequently grown. It is caused by a manually transmissible, soil-borne virus composed of slender, threadlike particles that contrast with the short rods of wheat (soil-borne) mosaic virus. It has caused yield losses of 7-59% in experimental plots of winter wheat. All cultivars of Triticum aestivum and T. durum tested developed symptoms, but cultivars of Secale cereale, Hordeum vulgare, and Avena sativa did not. Symptoms developed at 5-13 C on wheat grown in infective soil. Optimum conditions were 10 C with 1,000 ft-c of light 12 hr/day. Some plants developed symptoms in 31 days, but most required 60 days or more. In crop years when the disease was widespread and severe, there were more than 60 days with mean temperatures between 4.4 and 12.8 C (40-55 F). The disease occurs on wheat grown on sandy to clay soils, but only after winter wheat has been grown several times in the same field. Soil has remained infective after 5 years either moist or dry in a greenhouse, unprotected outside during all seasons, or moist in a room at 8-12 C. Infectivity was retained in fractions of soil separated by a 0.044-mm sieve or by differential rates of sedimentation in water. Infectivity in soil was eliminated by heating for 30 min at 52 C, drenching with solutions containing mercuric chloride, captan, ethyl alcohol, formalin, or 2,4,5-trichlorophenol, and by fumigating with preparations containing 1,3-dichloropropene and 1,2-dichloropropane, methyl bromide or sodium methyl dithiocarbamate at rates normally recommended for soil disinfection. Fertilizers used at normally recommended rates did not reduce disease development, but the following amendments mixed with soil at the rates indicated eliminated or greatly reduced disease development: urea or uric acid at 0.5 g, ammonium nitrate at 5 g, chicken manure (without litter) at 10 g, turkey manure (with litter) at 50 g, and sucrose at 20 g/liter.