01437naa a2200157 a 450000100080000000500110000800800410001910000190006024500570007926000090013652010260014565000100117165300140118170000180119577300660121318389752012-12-07       1990    bl ---       0--  u    #d1 aMAAS, E. M. C.  aCrop rotation and take-all of wheat in South Africa.  c1990  aThe effect of double-cropping with soybeans, maize, tobacco and sunflower, as well as fallowing and a single solarization treatment on take-all, soil fertility, microbial activity and microbial antagonism was investigated in 5 yr field experiment. Rotation crop exudates were evaluated for their effect on pathogenicity of Gaeumannomyces graminis var. tritici. Soybeans, sunflower and the fallow treatment significantly increased take-all disease level in comparison with maize, tobacco and the solarization treatment. Soil fertility levels and microbial activity could not be related to disease level. The number and kinds of micro-organisms antagonistic to Ggt were significantly affected by the rotation crop and were associated with the lower disease level resulting from rotation with maize and tobacco. Soybean root exudates significantly increased pathogenicity of Ggt in comparison with wheat, maize and tobacco root exudates as well as the no exudate control. Tobacco root exudates resulted in the least disease.  aTrigo  aRotação1 aKOTZÉ, J. M.  tSoil Biology and Biochemistrygv. 22, n. 4, p. 489-494, 1990.