Number of isolates of maize root fungi in different crop rotation systems

The effect of monoculture maize and rotation with soybeans, sunflower and groundnuts on the incidence of maize root rot were studied in a long-term rotation trial for three seasons. The number of isolates of the common root colonizing fungi was also determined. Seasonal variables (i.e. moisture) had a significant effect on root discolouration arid results suggested that some environmental conditions, in the presence of certain fungi, contributed more to root discolouration. The spectrum of isolated fungi differed between Seasons and may be ascribed to the effect of variable environmental conditions, particularly rainfall. The highest number of isolates was obtained for Phoma spp. and Fusarium spp .. A significant interaction was observed between rotation treatments and seasons on number of isolates of Fusarium equiseti (Corda) Sacc., Fusarium oxysporum Schlecht. emend. Snyd. & Hans. and Macrophomina phaseolina (Tassi) Goid .. The effect of crop rotation on the number of isolates of these fungi were, however, inconsistent and appears to be complex. Fungi were affected differently by various rotation systems, indicating that no single cropping system favoured all fungi. A Significant seasonal effect was found with regard to crop rotation treatments and grain yield. Although this trial was sampled for three successive seasons, crop rotation may have a long-term effect on soil fungus populations which may only be evident after a longer period of time.