Maize root rot in South Africa.
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Date
1995
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Abstract
Numerous fungal species are known to infect maize roots and eventually cause rot. The
spectrum of fungi differs over localities as well as their relative frequencies. Fungi isolated
from discoloured root tissue and root tissue without visible discolouration were classified as
root pathogens and root colonizers, based on their isolation frequency from the respective
samples. Exserohilum pedicellatum, Macrophomina phaseolina and Fusarium oxysporum were
classified as the major root pathogens and Phoma spp., Curvularia spp. and F.
chlamydosporum as root colonizers. Fungi classified as root pathogens tended to occur early
in the growing season in juvenile tissue as opposed to root colonizers which occurred later.
Treatments in an existing long-term water stress trial included no stress (irrigation), normal
rainfall, stress until flowering, stress after flowering until mid grain-fill, stress after
flowering and total stress. Root pathogens were isolated at higher frequencies in the no stress and normal rainfall treatments than in the total stress treatment. A positive linear relationship
between the water stress index and the isolation frequency of M. phaseolina was obtained.
Negative, non-linear relationships were, however, recorded for E. pedicellatum, F.
oxysporum and F. moniliforme. The effect of tillage practices on disease severity was carried
out in field trials at two localities. Tillage practices applied included rip, plough, chisel
plough and no-till treatments. Significant differences between isolation frequencies and tillage
treatments were recorded for F. oxysporum at Bloekomspruit and Trichoderma spp.,
Alternaria spp. and M. phaseolina at Mmabatho. Differences in isolation frequency of fungi
involved in maize root rot, were determined in a crop rotation system where maize was
rotated with soybeans, sunflowers and groundnuts. Crop rotation had a significant effect on
the isolation frequency of Thielavia ferricola, E. pedicellatum, F. moniliforme and F.
graminearum. The effect of crop rotation, however, seems to be complex since fungi were
affected differently in the various treatments.
Description
Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 1995.
Keywords
Corn--Diseases and pests--South Africa., Corn root rot., Fungal diseases of plants., Theses--Plant pathology.