Abstract:

Northern corn leaf blight (NCLB) is one of the major four
diseases threatening the maize industry in Uganda, in
addition to maize streak virus, common smut and rusts. This
study characterised four representative isolates of
Exserohilum turcicum obtained from the major maize growing
districts in Uganda. Isolates were assessed with respect to
their cultural variability, pathogenicity towards local
maize lines and an isogenic series containing the Ht genes
for resistance. Two other isolates one from Zimbabwe and a
2N isolates from USA were included for comparative
purposes.
Experiments conducted in vitro indicated that radial growth
rates between isolates were significantly different.
Ugandan isolates tended to have higher temperature optima
than the Zimbabwean, with the Kasese isolate growing the
fastest. This correlates with typical temperature at the
original location. The Zimbabwean isolate was obtained from
Henderson Research Station with comparatively low
temperatures between 8—26°C while Kasese district has a
minimum temperature of 25°C.
Results obtained from the study of the effect of light
regime on sporulation demonstrated that sporulation was
favoured by continuous darkness while continuous light was
inhibitory. The US (2N) isolate sporulated most vigorously.
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Of the Ugandan isolates, the Masindi isolate produced the
largest number of conidia, followed by Iganga, Mpigi and
Kasese isolates.
Race typing of the Ugandan and Zimbabwean isolates was
conducted in the greenhouse and under controlled
environmental conditions in the growth cabinet. Results
consistent under controlled conditions in the
growth cabinet but still correlated well with those
obtained in the greenhouse. The isogenic line (H4460)
without the Ht gene developed classic necrotic susceptible
type lesions following inoculation with all isolates whilst
H4460Htl, H4460Ht2 and H4460Ht3 exhibited the resistant
chlorotic lesion type. Line A697(W22HtN)
incubation period developing chlorotic flecks when
susceptible to the race 2N from USA.
The relative susceptibility/resistance of six Ugandan maize
cultivars (Babungo (3), Longe 1, topcross, singlecross, and
population 28 and 29) was assessed using one Ugandan
isolate (Kasese) and the 2N (US) isolate. Topcross, Longe
1 and Babungo (3) showed resistance to both isolates while
population 28 and 29 were found to be highly susceptible.
correlation between lesion length, percentage
leaf tissue blighted (% LTB) , lesion number, sporulation
rating, sporulation and susceptibility. Susceptible
cultivars had higher values for all parameters tested.
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but was
had a prolonged
inoculated with Ugandan and Zimbabwean isolates,
There was
were more
Reaction types varied, topcross did not develop any lesions
Babungo (3) developed chlorotic flecks and population 28
and 29 developed chlorotic type lesions
incubation periods compared with the Kasese isolate.
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when inoculated with the US isolate, whereas Longe 1 and
but had longer