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 characterised four their representative isolates of study Exserohilum turcicum obtained from the major maize growing districts in Uganda. Isolates were assessed with respect to pathogenicity towards local cultural variability, maize lines and an isogenic series containing the Ht genes for resistance. 2N Two other isolates one from Zimbabwe and a isolate from USA purposes. were included for comparative 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, fastest. with the Kasese isolate growing the 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 minimum temperature of 25°C. Results obtained while Kasese district from the study of the effect has a 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. Of the Ugandan isolates, the Masindi isolate produced the largest number of conidia, followed by Iganga, Mpigi and Kasese isolates. Race typing of conducted in environmental the Ugandan and the greenhouse conditions in were more consistent under the Zimbabwean isolates was and under controlled growth cabinet. controlled Results conditions in growth cabinet but still correlated well with the 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 chlorotic lesion type. Line A697(W22HtN) the resistant had a prolonged incubation period developing chlorotic flecks when inoculated with Ugandan and Zimbabwean isolates, susceptible to the race 2N from USA. but was The relative susceptibility/resistance of six Ugandan maize cultivars (Babungo (3), Longe 1, topcross, singlecross, and population 28 and 29) isolate (Kasese) was assessed and the 2N (US) using isolate. one Ugandan Topcross, Longe 1 and Babungo (3) showed resistance to both isolates while population 28 and 29 There 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 highervalues for all parameters tested. Reaction types varied, topcross did not develop any lesions when inoculated with the US isolate, whereas Longe 1 and Babungo (3) and 29 developed chlorotic flecks and population 28 developed chlorotic type lesions but had longer incubation periods compared with the Kasese isolate.