Variation in pathogenicity of Exserohilum turicicum and resistance of ohs10 and inbred maize lines to the pathogen in Uganda

Northern leaf light of maize, incited by the fungus Exserohilum turcicum (Pass) Leonard and Suggs, is a devastating disease of maize in all maize growing regions of Uganda. Variation in pathogen firness, level of resistance to E.turcicum on Oh$10 maize lines and reaction of inbred maize lines were studied in Kabanyolo, Uganda, with a view of characterizing host-pathogen interactions and to identify possible breeding materials for resistance to this pathogen. A greenhouse study was conducted to investigate variations in lesion numbers, size, sporulation incubation and latent periods following inoculation of three open-pollinated maize cultivators with six isolates of E.turcicum. Results obtained indicated tthat isolates were more varied among themselves than the cultivators tested, and cultivator X isolate interactions could be explained by random variations only. A single factor analysis was therefore performed, on pooled data of the three maize cultivators to characterize parasitic variations among the isolates. Spore production was significantly (P<_0.01) different on three cultivars, and the highest and least sporulation were recoreded on EV8428-SR and Babungo 3, respectively. Differences in area under disease progress curve of lesion number data showed that differences among isolates were significant (P<0.05). lesion number data were also transformed using the logistic model and max 10 was considered. The logit values were regressed over duration of disease assessment to determine the apparent infection rates. Differences in apparent infection rates were not significant (P>0.05). Lesion length and area, however, varied significantly (P<0.05) among the isolates while differences in lesion width were not significantly differently among the isolates. Generally isolates form Rakai. Kabale and Kabanyolo were more fit than the rest. In a separate field study, twenty ohS10 lines were evaluated for resistance to E.turiculum. plants were evaluated for resistance to E. turiculum. Plants were artificially inoculated using infested sorghum seeds. There was a wide range of resistance to E.turicicum. Generally ohS10 lines had fewer lesions and lower AUDPC values than Mo17, the polygenic resistant check. Lines S¬1-30, S2-30-2, S2-33-1 and S2-33-3 showed very high level of resistance to E.turicicum. the results suggest that about 30% of the lines evaluated had high level of rate-reducing resistance to E.turcicum. Reactions of maize inbred lines with and without Ht gene(s), an open-pollinated maize population (H99) and X-pioneer hybrid to E.turicicum were also studied under field conditions. Lines without Ht genes (A619, A635 and B73) were most susceptible. Lines with Ht, Ht2, Ht3 genes showed very low disease level and did not differ significantly among themselves. X-pioneer hybrid recorded high disease level, however, H99 showed significantly lower disease level than other maize genotypes. Reaction of maize inbreds with the Ht genes to E.turicicum indicated presence of only race 0.