Submitted to: Journal of Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/4/2008
Publication Date: 2/2/2009
Citation: Osiru, M., Olanya, O.M., Adipala, E., Lemaga, B., Kapinga, R. 2009. Stability of Sweet Potato Cultivars to Alternaria Leaf and Stem Blight Disease. Journal of Phytopathology. 157:172-180. Interpretive Summary: Alternaria leaf and stem blight is an important disease of sweet potato in tropical and sub-tropical environments. To assess the use of disease resistant cultivars, experiments were conducted in diverse environments in which disease levels and root yield were quantified. Variable disease levels were recorded among sweet potato cultivars, and across locations and years. Ranking of cultivar susceptibility based on statistical predictions varied among environments, but low disease estimates were consistently found for some cultivars. Statistical estimates of disease values were similar to actual values observed in field experiments. These results suggest that statistical models can be applied to estimate the relative reaction of sweet potato cultivars to Alternaria disease. The potential for increased sweet potato production may be enhanced by selectively deploying cultivars with low and stable disease susceptibility.
Technical Abstract: Alternaria leaf petiole and stem blight is an economically important disease of sweet potato (Ipomoea batatus L) in tropical and sub-tropical environments. Published research on cultivar resistance to the sweet potato disease is limited. To evaluate cultivar reaction and stability to the disease, multi-location and replicated experiments were established in twelve environments in Uganda. Disease severity (area under disease progress curves – AUDPC), and cultivar root yield were also assessed. Significant differences (P <0.001) in AUDPC were detected among cultivars. Mean AUDPC ranged from 46.3 (Araka Red) to 78.4 (New Kawogo) across locations and seasons, and the genotypes Araka Red and Tanzania had the lowest disease values. The location and season effects accounted for 67.1% and 7.5% of the total variance of AUDPC recorded among cultivars. Ranking of cultivars based on predicted AUDPC from the Additive Main Effect and Multiplicative Interactive model (AMMI) showed that the susceptible check and New Kawogo were most susceptible to the disease in 6 of 12 and 5 of 12 environments, respectively. Low and stable disease was consistently recorded and predicted on NASPOT 3 and the landrace cultivars Tanzania, Dimbuca, and Araka Red across environments. These results indicate that landrace cultivars had relative stability to the disease and wide adaptation across environments. In addition, the AMMI statistical model and other multivariate techniques are useful tools for predicting Alternaria disease stability.