Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/24/2005
Publication Date: 6/25/2006
Citation: Olanya, O.M., Ojiambo, P.S., Nyankanga, R.O. 2006. Dynamics of Development of Late Blight (Phytophthora Infestans) in Potato, and Comparative Resistance of Cultivars in the Highland Tropics. Canadian Journal of Plant Pathology. 28:84-94. Interpretive Summary: Host-resistance is an important component of potato late blight control, particularly in resource-poor regions of the world where growers cannot use fungicides effectively due to their high costs. Potato varieties with major resistance genes(population A), and with minor genes or horizontal resistance (population B), were evaluated for control of potato late blight in field studies during three cropping seasons. Infection rates, late blight severity, tuber blight and yield were quantified to determine the effectiveness of resistance under field conditions. Infection rates and disease severity were higher in susceptible check varieties than in the varieties from either population A or B. Varieties from population A had the lowest amount of late blight. Genotypes from population B had greater disease compared to population A, but also higher tuber yield. These results suggest that populations A and B can be used effectively to manage late blight under low or severe epidemic conditions. The varieties derived from population B appear to be best suited for late blight control in tropical environments due to their moderate resistance and higher yield under intensive disease pressure.
Technical Abstract: Field studies were conducted to determine the resistance of potato varieties to potato late blight at two locations in Kenya during the 2000, 2001 and 2002 cropping seasons. The varieties consisted of population A with R-genes and major resistance to foliar potato late blight, and population B with general resistance and minor genes or quantitative resistance to late blight. Infection rates, disease severity (AUDPC), tuber blight and tuber yield were assessed to determine the level of resistance to late blight. Significant (P = 0.05) differences in resistance were detected among potato varieties. Infection rates as determined by the Gompertz model were higher for the susceptible varieties and lower for resistant genotypes. The rates of disease progress were highest in susceptible check varieties and least on varieties from population A. Differences in late blight progress were detected among the cropping seasons. Similarly, significant differences in tuber blight development were also detected among the varieties, however the presence of major or minor genes in potato varieties were not significantly correlated with foliar resistance. Potato tuber yield was impacted by disease severity. Varieties from population A with major resistance genes and few minor genes had lowest amount of disease, but Population B had the highest tuber yield and appears to be best suited for controlling late blight in tropical highlands of Kenya.