Epidemiology and population dynamics of Phytophthora Infestants in Sub-Saharan Africa: Progress and constraints
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Date
2001
Journal Title
Journal ISSN
Volume Title
Publisher
African Crop Science Journal
Abstract
Global estimates of losses attributed to plant diseases are approximated at 24.8 million dollars, of this amount
3.4 million dollars has been recorded for potato. Of the potato diseases, late blight (Phytophthora infestans) is
the most significant constraint in tropical Africa. Variation in losses of potato caused by late blight have been
documented in several countries, and has shown that yield losses can range from 30 to 75% on susceptible
varieties. In terms of disease cycle, the sources of primary inoculum have not been adequately investigated,
however, the continuos cropping of potato and tomato ensures inoculum presence year-around in tropical Africa.
Data on the low incidence of tuber blight and the lack of evidence for potato seed-borne infection suggests that
tuber blight is not a significant source of primary inoculum in the tropics. Population studies of P. infestans in
Sub-Saharan Africa (SSA) have been conducted primarily on isolates from Uganda, Kenya and S. Africa. Mating
type tests with A1 tester isolates coupled with DNA analysis revealed that the fungal isolates from Uganda,
Kenya and S. Afirca are of A1 mating type (US 1 clonal lineage). Variation and lack of consistency in oospore
production (10 % selfing, 24 % mating, & 15 % non-oospore producers) have been detected among the isolates
from Uganda and Kenya. Similarly, variability in metalaxyl sensitivity, has been detected among these isolates.
Fungicide and variety reaction studies conducted in Uganda, Kenya and Ethiopia suggests that significant late
blight control can be achieved when the protectant fungicide, Dithane (a.i mancozeb) is applied on a scheduled
basis. On-farm research also indicates that three timely applications of a protectant or a protectant fungicide
alternated with systemic fungicide can be effective for late blight management. Results of in-vitro tuber blight
development and host-specificity studies imply that isolates from potato are more virulent than isolates from
tomato. Studies are underway to quantify general resistance of potato varieties as well as to monitor the
significance of fungal population deviations in the region. Decision support systems are in the process of being
developed to optimize fungicide application and variety resistance for late blight management
Description
Keywords
Phytophthora infestans, yield loss, fungal population, epidemiology
Citation
Olanya, O. M., Adipala, E., Hakiza, J. J., Kedera, J. C., Ojiambo, P., Mukalazi, J. M., ... & Nelson, R. (2001). Epidemiology and population dynamics of Phytophthora infestans in Sub-Saharan Africa: progress and constraints. African Crop Science Journal, 9(1), 185-193.