Proposed assessment scale for dieback disease severity on passion fruit
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Dieback disease is currently the most economically important disease in passion fruit production in Kenya. The disease gained epidemic status within 4 years of its first recording in 2004. It is estimated that the disease accounts for about 70% of total pre-harvest passion fruit loss in the country. Dieback exhibits a high level of complexity in its symptomatology, pathogenicity and epidemiology. The disease is fairly new in Kenya and has not been reported in other parts of the world where passion fruit is cultivated. These factors coupled with the lack of preparedness to mount an effective response have made it difficult to successfully manage dieback. To develop effective dieback management measures, it is necessary to establish standard tools and protocols for evaluating disease incidence and severity. This paper presents a proposed dieback disease severity assessment scale (scoring chart). The scale is based on observations over a period of over 8 months in Eastern and Central Kenya where passion fruit is an important crop and dieback disease is prevalent. Photographs of diseased plants showing disease evolution/progression were taken at regular intervals. Additional data were collected from controlled experiments to validate field observations. The proposed assessment scale comprises of 5 assessment levels assigned based on observed symptoms. Recommended disease management options are also discussed for each infection level. Photos to aid in symptom description are included.