Reaction of some citrus cultivars to Phaeoramularia fruit and leaf spot in Kenya

摘要

Phaeoramularia fruit and leaf spot of citrus was first reported in Kenya in 1984. It affects 20% of total citrus hectarage in Kenya and causes 20 to 100% yield loss. The reaction of commonly grown citrus cultivars to P. angolensis was studied. The study was carried out for a period of 2 years (4 seasons). Cultivars were assessed for susceptibility to P. angolensis using leaf assays under laboratory conditions and by field observations on disease incidence and severity on fruits and leaves. Susceptibility varied among citrus species and cultivars within a species; also in the same cultivar, fruit and leaves were not equally susceptible. Marsh seedless grapefruit was most susceptible while Tahiti lime was least. Incubation and latent periods rangedfrom 9 to 16 d and 16 to 32 d in Marsh seedless grapefruit and Tahiti lime, respectively. No significant differences were observed on relative sporulation of the fungus on the various species/cultivars. Spore germination and stomatal penetration percentages were not significantly different on Marsh seedless grapefruit and Tahiti lime but there was a marked difference in disease severity. Since all citrus types grown in Kenya are affected by the disease, susceptibility or resistance alone does not offera solution to the problem, and, therefore, incorporation of chemical intervention in disease management is necessary. It is concluded that the leaf assays used in this study could be useful in in vitro screening of citrus for resistance to P. angolensis.