Assessment of the infection avenues of Fusarium xylarioides into coffee and histopathology of the inoculated coffee tissues.

The aim of this study was to identify infection avenues of the fungus Fusarium Xylarioides and subsequent pathogen development within coffee tissues. Two commercial clonal varieties robusta coffee 1s/3, 257/53, one arabica (SL14) at 4 months oldand volunteer seedlings from traditional robusta were used for studying entry points. Seedlings were subjected to inoculation with 1.3 x 10 spores ml-1 suspensions of F.xylarioides through the leaves, roots and stem without and after wounding. Incidence of coffee wilt disease was recorded to be highly significant within treatments which involved wounding prior to inoculations (P<0.05). The highest incidence was recorded among wounded roots and stems. The Arabica (SL14) did not exhibit any other symptoms of CWD after loss of first symptomatic leaves. The symptoms observed on inoculated robusta seedlings varied form those observed on robusta coffee in the field by virtue of the type of necrosis exhibited. It was therefore shown that the pathogen penetrates the host through wounds on the stems and roots. Development of Fusarium Xylarioides in the coffee tissues was studied in 4 month old seedlings of robusta clones Is/3, Is/6, 223/32, 257/53 and Arabica variety SL14. These were inoculated by root dip method and stem nick wounding method using inoculum density stated earlier. All inoculated plants were maintained in the screen house at CORI ans sampled at 7,14,22,49 and 53 days post inoculation for sectioning. Sections (Icm) of stem/roots at 5 microns were made and fixed in formol acetic alcohol (10%), processed by paraffin method, stained with safranin and studied by light microscope at varying magnifications. The presence of Fusarium xylarioides in the coffee plant was characterized by mycelia (observed to be stained blue) in the vessel elements. Plugging of xylem vessel parenchyma cells and the formation of cavities in the vascular cylinder and pith regions of the stem were observed. The Arabian sections did not have any mycelium developing in the tissues, however, on the contrary no mycelium development was observed in the Arabian sections. Granulation was observed in the xylem and pith regions of the Arabian stems.