Does Xanthomonas campestris pv. musacearum Colonize Banana Cord Root Tissue

Xanthomonas wilt of banana and enset (XW) caused by Xanthomonas campestris pv. musacearum (Xcm) is a devastating bacterial disease. Infection of pre-flowering stage plants result in leaf yellowing/wilting and eventual plant death. Floral infections result in wilting of male bud bracts, followed by decaying of the rachis, premature fruit ripening and bunch rotting, and eventual death of the plant. The movement of Xcm in infected plants is systemic. However, the presence of Xcm in cord roots of banana plants has not yet been investigated. Cord roots of symptomatic pre-flowering stage and inflorescence-infected plants of an East African highland banana cultivar mixture (AAA-EA) and 'Pisang Awak' (ABB) were examined for Xcm presence, in naturally infested farmers' fields and after artificial inoculation. Pre-flowering stage plants were inoculated by cutting the three oldest leaves with a contaminated knife, while a Xcm suspension was smeared on male flower/bract scars of flowering plants. In addition, pre-flowering stage plants were inoculated by cutting the cord roots with a contaminated knife and drenching the surrounding soil with Xcm suspension. Plants were monitored during 12 months for symptom development. Overall, the presence of Xcm in the cord roots was significantly lower compared to corms. A higher incidence of cord root infection was observed in the artificially inoculated plants compared to plants assessed in farmers' fields. The incidence of cord root infections in inflorescence-infected plants increased with progressing disease development for both cultivars. The results suggest that cord roots could contribute to garden tool transmission, for example during weeding. Therefore, hand weeding and herbicide use are advised when diseased mats are present in a field. Long incubation periods and latent infections were noted after artificial cord root inoculations. The development and deployment of diagnostic kits sensitive to latent infections for routine surveillance is therefore recommended for effective XW management.