Spread of Xanthomonas campestris pv. musacearum in Banana (Musa spp.) Plants Following Infection of the Male Inflorescence

Xanthomonas campestris pv. musacearum (Xcm) causes Xanthomonas wilt of banana (Musa spp.) and enset (Ensete ventricosum) in East and Central Africa. The disease is spread by insects that visit the male inflorescence, through the use of infected planting materials and by contaminated garden tools. To evaluate the most appropriate control options, the spread of bacteria within the plant following natural flower infection was studied in Luwero and Mpigi districts of central Uganda. Banana tissue samples were collected from the corm, true stem and leaf sheaths of 'Pisang Awak' (ABB genome) and 'Matooke' (AAA genome) mother plants, showing four progressive stages of disease development: stage 1 - male bud wilting; stage 2 - decaying rachis; stage 3 - premature fruit ripening; and stage 4 -rotting of fruit bunches. Thirty plants were sampled per stage and per cultivar. Additional samples were taken from attached suckers. Bacteria were isolated from surface-sterilized plant samples and identified by colony characteristics on a semi-selective medium. Following inflorescence infection, Xcm moved along the true stem, into the youngest leaf sheaths inserted on the true stem, down into the corm and into the older leaf sheaths. At early stages of inflorescence infection (stage 1), bacteria were restricted to the upper parts of the true stem in 'Pisang Awak', but had moved further down the stem in 'Matooke'. Therefore, cutting down mother plants at stage 1 could stop Xcm from reaching the corm and eventually crossing to the suckers of 'Pisang Awak' but this was less likely to be effective for 'Matooke' plants. The bacteria were recovered from suckers of both cultivars showing symptoms at stage 4, but at stage 3 only from 'Pisang Awak'. It is recommended that whole mats should be completely uprooted or killed by herbicides in case mother plants show symptoms beyond stage 1 for 'Pisang Awak' and at all disease symptom stages for 'Matooke'.