Comparative importance of infection routes for banana Xanthomonas wilt and implications on disease epidemiology and management

Abstract

Banana Xanthomonas wilt (XW), caused by Xanthomonas campestris pv. musacearum (Xcm), results in up to 100% yield loss. The efficiency of XW infection through the corm, pseudostem inoculation at bunch harvest, leaf, female and male bud bracts was evaluated in banana plants. The male and female bud bract inoculations caused the highest incidence (81% and 93%) compared with 0–44% for harvest and corm inoculations. Naturally mediated insect transmission in ‘Pisang Awak’ resulted in up to 99% disease incidence. Floral inoculations and natural insect-mediated infections only resulted in floral symptoms. Symptom development in insect-transmitted infections simulated artificial male bud inoculations, confirming the male bud bract wounds as the main entry points for insect vector-mediated infections, thus reaffirming the importance of continuous and timely debudding to limit insect spread. Leaf and harvest inoculations resulted only in leaf symptoms, while corm inoculations resulted in late floral symptoms. Floral inoculations were the main mode of infection. Single leaf inoculations resulted in 30% plant mortality despite 100% incidence, with 70% of plants recovering and bearing visibly healthy bunches and suckers. Thus, detection of a diseased plant in a mat shouldn’t warrant the destruction of the whole mat. A significant difference in Xcm cfu g−1 was observed between symptomatic and symptomless leaves, suggesting that practices that keep the bacterial load below the disease-causing threshold could benefit the plant. This could explain the observed success of XW control through removal of single diseased stems in farms.