HISTOCHEMICAL AND CYTOCHEMICAL INVESTIGATIONS OF PHENOLS IN ROOTS OF BANANA INFECTED BY THE BURROWING NEMATODE RADOPHOLUS-SIMILIS

The burrowing nematode Radopholus similis is one of the most damaging pathogens on banana plantations. The role of phenolics in plant defens e responses to the nematode was histochemically and ultrastructurally investigated in susceptible and partially resistant cultivars. Histoch emical observations of healthy roots revealed that high levels of lign in, flavonoids, dopamine, cafeic esters, and ferulic acids were associ ated with a very low rate of nematode root penetration in the resistan t cultivar. The presence of lignified and suberized layers in endoderm al cells contributed to limit invasion of the vascular bundle by the p athogen. After infection, flavonoids were seen to accumulate early in walls of cells close to the nematode-migrating channel in both cultiva rs and in all tissues of the infected resistant roots including the va scular tissues. The labeling pattern obtained with the gold-complexed laccase and with anti-pectin monoclonal antibodies showed that phenoli cs were distributed in a loosened pectin-rich material surrounding the nematode. This study provides indications that constitutive phenolics in banana roots are associated with the limitation of host penetratio n and colonization by R. similis. Accumulation of flavonoids in respon se to infection was detected in the vascular tissues of susceptible pl ants and in all root tissues in the partially resistant plants.