Source Year: 1996

After inoculation with M. ulei, Hevea leaflets produced a coumarin, scopoletin, in the infected zones. The degree of resistance of 4 clones was related to the rapidity and intensity of scopoletin accumulation. Thus, 24 h after inoculation, the clones with total resistance and those with a high level of partial resistance displayed an early accumulation of scopoletin that intensified and lasted longer than 48 h in the fully resistant clones. The level of partial resistance was positively correlated with scopoletin concn 48 h after inoculation. The fungitoxic effect of scopoletin was verified in vitro on M. ulei where 2 mM cocn were sufficient to strongly inhibit germ tube elongation and conidium germination. In situ, 24 h after inoculation, conidium germination and number of infection sites were lower in the most resistant clones. The fungitoxic effect of scopoletin was tested on 2 other leaf pathogens of H. brasiliensis, Colletotrichum gloeosporioides [Glomerella cingulata] and Corynespora cassiicola. Cocn double or more than those tested on M. ulei were required for total inhibition of germination and germ tube elongation.