Chemical and structural barriers to Microcyclus ulei, the agent of South American leaf blight, in Hevea spp.

Abstract

SummaryYoung leaves of different rubber‐tree clones were inoculated with Microcyclus ulei under controlled conditions. Under ultraviolet light, intense blue fluorescent light was emitted from the penetration site 6 h after inoculation. The speed of the appearance of this fluorescence was related to the degree of resistance of the clones: 12–36 h in totally resistant clones, 36–120 h in marked partially resistant clones, and 120 h in weak partially resistant clones. The source of this fluorescence may have been scopoletin. Strong accumulation of this coumarin may inhibit pathogen invasion in a very early phase. Four days after inoculation, intense accumulation of lignins in only a few cells at the penetration sites was observed in totally resistant clones. Intense lignin accumulation around lesions may also stop pathogen development in some partially resistant clones