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This paper presents some aspects of latex coagulation inside latice vessels of roots of Hevea brasiliensis infected by two fungi: Rigidoporus lignosus and Phellinus noxius. Three stages are described in latex coagulation: the phase of latex destabilisation characterized by the bursting of vacuoles and lysosomes membranes; the phase of latex coagulation characterized by the fusion of rubber particles and the disorganization of the cytoplasm; the formation of shots of rubber clumps indicating the final stage of coagulation. [ABSTRACT FROM AUTHOR]

Two root-rot fungi, Rigidoporus lignosus and Phellinus noxius are the causal agents of severe damage in Ivory Coast rubber tree, Hevea brasiliensis, plantations. Mathematical investigations were made using data from a previous 6 year long epidemiological survey. Modelling of spatial spread of the pathogens and mortality of the infected trees, lead to simulations of the quantitative evolution versus time of root diseases. The theoretical kinetics obtained revealed intra and interspecific variability among the studied stands with respect to the damage caused.

Pathogenicity of isolates of R. lignosus and P. noxius collected from rubber and forest trees, was tested on young rubber plants (Hevea brasiliensis) using a technique of artificial inoculation under controlled conditions (e. g. soil moisture). After two months, almost all the plants inoculated with various isolated of R. lignosus were infected and differences in virulence were apparent. After five months, these differences were reflected in the mortality rates of the inoculated plants. For some isolates the attack begins early and abruptly, whereas for others, symptoms appear more gradually. With P. noxius, differences appear also very distinctly in the pathogenicity among the isolates during the entire duration of the experiment. Principal-component analysis of the data recorded has demonstrated variations in pathogenicity among populations of R. lignosus and of P. noxius. The fact must be borne in mind when control methods of these diseases of rubber tree are developed. [ABSTRACT FROM AUTHOR]

The aggression of Hevea brasiliensis roots by two root-rot fungi, Rigidoporus lignosus and Phellinus noxius is studied at cellular level. Ultrastructural observations reveal the root penetration and tissues colonization by the fungal hyphae, showing clearly alteration in the host cell wall, leading to the root decays This paper describes the different mechanisms used by these two fungi in degrading lignified and non lignified tissues. [ABSTRACT FROM AUTHOR]

The study of the degradation of slats shows that P. noxius, just as R. lignosus, is capable of degrading lignin. Both pathogens are thus white rot fungi. In this framework, the comparison of the behaviour of these two fungi with that of Antropodia sp. , a known brown rot agent, is particularly illustrative. Lignin assays showed the tendency of R. lignosus to preferentially degrade lignin, while P. noxius preferentially degrades the polysaccharide fraction. Finally, both fungi also cause considerable changes in the residual lignin by modifying the monomer composition of the polymer. In vivo and in comparison to healthy tissues, there is a significant increase in the lignin content of infested tissues removed from the front of R. lignosus progression. It would appear that Hevea reacts by an increased synthesis of lignin. This reaction is ineffective, since the pathogen ultimately degrades the polymer. Such reaction is much less evident in case of attack by P. noxius. In terms of the monomer composition of lignin, there are changes in the tissues colonized for the longest times, comparable to that observed in vitro. [ABSTRACT FROM AUTHOR]

In vitro and in vivo inoculation methods with two rooting fungi were tested on young rubber trees. In vitro, experimentation did not succeed. In vivo, under greenhouse conditions, the effect of different parameters has been quantified and a practical method for infecting plants is proposed. With Rigidoporus lignosus, an artificial inoculum i.e. eleven months preinfected wood segments of rubber branches, produced the best infections. Because of the particular biology of this fungus (pathogenicity controlled by an aerobic micro-environment), saturation of the soil of the inoculation pots increased plant mortality significantly. With Phellinus noxius, a similar method of inoculation has to be used. However, study of the effect of age of inoculum on the severity of attack revealed a better efficacy of a five months old inoculum. The nonexistence of rhizomorphs for this parasite necessitates direct host-parasite contact during the incubation. Finally, with this experimental model, it is possible to study plants infected by R. lignosus and P. noxius at all the pathogenic stages. [ABSTRACT FROM AUTHOR]

Three phenol oxidases, of which two are excreted by Rigidoporus lignosus and one by Phellinus noxius, have been isolated and purified from culture filtrates. Based on their substrate specificities and spectral characteristics, these enzymes are p-diphenol : oxygen oxidoreductases (laccases; EC 1.10.3.2). A number of their physicochemical properties have been determined. The fact that the two parasites excrete laccases indicates that they belong to the group of lignin degrading (white rot) fungi. Laccase L1 from R. lignosus was purified to homogeneity. [ABSTRACT FROM AUTHOR]