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Rigidoporus microporus is a major threat to Hevea brasiliensis in the rubber growing regions of the world. In vitro synthetic fungicidesensitivity assays of Tridemorph, Benomyl and Bayfidan at seven different concentrations, and in vivo effectiveness of the three fungicides on R. microporus inoculated on rubber seedlings were evaluated. The three chemical fungicides used in this study were effective on R. microporus, with Tridemorph being the most effective. The minimum inhibitory concentration value for Bayfidan was between fungicide concentrations of 0.001µg/ml and 0.005µg/ml. Percentage of plant death and presence of rhizomorph recorded at two months after inoculation were higher than that recorded at the termination of five months experimental period after inoculation. Tridemorphtreatment had the highest plant health both at two months and at five months after inoculation. Decline in plant death from the third months onward suggested a reduction in fungal activity of R. microporus. Tridemorph was most effective among the three fungicides tested as it exhibited higher mycelial percentage inhibition in the management of R. microporus in vitro and higher plant health of rubber seedlings in vivo.

The potential of fluorescent bacteria as biological control agents for white root disease caused by Rigidoporus lignosus has been investigated. Isolation of bacteria from the soil using S1 media produced two fluorescent bacteria isolates. Using the Microbact 12A+12B method, both bacteria were identified as Pseudomonas fluorescens and P. aeruginosa. These two species of bacteria were then used as antibiosis activity test against R. lignosus. Four series antibiosis activity tests were done, that were antibiosis test of media culture bacteria growth to R. lignosus colony, antibiosis test of dry fluorescent pigment extract to R. lignosus, influence of Fe3+ to antibiosis activity of bacteria test, and affinity of media supernatant to Fe3+. The results were: antibiosis activity of King’s B (KB) media was more effective than media 523 in the inhibition of R. lignosus colony growth. There was no significant different antibiosis activity of dry fluorescent pigment extract from media KB and media 523 in the inhibition of R. lignosus colony growth. The level of Fe3+ in the media might influence antibiosis activity of fluorescent pigment. Affinity test of KB supernatant from fluorescent bacteria culture with Fe3+ showed an absorption peak of 410 nm on spectrophotometer, and none for the fungi. These results indicate that P. fluorescens and P. aeruginosa produce cathecol-type siderophore with high affinity against Fe3+ compared with hydroxamate-type siderophore which is generally produced by fungus.

The study was conducted to evaluate in vitro and in vivo control of fungal antagonists on Rigidoporus lignosus (klotzsch) Imaz in Hevea brasiliensis (Willd. ex A. Juss.) Muell. Arg. in the rain forest zone of Nigeria. In vitro assessments of biological agents were carried out in dixenic cultures in Petri plates. In vivo tests were carried out in the nursery using Hypocrea virens and Hypocrea jecorina . Significant differences were observed with the dual inoculations of fungal antagonists and R. lignosus inoculated the same day, and the antagonists inoculated 24 h before inoculation of R. lignosus . Hypocrea jecorina was most effective in the control of R. lignosus with percentage inhibition of 86.83 %. Hypocrea virens , H. jecorina , Trichoderma spirale , Trichoderma sp., Trichoderma sp. Pers, and Hypocrea lixii were effective on R. lignosus . Fungal antagonists inoculated 24 h before inoculation of R. lignosus exhibited higher inhibitory efficacies than antagonists and R. lignosus inoculated the same day. In the in vivo evaluation of fungi antagonists on R. lignosus , seedlings in H. jecorina treatment at 60 d and H. virens treatment at 150 d after inoculations respectively had the highest plant heaths (highest length of stem and length of tap rot, lowest plant death, and least foliar symptom) compared to the control. Mortality rate was higher at 60 d after inoculation and decline from the third months onward. Significant differences were observed between the control and R. lignosus treatment in all the parameters evaluated. [ABSTRACT FROM AUTHOR]

Highlights: [•] The RIL activity at low pH value is controlled by an ionizable residue present in its active site. [•] DEPC derivatization of accessible His of RlL affect the kinetic behavior of RlL with pH and ionic strength. [•] Main role of His-457 in the control of the catalytic activity of laccase from Rigidoporus lignosus. [Copyright &y& Elsevier]

The white rot fungus Rigidoporus lignosus produces substantial amounts of extracellular laccase, a multicopper blue oxidase which is capable of oxidizing a wide range of organic substrates. Laccase production can be greatly enhanced in liquid cultures supplemented with various aromatic and phenolic compounds. The maximum enzyme activity was reached at the 21st or 24th day of fungal cultivation after the addition of inducers. The zymograms of extracellular fluid of culture preparation in the presence of inducers, at maximum activity day, revealed two bands with enzymatic activity, called Lac1 and Lac2, having different intensities. Lac2 band shows the higher intensity which changed with the different inducers. Laccase induction can be also obtained by adding to the culture medium olive mill wastewaters, which shows a high content of phenolic compounds [ABSTRACT FROM AUTHOR]

A study was conducted to determine the spatial distribution of somatic incompatibility groups (SIGs) in Rigidoporus lignosus populations responsible for white root disease in a south Sumatera rubber plantation. Most isolates colonizing the stumps were somatically compatible with isolates from either a nearby stump or a living rubber tree, which suggested evidence of stump-to-tree or stump-to-stump clonal growth of the fungus. SIGs of R. lignosus occupied an area territorially in which the minimum size estimate for the largest genotype was 25?m in length. [ABSTRACT FROM AUTHOR]

The structure and thermal stability of a laccase from Rigidoporus lignosus (Rl) was analysed by Fourier-transform infrared (FT-IR) spectroscopy. The enzyme was depleted of copper atoms, then part of the apoenzyme was re-metalled and these two forms of the protein were analysed as well. The enzymatic activity, lost by the removal of copper atoms, was restored in the re-metalled apoenzyme and resulted similar to that of native protein. The infrared data indicated that the enzyme contains a large amount of β-sheets and a small content of α-helices, and it displayed a marked thermostability showing the Tm at 92.5 °C. The apoenzyme and the re-metalled apoenzyme did not show remarkable differences in the secondary structure with respect to the native protein, but the thermal stability of the apoenzyme was dramatically reduced showing a Tm close to 72 °C, while the re-metalled protein displayed the Tm at 90 °C. These data indicate that copper atoms, beside their role in catalytic activity, play also an important role on the stabilisation of the structure of Rl laccase. About 35% of the polypeptide chain is buried and/or constitutes a particular compact structure, which, beside copper atoms, is probably involved in the high thermal stability of the protein. Another small part of the structure is particularly sensitive to high temperatures and it could be the cause of the loss of enzymatic activity when the temperature is raised above 45–50 °C. [Copyright &y& Elsevier]

Early detection of root diseases is a great problem in perennial crops, especially in rubber tree. Planters are continually confronted with the balance of efficiency/cost of the detection. Therefore, a trial was set up to compare three sampling densities and four exposure techniques for detection of white root rot in rubber plantings. A complete census of all trees is the only efficient method of detection in a control program. When reducing the sampling density, a lot of infected trees are not detected and they remain an inoculum source for the spread of the disease. Mulching for one month followed by root exposure is the best technique to reveal the presence of the fungus. The sampling density is of greater significance than the infection exposure method. [Copyright &y& Elsevier]

A comparative study has been performed on five native laccases purified from the three basidiomycete fungi Pleurotus ostreatus, Rigidoporus lignosus, and Trametes trogii to relate their different catalytic capacities to their structural properties. Spectroscopic absorption features and EPR spectra at various pH values of the five enzymes are very similar and typical of the blue oxidases. The analysis of the dependence of kinetic parameters on pH suggested that a histidine residue is involved in the binding of nonphenolic substrates, whereas both a histidine and an acidic residue may be involved in the binding of phenolic compounds. His and an Asp residue are indeed found at the bottom of a cavity which may be regarded as a suitable substrate channel for approaching to type 1 copper in the 3D homology models of the two laccases from Pleuorotus ostreatus (POXC and POXA1b) whose sequences are known. [ABSTRACT FROM AUTHOR]

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]

Growth and differentiation of mycelial strands in Rigidoporus lignosus have been shown to depend on suitable combinations of the pH of the media and the nature of the nitrogen and carbon sources. Amino acids as sole nitrogen sources gave rise to vegetative mycelium. At pH 4.5, growth and mycelial strand differentiation required asparagine, as the fungus failed to grow in the absence of this amino acid. However, at pH 6, differentiation of strands occurred appreciably in asparagine-deficient media, suggesting a close balance between pH and amino acid requirements. Ammonium was required for strand differentiation, while nitrate, as a sole nitrogen source, maintained the fungus undifferentiated. Of the carbohydrates tested, only glucose, fructose and mannose supported strand differentiation. Starch was found to be particularly effective in promoting growth of vegetative mycelium. Strand differentiation required more specific conditions than growth of the vegetative mycelium. [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]