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Biology and Control of White Root Disease of Hevea Rubber Cause by Rigidoporus Lignosus (Klotzsch) Imazeki
Thesis Abstract:
White root disease is, by far, the most serious among the three root diseases of rubber. Current methods to control the disease include: re-planting control procedures such as mechanical or hand clearing, sulphur amendment, use of covers, and intercrops; post-planting conttrol procedures such as disease detection and treatment with collar protectant dressing; use of isolation trenches in mature rubber; and more recently, the application of Calixin emulsion as soil drench. High costs of labor and chemicals, however, made these methods rather expensive. Moreover, the chemicals pose a serious hazard to the environment.
This study explores possible methods of white root disease control which minimized, if not completely avoided, dependency on chemicals. Such methods as introduction of antagonists, application of chemicals at minimal rate and addition of organic matter supplement applied either individually or in combination were included in the study.
Results demonstrated that chemically-assisted biological control against white root disease could be achieved with combined application of the different treatments. It was also evident that the inclusion of antagonists and cow manure in the treatments contributed to the population increase of mycoflora.
Fifty percent of the treatments with significantly higher population than that of the control included both antagonists and cow manure.
Sulphur as a single treatment likewise achieved good results in terms of enchancing mycoflora population growth, and consequently, Trichoderma spp. Treatment 224 (sulphur alone) had always resulted in a significantly higher (1 level) population over that of the control (T0).
With the enchancement of soil mycoflora activity, especially Trichoderma spp., by one or a combination of the different treatments, survival of propagative units and, consequently, the activity of Rigidporus lignosus as a whole was adversely affected. Results in field inoculation with the pathogen supported this contention.
Disease rating of inoculated roots was rather low and percentage recovery in previously infected trees was high (70%). An overall increase in mycoflora population was noted.
Preliminary findings on the morphology of R. lignosus tended to point out that variations ampng isolates of the pathogen exist. This could be a very relevant area for future research as nothing has so far been done on this in Southeast Asia. It is most likely that along with variations in these characteristics there also exist variations in pathogenicity of R. lignosus. A knowledge along this line, therefore, would be an invaluable help to plant protectionists and agronomists in planning out research, especially in the areas of disease resistance.
