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Biology and Control of White Root Disease· of Hevea Rubber Caused by Rigidoporus lignosus (Kiotzsch) lmazeki
Thesis Abstract:
White root disease is by far the most serious among the three root diseases of rubber. Current methods of control of the disease include replanting control procedures such as mechanical or hand clearing, sulphur amendment, use of covers and intercrops, post-planting control procedures, (i .e., disease detection, treatment with collar protectant dressing), use of isolation trenches in mature rubber and, more recently, the application of Calixin emulsion as soil drench.
However, these methods were made expensive by the high costs of labor and chemicals, not to mention the serious hazard chemicals pose to the environment.
This study explored possible methods of white root disease control that would minimize, if not completely avoid, dependency on chemicals.
Methods such as introduction of antagonists, application of chemicals at minimal rate, and addition of organic matter supplement applied either individually or in combination with each other were used in the study.
Results showed that chemically-assisted biological control of 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 further enhanced increase of the mycotlora population. Fifty percent of the treatments with total population of mycotlora significantly higher than that of the control included both antagonists and cow manure.
Sulphur as a single treatment also achieved good results in terms of enhancing population growth of the mycotlora 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 enhancement of the activity of the soil mycotlora (especially Trichoderma spp.), by one or a combination of the different treatments, survival of propagative units and activity of R. lignosus as a whole were 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%) while an overall increase in population of the mycotlora was noted.
Preliminary findings on the morphology of R. lignosus pointed-out that variations among isolates of the pathogen existed. This could be a very relevant area of study in future thrusts of research since nothing has been done so far along this line in Southeast Asia. It is most likely that along with variations in these characteristics, variation in pathogenicity of R. lignosus also exists. Information along this line, therefore, would be an invaluable help to plant protectionists and agronomists in planning out researches, especially in disease resistance of plants.