Abstract

Teak (Tectona grandis L.f.) is a valuable commercial timber species which always faces a serious threat from leaf skeletonizer, Eutectona machaeralis and defoliator, Hyblaea puera. Selection of resistant teak clones on the basis of foliar defensive biochemicals is a very new approach of controlling this problem. In the studies carried out, 167 clones of teak belonging to ten states of India, introduced and planted during the years 1979-84 at National Teak Germ Plasm Bank, Chandrapur (Maharashtra) were considered as experimental host plants to evaluate resistant teak clones. In field, quantitative assessment of the severity of the damage was made by rating infested leaves visually on the basis of percentage of affected leaves individually in all four directions of all the clones. On the basis of visual observations, the clones were categorized into 9 groups, viz., most resistant, highly resistant, resistant, moderately resistant, least resistant, moderately susceptible, susceptible, highly susceptible and most susceptible. Some clones from each category were randomly selected for further confirmation of resistance against leaf skeletonizer and defoliator. In laboratory, feeding bioassay through no-choice and choice tests was carried out. Chemical screening of the contributory leaves of respective clones was also done. On the basis of data on leaf area consumed and foliar constituents, some resistant teak clones were identified.

The inference drawn can be used as a screening criterion for selection of teak clones resistant to E. machaeralis and H. puera to large-scale plantation programmes.

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