Forestry and Enironment Symposium 2000, Sri lanka

Sixth Annual Symposium of the Department of Forestry and Environmental Science, Sri Lanka. 15- 16 December 2000, Kandy, Sri Lanka

Tuesday, October 31, 2006


Rizana M Mahroof1 Jayanthi P Edirisinghe1 Caroline Hauxwall2
1Department of Zoology, Faculty of Science
University of Peradeniya
2Institute of Ecology and Resource Management
University of Edinburgh

The main factor limiting cultivation of mahogany, Swletenia macrophylla King (Meliaceae), in plantations is damage by shoot borers (Hypsloyla spp.). Shade has been repeatedly cited as reducing shoot borer attack but the responsible mechanisms have not been determined by experimentation. Shade may alter either secondary compounds such as limonoids or nitrogen concentrations or both in the plants making them unsuitable for insect survival and development. Previous studies have not examined whether shade influences limonoid and nitrogen content of S.marcrophylla and thereby alter shoot-borer attack. Therefore, these studies were designed to identify the variation in incidence of shoot borer attack under three levels of shade treatments in the field conditions and the variation in plant chemistry of S.marcrophylla shoots grown under three different artificial shade treatments. The hypotheses tested were under high light availability (i) incidence of shoot borer attack increases (ii) the concentration of limonoids present in the shoots of S. macrophylla decreases ind(iii) total nitrogen content of shoots increases.

This study was done from 1997-99 in Sri Lanka and UK. Attack by the shoot borer was assessed 54 weeks after planting. The Limonoid content was investigated by Thin Layer Chromatography (TLC) and the total nitrogen by Kjeldhl method using freeze-dried ppowdered shoots. The incidence of shoot borer attack was significantly higher under low shaade (d.f.=2, F=8.6, p=0.0003). The intensity of the green-blue fluerescence under UV seen in the TLC plates was greater using the extracts from the high shade treatment compared to that from the low shade treatment. The total nitgrogent content was satistically lower in the high shade (1.114± 0.22%, n=33) compared to that in full light (1.36± 0.22%; n=31). These results suggest that light environment may have a significant effect on the concentrations of limonoids and nitrogen in S.macrophylla which in turn influences the shoot borer attack.

The study forms part of a larger project on 'Silvicultural prescription for mahogany plantation establishment; Research grant funded by DFID, UK is greatfully acknowledged


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