Abstract
Host plant resistance to phytophagus insects has been investigated in four Egyptian cotton cultivar varieties. The study centered on the indigenous content of plants of terpenoid aldehydes and their infestation by boll and leaf worms. Terpenoids in the four varieties have been extracted, resolved and quantitatively determined in different plant organ extracts over several periods of plant lifetime. Nine different compounds; gossypol“G”, methyl gossypol“MG”,dimethyl gossypol“DMG”, hemigossypolon“HGQ”, methyl hemigossypolon“MHGQ” and the heliocides; H1,H4,B1,and B4 have been identified in the extracts of tissue organs of different plant cultivars. These compounds were separated and purified using solvent extraction, column and TLC chromatography, crystalized and identified by their melting points, specific optical rotations, UV spectra and molar extinction coefficients, and by IR spectroscopy and GC‐MS to determine their structure. The toxicity of the nine compounds againist cotton insect boll and leaf worms has been determined in the laboratory. They were generally more toxic to the boll worms than the leaf worm and to the pink more than the spiny boll worm. Heliocide H1 was the most toxic followed by HGQ and MHGQ which were more toxic than the heliocides B1, B4 and H4. The least toxic were G, MG and DMG compounds. Although there is no clear understanding of the interactions of these compounds and how they relate to actual field resistance,the contents of the 4 cultivars of these compounds and their insect infestation in the field correlated well with the toxicity values mentioned above. The above results could be a useful guide to biochemists and plant breeders to exploit a modified chemical profile of this group for effective insect control and host plant resistance.
Supported, partially, from the Swedish Research Council grant no: Dnr nr 348‐2004‐4977.