Stigmasterol-3-O-Glucoside, An Allelopathic Molecule Responsible For Pest Resistance of Thenkaali (AAB), a Musa Cultivar against Odoiporus longicollis [Olivier]

Thenkaali, a Musa cultivar with genetic constitution AAB shows no infestation by Odoiporus longicollis Olivier, the pseudostem borer (PSB) under field conditions. The whole life cycle of this highly destructive pest is completed within the host plants. Thenkaali possesses high content of secondary metabolites such as total phenols, total flavonoids and elevated activity of related enzymes such as phenylalanine ammonia lyase, polyphenol oxidase and peroxidase. Rearing of larvae of PSB in the live pseudostem of Thenkaali has resulted in 100% mortality within one week. The pseudostem possesses a larvicidal compound stigma-sterol-3-O-glucoside, a steroid present at very low concentration (less than 0.0001%). The compound induces strong allelopathy on PSB, resulting in haemocytopenia and numerical changes in haemocytes. Other allelopathic changes are hyperprotenemia of haemolymph with changes in protein profile and sharp decrease in total free amino acids. The allelopathic compound induces antagonistic response on two proteolytic enzymes, evidenced by elevation of cathepsin D and inhibition of leucine amino peptidase activity. Imbalance in the activity of aspartate amino transferase and alanine amino transferase results in increased catabolism of amino acids, which leads to sharp increase in the haemolymph uric acid. Toxicity by stigmasterol-3-O-glucoside results in sharp elevation of 20 hydroxy ecdysone in the haemolymph and subsequent disruption of the endocrine system of the larvae might have contributedto cessation of feeding activity and its death.