QUALITATIVE DETERMINATION OF ALLELOCHEMICALS IN Psidium guajava L. LEAVES FOR THEIR EFFECT AGAINST WHEAT AND CANARY GRASS

Excessive use of herbicides in fields threatens the environment by destroying flora and fauna. Allelopathic substances might be proved as a substitute of chemical herbicides to suppress the target weeds. In this study, the Psidium guajava L. leaves were extracted with 70% (v/v) methanol for the constitutional composition. The allelopathic effects were investigated against pre- and postgerminated wheat and canary grass seeds. Among the evaluated 16 allelochemicals, some eight components (Ellagic acid, 3,4- dihydroxybenzoic acid, Feruic acid, Galluic acid, Vivillic acid, 3- hydroxy-benzoic acid, Gallic acid and p-coumaric acid) were identified by comparing the chromatograms of the unknown with standard ones. The pre- and post-germinated bioassays were taken into consideration for wheat and canary grass separately. The results showed that over all 70% methanol extract of P. guajava L. leaves (2.5-10%) increased the shoot length and root linearly for both pre-germinated wheat bioassays (14.0 – 16.5cm and 12.9 - 15.0cm and post germinated wheat bioassays 13.85 - 16.25 cm and 11.15 - 14.50 cm, respectively) as compared with control ones. Similarly, allelochemicals of P. guajava L. suppressed both the pregerminated and post-germination bioassays of canary grass as compared with control ones (7.35 - 0.45cm and 6.50 - 2.75cm for shoot and 1.65 - 0.05cm and 2.15 - 0.75cm for root, respectively). These results suggest that P. guajava L. may contain growth inhibitory substances and may possess allelopathic potential. Therefore, leaves of P. guajava L. may be a possible candidate for the isolation and identification of allelopathic substances and for the development of natural herbicides for sustainable agricultural production.