Studies On The Allelopathic Potential Of E.grandis×E.urophylla

It is a widespread problem in Eucalyptus plantations that the plant community is simple in structure and low in biodiversity status. Allelopathy is believed to be an important factor of the Eucalyptus to compete with other associated plants where resources are limited no matter it is under monoculture or mixed culture.E.grandis×E.urophylla is a popular cultivar over Hainan's Eucalyptus plantation forests. The present study examined the allelopathic effect of E.grandis×E.urophylla with water extracts of fresh leaves, stem bark and twigs as well as leaf oil on the seed germination and seedling growth of recipient plants species in lab conditions. Another assay was made on the allelopathic activity on some agricultural pest insects and pathogenic microorganisms. The objective of the study was to have a good understanding of the allelopathic potentials of E.grandisX E.urophylla, which will be the basis of some recommendations to the Eucalyptus plantation sector and to research institutions.Our experimental results indicated that the water extracts from E.grandis X E.urophylla especially from fresh leaf inhibited the seed germination and seedling growth of the recipient plants species. The leaf water extracts inhibited the seed germination, shoot height, root elongation and fresh weight of the tested plants significantly. Furthermore, the higher the concentration of the leaf water extracts, the stronger the inhibition. Similarly, the twigs and stem bark water extracts of E.grandis X E. urophylla showed certain allelopathic effects on the recipient plants, with promotional effects at low concentration while inhibitory effects at higher concentration. In any case, however, the allelopathic effect of the leaf water extracts was much more noticeable than that of the twig and stem bark water extract.The leaf oil containing volatiles of E.grandisX E.urophylla also inhibited the seed germination and seedling growth of the recipient plants, but the inhibition effect of oil volatiles was much stronger than that of fresh leaf volatiles. Furthermore, the oil inhibition effect became stronger as the concentration went higher.Among the recipient plants, the cruciferae and Raphanus sativa were more sensitive to the allelopathic effect of E.grandisX E.urophylla than Stylosanthes guianensis cv. Reyan No.2 and Acacia mangium. The latter seemed defying the allelochemicals of the E.grandis...