| Summary: | Studies have been: done to investigate the allelopathic effect of Chromolaena odorata
and Mikania micrantha on the germination, growth and biochemical activities of
selected bioassay species (three weed species namely Eleusine indica, Cyperus iria
andAgeratum conyzoides and three vegetable crop species namely Zea mays, Brassica
chinensis and Cucumis sativus) in Malaysia. The experiments were done in the
laboratory and greenhouse to investigate the effect of aqueous leaf extract, leaf debris
and weed infested soil on the germination and growth of bioassay species. Three
concentrations of aqueous leaf extract (12.5, 25 and 50 g/L) and leaf debris (2.5, 5.0
and 10.0 g/500 g soil) were used in these experiments. Besides, the allelopathic effect
of C. odorata and M. micrantha leaves were also investigated on the malondialdehyde
(MDA) content, concentration of protein and the enzyme activities of peroxidase
(POD) and catalase (CAT) in the bioassay species. Studies have also been done to
determine the effect of leaf leachate (sandwich method), leaf volatilization (dish pack
method) and root exudate (plant box method) of C. odorata and M. micrantha on the
germination and growth of bioassay species. Results showed that the growth of E.
indica,A. conyzoides and B. chinensis were significantly inhibited by more than 90%
of control when 50.0 g/L concentration of C. odorata and M micrantha aqueous leaf
extract were applied. As concentration increased, the germination rate of bioassay
species decreased. Leaf debris of C. odorata and M micrantha significantly
stimulated the growth of bioassay crop species especially B. chinensis. However? leaf
debris of M. micrantha significantly inhibited the germination and by more than 50%
of control the growth of C. iria and A. conyzoides at concentration of 10.0 g / 500 g
soil. Meanwhile, only the germination of B. chinensis was inhibited by 43% when
grown in weed infested soil. Based on these experiments, B. chinensis was highly
inhibited by C. odorata and M micrantha leaves compared to other species. The
content of MDA and the enzyme activities of catalase were increased by more than
50%compared to control but the concentration of protein decreased by 38% of control
in the root part of B. chinensis when applied by 50.0 g/L concentration of C. odorata
aqueous leaf extract. Studies also indicated that the leaf leachates of 50 mg of C.
odorata and M micrantha inhibited the radicle length of B. chinensis by more than
90% of control. Besides, the radicle length of B. chinensis was inhibited by 64% of
control at the distance of 41 mm from the volatilization of C. odorata leaf.
Meanwhile, the root exudates of C. odorata and M. micrantha inhibited the root
length by 49% and 34% of control, respectively. Thus, allelopathic potential of C.
odorata and M micrantha leaf were concentration dependent and also depended on
the bioassay species. Based on allelochemicals screening of volatile organic
compounds by HS-GC-MS, the leaf of C. odorata released a-pinene, gennacrene D
and B-pinene, whilst M micrantha leaf released gennacrene D, ~-caryophyllene and
~-himachalene into the environment.
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