Allelochemicals Biologica... - Name

114
RAMANATHAN KATHIRESAN, CLIFFORD H. KOGER , KRISHNA N. REDDY
Bioassay for searching of allelopathy in aquatic weeds is comparatively easier
and this could be designed under both laboratory or greenhouse conditions using
either part or whole plant of the aquatic weed (Kathiresan, 2000; Kannan, 2002).
Whole plants of floating or submerged aquatic weeds targeted for allelopathic control
can be grown in suitable containers with water containing standardized nutrients.
The powder of candidate allelopathic substances or plant products are added to water
either on w/v or v/v basis with appropriate untreated controls. Periodic observations
at designated intervals could include reduction in root length and mass, reduction in
shoot length and mass, desiccation, scorching and bleaching or mortality score similar
to herbicide injury. Based on the screening data, plant products could be classified in
to highly allelopathic, moderately allelopathic, and less allelopathic. For example, 55
different plant products were screened for allelopathic inhibition of water hyacinth
involving whole plants as well as cut leaves at Annamalai University. In bio-assays
involving whole plants, ten of them including C. amboinicus, P. hysterophorus and
L. leucocephala were highly allelopathic based on fresh weight reduction (>30%) of
water hyacinth within 48 hr after treatment. Another 12 including Acalypha indica
Linn., Trianthema portulacastum L. and Sesbania grandiflora (L.) Pers. showed
moderate allelopathy, fresh weight reduction of water hyacinth was 15-30% within
48 hr after treatment. Twelve other plant products including Croton sparsiflorus
Morong, Cleome viscosa L. and Eclipta alba L. showed less allelopathy, fresh weight
reduction of water hyacinth was less than 15% within 48 hr after treatment (Table 1).
The remaining 21 plant species including Leucas aspera Spreng. Curcuma longa L.
and Euphorbia hirta L. did not show any allelopathic effect on water hyacinth (Kannan,
2002). To measure dose dependant responses of allelopathic substances more precisely
Table 1 : Percentage reduction in fresh weight of water hyacinth (Eichhornia
crassipes.) due to various plant products. (Kannan, 2002) a .
Treatments Days After Treatment
plant products @ 30 g L-1 2 4 6 8
Coleus amboinicus 56.57 (69.66) 90.00 (100.00) 90.00 (100.00) 90.00 (100.00)
Acalypha indica 29.98 (24.97) 44.24 (48.68) 90.00 (100.00) 90.00 (100.00)
Leucas aspera -b - - -
Croton sparsiflorus 20.53 (12.30) 34.51 (32.11) 45.37 (50.66) 90.00 (100.00)
Curcuma longa - - - -
Trianthema portulacastum 27.06 (20.70) 45.09 (50.17) 90.00 (100.00) 90.00 (100.00)
Cleome viscosa 21.10 (12.96) 35.77 (34.17) 45.66 (51.16) 90.00 (100.00)
Leucaena leucocephala 34.84 (32.65) 90.00 (100.00) 90.00 (100.00) 90.00 (100.00)
Sesbania grandiflora 27.17 (20.86) 44.51 (49.16) 90.00 (100.00) 90.00 (100.00)
Parthenium hysterophorous 36.92 (36.10) 90.00 (100.00) 90.00 (100.00) 90.00 (100.00)
Euphorbia hirta - - - -
Eclipta alba 21.27 (13.17) 33.93 (31.17) 44.94 (49.91) 90.00 (100.00)
Control - - - -
SED CD (P = 0.05)
2.40
4.80
2.34
4.69
1.25
2.51
-
-
a Figures in parenthesis are original values before arc-sine transformation.
b No allelopathic effect.