The effectiveness of aqueous extracts derived from nine algal species at
different concentrations on egg hatching and mortality of Meloidogyne incognita
(Kofoid and White) Chitwood juveniles after various exposure times were
determined in vitro. Results indicated that Enteromorpha flexuosa at the
concentration of 80% was the best treatment for suppressing the egg hatching with
value of 2 % after 5 days of exposure, followed by Dilsea carnosa extract (3%) and
Codium fragile (4%) at the same concentration and exposure time. Likewise,
application of C. fragile, D. carnosa , E. flexuosa and Cystoseira myrica extracts at
the concentrations of 80 and 60% were highly toxic to the nematodes, killing more
than 90 % of nematode larva after 72 hours of exposure while the others gave quite
low mortalities. The characteristic appearances in shape of the nematodes killed by
C. fragile, D. carnosa , C. myrica, E. flexuosa and Sargassum muticum was
sigmoid (Σ-shape) with some curved shape; whereas, the nematodes killed by other
algal species mostly followed straight or bent shapes. The present study proved that
four species of algae C. fragile, D. carnosa, C. myrica and E. flexuosa could be
used for the bio-control of root-knot nematodes.