Petroleum ether extracts and unsaponified fractions of red and green seaweeds and methanol extracts, lipophilic fractions and unsaponified fractions of brown seaweeds separated on TLC were tested for their efficacy against Xanthomonas oryzae pv. oryzae. Two active zones from red seaweeds, one to five from brown seaweeds and two to three from green seaweeds were isolated through TLC profiles. Among eleven seaweeds Gracilaria edulis, Sargassum wightii and Enteromorpha flexuosa showed high antibacterial activity. The Rf 0.30 substance obtained from unsaponified fractions of E. flexuosa showed the maximum antibacterial activity against the test bacterium.
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