Abstract
Allelopathic potentiality of 139 rice varieties/accessions were evaluated against Echinochloa
crusgalli under laboratory, greenhouse and field situation at the Bangladesh Rice Research
Institute, Gazipur. In laboratory, the relay seeding technique was followed for screening 139
rice germplasm. Thirteen rice varieties/accessions including Kataribhog, Woo co Chin Yu
(Woo co), WITA12, Dular, Lalpaika and BRRI dhan27 caused more than 60% weed
inhibition. Although some of the local varieties had the strong allelopathic property, in
general the modern varieties produced the greater inhibition of the weed. The late maturing
(< 140 days) varieties were more allelopathic than early maturing ones. Under greenhouse
conditions double-pot technique was used both in autumn and winter seasons to separate the
effects of competition from allelopathy. The selected highly allelopathic varieties (as per
laboratory screening) also caused significant weed inhibition in both the seasons. In autumn,
Kataribhog, FARO8, WITA8, WITA12, BRRI dhan39 produced 51 to 59% weed inhibition.
In winter, Kataribhog, Woo co, WITA3, IR64, BR26 and Dular produced 47 to 55% weed
inhibition. Under field situation, the varieties produced 40 to 47% weed inhibition in autumn
and 36 to 49% in winter. Weed tolerance of these autumn and winter rice varieties under field
conditions was measured by calculating their relative yields (RYs) against the test weed. All
the varieties produced RYs close to unity indicating highly competitive and/or allelopathic to
the weed. The rice varieties were more inhibitory at early growth stage (30 to 45 DAT) than
at the later stage. The light transmission ratio of the allelopathic rice varieties was not related
to percent weed inhibition. The percent weed inhibition in petridish under laboratory
condition was not correlated to that of test tube condition. Although the percent inhibition of
the laboratory petridish experiment was not related to percent inhibition in greenhouse or
field experiments of autumn but it was highly correlated to that of winter seasons. The
average percent inhibition of greenhouse experiments was highly correlated to the data of
field experiments of both the seasons. The aqueous extracts of selected four rice varieties
namely, Woo co, WITA12, Dular and Hashikalmi, caused 17 to 36% weed inhibition under
laboratory condition. Among the plant parts, the stem and leaf extracts were more inhibitory
than those of root or whole plant. The inhibitory actions of rice extracts were dependent on
their concentration. Greater inhibition of weed growth was due to higher concentration of
extract and vice - varsa.