There has been significant progress in isolating rice
allelochemicals (Rimando et al., 2001) and locating
genes controlling allelopathic effects of rice (Jensen et al.,
2001). Using a relay seeding technique, cultivar IAC 165
was shown to possess strong allelopathic activity
compared to CO 39 having weak allelopathic activity
(Jensen et al., 2001). These same workers identified
quantitative trait loci (QTL) associated with the rice
allelochemicals against barnyardgrass. This is an im-
portant step toward breeding allelopathic rice varieties.
It was found that 35% of the total phenotypic variation
of allelopathic activity of population was explained by
four main effect QTLs situated on three chromosomes.
There are, however, some questions yet to be answered.
For example: Do allelopathic rice varieties have auto-
toxic effects? (Jensen et al., 2001). Does the allelopathic
potential of rice cultivars adversely influence cyanobac-
teria population of the paddy field? Cyanobacteria
are known to fix nitrogen in paddy fields (Brady,
1996). Any adverse effect of allelopathic rice cultivars on
nitrogen-fixing potential of cyanobacteria may not be
desirable.