HERBICIDES in Asian rice - IRRI books - International Rice ...

Table 6. Reduction in weed root dry weight and
aquatic weed dry weight of six rice cultivars that
demonstrated allelopathic activity to ducksalad,
compared with check cultivar, Rexmont, which
demonstrated no allelopathic activity in the field.
Cultivar
Root dry Reduction in
weight aquatic weed
(g kg soil -1 ) dry weight
(%)
IET60 (HR12X/TN-1) 8.0 81
Sh30-21 7.5 81
lR788-16-1-1-1 7.4 87
T65/2*TN1 7.4 81
lR643-75-1-1 5.2 76
Afghanistan no. 2 4.8 81
Rexmont 0.8 0
LSD (0.05) 4.0 39
These results tend to support the theory that wild ancestors of existing crops may
have possessed high allelopathic activity, and that this character was reduced or lost
as the wild ancestors were hybridized and selected for other characteristics (Putman
and Duke 1974).
Test 5. Root extracts of allelopathic rice cultivars reduced ducksalad germination
significantly more than leaf extracts (Table 5). This suggests that compounds present
in both leaves and roots, but especially in the roots, of all the germplasm accessions,
including the checks, can inhibit weed germination. Most of the cultivars with allelopathic
activity to aquatic weeds in the field have as much as 10 times greater
aboveground fibrous root biomass than check cultivars (Table 6).
SUMMARY AND CONCLUSIONS
Approximately 4% of the rice germplasm accessions that were evaluated for allelopathy
to ducksalad demonstrated some activity. The 347 accessions that demonstrated
allelopathic activity also exhibited genetic diversity for such plant characteristics as
plant height, maturity, grain type, plant type, hull cover, hull color, and culm strength.
In laboratory tests, allelochemicals that inhibit seed germination and radicle length
of lettuce, a common indicator plant, were present in rice straw of accessions that
showed allelopathic activity to aquatic weeds in the field. Tests to isolate and identify
the allelochemicals that are responsible for the allelopathic activity are being conducted.
Root extracts from some germplasm accessions also reduced weed germination.
These differences are important in comparing laboratory results with field results.
Filtrate extracted from the same root dry-weight biomass of both allelopathic accession
and checks would not be representative of field conditions.
Identifying allelopathy in rice germplasm 227