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Allelopathic property of plants can be utilized for weed control as
allelochemicals suppress plant growth, and regulate species diversity
(like herbicides) in the habitat of the producer plant. Further,
because majority of the naturally occurring allelochemicals is
rapidly degraded into non-toxic compounds, these are considered
eco-friendly as compared to the commercially used herbicides. One of
the ways to use crop allelopathy for weed control is to employ
residues of crop plants like rye (Secale cereale) and sorghum
(Sorghum bicolor) (Putnam and DeFrank 1979; Shilling et
al. 1985). Another way to use allelopathy for weed control is to use
purified allelochemicals or their derivatives as weed killers.
Alfa-terthienyl, a potent phototoxin, isolated from members of
Asteraceae acts as a contact herbicide on broad-leaf weeds (Lambert
et al. 1991). Several other allelochemicals like, ailanthone,
caffeine, cineole, citronellol, mimosine and azadirachtin have been
identified with weed controlling activity (Rizvi et al. 1999).
Due to environmental concerns attention has recently been focussed on
a new 1 aspect of crop allelopathy which can be used for weed
control. There is variable degree of allelopathic activity by
different genotypes of a particular crop species against weeds. It
has been found that amongst the several accessions of cucumber
(Cucumis sativus), one inhibited Brassica hirta
by 87%, and 25 others by 50%. Out of the tested 100 accessions of
sorghum, 25 inhibited the germination and growth of Amaranthus
retroflexus by 82% and 85%, respectively (Rice 1995; Weston
1996). However, the most convincing work on selection of crop
germplasm with allelopathic activity against weeds has been done on
rice. Dilday et al. (1998) evaluated more than 16000 accessions of
rice for allelopathic control of Heteranthera limosa and
Ammannia coccinea. Out of these, about 3.4% accessions showed
considerable activity. Cultivars like Taichung Native 1, Johna 349,
Masrai, CR52-3, IR788-16-1-1-1 and S 12 DZK etc. inhibited the test
weeds ranging from 60% to 90 %. So far no attempt seems to have been
made to evaluate the allelopathic potential of wheat genotypes.
However, allelopathic effects of wheat straw against plants including
weeds have been demonstrated (Perez 1990; Alsaadawi et al. 1998).
This indicates. that wheat genotypes are capable of producing
allelochemicals, which can regulate the growth of other plants.
Therefore, possibility does exist to identify wheat varieties/
genotypes with major gene(s) for allelopathic activity against weeds.
Present study was initiated to study the genetic diversity for the
allelopathic trait in bread wheat genotypes.
Materials and methods
Thirty-four bread wheat genotypes with diversegrowth habit and
plant height out of modem improved cultivars and landraces were
selected for the evaluation of their allelopathic trait against the
most prevalent weed, Avena ludoviciana. For this, different
bioassays were tried, and the 'greenhouse-box-assay' was found to be
reliable, efficient and inexpensive. For the assay, plastic boxes (18
x 12 x 7 cm) filled with 1 kg greenhouse soil, a guide-plate (having
3 rows at 4 cm distance with 8 holes in each row at 2 cm interval)
and a steel borer (adjusted to make 1.0 cm deep holes for seed
sowing) were used. Fourteen seeds of wheat and seven of test weed
were maintained in the two border rows and the central row,
respectively. Twenty- four hours prior to sowing, each box was
supplied with 150 ml of distilled water. Four replicates for each
variety were randomized in a greenhouse maintained at 20C and 12 hour
light (2800 lux ca) / dark cycle. Each box was watered with 70 ml of
distilled water/day. To see if the wheat density has any effect on
its allelopathic activity, the number of wheat seeds were doubled in
one of the experiments. Heights of Avena plants were recorded on
every 4th day. Plant height (cm) above the ground and dry plant
weight (g) of Avena, and height of wheat plants were recorded on day
26th after sowing, when the experiment was terminated. Percent
inhibition (-) or promotion (+) in plant height and dry weight of
Avena were calculated. Duncan's multiple range test was employed for
comparing the means at 5% level. Variation in the allelopathic
activity of different wheat varieties and correlation (using linear
regression) with their vigour (height) was established.
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