Evaluation of the allelopathic effect of wheat and redroot pigweed on growth indices and antioxidant system activity in intercropping

چکیده مقاله

Allelopathy refers to the beneficial and detrimental effects of one plant on another plant in
both crops and weeds through the production of secondary compounds. In order to evaluate
the allelopathic effects of wheat (Triticum aestivum L.) as a crop and redroot pigweed
(Amaranthus retroflexus L.) as a common weed worldwide on each other in intercropping,
these plants were cultivated under controlled conditions at Tabriz University laboratory.
The ratios of wheat to redroot pigweed were, 100 : 0 and vice versa as a control, 75 : 25,
50 : 50, and 25 : 75. The results showed that at the ratio of 25 : 75 (wheat : redroot pigweed),
the fresh and dry weight of roots and shoot length of wheat decreased significantly
compared to the control. The fresh and dry weight of wheat shoots showed a significant
decrease at different ratios compared to the control. Shoot peroxidase (POD), root superoxide
dismutase (SOD), and root and shoot catalase (CAT) activities in redroot pigweed
increased in all intercropping ratios compared to the control. POD activity in wheat roots
was higher at all ratios than in the control. Furthermore, the ratio of 75 : 25 (wheat : redroot
pigweed) led to increased activity of POD enzymes and malonedialdehyde (MDA) content
in wheat shoots. Moreover, roots of redroot pigweed showed increased activity of ascorbate
peroxidase (APX) and SOD enzymes and MDA content. With increased density of
redroot pigweed, the soluble sugar content of wheat roots reduced significantly. However,
the content of insoluble sugar and total protein increased. Root exudate compounds such
as terpenoids, phenolic compounds, fatty alcohol, steroids, fatty acids, and alkanes were
identified using gas chromatography/mass spectrometry (GC/MS). The findings showed
that the roots were more exposed to oxidative stress due to direct contact with allelochemical
compounds. Our results support the hypothesis that increasing the density can reduce
the toxicity of allelochemical compounds and that increasing the activity of the antioxidant
system will improve plant growth under allelochemical stress.