Weeds Cause Losses in Field Crops through Allelopathy

Abstract

A large number of weeds are known to be associated with crops and causing economic losses. Weeds interfere with crops through competition and allelopathy. They produce secondary metabolites known as allelochemicals, which belong to numerous chemical classes such as phenolics, alkaloids, fatty acids, indoles, terpens etc. However, phenolics are the predominant class of allelochemicals. The allelochemicals release from weed plants takes place through leaf leachates, decomposition of plant residues, volatilization and root exudates. Weeds leave huge quantities of their residues in field and affect the associated, as well as succeeding crops, in various cropping systems. Liberation of allelochemicals from weeds affects the germination, stand establishment, growth, yield and physiology of crop plants. They cause substantial reduction in germination and growth of the crop plants by altering various physiological processes such as enzyme activity, protein synthesis, photosynthesis, respiration, cell division and enlargement, which ultimately leads to a significant reduction in crop yield. In crux, allelopathic weeds represent a potential threat for crop plants and cause economic losses.

The Allelopathic Potential of Rosa blanda Aiton on Selected Wild-Growing Native and Cultivated Plants in Europe

“…Many invasive species also use allelopathy as an added settlement asset, as already mentioned in the introduction. Allelochemical substances are responsible for modulating the basic and complex physiological mechanisms that occur in plants at various stages of their development [48]. The results of studies on the impact of allelochemical compounds on the increase in the invasiveness of certain plants in ecosystems confirm the important ecological role of this type of interactions [49,50].…”

“…The extracts had a greater inhibitory effect on cucumber than on sunflower [59]. The reduced germination capacity observed in both cases could be a consequence of a disturbed hormonal balance, especially a change in the activity of gibberellic acid, which regulates the synthesis of de novo amylase during the germination process, as well as disturbances in protein synthesis, activity of enzymes, photosynthesis, and respiration [48]. From an ecological point of view, in highly competitive environments, even slight germination delays can be an advantage for the aggressive neighbor and affect the adaptability of alien taxa.…”

Allelopathic Effect of Some Associated Weeds of Wheat on Germinability and Biomass Production of Wheat Seedlings

“…Inhibition of germinability and biomass production might be attributed to the water soluble phenolics present in the water extracts of weeds (Zohaib et al, 2014a). Reduced germinability might have occurred as a result of perturbed hormonal balance, protein synthesis, enzyme activity, photosynthesis and respiration (Zohaib et al, 2016). It has been observed that depressed and delayed germination by allelochemicals (phenolics) happens due to the suppression of respiration by hindrance of respiratory enzymes and the enzymes involved in oxidative pentose phosphate pathway (Muscolo et al, 2001) which is necessary for synthesis of RNA and DNA, production of ATP and generation of intermediates for Calvin cycle in early stages of greening of leaves during seedling germination (Taiz and Zeiger, 2002).…”

“…This was further evidenced by the fact that root/shoot ratio and correlation analysis showed a positive relationship between root dry biomass and root shoot ratio (Table 6). This decreased inhibition of root biomass production might be due to reduced respiration losses in roots because of hindrance in activities of respiratory enzymes caused by allelochemicals (Zohaib et al, 2016).…”

“…However, in field conditions, the release of allelochemicals mostly takes place through decomposition of plant residues (Singh et al, 2001). Seed germination, plant growth and biomass production are hindered by numerous allelochemicals through disruption of a variety of physiological functions taking place within plant body (Zohaib et al, 2016). The plant functions of prime importance which are affected by allelochemicals include photosynthesis, respiration, mitosis, cell elongation and enlargement, metabolic activities, synthesis of proteins and amino acids, and enzyme activities .…”