Allelochemical interference allelopathic weeds

The results of these experiments support the hypothesis that inhibitory allelochemicals may interfere with the water balance of seedlings. Alterations in the water status of grain sorghum seedlings were caused both by known phenolic acids and by allelopathic weeds. 

Phenolic acids interfere with many major physiological processes of higher plants (35). These disruptions of function include an alteration of plant water balance. We found depression of leaf water potential to be an early indicator of allelochemical stress from ferulic and p-coumaric acids (42). Likewise one mechanism of allelopathic action by cultivated sunflower, velvetleaf Abutilon theophrasti Medic.), Koahia [Koahia saoparia (L.) Schrad.], and several other weeds was water stress (43-45). Since some allelochemicals interfere with plant-water relationships, it seemed logical that their action might be most critical at times when plants are under water stress from other causes. 

Although indirect and probably quite rare, another route has been reported for allelochemical interference with plant-water relationships. Lovett and Duffield (47) identified benzylamine as an allelochemical in the leaf washings from the cruciferous weed Cametina sativa (L.) Crantz. Subsequent work showed benzylamine induced hydrophobic conditions in the soil, and these conditions could reduce water availability for plant growth (48). Thus, indirect action through changes in soil structure could be partially responsible for adverse effects on linseed (Linseed usitatissimm L.) and could enhance more direct allelopathic effects. 

We should determine which plant pests inflict their damage through production of phytotoxins. It now appears that several pathogenic fungi may do this. Numerous weed species may impose interference on crop growth, at least in part through allelochemicals. More than 70 species have now been alleged to have allelopathic potential. 

Phytotoxic compounds are produced by many crop species, and some of these compounds may play a role as allelochemicals in plant interference. This has bear hard to prove, much less taken advantage of in weed management. Many crops have been screened for allelopathic potential [28]. However, in all but a few cases, the effects of crop allelopathy are quite subtle compared to the effects of chemical herbicides. Efforts to produce allelopathic crop varieties through conventional breeding have not generated commercial varieties sold with this trait. Molecular biology approaches to this problem might be helpful. 

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