Allelopathic potentiality of Trianthema portulacastrum L. shoot extract and mulch on germination and growth of two summer weeds

Trianthema portulacastrum L. is an alien naturalized noxious summer weed belonging to Aizoaceae. Our field observations revealed that it was the dominant weed in the fields planted with maize and other summer crops, and on roadsides of wastelands and farmlands . This study was conducted to evaluate the potential allelopathic effects of the aqueous shoot extracts and mulching with different rates of air-dried shoots of T. portulacastrum collected from maize fields on two associating weeds namely, Corchorus olitorius and Euphorbia heterophylla. Seed germination and seedling growth of the test weeds decreased with increasing concentrations of the aqueous extract. The seeds bioassay experiments confirmed the autotoxicity of T. portulacastrum. We have found that the allelopathic effects of the target species on the two weeds, and the autotoxic effects on itself were mainly attributed to the presence of allelochemicals and not to the osmotic potential of the aqueous extracts. Mulching had inhibitory effects on the percentage of dry matter allocations and the growth parameters of the test weed species. The relative growth rate, the net assimilation rate, and the leaf area ratio of the non-mulched weeds were higher than those of mulched ones. The phytochemical screening of the dry shoots of T. portulacastrum indicated the presence of phenolic compounds, flavonoids, tannins, and alkaloids. The high concentration of alkaloids in the shoot deserves further research. The high-performance liquid chromatography confirmed the presence of 14 phenolic substances, which included 12 phenolic compounds, and 2 flavonoids. Evaluation of seed bioassay and mulching experiments revealed that the aqueous extract concentrations of 4 and 6 % of T. portulacastrum inhibited the germination of E. heterophylla, while the mulched plants showed tolerance at the juvenile-flowering stage. We conclude that tolerance to allelopathic stress varied among the tested weed species and the growth stages of the same species. The suitability of using either aqueous shoot extract or mulch of T. portulacastrum as a potential bioherbicide deserves further monitoring under field conditions.