Allelopathic effects of Alternanthera philoxeroides extract on Medicago sativa, Cichorium intybus, and Avena sativa

Alternanthera philoxeroides, a noxious weed whose removal is difficult, is widely distributed over land and water surface in more than 20 provinces (or municipalities) of China, and leads to devastating ecological disasters and considerable economical loss. Investigation of the allelopathic effects of this noxious weed on pasture grass would provide useful information on the elimination of A. philoxeroides and selection of pasture grass species for cultivation. Therefore, pure culture and greenhouse pot experiment were conducted to evaluate the allelopathic effects of extracts of both shoot regions (ESA) and roots (ERA) of A. philoxeroides on seed germination and growth of Medicago sativa, Cichorium intybus, and Avena sativa seedlings. The results showed that seed soak in ESA and ERA inhibited the hydrolysis of proteins, starch, and inositol phosphates in the endosperm, and reduced the levels of free amino acids, soluble sugars, and soluble inorganic phosphates in seeds; it even damaged the seed cell membrane. The results showed that seed germination rate, germination index, and seed vigor index were reduced by 95.66%, 96.15%, and 98.63%, respectively. Irrigation of pasture grass seedlings with A. philoxeroides extracts reduced root vigor, nitrate reductase activity, chlorophyll content, and uptake of nitrogen, phosphorus, and potassium, resulting in the inhibition of seedling growth. The highest rate of seedling biomass reduction ranged from 52.27% (ESA) to 63.74% (ERA). Furthermore, the allelopathic response index and allelopathic synthetic effect of A. philoxeroides on the three grasses, whose absolute values increased with increase in A. philoxeroides extract concentrations, were negative; the allelopathic inhibitory effect was stronger for Avena sativa than for Cichorium intybus and Medicago sativa, and the intensity of the allelopathic effect of ERA was higher than that of ESA. Therefore, the extracts exerted allelopathic effects on the three pasture grasses, with ERA showing a stronger effect than ESA. Seed germination and growth of A. sativa seedlings were more sensitive than those of C. intybus and M. sativa. The selection of insensitive M. sativa and C. intybus for pasture grass cultivation could reduce harm and economic loss.