Allelopathy Of Alien Invasive Weed Sorghum Halepense (L.) Pers

Sorghum halepense (L.) Pers. (johnsongrass), a grass weed of Sorghum moench, in the family of poaceae and native to mediterranean, is a noxious invasive weed in more than 58 coutries one of the ten worsest weed in the world. The invasive mechanism of invasive species is the important topic which was received much attention of many scientists. For better understanding the chemical mechanism of its invasion, the allelopathy effects of Sorghum halepense on native plants were evaluated and the allelochemicals were investigated.1) The allelopathic potential of Sorghum halepense shoots to three crops, wheat, maize and cotton was investigated by seed germination and seedling growth in Laboratory. The results demonstrated that Johnsongrass inhibited seeds germination and seedling growth of the crops. The allelopathy of Sorghum halepense increased with its concentrations but decreased with time. From the EtOH extract of the above-ground tissues of Sorghum halepense, five compounds were isolated by column chromatography over silica gel, RP-18 silica gel, as well as Sephadex LH-20.2) By spectroscopic (MS, NMR) analysis, five compounds were identified: p-hydroxybenzaldehyde, tricin, 4-hydroxybenzoic acid, (E)-p- hydroxycinnamic acid, luteolin3) Laboratory biological tests of growth of lettuce showed that p-hydroxybenzaldehyde, 4-hydroxybenzoic acid, (E)-p- hydroxycinnamic acid , luteolin isolated from Sorghum halepense, could significantly inhibited the growth of lettuce, demonstrated strong allelopathic potential.4) The volatile oil was obtained by steam distillation from Sorghum halepense shoots. Its chemical components were analyzed by the means of GC and GC-MS. Twenty-six chemicals, 76.51% of total content, were isolated and identified from the volatile oil. The main component was sesquiterpenes, such as trans-α-berg-amotene (21.95%),α-Patchoulene (10.77%),α-Himachalene (4.66%), etc.5) The volatile oil extracted from Sorghum halepense shoots, its biological effects on crops, weeds and microbial populations were studied. Weed germination, crop shoot height and dry weight were significantly inhibited by the volatile oil. The volatile oil also significantly reduced the population of fungi and actinomycetes in the test soils, but significantly increased the population of bacteria in the soils. The results indicated that the volatile oil from Sorghum halepense e demonstrated significant allelopathic potential on depressing surrounding plants and affecting microbial populations.6) The volatile oil had a strong antifungal activity against tested fungus, and the antifungal activity increased significantly with its concentration. When the concentration was 3000μl/L, the inhibition rate of all the tested fungus was more than 78%, and the volatile oil had the strongest antifungal activity against cotton (Rhizoctonia solani), the EC50 was 615.18-909.91μl/L.This is the first time that the allelopahty of Sorghum halepens was studied in China, some of the allelochemicals of Sorghum halepens were identified, and the allelopathic effect on other plants, fungi and soil microbial was studied. The allelopath of Sorghum halepense may be one of the reasons of depressing surrounding plants and making its growth vigorous, devote to its successful invasion.