Selective Isolation and Screening of Soil Microorganisms for Metabolites with Herbicidal Potential

Abstract

Crop losses from weeds worldwide average 10% annually. Herbicide application is almost essential in modern agriculture to maintain high productivity. Increased awareness of the environmental damage caused by continued use of conventional synthetic herbicides has aroused great interest in biodegradable, selective and environmentally friendly herbicides. The increasing incidence of herbicide resistance in weeds has stimulated research for herbicidal compounds with new or novel sites and modes of action. Microbial metabolites have become the focus of attention of researchers searching for natural product alternatives to conventional herbicides. Two well-known commercial herbicides of microbial origin are anisomycin (commercial analogue, methoxyphenon) and bialaphos. Both were isolated from members of actinomycetes. Several phytotoxins have been isolated from microbial metabolites, e.g., herbicidins A and B, herbimycins A and B, nigericin, tentoxin and others. The list of microbial phytotoxins continues to M. increase. Actinomycetes are the major source of several herbicides and other bioactive compounds. The potential of discovering new phytotoxins from metabolites of microorganisms is still unlimited. Methods of isolation of actinomycetes, their screening for phytotoxins, separation of phytotoxins from metabolites and partial purification of the toxins are described. Included are screening of soil fungi for phytotoxin, mass culture of fungi, and bioassays.

Two Phytotoxins Isolated from the Pathogenic Fungus of the Invasive Weed Xanthium italicum

“…Other non‐host‐specific phytotoxins include α , β ‐dehydrocurvularin and brefeldin A from A. zinnia , which caused phytotoxicity to Xanthium occidentale L., a harmful weed widely found in summer crops and pastures in Australia. The fungus A. zinniae and its toxins may be used as mycoherbicides in integrated biological weed control, while some fungal phytotoxins are also toxic to weeds and show herbicidal potential in agriculture and forestry …”

Metabolites from Alternaria Fungi and Their Bioactivities

“…Some fungal phytotoxins were toxic to weed species to show their herbicidal potentials in agriculture and forestry [ 10 , 163 , 164 , 165 ]. Some examples are shown in Table 3 .…”

Evaluation of the toxicity of Streptomyces aburaviensis (R9) extract towards various agricultural pests

“…Biological methods and technologies in coordination with agricultural production [1,2] were established to solve problems of the deleterious effects of chemical fertilizers and pesticides on the environment and the appearance of organisms with resistance resulting from the high application rates of currently used agrochemicals [3][4][5]. Such chemicals are widely used despite the growing public concerns of several undesirable consequences of using them such as accumulation in the environment, biomagnification and excessive persistence [6].…”

“…have been advocated as promising biocontrol agents against several phytopathogenic fungi and bacteria [9][10][11][12][13][14]. In addition, members of the genus Streptomyces are well known for their potential to produce herbicides [5,15]. Natural compounds, such as the secondary metabolites of actinomycetes and particularly streptomycetes, have been demonstrated to be bioherbicides and include anisomycin, bialaphos, herbicidans A and B [5].…”

“…In addition, members of the genus Streptomyces are well known for their potential to produce herbicides [5,15]. Natural compounds, such as the secondary metabolites of actinomycetes and particularly streptomycetes, have been demonstrated to be bioherbicides and include anisomycin, bialaphos, herbicidans A and B [5]. Therefore, attempts have been made to isolate streptomycetes with bioherbicidal properties.…”