The initiative to use plant pathogens and allelochemicals from pathogens and other microorganisms as biological weed control agents (bioherbicides) began about 30 yr ago. Since then, numerous plant pathogens (bacteria and fungi) and microbial allelochemicals have been isolated, identified, and tested for their bioherbicidal potential. Pathogens (and in some cases microbial phytotoxins) may be used directly on target weed species, or such allelochemicals may provide unique chemical templates for the synthesis of new herbicide classes with novel molecular modes of action. To date, the most successful microbial products that have led to the development of commercial herbicides are bialaphos (commercially available in Japan) and glufosinate (marketed worldwide). Glufosinate is the ammonium salt of phosphinothricin, which is the active ingredient of bialaphos derived from a nonphytopathogenic Streptomyces species. This overview will examine selected advances in the isolation and identification of novel plant pathogens that have weed hosts, and some microbial allelochemicals with phytotoxic properties. Perspectives on the use of these bioherbicides in weed control, relative to their allelopathic interactions with plants will be discussed.
Nomenclature: Bialaphos; glufosinate.
Additional index words: Mode of action, rhizobacteria, mycoherbicide, phytopathogen, allelopathy, phytotoxin, natural product, enzyme inhibitor.
Abbreviations: AAL toxin, toxin produced by Alternaria alternata (Fr.:Fr.) Keissl. f.sp. lycopersici; AAT, aspartate amino transferase; AOA, aminooxyacetate; DRB, deleterious rhizobacteria; FB1, fumonisin B1; GS, glutamine synthetase; HMG-CoA, 3-hydroxy-3-methylglutaryl-coenzyme A; PGPR, plant growth–promoting rhizobacteria; PPT, phosphinothricin.