PARENT SESSION
Organized Oral Session 16: Allelopathy: Biochemical interactions among plants affecting community structure, exotic invasions and evolutionary theory
Organizer(s): A Mallik and R Callaway
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 511 C, Level 5, Palais des congrès de Montréal
Microbial allelopathy in agroecosystems.
Zeng, Ren-sen1, 1 South China Agricultural University, Wushan
ABSTRACT- Metabolites of many microorganisms may have adverse or stimulatory effects on plants. Aspergillus japonicusis a common soil fungus, and also exists on the surface of seeds of some crops. Secalonic acid A, C, D, F, G, H, I were isolated and identified from the fungus. Bioassays showed that these secalonic acids strongly inhibited the seedling growth of rape, radish, barnyardgrass, and hairy beggarticks (Bidens pilosa), but stimulated the seedling growth of corn and sorghum at low concentrations. The fungus also released a large amount of oxalic acid and citric acid contributing to additional growth inhibitory effects on higher plants. Actinomyces are common soil-borne bacteria. Fifteen strains of Streptomyces isolated from soils in South China produce phytotoxic compounds. Some compounds have been isolated from Streptomyces sp. Pisolithus tinctorius is an ectomycorrhizal fungus which are important for the growth of many tree seedlings. Aqueous extracts of P. tinctorius fruitbodies inhibited the seedling growth of barnyardgrass, rice, crabgrass (Digitaria sanguinalis), Chinese Pennisetum (Pennisetum alopecuroides), rape and radish. The main allochemical in the fungal fruitbodies was norbadione-A, a naphthalenoid pulvinic acid derivative. Several other flavonoids and a flavone glycoside, pisolactone, 25-methyl-pisolactone and pisosterol which belonged to triterpenoids were also isolated from the fungus. The compounds inhibited seedling growth of many weed species. Some compounds have synergistic effects on plant growth. Ecological implication of the microbial allelopathy will be discussed.
Key words: Allelopathy, allelochemicals, ectomycorrhiza, secalonic acids