TRICHODERMA SPECIES —
OPPORTUNISTIC,AVIRULENT
PLANT SYMBIONTS
Gary E.Harman*, Charles R.Howell‡, Ada Viterbo§, Ilan Chet§ and Matteo Lorito||
Abstract:
Trichoderma spp. are free-living fungi that are common in soil and root ecosystems. Recent
discoveries show that they are opportunistic, avirulent plant symbionts, as well as being
parasites of other fungi. At least some strains establish robust and long-lasting colonizations of
root surfaces and penetrate into the epidermis and a few cells below this level. They produce or release a variety of compounds that induce localized or systemic resistance responses, and this explains their lack of pathogenicity to plants. These root–microorganism associations cause
substantial changes to the plant proteome and metabolism. Plants are protected from
numerous classes of plant pathogen by responses that are similar to systemic acquired
resistance and rhizobacteria-induced systemic resistance. Root colonization by Trichoderma spp.
also frequently enhances root growth and development, crop productivity, resistance to abiotic
stresses and the uptake and use of nutrients.
In Vivo Study of Trichoderma-Pathogen-Plant Interactions, Using
Constitutive and Inducible Green Fluorescent Protein
Reporter Systems
Zexun Lu,1 Riccardo Tombolini,2 Sheridan Woo,3 Susanne Zeilinger,4
Matteo Lorito,3 and Janet K. Jansson1,5*
Section for Natural Sciences, So¨derto¨rn University College, 14189 Huddinge,1 and Plant Pathology and Biocontrol Unit2 and
Department of Microbiology,5 Swedish University of Agricultural Sciences, 75007 Uppsala, Sweden;
Universita´ degli Studi di Napoli Federico II and Centro di Studio CNR per le Tecniche di Lotta Biologica,
80050 Portici, Italy3; and Abteilung fu¨r Mikrobielle Biochemie, Institut fu¨r Biochemische
Technologie und Mikrobiologie, Technische Universita¨t Wien, A-1060 Vienna, Austria4
Received 14 July 2003/Accepted 27 January 2004
Abstract:
Plant tissue colonization by Trichoderma atroviride plays a critical role in the reduction of diseases caused by phytopathogenic fungi, but this process has not been thoroughly studied in situ. We monitored in situ interactions between gfp-tagged biocontrol strains of T. atroviride and soilborne plant pathogens that were grown in cocultures and on cucumber seeds by confocal scanning laser microscopy and fluorescence stereomicroscopy.
Spores of T. atroviride adhered to Pythium ultimum mycelia in coculture experiments. In mycoparasitic interactions of T. atroviride with P. ultimum or Rhizoctonia solani, the mycoparasitic hyphae grew alongside the pathogen mycelia, and this was followed by coiling and formation of specialized structures similar to hooks,
appressoria, and papillae. The morphological changes observed depended on the pathogen tested. Branching of T. atroviride mycelium appeared to be an active response to the presence of the pathogenic host. Mycoparasitism
of P. ultimum by T. atroviride occurred on cucumber seed surfaces while the seeds were germinating. The interaction of these fungi on the cucumber seeds was similar to the interaction observed in coculture experiments.
Green fluorescent protein expression under the control of host-inducible promoters was also studied. The induction of specific Trichoderma genes was monitored visually in cocultures, on plant surfaces, and in soil in the presence of colloidal chitin or Rhizoctonia by confocal microscopy and fluorescence stereomicroscopy.
These tools allowed initiation of the mycoparasitic gene expression cascade to be monitored in vivo.
et. al., There are literally mounds of peer reviewed research papers on the subject.
HTH's
Butch
