Interactions Between Trichoderma harzianum Strain T22 and Maize Inbred Line Mo17 and Effects of These Interactions on Diseases Caused by Pythium ultimum and Colletotrichum graminicola

Abstract

Seed treatment with Trichoderma harzianum strain T22, which results in colonization of plant roots but little or no colonization of shoots or leaves, had substantial effects on growth of and disease expression in maize inbred line Mo17. Shoots and roots of 10-day-old seedlings grown in a sandy loam field soil were larger (roots were nearly twice as long) in the presence of T22 than in its absence. Both main and secondary roots were increased in size and area and the root hair area was greater with T22. However, root hair area per unit of root length was greater in control plants. Increased growth probably was due to direct stimulation of plant growth in addition to effects from biological control of deleterious microflora. Seedlings of Mo17 grown in autoclaved or mefenoxamtreated sandy loam field soil were larger than those produced in untreated soil. However, seedlings grown in the presence of T22, either in treated or untreated soil, were larger than those produced in its absence. Infestation of soil with Pythium ultimum had little effect upon growth of Mo17. The presence of T22 increased protein levels and activities of beta-1,3 glucanase, exochitinase, and endochitinase in both roots and shoots, even though T22 colonized roots well but colonized shoots hardly at all. With some enzymes, the combination of T22 plus P. ultimum gave the greatest activity. Plants grown from T22-treated seed had reduced symptoms of anthracnose following inoculation of leaves with Colletotrichum graminicola, which indicates that root colonization by T22 induces systemic resistance in maize.

Genome-wide identification, expression and chromosomal location of the genes encoding chitinolytic enzymes in Zea mays

“…Root colonization by T. harzianum strongly inXuenced the chitinolytic enzymes that were detected in both roots and shoots even though T. harzianum was present only on roots; it is known to induce systemic resistance to plant diseases (Harman et al 2004b). We were surprised to observe in both roots and shoots an activity band of about 95 kDa, which is larger than any chitinase that we identiWed.…”

“…Seven-day-old seedlings were harvested: shoot heights were measured and then the shoots were excised at the soil level. Roots were carefully removed from the soil, omitting the region containing the germinated seed, and then gently washed (Harman et al 2004b). All tissues were immediately frozen in liquid nitrogen and stored at ¡70°C until used.…”

“…This was important to us since we had shown that both exo-and endochitinase activity increased in maize seedlings grown from seeds treated with the biocontrol fungus Trichoderma harzianum T22 and that this increase in chitinase activity was systemic throughout the plant (Harman et al 2004b;Harman and Shoresh 2007). This increase in activity was associated with increased resistance to foliar leaf pathogens (Harman et al 2004b).…”

“…This increase in activity was associated with increased resistance to foliar leaf pathogens (Harman et al 2004b). Similar results have been reported for a wide range of biocontrol interactions (Harman et al 2004a;Shoresh et al 2005).…”

The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

“…This is mainly documented for Trichoderma and Gliocladium, and it affects various fungal pathogens, such as Rhizoctonia, Sclerotinia, Verticillium and Gaeumannomyces (Harman et al 2004). Hyperparasitism by Trichoderma involves secretion of chitinases and cellulases, which release small molecules from the target pathogen and trigger chemotropism towards the latter (Zeilinger et al 1999).…”