Evaluation of Trichoderma harzianum-Impregnated Clay Granules as a Biocontrol for Phytophthora cinnamomi Causing Damping-Off of Pine Seedlings

Abstract

A molasses-amended, T. harzianum-infested preparation of attapulgus clay granules was tested in the greenhouse as a biocontrol for P. cinnamomi-induced damping-off of shortleaf pine [Pinus echinata] seedlings. Tests were conducted in flats containing either autoclaved or nonautoclaved soil; flats were watered twice weekly or kept near saturation under a mist system. When incorporated into the soil simultaneously with the P. cinnamomi inoculum, T. harzianum was most effective in reducing disease incidence in flats that received water twice weekly; an additional application of Trichoderma-granules to the soil surface after 2 wk resulted in a reduced seedling stand, indicating that leaching possibly provided a nutrient source for P. cinnamomi. Seedling survival was poorest in flats in which soil moisture was maintained at near saturation, indicating that T. harzianum could not compete and that the residual nutrients contained in the granules were utilized by P. cinnamomi. Examination of seedlings along demarcation lines between treatments in multi-treatment flats revealed that neither T. harzianum nor P. cinnamomi affected seedling survival in adjacent treatments; thus, growth and/or mobility of each organism beyond its respective inoculated area apparently was restricted. For nonautoclaved soil, evaluation of T. harzianum for control of P. cinnamomi was hindering owing to interactions with other damping-off pathogens. Such a preparation of T. harzianum cannot be considered an effective biocontrol agent for P. cinnamomi.