Non-target impacts of the biocontrol agent Trichoderma atroviride on plant health and soil microbial communities in two native ecosystems in New Zealand

Abstract

Eleven plant species representing two native ecosystems (1) podocarp forest (Dacrycarpus dacrydioides, Plagianthus regius, Pittosporum eugenioides, Cordyline australis, Melicytus ramiflorus, Coprosma robusta and Asplenium gracillimum) and (2) grassland (Poa cita, Chionochloa rubra, Chionochloa rigida and Festuca novae-zelandiae) and representatives of a wider beneficial microbe population (arbuscular mycorrhizae (AM) and Pseudomonas spp.) were studied to assess possible non-target effects of a commercial T. atroviride product. Comparison of several physical markers (plant height, basal diameter, total leaf number, total leaf area, and fresh and dry weight of leaves, shoots and roots) showed that this T. atroviride isolate had no negative effect on plant health. Although photosynthetic pigment analysis indicated significant differences in chlorophyll and carotene levels between the Trichoderma and control treatments for some plants, this variation was not supported by physical changes in plant health. Culture-dependent and -independent analysis of AM fungi and Pseudomonads demonstrated that T. atroviride had no effect on these potential plant beneficial taxa in either ecosystem. The findings from this study suggest using Pittosporum eugenioides and Pagianthus regius for assessing the impact of imported microbial biocontrol agents on the plant growth of established podocarp forest plants, and Cordyline australis and P. regius for assessing the impact of these agents on seedling establishment. In tussock grassland ecosystems, Festuca novae-zelandiae and Poa cita are suggested for growth impact assessments, and P. cita and Chionochloa rubra for seedling establishment trials. The use of a combination of basic culture-dependent and -independent techniques for assessing changes in soil microbial communities often associated with plant health is also suggested.