In order to study the influence of Arbuscular Mycorrhiza (AM) on the development of root rot infection, tomato plants were raised with or without Glomus mosseae and/or Phytophthora nicotianae var. parasitica in a sand culture system. All plants were fed with a nutrient solution containing one of two phosphorus (P) levels, 32 #M (I P) or 96 #M (IIP), to test the consequence of enhanced P nutrition by the AM fungus on disease dynamics. Mycorrhizal plants had a similar development to that of control plants. Treatment with Phytophthora nicotianae var. parasitica resulted in a visible reduction in plant weight and in a widespread root necrosis in plants without mycorrhiza. The presence of the AM fungus decreased both weight reduction and root necrosis. The percentage reduction of adventitious root necrosis and of necrotic root apices ranged between 63 and 89% The enhancement of P nutrition increased plant development, but did not appreciably decrease disease spread. In our system, mycorrhiza increased plant resistance to P. nicotianae var. parasitica infection. Although a contribution of P nutrition by mycorrhiza cannot be excluded, other mechanisms appear to play a crucial role.Abbreviations: AM -arbuscular mycorrhizae, G-Phy--plants without G. mosseae nor P. nicotianae var. parasitica, G + Phy--plants with G. mosseae but without P. nicotianae var. parasitica, G-Phy + -plants without G. mosseae but with R nicotianae var. parasitica, G + Phy + -plants with both G. mosseae and P nicotianae var. parasitica, I P -first phosphorus level (32 #M), IIP -second phosphorus level (96/zM).

The purpose of this study was to evaluate the level and composition of bacteria and fungi in the indoor air of an Italian office building equipped with a heating, ventilation and air conditioning (HVAC) system. Airborne bacteria and fungi were collected in three open-space offices during different seasons. The microbial levels in the outdoor air, supply air diffusers, fan coil air flow and air treatment unit humidification water tank were used to evaluate the influence of the HVAC system on indoor air quality (IAQ). A medium-low level of bacterial contamination (50-500 CFU/m(3)) was found in indoor air. Staphylococcus and Micrococcus were the most commonly found genera, probably due to human presence. A high fungal concentration was measured due to a flood that occurred during the winter. The indoor seasonal distribution of fungal genera was related to the fungal outdoor distribution. Significant seasonal and daily variation in airborne microorganisms was found, underlining a relationship with the frequency of HVAC system switching on/off. The results of this monitoring highlight the role of the HVAC system on IAQ and could be useful to better characterise bacterial and fungal population in the indoor air of office buildings.

Rhizoctonia solani root-rot is a major soilborne disease causing growth and yield depression. The ability of Glomus mosseae BEG12 and Pseudomonas fluorescens A6RI to suppress this soilborne disease in tomato was assessed by comparing the shoot and root growth of plants infested with R. solani 1556 when protected or not by these beneficial strains. The epiphytic and parasitic growth of the pathogenic R. solani 1556 was compared in the presence and absence of the biocontrol agents by microscopical observations allowing the quantification of roots with hyphae appressed to epidermal cells (epiphytic growth) and of roots with intraradical infection (parasitic growth). The root architecture of the tomato plants under the different experimental conditions was further characterized by measuring total root length, mean root diameter, number of root tips and by calculating degree of root branching. G. mosseae BEG12 and P. fluorescens A6RI fully overcame the growth depression caused by R. solani 1556. This disease suppression was associated with a significant decrease of the epiphytic and parasitic growth of the pathogen together with an increase of root length and of the number of root tips of inoculated tomato plants. The combined effects of G. mosseae BEG12 and P. fluorescens A6RI on pathogen growth and on root morphogenesis are suggested to be involved in the efficient disease suppression.

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