Investigations on specific apple replant disease (SARD) in Sweden

SIGLEAvailable from: Hannover Univ. (Germany, F.R.). Universitaetsbibliothek / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Microbial community responses associated with the development of oomycete plant pathogens on tomato roots in soilless growing systems

Aims: To determine the spread of different oomycete pathogens in hydroponic, soilless tomato growing systems and their impact on established microbial communities, as baseline studies prior to future introduction of microbial inoculants for disease suppression. Methods and Results: The oomycete pathogens, Pythium group F, Pythium aphanidermatum and Phytophthora cryptogea, were introduced into small-scale recirculating tomato growing systems containing rockwool 6 weeks after set-up when roots were well-established. Two weeks later, half of the systems were switched over to run-to-waste. Pythium aphanidermatum spreads the fastest, Pythium group F the slowest and Ph. cryptogea was intermediate in its spread. The switch to run-to-waste had no effect on pathogen recovery. Microbial communities, monitored by dilution plating, were well-established at the first sampling, 6 weeks after set-up and although differences in community levels were found between experiments, changes during any one experiment were small, generally less than 1 log(10) CFU g(-1) for bacteria. Pathogen introduction increased microbial community levels in roots but the switch to run-to-waste had no effect. Analysis of bacterial communities through amplification of a fragment of the 16S rRNA gene and DGGE profiling showed that different communities were established within each pathogen experiment and that different communities were established on roots, rockwool and in nutrient solutions. However, no significant changes in microbial profiles were found over time in any experiment. Conclusions: In these systems, the microbial communities were well-established 6 weeks after set-up and were resistant to biological and physical perturbation. Significance and Impact of the Study: The implication for microbial inoculation of such systems for disease suppression is that the micro-organisms would either have to be introduced very early during the set-up of the system or be able to replace an established but variable community

Closed hydroponic systems : operational parameters, root exudates occurrence and related water treatment

Greenhouse production of vegetables in closed hydroponic cropping systems is a resource-efficient technique for the production of high-quality produce with a high yield per unit area. Recently, there have been considerable progresses in the development of hydroponic culture. While this type of cropping system allows savings in terms of water and nutrient use, the recirculation of water increases the risk of root exudates dispersal. Plant roots often exude numerous organic acids, which are known to inhibit growth. So far several methods have been found to be effective in removing or degrading the phytotoxic substances released from plant roots during autotoxicity such as adsorption by activated carbon, electrodegradation of root exudates and TiO2 photocatalysis. In this review an overview will be presented of hydroponic systems and their related root exudates occurrence and removal