Microbial optimisation in soilless cultivation, a replacement for methyl bromide

In Europe the soil fumigant methyl bromide is still in use to control soil-borne diseases in greenhouses and open air vegetables. Methyl bromide is extremely toxic and environmental harmful. Countries under the Montreal protocol are demanded to reduce the use of methyl bromide with respect to the average use between 1991 and 1994 resulting in a total phase out from 2005 onwards for all applications except critical uses. For greenhouses replacement of soil grown crops by closed soilless growing systems has significant advantages: conservation of scarce water resources, no leaching of nutrients and pesticides and improved quality of products. A disadvantage of the closed system is the rapid dispersal of soil-borne pathogens by the recirculating nutrient solution. Disinfection of the nutrient solution either by active (sterilisation) or passive (part of the resident microflora survives the treatment) methods may eliminate harmful pathogens, but the hypothesis is that with passive methods a suppressive microflora can be built up, preventing (severe) outbreaks of certain pathogens. A 4-year EU-funded project had the aims to characterise the (suppressive) microflora and metabolites in the nutrient solution, to detect its dynamic behaviour during the cultivation of three crops (tomato, cucumber, gerbera) in a two year period and to demonstrate results to commercial users. Part of the crop was inoculated with Pythium aphanidermatum or Phytophthora cryptogea, while the nutrient solution was disinfected either with Ultra Violet radiation (active method) or slow sand filtration (passive method) or not at all (control). This paper emphasise on practical aspects of disinfection of the nutrient solution in relation to the presence and behaviour of the microflora. Results indicate that disinfection of the nutrient solution is needed to achieve proper yields. It was not proven that a suppressive microflora could be built up by a passive disinfection method, compared with active disinfection. However, a shift in the composition of the microflora could be detected, but the microflora in the stone wool growing system is mainly plant-driven, realising a microbial balanced system. Application of certain antagonists did also shift the total microflora during cropping, but did not suppress the mentioned pathogens with the exception of a Trichoderma-strain

In vitro compatibility of microbial agents for simultaneous application to control strawberry powdery mildew (Podosphaera aphanis)

Biological control of plant pathogens on strawberries may be improved by the simultaneous application of different biological control agents (BCAs). Therefore, the compatibility of various BCAs which had previously shown to be effective against powdery mildew (Podosphaera aphanis (Wallr.) U. Braun & S. Takam) under laboratory conditions was examined in vitro. Inhibitory effects between fungal and bacterial BCAs were demonstrated in dual culture tests on two solid nutrient media. Leaf disc assays with single and multiple strain treatments demonstrated either unaffected or significantly improved control of P. aphanis for many multiple strain treatments, even if antagonistic interactions previously occurred in dual culture tests. Highest inhibition of powdery mildew conidiation (80.7% reduction) was achieved with multiple strain treatments with Bacillus subtilis FZB24 and Metarhizium anisopliae (p<0.001). In this combination, conidiation was 3.7 times lower than in single treatments with B. subtilis indicating synergistic interactions between these BCAs. Combinations of Trichoderma harzianum T58 and B. subtilis FZB24 showed antagonistic interactions in dual culture tests as well as in leaf disc assays. In this combination, powdery mildew conidiation on leaf discs was four times higher compared to single treatments with T. harzianum T58

Leaf microbiota of strawberries as affected by biological control agents

The increasing use of biological control agents (BCAs) against Botrytis cinerea in strawberry raises the question of whether there are any undesirable impacts of foliar applications of BCAs on nontarget microorganisms in the phyllosphere. Therefore, our objective was to investigate this issue within a field study. Strawberry plants were repeatedly sprayed with three BCAs—namely, RhizoVital 42 fl. (Bacillus amyloliquefaciens FZB42), Trianum-P (Trichoderma harzianum T22), and Naturalis (Beauveria bassiana ATCC 74040)—to suppress Botrytis cinerea infections. Microbial communities of differentially treated leaves were analyzed using plate counts and pyrosequencing and compared with the microbial community of nontreated leaves. Plate count results indicate that the applied Bacillus and Trichoderma spp. survived in the strawberry phyllosphere throughout the strawberry season. However, no significant impacts on the leaf microbiota could be detected by this culture-dependent technique. Pyrosequencing of internal transcribed spacer ribosomal RNA and 16S RNA sequences revealed a change in fungal composition and diversity at class level after the introduction of T. harzianum T22 to the phyllosphere, whereas the bacterial composition and diversity was not affected by either this Trichoderma preparation or the other two BCAs. Our results suggest that pyrosequencing represents a useful method for studying microbial interactions in the phyllosphere

Transmission of pelargonium flower break virus (PFBV) by irrigation systems, pelargonium pollen and thrips

International audienc

Transmission of pelargonium flower break virus (PFBV) by irrigation systems, pelargonium pollen and thrips

International audienc