Biopesticides

The spectrum of plant defence reactions to microbial infections is intricate but similar in many plant/pathogen interactions. The triggering of a part of these responses is based on the transcriptional activation of genes coding for defence-related proteins with different tasks and sometimes unknown functions. Other comparatively early defence reactions are due to the activation of specific enzymes. In many plant species defence responses in the tissue surrounding the infected site (local) are sometimes connected with the activation of resistance in non-infected parts (systemic) of the plant. This systemic induced resistance can also be generated by the application of compounds of different substance classes (e.g. peptides, sugar polymers, etc.), so-called elicitors. This strategy is a useful amelioration of the generally performed pest control with synthetic plant protecting agents directly acting against the pathogen. The indirect mode of action of these resistance inducers on phytopathogens is solely based on the activation of the plant's own defence potential. An aspired market launch of such innovative resistance inducers based on natural compounds of advantageous ecotoxicological quality should provide both a reduction in environmental load as well as consumer and user protection. For this reason, the ongoing projects focus on agriculturally and horticulturally important plants (apples, tomatoes) and pathogens where effective pesticides are not available or are applied in sometimes questionable quantities. Biotests developed or optimised by AlPlanta, extracts or refined fractions from extracts from soil-borne Actinobacteria or from the Trichoderma (Ascomycota, sac fungi) were examined for direct and indirect action against the above-mentioned plant diseases. In co-operation with medium-sized industrial partners Sourcon-Padena GmbH and NEWBIOTECHNIC, S.A. , screening by means of specific biotests in combination with analytical techniques performed by the co-operation partners allows the isolation and identification of the effective compounds.

Biotests

Furanocoumarins in parsley cell culture

A suspension culture from parsley is used as an efficient system for testing a potential plant resistance induction. These cells respond to effective substances by forming blue fluorescent furanocoumarins. Using a microwell reader, this fluorescence, depending on the nature and concentration of the tested compound, can be measured in large sample numbers. In the course of 2005, more than 10,000 extracts from Actinobacteria were tested in terms of stimulating the defence reaction of the plant cells. Positively assessed samples are being further tested on intact leaves or plants.


In vitro apple plantlets inoculated with fireblight bacteria. Sprayed with an active extract from Actinobacteria (left) and water treated control (right).

Growth test of the fire blight agent

A photometric growth test on a 96-well microplate scale was developed to measure the direct influence of microbial extracts on the growth of Erwinia amylovora, the agent of fireblight, in vitro. Positively assessed samples were then tested on in vitro apple plantlets for the disease pattern.




Growth test of Phytophthora infestans based on GFP fluorescence measurements

A 96-well plate high throughput assay was developed to assess the influence of microbial extracts on the growth of Phytophthora infestans, the causal agent of late blight in potato and tomato. Its principle is based on the quantitative measurement of fluorescence green fluorescent protein (GFP) in the mycelium of the transgenic strain 208m2 (Si-Ammour et al., 2003; Mol Plant Pathol 4(4), 237-248). Promising extracts are also assessed on detached tomato leaves and intact plants.


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