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Nieuwe teeltsystemen, meer onderzoek naar het microbioom van planten en een snellere toelating van biologische gewasbeschermingsmiddelen; uit het congres ‘Biocontrol needs and challenges in future cropping systems’ blijkt dat deze ingrediënten nodig zijn om gewassen te telen met een hogere veerkracht tegen plantenziekten. Het congres werd georganiseerd door de IOBC-WPRS working group Biological control of plant pathogens samen met Wageningen University & Research (WUR).

Bacteriën die de bodem beschermen tegen ziekten, en schimmels die schadelijke insecten doden. Brazilië is wereldwijd koploper in de biologische bescherming van gewassen tegen ziekten en plagen. Hoe Brazilië die plek heeft veroverd? Mede dankzij de traditie die boeren kennen om deze middelen zelf te produceren.

European canker is one of the most devastating fungal diseases of apple in most temperate regions. The causal agent, Neonectria ditissima, infects trees through wounds in the bark forming cankers that girdle the stem and eventually cause tree death. Timely protection of the trees is challenged by stagnation of symptom expression after infections for a long period of time. The objective of this research is to use a novel TaqMan PCR assay to detect and quantify N. ditissima during the asymptomatic colonization of apple wood. Pruning wounds on branches of the cultivars Elstar and Gala were inoculated with N. ditissima and wood discs were sampled at 2–6, 10–14, and 30–34 mm distance from the inoculation site after 3 hours, 2 weeks, 4 weeks and 8 weeks for the detection and quantification of the pathogen. The TaqMan PCR assay detected N. ditissima in 51% of the inoculated apple tree samples. This was more sensitive than the culturing method detecting N. ditissima in 11% of the samples. An accumulation of N. ditissima DNA up to 34 mm distance from the inoculation site was observed without development of visible symptoms. To our knowledge this is the first time colonization of N. ditissima was detected and quantified in the absence of symptoms of European canker. The implications of this research are discussed.

Neonectria ditissima is the causal agent of European canker. This pathogen causes cankers on apple branches and the main stem, which may lead to the loss of the whole tree. Chemical control is the essential component in disease management and no suitable biocontrol products are commercially available. This study aimed at selecting potential microbial antagonists against N. ditissima through a systematic stepwise screening program for the development of a new biocontrol product. A total of 520 potential candidates were isolated from apple branches showing canker symptoms. Important characteristics for application of Microbial Biological Control Agents were tested per each candidate: spore production, spore survival during storage, cold tolerance, drought tolerance and UV-B resistance. Isolates able to germinate and grow at human body temperature were excluded. A total of 252 candidates fulfilled the stablished criteria. All 520 candidates belonged to 44 different taxonomic groups, being the most abundant Alternaria spp. (22.2 %), Aureobasidium pullulans (16.1 %), Cladosporium spp. (9.5 %) and Fusarium spp. (9.0 %). Information on possible pathogenicity and toxicity for humans, animals, plants and the environment and on patents in biocontrol use was collected per each identified species. A total of 158 candidates belonging to species that did not show potential risks or patent conflicts were assessed by their antagonistic behaviour against N. ditissima in bioassays in planta. Each candidate was inoculated in ‘Elstar’ apple branches inoculated with N. ditissima 24 h before. Inoculated branches were incubated at 17 °C, 16 h light per day and RH > 90 %. After four weeks, canker symptom expression was visually assessed. The capacity of the candidates to reduce colonisation of N. ditissima in the branches was evaluated by quantifying N. ditissima DNA concentration using qPCR. Four candidates of Clonostachys rosea showed antagonistic properties; after four weeks of treatmen

Als alles gericht is op preventie, waarom zijn er dan nog steeds plantenziekten? Helaas is resistentie tegen lang niet alle plantenbelagers beschikbaar. En soms kan een plantenbelager dankzij genetische mutatie de resistentie omzeilen. Wat dan resteert is een directe vorm van bestrijding, biologisch dan wel chemisch. De discussie of we zonder chemische bestrijding kunnen, wordt momenteel volop gevoerd; de overheid wil er in ieder geval binnen tien jaar afscheid van nemen. De suikerbiet kunnen we dan kwijtraken, gezien de grote druk van allerlei ziekten en plagen. Aardappelteelt blijft wel mogelijk, maar de opbrengsten zullen sterk achteruitgaan. Biologische bestrijding zou een alternatief kunnen zijn, maar zijn er wel voldoende goedwerkende ‘groene middelen’ beschikbaar?

There is a need to develop more biological control agents to fulfil the increasing demand for biological crop protection. Testing for consistent efficacy in disease control under the relevant range of environmental conditions is one of the most demanding steps during screening programs. Bioassays were conducted to target three major diseases of tomato, stem canker caused by Botrytis cinerea, leaf spot caused by B. cinerea, and bacterial spot caused by Pseudomonas syringae pv. tomato, and to assess possible growth promotion of tomato seedlings. Nine quantitative screening approaches were analyzed for a test panel of approximately 100 isolates of bacteria and fungi, all obtained from tomato, and several known antagonists as reference isolates. Even with such a limited number of isolates promising antagonists, partly not yet described as antagonists, could be selected for control of the targeted diseases when labor and resource demanding in planta bioassays had been applied. Also some promising isolates enhancing seedling development could be identified. Independent screening assays for the different traits were needed since no correlation between the different traits were found. Attempts to simplify screening assays to high-throughput systems failed since there were no positive correlations with in planta bioassays. In conclusion, the often suggested first screening rounds using in vitro tests for huge numbers of isolates followed by in planta testing of a selected group of candidates, e.g. those with high in vitro production of certain secondary metabolites or biosurfactants, may not exploit the entire potential of antagonists. Especially antagonists combining various modes of action may be excluded by in vitro screening with a bias on a specific mode of action. Therefore, independent in planta assays are proposed to screen against different pathogens and for growth promotion.

Microbiome management is a promising way to suppress verticillium wilt, a severe disease in Brassica caused by Verticillium longisporum. In order to improve current biocontrol strategies, we compared bacterial Verticillium antagonists in different assays using a hierarchical selection and evaluation scheme, and we integrated outcomes of our previous studies. The result was strongly dependent on the assessment method chosen (in vitro, in vivo, in situ), on the growth conditions of the plants and their genotype. The most promising biocontrol candidate identified was a Brassica endophyte Serratia plymuthica F20. Positive results were confirmed in field trials and by microscopically visualizing the three-way interaction. Applying antagonists in seed treatment contributes to an exceptionally low ecological footprint, supporting efficient economic and ecological solutions to controlling verticillium wilt. Indigenous microbiome, especially soil and seed microbiome, has been identified as key to understanding disease outbreaks and suppression. We suggest that verticillium wilt is a microbiome-driven disease caused by a reduction in microbial diversity within seeds and in the soil surrounding them. We strongly recommend integrating microbiome data in the development of new biocontrol and breeding strategies and combining both strategies with the aim of designing healthy microbiomes, thus making plants more resilient toward soil-borne pathogens.

Microbial biological control agents (MBCAs) against pests and diseases in crops are regarded as sustainable tools in integrated pest management.In the European Union, biological control should be preferred to conventional chemical methods if they provide satisfactory pest reduction. There is no reason to believe that all forms of biocontrol are intrinsically safe. Therefore requirements for registration to assure safety are needed. In the current registration procedure in the European Union, MBCAs are primarily treated as potentially risky organisms that not only produce toxic substances but are also dangerous because they can multiply, spread and genetically adapt. These characteristics give rise to a concern that released MBCAs will spread and become dominant in the environment, resulting in negative effects on other organisms in the natural environment or even humans. These assumption led to extensive data requirements that are a time consuming and costly hurdle for bringing MBCAs onto the market. This paper focuses on the relevance and irrelevance of the data requirements for environmental fate and persistence of MBCAs. MBCAs are naturally occurring living organisms that are numerically enhanced to reduce specific plant pathogens or pests.In contrast to chemicals, direct toxicity is not the main mode of action, but rather a variety of mechanisms is involved, including competition, parasitism and activity of secondary metabolites. Their effects and residues cannot be evaluated as done for chemical substances and their breakdown products. Populations of introduced microorganisms always decline due to the natural biological buffering of the environment to levels that are within common fluctuations and ranges without strongly affecting microbial communities. However, the currently used concept of a natural background level as a reference to which densities of MBCAs should decline is of limited value, in particular when endpoints cannot be defined from ecological the