Nature's Concept. The ‘New Agriculture’ amidst Ecology,Economy and the Demythologization of the Gene

From worldwide discussions about the limits of agriculture has arisen a powerful vision of sustainable development. Phrases like ‘limitation’, ‘sustainability’, ‘sufficient supply’, ‘fair distribution’ and ‘productivity of resources’ are no longer hindrances but guidelines for a fairer and safer world. ‘Nature's Concept' focuses on biological and ecological principles. On this basis, criteria of action have to be defined in order to determine long‐term economic consequences of agri‐production. The costs of destruction of natural resources, such as reduction of genetic resources, changes to the world climate and soil degradation, are inestimably large. The long‐term effects show the real substance of the agri‐shift and the demands on research. The solution for sustainable agriculture is more than ever a scientific development of ‘tools’ for a sensible management of resources. Gene technology may be an option to reduce the ecological risks of agriculture, especially those of devastating land use. For this purpose, new education programmes with international links and interventions by states are crucial in order to solve conflicts when short‐term interests interfere with long‐term ecological values. The international agri‐centres could have a further impact to guarantee access to new techniques for all countries. Thus agriculture could finally become a major pillar in a fair world order.     

Development of a cDNA-AFLP derived CAPS marker co-segregating with the powdery mildew resistance gene Mlg in barley

Powdery mildew is an important pathogen of barley in many barley-growing areas. To identify molecular markers for the resistance gene Mlg located on chromosome 4H, a cDNA-AFLP approach was carried out on near-isogenic lines. Based on the identification of a differentiating fragment of 37 bp, which turned out to be part of a nucleoside diphosphate kinase as estimated by blastn , a CAPS marker has been developed, which co-segregated with Mlg in a population of 738 F₂-plants. Due to its co-dominant inheritance, clear banding pattern and close linkage this marker is well suited for marker-based selection procedures.     

Resistance to western flower thrips in greenhouse cucumber: effect of leaf position and plant age on thrips reproduction

Three greenhouse cucumber (Cucumis sativus L.) accessions, previously selected for low levels of damage after infestation with Frankliniella occidentalis (Pergande), were tested for resistance against F. occidentalis in a no-choice greenhouse experiment at the mature plant stage. The three accessions showed a strong reduction in thrips damage compared to the susceptible control. The effects of leaf position and plant age of the four cucumber accessions on the reproduction of F. occidentalis were determined in a leaf disc assay. Leaf position had a significant effect on thrips reproduction, whereas plant age, within the test range, had not. In general, reproduction was higher on young leaves. Reproduction as measured on leaf discs from certain leaf positions was strongly correlated with resistance of mature plants in the greenhouse, and can therefore be used as a quick test to screen cucumber accessions for resistance against thrips. This revised version was published online in July 2006 with corrections to the Cover Date.     

RNA-based disease control as a complementary measure to fight Fusarium fungi through silencing of the azole target <Emphasis Type="Italic">Cytochrome P450 Lanosterol C-14 α-Demethylase</Emphasis>

RNA-based disease control has shown great potential for controlling pest and diseases in crop plants. While delivery of inhibitory noncoding double-stranded (ds)RNA by transgenic expression is a promising concept, it requires the generation of transgenic crop plants, which may cause substantial delay for application strategies depending on the transformability and genetic stability of the crop plant species. Focusing on agronomic important barley - Fusarium spec. pathosystems, we have sought for alternative strategies to apply dsRNAs for fungal control. Recently, we have demonstrated that a spray application of a long noncoding dsRNA termed CYP3RNA, which targets the three fungal Cytochrome P450 lanosterol C-14α-demethylase genes FgCYP51A, FgCYP51B, and FgCYP51C, inhibits Fusarium graminearum (Fg) on barley leaves (Koch et al., PLoS Pathogens, 12, e1005901, 2016). Here we show that another Fusarium species, F. culmorum (Fc), also is sensitive to CYP51-derived dsRNAs. Treating Fc with various dsRNAs targeting the genes FcCYP51A, FcCYP51B and FcCYP51C was destructive to the fungus and resulted in growth retardation in in vitro cultures. We discuss important consequences of this finding on future RNA-based disease control strategies. Given the ease of design, high specificity, and applicability to diverse pathogens, the use of target-specific dsRNA as an anti-fungal agent offers unprecedented potential for novel plant protection strategies.     

Evaluation of dsRNA delivery methods for targeting macrophage migration inhibitory factor MIF in RNAi-based aphid control

Journal of Plant Diseases and Protection - Macrophage migration inhibitory factors (MIFs) are multifunctional proteins regulating major processes in mammals, including activation of innate immune...     

A review of pest surveillance techniques for detecting quarantine pests in Europe

This paper provides reviews of the most commonly used methods to detect plant pests belonging to groups of invasive organisms with high economic relevance, including Coleoptera (bark beetles, flathead borers, leaf beetles, longhorn beetles, weevils), Diptera (cone and seed flies, fruit flies), Homoptera (aphids, leafhoppers and psyllids, whiteflies), Lepidoptera (moths and butterflies), Thysanoptera (thrips), bacteria (potato brown rot Ralstonia solanacearum) and fungi (pitch canker disease Gibberella circinata, brown rot disease Monilinia fructicola). Future perspectives in detection methods are discussed, with particular reference to the considerable increase in the volume, commodity type and origins of trade in plant material from third countries, the introduction of new crops, the continuous expansion of the EU with new border countries being added, and the impact of climate change affecting the geographical boundaries of pests and their vectors.     

Ectopic expression of barley constitutively activated ROPs supports susceptibility to powdery mildew and bacterial wildfire in tobacco

ROPs (also called RACs) are RHO-like monomeric G-proteins of plants, well-known as molecular switches in plant signal transduction processes, which are involved in plant development and a variety of biotic and abiotic stress responses. The barley (Hordeum vulgare) ROPs RACB, RAC1 and RAC3 have been shown to be involved in cellular growth, polarity and in susceptibility to the biotrophic barley powdery mildew fungus Blumeria graminis f.sp. hordei. We produced transgenic tobacco (Nicotiana tabacum) plants expressing constitutively activated (CA) mutants of the barley ROPs RACB and RAC3 to monitor the impact of heterologous ROP expression on cell polarity and disease susceptibility of tobacco. CA HvROPs influenced leaf texture, disturbed root hair polarity and induced cell expansion in tobacco. Both barley ROPs induced super-susceptibility to the compatible powdery mildew fungus Golovinomyces cichoracearum but only CA HvRAC3 induced super-susceptibility to the bacterial leaf pathogen Pseudomonas syringae pv. tabaci. Data suggest involvements of ROPs in tobacco cell expansion, polar growth and in response to bacterial and fungal leaf pathogens.     

Variation in performance of western flower thrips populations on a susceptible and a partially resistant chrysanthemum cultivar

Variation in host plant performance among populations of a phytophagous insect pest is a potential threat to the durability of host plant resistance. Aggressive biotypes may overcome the protective properties of formerly resistant cultivars. Therefore, it is of interest to study such variation in breeding programs for host plant resistance to insects. In the present study, the performance of ten populations of Frankliniella occidentalis, the western flower thrips, was determined on a susceptible and a partially resistant cultivar of chrysanthemum, Dendranthema grandiflora. Damage, reproduction, and adult survival were determined using an excised leaf assay. Significant differences between the two cultivars and among the ten populations were found for all three characteristics. In general, damage, reproduction and adult survival were reduced on the resistant cultivar when compared to the susceptible cultivar. Some populations showed, in comparison to the reference population from the Netherlands, much higher damage and reproduction on one or both chrysanthemum cultivars. But also in these populations performance on the resistant cultivar was poor compared to the susceptible cultivar. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Compromised Mlo Pathway Affects the Response of Barley to the Necrotrophic Fungus Bipolaris sorokiniana (Teleomorph: Cochliobolus sativus) and Its Toxins

ABSTRACT In search of new durable disease resistance traits in barley to control leaf spot blotch disease caused by the necrotrophic fungus Bipolaris sorokiniana (teleomorph: Cochliobolus sativus), we developed macroscopic and microscopic scales to judge spot blotch disease development on barley. Infection of barley was associated with cell wall penetration and accumulation of hydrogen peroxide. The latter appeared to take place in cell wall swellings under fungal penetration attempts as well as during cell death provoked by the necrotrophic pathogen. Additionally, we tested the influence of a compromised Mlo pathway that confers broad resistance against powdery mildew fungus (Blumeria graminis f. sp. hordei). Powdery mildew-resistant genotypes with mutations at the Mlo locus (mlo genotypes) showed a higher sensitivity to infiltration of toxic culture filtrate of Bipolaris sorokiniana as compared with wild-type barley. Mutants defective in Ror, a gene required for mlo-specified powdery mildew resistance, were also more sensitive to Bipolaris sorokiniana toxins than wild-type barley but showed less symptoms than mlo5 parents. Fungal culture filtrates induced an H2O2 burst in all mutants, whereas wild-type (Mlo) barley was less sensitive. The results support the hypothesis that the barley Mlo gene product functions as a suppresser of cell death. Therefore, a compromised Mlo pathway is effective for control of biotrophic powdery mildew fungus but not for necrotrophic Bipolaris sorokiniana. We discuss the problem of finding resistance traits that are effective against both biotrophic and necrotrophic pathogens with emphasis on the role of the anti-oxidative system of plant cells.