Development of a monoclonal antibody to detect predation of the brown planthopper Nilaparvata lugens (Stål)

A monoclonal antibody (McAb), 4B8, was developed to whole homogenates of the brown planthopper, Nilaparvata lugens (Stål), using hybridoma technology. It reacted with all the stages of BPH but did not cross-react with other insects and predator species tested with an indirect enzyme-linked immunosorbent assay (ELISA). Immunodiffusion revealed it to belong to the IgG₃ subclass. The ascites developed with 4B8?cell lines had high absorbance values until it was diluted over 6.5536?×?10⁷ times tested by indirect ELISA. It could recognize the BPH proteins after one female was ingested by Pardosa pseudoannulata for about 2.13 days at 25°C. The results of extended antigen detection period and the high specificity of the antibody indicated that 4B8 could be used to study interactions between planthoppers and their predators in the field. Application of the McAb to assess relative importance of four major spider species in subtropical rice ecosystem showed that P. pseudoannulata was more important than Ummeliata insecticeps, and those were more important than Tetragnatha sp. and Coleosoma octomaculatum.     

Characterization of the defence response to Venturia inaequalis in ‘Honeycrisp’ apple,its ancestors,and progeny

The apple cultivar Honeycrisp exhibits genetic resistance to apple scab. The characterization of the macroscopic and microscopic responses on leaves infected by the pathogen Venturia inaequalis is described. The macroscopic resistance reactions observed in ‘Honeycrisp’, its parent ‘Keepsake’, and grandparents ‘Frostbite’ and ‘Northern Spy’ ranged from 0 (no reaction) to chlorotic flecking, stellate chlorosis, necrotic flecking, and sporulation. No hypersensitive response was observed. The resistance response occurred as early as 7 days post inoculation (dpi) at the same time that susceptible plants exhibited macroscopic signs of the disease. The resistance reactions were similar in the progeny population of ‘Honeycrisp’ × ‘Twin Bee Gala’, although they were delayed to 10–14 dpi possibly due to variable greenhouse conditions. This population segregated 3 resistant:1 susceptible, which suggests the presence of two genes in ‘Honeycrisp’ and agrees with the finding that different responses within ‘Honeycrisp’ to mixed inoculum are due to differential recognition of pathogen effectors.     

Annual dynamics of Zymoseptoria tritici populations in wheat cultivar mixtures: A compromise between the efficacy and durability of a recently broken-down resistance gene?

Cultivar mixtures slow polycyclic epidemics but may also affect the evolution of pathogen populations by diversifying the selection pressures exerted by their plant hosts at field scale. We compared the dynamics of natural populations of the fungal pathogen Zymoseptoria tritici in pure stands and in three binary mixtures of wheat cultivars (one susceptible cultivar and one cultivar carrying the recently broken-down Stb16q gene) over two annual field epidemics. We combined analyses of population “size” based on disease severity, and of population “composition” based on changes in the frequency of virulence against Stb16q in seedling assays with more than 3000 strains. Disease reductions were observed in mixtures late in the epidemic, at the whole-canopy scale and on both cultivars, suggesting the existence of a reciprocal protective effect. The three cultivar proportions in the mixtures (0.25, 0.5, and 0.75) modulated the decrease in (a) the size of the pathogen population relative to the two pure stands, (b) the size of the virulent subpopulation, and (c) the frequency of virulence relative to the pure stand of the cultivar carrying Stb16q. Our findings suggest that optimal proportions may differ slightly between the three indicators considered. We argue potential trade-offs that should be taken into account when deploying a resistance gene in cultivar mixtures: between the dual objectives “efficacy” and “durability,” and between the “size” and “frequency” of the virulent subpopulation. Based on current knowledge, it remains unclear whether virulent subpopulation size or frequency has the largest influence on interepidemic virulence transmission.     

Plant and veterinary disease diagnosis: a generic approach to the development of field tools for rapid decision making?

Rapid and accurate diagnostic tests make an important contribution to programmes to monitor and eradicate infectious diseases that impact animal and plant health. Using foot-and-mouth disease (FMD) and sudden oak death as examples, this review outlines recent progress to develop new field tools for detection of the infectious agents that cause high-impact livestock and plant diseases. The principal driver for this work is to develop tools that can be used locally to assist in decision making. Advances in this area have developed simple-to-use lateral-flow devices for the detection of FMD virus and the genus Phytophthora (including Phytophthora ramorum , the causal agent of sudden oak death and the related pathogen P. kernoviae ), as well as new hardware platforms to allow PCR testing for these agents by non-specialists in the field. Although developed for different diseases, the user requirements for rapid diagnostic tools for FMD and sudden oak death share many similarities. Using generic solutions to these challenging problems, it is now possible to imagine a new paradigm for how the collection and testing of samples to monitor the spread of important livestock and plant diseases might be achieved.     

SCAR–based PCR primers to detect the hybrid pathogen <Emphasis Type="Italic">Phytophthora alni</Emphasis> and its subspecies causing alder disease in Europe

Since the 1990s, a new Phytophthora species hybrid has been jeopardizing the natural population of alders throughout Europe. This new Phytophthora, P. alni, has been suggested as a natural hybrid between two closely related species of Phytophthora. Little is known about the epidemiology of this pathogen, because its direct isolation is not always satisfactory. In this study we developed three pairs of Polymerase Chain Reaction (PCR) primers derived from Sequence Characterized Amplified Regions (SCAR) that allow discrimination among the three subspecies of P. alni: P. alni subsp. alni, P. alni subsp. uniformis and P. alni subsp. multiformis. These molecular tools were successfully used to detect P. alni directly in different substrates such as infested river water and soil, and necrotic alder bark, without the need for any prior baiting or isolation stages. An Internal Amplification Control (IAC) was included to help discriminate against false negative samples due to the potential presence of inhibitory compounds in DNA extracts. These molecular tools should be useful for epidemiological studies on this emerging disease.     

Identifying potential novel resistance to the foliar disease ‘Scald’ (Rhynchosporium commune) in a population of Scottish Bere barley landrace (Hordeum vulgare L.)

Journal of Plant Diseases and Protection - Barley ‘Scald’ is an economically damaging fungal disease that is a global problem, causing significant yield and economical losses in the UK...     

Transgenic citrus expressing the antimicrobial gene <Emphasis Type="Italic">Attacin E</Emphasis> (<Emphasis Type="Italic">attE</Emphasis>) reduces the susceptibility of ‘Duncan’ grapefruit to the citrus scab caused by <Emphasis Type="Italic">Elsinoë fawcettii</Emphasis>

Citrus scab, caused by Elsinoë fawcettii (anamorph Sphaceloma fawcettii), is a common foliar fungal disease affecting many citrus cultivars, including grapefruit. No commercial grapefruit cultivar is resistant to scab, and the disease results in severely blemished fruit which reduces its marketability. Transgenic ‘Duncan’ grapefruit trees expressing the antimicrobial attE gene were produced via Agrobacterium-mediated transformation. In in vitro leaf and greenhouse assays, several transgenic-lines had significantly lower susceptibility to E. fawcettii compared to the non-transformed control (P?P?P?attE mRNA was inversely related to the number of copies detected by Southern blot. The least susceptible line had a single inserted copy of the attE transgene whereas more susceptible lines had multiple copies. Since the attacin mode of action was thought to be specific to Gram-negative bacteria, it was unexpected to find that there was a significant activity against E. fawcettii.     

Analysis of the relationship between parameters of resistance to <Emphasis Type="Italic">Fusarium</Emphasis> head blight and <Emphasis Type="Italic">in vitro</Emphasis> tolerance to deoxynivalenol of the winter wheat cultivar WEK0609 <Superscript>®</Superscript>

Fusarium head blight (FHB) symptom development, relative spikelet weight (RSW), fungal DNA (FDNA) and deoxynivalenol (DON) content of grain was assessed in the FHB resistant winter wheat cv. WEK0609 and the FHB susceptible cv. Hobbit sib, and among doubled haploid progeny lines (DHLs) developed from a cross between these cultivars. In addition, the relationship between FHB resistance traits and germination on DON-containing medium (in vitro DON tolerance (IVDT)) was also investigated to assess the possibility of using this test as in vitro method of screening for FHB resistance in this cultivar. Analysis indicated that WEK0609 resistance significantly reduced symptom development, yield loss and the FDNA and DON content of grain relative to Hobbit sib. Although both the DON and FDNA content were greater in susceptible than in resistant progeny lines, the ratio of DON to FDNA decreased with increasing susceptibility. The resistance derived from WEK0609 appears to have a greater effect on colonisation of the grain by the fungus than on the accumulation of DON within the grain. In vitro tolerance to DON does not appear to relate to FHB resistance in WEK0609 and thus does not provide a means of selecting for FHB resistance derived from this cultivar.     

Suppression of mRNAs for lipoxygenase (LOX), allene oxide synthase (AOS), allene oxide cyclase (AOC) and 12-oxo-phytodienoic acid reductase (OPR) in pea reduces sensitivity to the phytotoxin coronatine and disease development by Mycosphaerella pinodes

Using a recently developed model pathosystem involving Medicago truncatula and Mycosphaerella pinodes, causal agent of Mycosphaerella blight on pea to understand host molecular response to a fungal suppressor, we applied the suppressor to leaves of M. truncatula and identified 151 nonredundant cDNA fragments as newly expressed genes. These included genes encoding lipoxygenase (LOX) and enoyl-CoA hydratase, which are presumably involved in jasmonic acid (JA) synthesis. Potential genes encoding plastidic enzymes, including allene oxide synthase (AOS) and allene oxide cyclase (AOC), and other peroxisomal enzymes involved in β-oxidation were predicted from the Medicago Gene Index EST database and tested for altered expression by semiquantitative RT-PCR. The coordinated expression of genes encoding both plastidic and peroxisomal enzymes showed that the suppressor likely conditions certain cellular process(es) through the JA synthesis in M. truncatula. To explore the role of JA or JA-regulated cellular process(es) in conditioning susceptibility, we used an Apple latent spherical virus (ALSV)-based virus-induced gene silencing (VIGS) technology to silence pea genes including LOX, AOS, AOC and 12-oxo-phytodienoic acid reductase (OPR). In LOX-, AOS-, AOC- or OPR-silenced pea plants, disease development induced by M. pinodes was remarkably reduced. Similarly, silencing of mRNA for LOX, AOS, AOC or OPR reduced the sensitivity to a phytotoxin, coronatine, which is believed to act through a JA-dependent process. On the basis of these results, it is conceivable that M. pinodes has evolved a strategy to condition susceptibility by manipulating the physiology of host cells, in particular JA-regulated cellular process(es), to promote disease development in pea.