Peeling the onion: towards a better understanding of Botrytis diseases of onion

Onion is cultivated worldwide for its bulbs, but production is threatened by pathogens and pests. Three distinct diseases of onion are caused by species that belong to the fungal genus Botrytis. Leaf blight is a well-known foliar disease caused by B. squamosa that can cause serious yield losses. Neck rot is a post-harvest disease that manifests in bulbs after storage and to which three species are associated with; B. aclada, B. allii and B. byssoidea. The symptomless infection of onion plants in the field make it difficult to predict the incidence of neck rot in storage although progression on the detection of latent infection has been made. In onion cultivation for seed production, blighting of the inflorescence is caused by all four onion-specific Botrytis species plus the broad host range pathogen B. cinerea. Flower blight can lead to heavily reduced seed yield and contaminated seed. In this review, the long history of Botrytis diseases of onion is discussed, as well as recent and future approaches to acquire a better understanding of the biology and ecology of Botrytis spp. pathogenic on onion. New fundamental insights in the genetic, biochemical and physiological aspects of Botrytis-onion interactions are essential to improve the breeding of Botrytis-resistant onion cultivars.

Leptospirosis in swine in the light of accepted characterization

The publication is presenting changes in epidemiology and economic importance of leptospirosis in swine. During the fifties or even earlier or later of the twenty century this disease in swine was causing remarkable losses occurring worldwide. During the end of the twenty century and during the twenty first century the importance of leptospirosis of swine has decreased, being restricted to Argentina, Brasil, Northern Hemisphere, Northern Australia and New Zealand. In Europe, including Poland, endemic, very often symptomless infection or presentation of reproductive failer as abortion, stillbirth, the birth of weak piglets, reduced viability was demonstrated. Other symptoms and pathological changes, if developed were similar do occurring also in other infectious diseases of swine and did not present diagnostic value for swine leptospirosis. Therfore for diagnosis of swine leptospirosis, laboratory tests have to be used. This publication is mentioning as the prescribed and most widely used microscopic agglutination test (MAT), and as alternative the competitive ELISA. For detection and identification of nucleic acids of leptospira serovars the PCR is recommended. Control of leptospirosis in swine is dependent on the combined use of antibiotics, vaccination and management. However antibiotics are in many countries prohibited for use, against leptospirosis of swine. Vaccines are very seldom available and theirs used is not on satisfied level. Management is difficult to perform and economically in many cases not respected

Experimental Verification of Seed Transmission of Zucchini yellow mosaic virus

Within two decades of its discovery, Zucchini yellow mosaic virus (ZYMV) achieved a global distribution. However, whether or not seed transmission occurs in this economically significant crop pathogen is controversial, and the relative impact of seed transmission on the epidemiology of ZYMV remains unclear. Using reverse transcription–polymerase chain reaction, we observed a seed transmission rate of 1.6% in Cucurbita pepo subsp. texana and show that seed-infected C. pepo plants are capable of initiating horizontal ZYMV infections, both mechanically and via an aphid vector (Myzus persicae). We also provide evidence that ZYMV-infected seeds may act as effective viral reservoirs, partially accounting for the current geographic distribution of ZYMV. Finally, the observation that ZYMV infection of C. pepo seeds results in virtually symptomless infection, coupled with our finding that an antibody test failed to detect vertically transmitted ZYMV in infected seed, highlights the urgent need to standardize current detection methods for seed infection.

Characterisation of theFusarium graminearum-Wheat Floral Interaction

Fusarium Ear Blight is a destructive fungal disease of cereals including wheat and can contaminate the crop with various trichothecene mycotoxins. This investigation has produced a newβ-glucuronidase (GUS) reporter strain that facilitates the quick and easy assessment of plant infection. The constitutively expressedgpdA:GUSstrain ofFusarium graminearumwas used to quantify the overall colonisation pattern. Histochemical and biochemical approaches confirmed, in susceptible wheat ear infections, the presence of a substantial phase of symptomless fungal growth. Separate analyses demonstrated that there was a reduction in the quantity of physiologically active hyphae as the wheat ear infection proceeded. A simplified linear system of rachis infection was then utilised to evaluate the expression of severalTRIgenes by RT-qPCR. Fungal gene expression at the advancing front of symptomless infection was compared with the origin of infection in the rachis. This revealed thatTRIgene expression was maximal at the advancing front and supports the hypothesis that the mycotoxin deoxynivalenol plays a role in inhibiting plant defences in advance of the invading intercellular hyphae. This study has also demonstrated that there are transcriptional differences between the various phases of fungal infection and that these differences are maintained as the infection proceeds.

Analysis of resistance to Yam mosaic virus, genus Potyvirus in white guinea yam (Dioscorea rotundata Poir.) genotypes

Resistance to Yam mosaic virus (YMV), genus Potyvirus was studied in 10 populations of selected white Guinea yam (Dioscorea rotundata). Plants of resistant genotypes: TDr 35, TDr 1621, TDr 93-1, TDr 93-32, TDr 95-107, TDr 93-23, and susceptible ones: TDr 87/00211, TDr 87/00571 and TDr 95-127 were screened for their reaction to the pathogen by symptom severity scoring scale of 1-5, and by quantifying virus multiplication by triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA). Controlled crosses were made among the genotypes within and between the groups according to reactions to the pathogen. The resultant F1 progenies were evaluated for the infection by disease symptom development and by TAS ELISA to detect a symptomless infection in an insect-proof screenhouse for the assessment of inheritance of resistance to YMV. A genetic analysis of the reactions of progenies derived from the D. rotundata genotypes to inoculation with YMV strongly suggests that resistance to the virus is a dominantly inherited trait. Segregation ratios obtained from the families indicate that at least two dominant genes are involved.

Symptom Remission and Specific Resistance of Pepper Plants After Infection by Pepper golden mosaic virus

Pepper golden mosaic virus (PepGMV) is an important begomovirus infecting solanaceous crops in Mexico and Central America. Under controlled conditions for growth and inoculation with a low-pressure biolistic device, PepGMV-infected pepper plants consistently showed symptom remission or host recovery 12 to 15 days postinoculation (dpi). Inoculated plants initially developed the characteristic PepGMV symptoms; however, newer leaves presented a significant decrease or disappearance of symptoms. Younger asymptomatic, recovered leaves accumulated lower quantities of viral DNA and transcripts than the ones found in the symptomatic tissue. Nonetheless, viral DNA did not disappear during the evaluation period (up to 35 dpi), suggesting that a population of viral molecules escape from plant defensive mechanisms to maintain a subliminal, symptomless infection. Recovery was correlated with a specific resistance to PepGMV but not to Pepper huasteco yellow vein virus, a different gemi-nivirus commonly found in mixed infections with PepGMV. Virus-related small interfering RNAs were detected in practically all tissues (from symptomatic to recovered leaves) but it was not possible to establish a correlation between concentration and symptom severity. The participation of a posttranscriptional gene silencing mechanism in the recovery process and specific resistance is discussed.

New Polish Isolate of Pepino mosaic virus Highly Distinct from European Tomato, Peruvian, and US2 Strains

Pepino mosaic virus (PepMV, genus Potexvirus) was first described on pepino (Solanum muricatum) in Peru during 1980. Since 1999, the virus was reported in several European countries and in North and South America as an agent of viral disease of tomato crops. In Poland in 2002, the PepMV-SW isolate that was genetically similar to European isolates (approximately 99% identity) was identified (3). In November 2005, in the western part of the Wielkopolska Region, a virus with flexuous filamentous particles approximately 500 nm long was isolated from tomato fruits exhibiting symptoms of discoloration. Crude sap from Nicotiana benthamiana leaves was used for mechanical inoculation of indicator plants. The virus caused symptoms on N. benthamiana, N. clevelandii, Datura inoxia, and Lycopersicon esculentum. Symptomless infection on N. tabacum cv. Xanthi nc, N. tabacum cv. White Burley, and N. debneyi was confirmed by back-inoculation on N. benthamiana. The virus did not infect N. glutinosa, Physalis floridana, Petunia hybrida, Capsicum annuum, Chenopodium quinoa, Cucumis sativus, or Phaseolus vulgaris. The virus was initially identified using double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) with polyclonal antiserum against PepMV (DSMZ, Braunschweig, Germany). Positive serological reactions were obtained with sap from inoculated N. benthamiana, L. esculentum, and N. clevelandii plants. The serological identification was confirmed using a reverse transcription-polymerase chain reaction (RT-PCR) with primers generated from a sequence of the RNA polymerase region of an isolate of PepMV reported in the United Kingdom (1). Sequence information obtained from the amplified fragment of the virus designated PepMV-PK (GenBank Accession No. DQ387870), showed only 81% nt identity and 89% amino acid identity with PepMV-SW (GenBank Accession No. DQ387869). PepMV isolates can be divided into three strains including European tomato, Peruvian, and US2 based on their genetic diversity (2). The PepMV-PK isolate resulted in nucleotide identities ranging from 79 to 81% with isolates of the European tomato strain (GenBank Accession Nos. AJ438767, AF340024, AF484251, AJ271991, AJ606359, and AJ290424), 81% with the Peruvian strain (GenBank Accession Nos. AM109896 and AJ606361), and 78% identity with each of the U.S. isolates US1 (GenBank Accession No. AY509926) and US2 (GenBank Accession No. AY509927). These results show that the new Polish isolate is distinct from all other PepMV isolates reported to date. References: (1) C. J. French et al. Plant Dis. 85:1121, 2001. (2) L. Pagan et al. Phytopathology 96:274, 2006. (3) H. Pospieszny et al. Phytopathol. Pol. 26:91, 2002.

Pea Tissue Necrosis Induced by Cucumber mosaic virus Alone or Together with Watermelon mosaic virus

Necrotic diseases of the stems, petioles, and leaves of pea plants (Pisum sativumL.), leading to wilting and death, occur in the Wakayama and Mie Prefectures of Japan. Based on host range, symptomatology, electron microscopy, and serological relationships, Watermelon mosaic virus (WMV) and three Cucumber mosaic virus (CMV) isolates (PE2, PE3A, and PB1) were isolated from diseased plants in the Wakayama Prefecture. In the Mie Prefecture, CMV (PEAN) also was isolated from pea plants with similar symptoms. Single infection with CMV (PB1 or PEAN) caused stem necrosis and eventual death of pea plants. Similar symptoms developed after double infection with WMV and PE2 or PE3A, whereas single infection with PE2 and PE3A induced symptomless infection in pea plants. We concluded either CMV alone or synergistic effects of mixed infection with CMV and WMV induced pea plant stem necrosis.