Insights into the epidemiology of Pierce's disease in vineyards of Mallorca,Spain

Xylella fastidiosa (Xf), the causal agent of Pierce's disease (PD), has long been considered a major threat to prosperous European viticulture. In May of 2017, PD was officially detected on a grapevine in Mallorca. To better understand the epidemiology of the first established outbreak of PD in Europe, the disease incidence and severity were assessed, vector transmission experiments were performed, and cultivar responses to Xf infections both in the field and in inoculation experiments were monitored. The genetic structure of Xf local populations was also investigated by multilocus sequence typing analysis, and their whole genome sequences and phylogenetic positions compared with respect to PD strains worldwide. Disease incidence was moderately low (0.07) and highly variable, ranging from 0.0 to 0.99. Its economic impact on wine production was considered low. Vineyards managed under conventional viticulture were significantly less infected than organic farming. Under greenhouse conditions, the insect Philaenus spumarius efficiently transmitted the pathogen from infected to healthy grapevines. In the inoculation experiments, Xf infected, to some degree, 29 of the 30 cultivar × rootstock combinations (n = 239). Cultivars Viura, Gorgollasa and Sauvignon Blanc were the most susceptible ones. All Xf isolates from grapevines belonged to sequence type ST1; they phylogenetically clustered within the Californian ST1 clade, with which they shared a 99.94% identity and the same plasmid. In addition, ST1 caused almond leaf scorch disease, where notably its incidence (0.78) and severity was much higher than PD. The likely reasons for these wide differences are discussed in the context of a 20-year Xf introduction scenario.     

Immunolocalization of Pepper mild mottle virus in Capsicum annuum seeds

To clarify the mechanism of seed transmission of Pepper mild mottle virus (PMMoV), the virus was immunolocalized in Capsicum annuum seeds using fluorescence microscopy. Two distinct patterns were observed: In the first, PMMoV was present in the epidermis and parenchyma but not in the endosperm or embryo; in the second, the virus was restricted to the surface of the epidermis and parenchyma. These findings shed light on the fundamental mechanisms of seed transmission of tobamoviruses and may aid in the design of new methods to prevent the spread of seedborne virus diseases.     

PCR法证实棉铃虫核型多角体病毒对棉铃虫经卵和蛹的垂直传播

根据棉铃虫核型多角体病毒的多角体蛋白基因设计5’引物和3’引物，通过PCR技术成功扩增389bp的目的片段，并对该片段进行了克隆和测序。结果表明，扩增片段为棉铃虫核型多角体病毒多角体蛋白基因序列。该检测方法的灵敏度为10fg，应用此技术从带毒的虫卵和蛹的总DNA中也检测到该病毒的存在。该方法从分子水平上证明了病毒的垂直传递。     

New aphid vectors and efficiency of transmission of Potato virus A and strains of Potato virus Y in the UK

The aphid‐transmitted viruses Potato virus Y (PVY) and Potato virus A (PVA) commonly affect seed potatoes in the UK. The transmission efficiency for aphid species is used to calculate a potential transmission risk and is expressed as a relative efficiency factor (REF). These REFs have not previously been calculated for UK strains of viruses or aphid clones. Using a previously published method, REFs have been calculated for the aphid species and viruses commonly occurring in UK potatoes. The efficiency of transmission of Myzus persicae is nominally set to a REF of 1 and REFs for other species are calculated relative to this. These data represent the first set of REFs calculated for PVA transmission. Macrosiphum euphorbiae (REF 0.91) was almost as efficient as M. persicae at PVA transmission. The data were further analysed to compare transmission rates of PVY and PVA using a binomial (logit) generalized mixed model to take into account the potential influence of variation in virus titre between leaves. This approach found that there is little variation between the efficiency of transmission between clones of each aphid species or between strains within a virus species. This is a first report that Aphis fabae, Metopolophium dirhodum, Sitobion avenae, Acyrthosiphon pisum and Cavariella aegopodii have the ability to vector PVA. This study also represents a first report that C. aegopodii has the ability to vector PVY and confirms the potential of S. avenae, A. fabae, M. euphorbiae and Rhopalosiphum padi as important PVY vectors.     

Broad bean mottle virus in Morocco; curculionid vectors,and natural occurrence in food legumes other than faba bean (Vicia faba)

Broad bean mottle virus (BBMV) was transmitted from infected to healthy faba-bean plants by the curculionid weevilsApion radiolus Kirby,Hypera variabilis Herbst,Pachytychius strumarius Gyll,Smicronyx cyaneus Gyll, andSitona lineatus L. The latter appeared to be an efficient vector: acquisition and inoculation occurred at the first bite, the rate of transmission was c. 41%, and virus retention lasted for at least seven days.S. lineatus transmitted the virus from faba bean to lentil and pea, but not to the three genotypes of chickpea tested. This is the first report on the generaHypera, Pachytychius, andSmicronyx as virus vectors, and onA. radiolus, H. variabilis, P. strumarius, andS. cyaneus as vectors of BBMV.Out of 351 samples of food legumes with symptoms suggestive of virus infection, 16, 11, 19, and 17% of the samples of chickpea, lentil, pea, and common bean, respectively, were found infected when tested for BBMV in DAS-ELISA. This is the first report on the natural occurrence of BBMV in chickpea, lentil, pea, and common bean. The virus should be regarded as a food-legume virus rather than a faba-bean virus solely, and is considered an actual threat to food legume improvement programmes.     

Pymetrozine interferes with transmission of<Emphasis Type="Italic">Tomato yellow leaf curl virus</Emphasis> by the whitefly<Emphasis Type="Italic">Bemisia tabaci</Emphasis>

Pymetrozine, a novel compound belonging to the class pyridine-azomethines, is a feeding inhibitor labeled for use against plant pests in the order Hemiptera. Pymetrozine was evaluated for its ability to interfere with whitefly transmission of the begomovirusTomato yellow leaf curl virus (TYLCV). Pymetrozine was applied as Fulfill ^TM 50 WG at two rates (0.291 and 0.582 g formulationl ⁻¹) to tomato seedlings with four to six true leaves. Viruliferous whiteflies (three to five per plant) were added 1, 4, 7 and 11 d after a single application of pymetrozine, and transmission rates were determined 4 wk after the addition of whiteflies. Pymetrozine provided protection against transmission of TYLCV by viruliferous whiteflies for up to 1 wk after a single apliation. No phytotoxicity was observed on tomato transplants. These results indicate that pymetrozine could be an effective tool for tomato transplant producers to protect susceptible transplants from infection by begomoviruses, such as TYLCV. Pymetrozine might also work well as part of an integrated approach to begomovirus management in greenhouse tomato fruit production. http://www.phytoparasitica.org positing Oct. 20, 2003.     

Translocation of apple proliferation phytoplasma via natural root grafts – a case study

Apple proliferation (AP), a phytoplasma-induced disease of apple trees, was proven to be transmitted through infected grafting material and sap-sucking insects. To date there are little firm data on disease propagation in the field via natural root grafts. This question was thus addressed in the present case study by investigating trees of a 24-year old commercial apple orchard (‘Red Chief’ on MM 111), where the existence of root connections was discovered accidentally. After having displayed specific AP symptoms, nine trees were cut down and the stubs were infiltrated or brushed with glyphosate. Herbicide injury, however, remained not only restricted to the treated stubs, but also spread to approximately 50 neighbouring trees. Surprisingly, none of the pollinators (‘Granny Smith’ on M 9) growing interjacently and alternating between herbicide-damaged main crop trees was affected. Respective to the position of the nine AP-infected and glyphosate-treated cut stumps, four sections in the orchard were defined, from which a total of 122 trees was sampled and analysed using qualitative real-time PCR for detection of AP phytoplasma. The pathogen was found in 71.4% of ‘Red Chief’ trees with severe herbicide damage and 18.8% of trees with partial herbicide damage. None of the 31 investigated pollinators was AP-infected. Our data indicate that root connections seem to play a role for the spread of AP phytoplasma at least in older orchards and between trees on vigorous rootstocks.     

黄瓜绿斑驳花叶病毒在葫芦上的种传规律及热处理效果评价

为明确黄瓜绿斑驳花叶病毒(Cucumber green mottle mosaic virus,CGMMV)在葫芦上的种传规律,以西瓜砧木葫芦种子为材料,采用双抗体夹心酶联免疫吸附测定法(DAS-ELISA)、反转录聚合酶链式反应(RT-PCR)与生物学检测相结合的方法研究葫芦种子的带毒率和传毒率的关系,并评价了干热处理对病毒的钝化效果。结果表明,DAS-ELISA灵敏度检测种子时,在感染种子研磨液∶健康种子研磨液为1∶1 000时,带毒量仍能检测出阳性,RT-PCR和DAS-ELISA两种方法均能准确检测葫芦种子的带毒情况;6个批次的葫芦种子有4个批次呈阳性,带毒率在0~100%之间,贮藏1年后的传毒率在0~5.6%之间;4个为CGMMV阳性的种子批经干热处理后,仅1株实生苗呈阳性。研究表明,CGMMV在葫芦作物上的隐性带毒现象非常普遍;种子的带毒率高而传毒率低,以表面带毒为主,且非常稳定;72℃72 h干热处理葫芦种子能有效地钝化CGMMV。     

Importance of cucurbits in the epidemiology of Papaya ringspot virus type P

Papaya ringspot virus type P (PRSV‐P) systemically infects Carica papaya and species belonging to the family Cucurbitaceae. Attempts to recover PRSV‐P from naturally infected cucurbit plants grown near or among diseased papaya trees have shown conflicting results worldwide. This study aimed to evaluate the natural infection of cucurbit species grown among and near papaya trees infected with PRSV‐P in Brazil. Natural infection of cucurbits with PRSV‐P occurred in zucchini squash but not in watermelon and cucumber. However, several attempts to recover PRSV‐P from numerous Cucurbita pepo cv. Caserta (zucchini squash) plants grown 5–80 m from diseased papaya trees in the field failed. Mechanical inoculations of Cucurbita pepo cv. Caserta, Cucurbita maxima cv. Exposição (pumpkin), Cucumis sativus cv. Primepack Plus (cucumber) and Citrullus lanatus cv. Crimson Sweet (watermelon) with five Brazilian PRSV‐P isolates showed that zucchini squash was the most susceptible species followed by watermelon and cucumber, while pumpkin was not infected. The results confirmed the variable susceptibility of cucurbit species to experimental and natural PRSV‐P infection. Given these facts, the control of the disease through roguing should focus mainly on diseased papaya plants, as has been practised successfully in Brazil for many years, and on those cucurbits particularly known to be susceptible to natural infection with PRSV‐P.     

Aphid vectors of potato virus YN

BesideMyzus persicae a dozen other species were found to be vectors of potato virus Y^N. Eleven other species did not transmit the virus.White Burley tobacco and A6 potato are equally suitable as test plant to monitor the efficency ofRhopalosiphum padi as vector of PVY^N, but as PVY^N source tobacco is not suitable for this aphid species.Between some aphid species rather large differences exist in retention periods of PVY^N. WithR. insertum andAphis fabae transmission after a 1 h starvation period was still 50% of that without starvation. WithPhorodon humuli, M. certus andM. persicae this value was only 15, 30 and 30%, respectively.Samenvatting Van 12 bladluissoorten werd vastgesteld dat zij, evenalsMyzus persicae, vectoren van het aardappelvirus Y^N (PVY^N) zijn. Van 11 andere soorten kon dit niet worden vastgesteld. Nicotiana tabacum cv. White Burley enSolanum tuberosum cv. A6 bleken beide goed bruikbaar als toetsplant voor het vaststellen van de efficiëntie vanRhopalosiphum padi als vector van het PVY^N; voor deze bladluissoort is tabak ongeschikt als bron van PVY^N.De retentieperiode van het PVY^N lijkt bij verschillende bladluissoorten aanzienlijk te variëren. BijRhopalosiphum insertum enAphis fabae bracht één uur vasten na de acquisitie de overbrenging terug tot 50% van die welke zonder vasten werd verkregen. BijPhorodon humuli was de reductie in overbrenging na één uur vasten 85%, bijMyzus certus enM. persicae was deze 70%.