The effect of temperature on the development of wilting and on progeny tuber infection of potatoes inoculated with South African strains of biovar 2 and 3 ofPseudomonas solanacearum

Summary Potato plants, after inoculation with a South African strain of biovar 2 or a strain of biovar 3 ofPseudomonas solanacearum were grown in growth chambers at temperatures ranging from 14/16°C (dark/light) up to 25/30°C. When grown at 14/16°C or higher, plants inoculated with the biovar 2 strain developed wilting symptoms and internal symptoms on progeny tubers and the disease was transmitted by the progeny tubers. When the plants were inoculated with the biovar 3 strain, wilting symptoms developed from 18/20°C, internal symptoms on progeny tubers from 20/22°C and the disease was transmitted by progeny tubers from plants grown at 16/18°C or higher.     

Henbane mosaic potyvirus pathogenic to wild and cultivated potato

Summary A virus isolated from severely diseased wild plants ofDatura stramonium in Hungary was identified as a strain of henbane mosaic potyvirus (HeMV) by its host range, vector transmissibility, electron microscopy and serology. This W/H isolate of HeMV induced necrotic local lesions onChenopodium quinoa and characteristic systemic symptoms in species ofDatura, Nicotiana andPhysalis but it was apathogenic to species ofCapsicum, Cucumis andPhaseolus. The virus is transmissible by aphids,Myzus persicae, in a non-persistent manner. Electron microscopy showed that it consisted of flexuous filaments, c. 180×12 nm. In plants ofDatura andNicotiana spontaneously infected by and artificially inoculated with HeMV-W/H, pinwheel structures typical of the potyvirus group were found. Serological examinations confirmed the identity of HeMV-W/H with the standard strain of the virus, HeMV-R. Plants of the potato cultivars Désirée and Gracia, graft-inoculated with HeMV-W/H, were latently infected. Inoculated plants of wildSolanum species responded to the virus with systemic symptoms.     

Alternative hosts for potato mop-top virus, genus Pomovirus and its vectorSpongospora subterranea f.sp. subterranea

Summary Seventeen weed species common in the potato fields in Denmark were grown in a hydroponic system infested with viruliferous zoospores ofSpongospora subterranea f.sp.subterranea carrying potato mop-top virus (PMTV). The plants were examined for infection with PMTV andS.s.s. using DAS-ELISA and based on visible symptoms. Only two weed species were found to be infected with PMTV,Chenopodium album andSolanum nigrum, whereas 13 became infected withS.s.s. C. album was infected with PMTV by mechanical inoculation were the infection became systemically and the leaves showed necrotic spots.S. nigrum became local infected with PMTV by mechanical inoculation. By inoculation with viruliferousS.s.s. the roots ofS. nigrum became infected but in three weeks PMTV had not spread into the top of the plants.Nicotiana benthamiana was used as a control susceptible toS.s.s. and PMTV.     

Survival and possibilities for extinction ofPseudomonas solanacearum (Smith) Smith in cool climates

Summary The importance of biovar 2 ofPseudomonas solanacearum (syn.Burkholderia solanacearum; syn.Ralstonia solanacearum) in cool temperate climates has been recently emphasised by outbreaks of potato brown rot disease in some European countries. Dissemination of the pathogen in latently infected potato tubers and in contaminated irrigation water, and overwintering in aquatic roots of the weed hostSolanum dulcamara have been implicated. Evidence from the literature suggests that in cool climates the organism is unlikely to persist long term in soil in the absence of a susceptible host. Effective control strategies rely on the enforcement of quarantine legislation at both national and European Community levels. This requires knowledge of the biology of the pathogen in cool environments, methods for accurate monitoring of its survival and distribution at and around disease outbreak sites and application of effective measures for pathogen exclusion, containment and eventual eradication. This paper reviews current knowledge on the above.     

小麦茎基褐腐病病原菌组成及其致病力研究

为明确小麦茎基褐腐病（brown foot rot）病原菌的组成,于2008-2009年春从江苏、安徽、河南、湖北、河北和四川6省48个县市的65个地点采集了具有茎基褐腐症状的病株,并分离到110株病原真菌。根据其培养性状、形态学特征以及分子生物学鉴定,可将这些病原菌分为4类,分别为小麦根腐离蠕孢(Bipolaris sorokiniana,41株)、镰孢菌(Fusarium spp.,33株)、雪霉叶枯病菌(Microdochium nivale,24株)和黑附球菌(Epicoccum nigrum,12株)。对这些菌株在小麦苗期的致病力及重新分离得率的测定结果表明,4类病原菌之间的致病力存在明显差异,其中以小麦根腐离蠕孢(B. sorokiniana)发病率和致病力最强,其次是镰孢菌(Fusarium spp.),雪霉叶枯病菌(M. nivale)和黑附球菌(E. nigrum）则相对较弱;病菌的重新分离得率与其致病力呈正相关。     

Impact of managing cover crop residues on the floristic composition and species diversity of the weed community of pepper crop (Capsicum annuum L.)

The decline of farmland biodiversity is mainly attributed to the intensive use of chemical inputs in agriculture. Cover crop residues may contribute to improve weed management while maintaining a high level of weed diversity. A 2-year field experiment was carried out in central Italy to study the effect of cover crop species and their residue management on weed community composition and weed species diversity in a winter cover crop – pepper sequence. Hairy vetch (Vicia villosa Roth.), oat (Avena sativa L.) and canola (Brassica napus L.) were sown in September 2009 and 2010 and grew undisturbed during the winter season until spring when they were suppressed one week before pepper transplanting. Cover crop residues were: (i) green manured at 30 cm depth (conventional tillage, CT), (ii) green manured at 10 cm depth (minimum tillage, MT), and (iii) left on the soil surface as mulch strips covering 50% of the ground area in no-tilled soil (NT). A winter weedy fallow and a bare soil without cover crop in NT, MT and CT were also included as controls. Weed plant density data in pepper were used for calculating weed species richness. Compared to weedy fallow, oat, hairy vetch and canola consistently reduced the weed density and weed aboveground biomass by the time of their suppression (on average 3.6, 21.5, and 41.3 plants m⁻² and 11.0, 49.2, and 161.8 g m⁻² of DM, respectively). In pepper, oat residues generally determined a higher reduction of weed density and species richness compared to hairy vetch and canola regardless the residue management treatments. Converting cover crop aboveground biomass into mulch strips greatly reduced weed species density but did not always imply a reduction of weed species diversity in pepper compared to MT and CT. The weed species richness was reduced inside the mulch strips, while a richer and more diverse weed community was found outside the mulch strips in NT. Weed community in pepper was mainly composed of annual dicot weeds such as Amaranthus retroflexus, Chenopodium album, Solanum nigrum, Polygonum aviculare which were mostly associated with MT and CT tillage systems, while in NT an increase of perennial species such as Rumex crispus was observed. These results suggest that it is possible to manage cover crop residues in NT in order to obtain a lower weed density and consequently a higher yield in pepper compared to MT and CT while maintaining a high level of weed diversity.     

Weed hosts of the tobacco rattle virus in Idaho

The corky ringspot disease of potato (Solanum tuberosum) caused by the tobacco rattle virus (TRV) is a serious problem in certain Idaho localities. To investigate natural TRV sources, weeds and plants from rotation crops were randomly collected from six fields with a history of corky ringspot symptoms. Transmission trials, Ouchterlony agar double-diffusion tests, and electron-microscopy showed evidence of TRV in three Idaho counties (Fremont, Ada, and Canyon). Inoculations were made from 27 species and TRV was recovered from the roots of three:Solanum nigrum, Brassica campestris, andErodium cicutarium. Solanum nigrum was the most consistent source of TRV and it generally incited the severest symptoms onNicotiana tabacum (Samsun NN). The results show thatS. nigrum, besides being an important wild host of TRV, may be a useful naturallyoccurring bait plant for detection of TRV in field soils.     

Resistance to potato leaf roll virus inSolanum brevidens

Summary Plants ofSolanum brevidens graft-inoculated with potato leaf roll virus (PLRV) grew vigorously and had a normal healthy appearance. Although presence of the virus was confirmed in all inoculated plants by graft tests to potato and/orDatura stramonium, recovery of PLRV fromS. brevidens PI 218228 usingPhysalis floridana and the aphidMyzus persicae was erratic and only few test seedlings became infected. Ease of recovery of the virus using aphids was not influenced by presence of a continuous graft union with infected potato. Testing ofS. brevidens PI 245763 withM. persicae was not possible due to poor aphid survival on plants of this accession.     

海南桑树青枯病病原菌鉴定及其分子鉴定

桑树青枯病是由青枯雷尔氏菌引起的细菌性病害,热带、亚热带地区发病严重,严重影响蚕桑产业的可持续发展。雷尔氏菌不同种间致病力和宿主各不相同,其防治策略也相应不同,准确地分离鉴定病原菌是青枯病有效防控的先决条件。本研究采集、分离了海南省琼中县桑青枯病发病桑园（‘桂桑优62’）桑树根部、茎部病原菌,并通过致病性、生理小种、生化变种测定,结合16S rDNA、特异性引物、复合PCR检测体系、序列变种等分子鉴定方法初步确定了病原菌的种类和分类地位。结果表明,引发海南省琼中县桑青枯病的病原菌属于青枯雷尔氏菌（Ralstonia solanacearum）、生理小种5（race 5）、生化变种Ⅴ（biovar Ⅴ）,病原菌遗传进化分析结果显示病原菌属演化型Ⅰ（phylotype Ⅰ）即亚洲分支菌株,序列变种12（sequevar 12）。这些结果将为海南桑青枯病的有效防控奠定基础。     

曼陀罗不同提取液对玉米螟的触杀活性研究

应用均匀设计法研究了曼陀罗全草的不同提取液对玉米螟的触杀作用。结果表明：乙醇浸提液对玉米螟具有较高的触杀作用,对玉米螟72 h的致死浓度(LC₅₀)为17.328 1 mg/mL,触杀致死率为96.1%;乙醚浸提液和水蒸气蒸馏液对玉米螟的触杀作用不显著。     

Genetic and Pathogenic Diversity of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> Causing Potato Brown Rot in China

Causing potato brown rot, Ralstonia solanacearum (R. solanacearum) strains are reported as one of the most destructive bacteria to potato (Solanum tuberosum L.) in China. In this study, 113 strains were isolated from potato, collected in the four major agroecological zones in China. The study showed that 102 strains belonged to the phylotype IIB sequevar 1 (race 3 biovar 2). The 11 remaining strains belonged to the phylotype I, sequevar 13, 17, 18, 16 or 14 M, a new sequevar closely related to sequevar 14. Thirty-four strains were further characterized according to their virulence at low temperature on three wild potato species. IIB-1 strains all belonged to high and moderate virulence, while others belonged to the low virulence group, which had limited pathogenicity.     

Host range,symptomology, and serology of isolates of potato virus Y (PVY) that share properties with both the PVYN and PVYO strain groups

In surveys for the tobacco veinal necrosis strain of potato virus Y (PVY^N) in potato, two isolates (I-136 and I-L56) were obtained that shared properties with both the PVY^N and the common (PVY^O) strain groups. The isolates produced veinal necrosis on tobacco (Nicotiana tabacum L.) and mild symptoms on potato (Solanum tuberosum L.) cv. Jemseg, typical of PVY^N but their symptoms on some other indicator species such asCapsicum frutescens L.,Chenopodium amaranticolor Coste & Reyn.),Physalis angulata L.,P. floridana Rybd. were more typical of PVY^O. Their serological properties were also more typical of PVY^O in that they reacted with a PVY^O-specific monoclonal antibody (MAb) in ELISA and they failed to react with four PVY^N-specific MAbs. The possible taxonomic position of these isolates is discussed.     

Translocation and distribution of P labelled potassium phosphonate in black pepper (Piper nigrum L)

The aim of this project was to study the translocation of potassium phosphonate within black pepper (Piper nigrum L.) and to elucidate the amount of chemical distributed through out the plant based on a tracer technique. Potassium phosphonate is a potential fungicide used against the pathogen Phytophthora capsici, which causes Phytophthora foot rot (Quick wilt) in the plant. Reports indicate that translocation of phosphonate is ambimobile, but there is no visual evidence for this. Potassium phosphonate labelled with radioactive phosphorus, ³²P, was applied to the black pepper vine and bush pepper and its translocation to different parts of the pepper plant was studied using an autoradiography technique. The chemical which migrated to different parts of the plant was quantitatively estimated by measuring ³²P on a liquid scintillation spectrometer following Cerenkov counting. Only traces of the chemical were lost to the soil through root systems. These results indicate that foliar sprays of potassium phosphonate to pepper could be a viable method of application for soil and foliar pathogens.     

Induction of hydrolytic enzymes and antifungal in vitro activity inS. tuberosum subsp.andigena after infection withFusarium solani f. sp.eumartii

Summary Fusarium solani (Mart.) Sacc. f. sp.eumartii (Carp.) Snyder & Hansen is the causative agent of two important types of disease in potato (Solanum tuberosum) plants: wilt in stems and leaves and dry rot in tubers. The aim of this work was to study the molecular response of the potato to fungal attack. Micropropagated plantlets were tested, using a biological assay to detect antifungal proteins. An inhibitory activity of spore germination was detected in protein fractions from infected plantlets 7 days after inoculation with the pathogen. In addition, β-1,3-glucanase activity (glucanase III) was measured in protein fractions with antifungal activity. Induction of hydrolytic enzymes and antifungal activity in infected plantlets ofSolanum tuberosum subp.andigena suggests that it could be a suitable source of resistance genes.     

Identification,ecological evaluation and phylogenetic analysis of non‐symbiotic endophytic fungi colonizing timothy grass and perennial ryegrass grown in adjacent plots

Non‐systemic endophytes coexist with grasses and produce positive or negative effects for the host. In agricultural grasses, endophytes such as Epichloë spp. (formerly: Neotyphodium spp.) enhance the biometric parameters and agricultural value of grass biomass and seeds. Some endophytic fungi produce active substances that exert a negative influence on grass‐fed livestock. There is a general scarcity of studies investigating other endophytic fungi, the species composition of fungal communities, fungal species capable of colonizing different grasses and endophyte transfer between grass taxa. This study aims to fill in the existing knowledge gap by describing the relationships between fungal species and grass species. Timothy grass (Phleum pratense L.) is more readily colonized by endophytic fungi than perennial ryegrass (Lolium perenne L.), and the ratio of fungi isolated from the above species was determined at 3:1. Ecological indicators, especially diversity, were also higher in the fungal community colonizing timothy grass. The vast majority of the isolated fungi were ascomycetes. In addition, two Basidiomycota isolates and three Oomycota isolates (Phythium acanthicum) were also obtained from timothy grass. The most prevalent fungal species were Alternaria alternata, Microdochium bolleyi and Epicoccum nigrum. An analysis of minisatellite DNA regions revealed high levels of genetic polymorphism in A. alternata, whereas the remaining isolates were characterized by low levels of genetic variation or genetic homogeneity. The transfer of endophytic fungi between grass species was determined, which was one of the most important observations made in the study. The Sørensen–Dice coefficient reached 50%, which indicates that all fungal species isolated from perennial ryegrass are capable of colonizing timothy grass.     

Sourcing Rhizobium leguminosarum biovar viciae strains from Mediterranean centres of origin to optimize nitrogen fixation in forage legumes grown on acid soils

Over the last three decades, farming systems in Europe and Australia have seen a decline in legume plantings, leading to reduced soil carbon and fertility, and an increase in plant disease, reliance on industrial nitrogen fertilizer and herbicides. In Australia, one reason for this decline has been the movement towards sowing crops and forages into dry soil, before the opening rains, as a consequence of climate variability. This practice predicates against the survival of rhizobial inoculants, and hence generates uncertainty about legume performance. The research reported here was initiated to improve the robustness of a specific forage legume/rhizobia symbiosis to increase nitrogen fixation in low pH, infertile soils. Rhizobial strains (Rhizobium leguminosarum biovar viciae) from Pisum sativum L. were sourced from acid soils in southern Italy and southern Australia. Strains were evaluated for N fixation on the forage legumes P. sativum, Vicia sativa and Vicia villosa, then for survival and persistence in acid soils (pH_Ca 4.6). Fourteen of the strains produced a higher percentage of nitrogen derived from the atmosphere (%Ndfa) compared to commercial comparator strain SU303 (<78%). Twenty‐two strains survived sufficiently into the second season to form more nodules than SU303, which only achieved 3% of plants nodulated. Elite strains WSM4643 and WSM4645 produced six times more nodulated plants than SU303 and had significantly higher saprophytic competence in acid soil. These strains have the ability to optimize symbiotic associations with field peas and vetch in soils with low fertility, carbon and pH that are restrictive to the current commercial strain SU303.     

Detection methods forVerticillium species in naturally infested and inoculated soils

The detection and identification of threeVerticillium species in field soils with a polymerase chain reaction (PCR)-based assay was compared to the traditional plating assay method. The two methods were both able to detect the commonVerticillium species in soils although the PCR method detectedV. tricorpus in three soil samples that the traditional method did not. In addition, the PCR assay was rapid, efficient, and required only 1 to 2 days for positive identification whereas the traditional methods required 4 to 8 weeks. The traditional method provided a quantitative measure of pathogen propagules in the soil with population levels ranging from 0 to 21, 625 colony-forming units per gram of soil. However, it was not able to differentiate between the weakly pathogenicV. albo-atrum strain 2 and the more aggressiveV. albo-atrum strain 1, but these two were distinguished with the PCR assay. Results from this study demonstrate that when symptoms of verticillium wilt are observed in potato plants in the field, the major verticillium wilt pathogens present in field soils can be rapidly and reliably detected by the PCR assay.     

Induction of systemic resistance and defense-related enzymes after elicitation of resistance by rhizobacteria and silicon application against Ralstonia solanacearum in tomato (Solanum lycopersicum)

Bacterial wilt caused by Ralstonia solanacearum is a devastating plant disease affecting several economically important crops. To trigger plant-mediated systemic resistance against the pathogen, silicon and the rhizobacteria strain Bacillus pumilis were applied as elicitors. The impact of each elicitor in the induction of systemic resistance was evaluated by individual or dual application in pathogen inoculated tomato genotypes. Application of silicon and B. pumilis significantly reduced bacterial wilt incidence by 50.7 and 26.7%, respectively, in the King Kong 2 genotype (moderately resistant) and by 31.1 and 22.2%, respectively, in the L390 genotype (susceptible) but the dual application of the elicitors did not. The pathogen responsive lipoxygenase (LOX) activity was decreased in the silicon-treated tomato plants and no significant difference was detected in B. pumilis treated-pathogen inoculated plants compared to the control. In addition, a non-significant increases of peroxidase (PO) activity and phenylalanine ammonia lyase (PAL) activity were observed in either silicon/B. pumilis treated and pathogen inoculated plants. However, the PO, PAL and LOX activities declined during the dual application due to antagonistic effect of the two pathways triggered by the two elicitors. Therefore, separate application of each elicitor is recommended as the best strategy for induction of systemic resistance against bacterial wilt in tomato with silicon being a stronger inducer than B. pumilis.     

Effect of Soil Temperature,Injection Depth,and Metam Sodium Rate on the Management of Verticillium Wilt of Potato

Verticillium wilt, caused by Verticillium dahliae Kleb., is a primary component of the early dying complex of potato (Solanum tuberosum L.) in the United States. Although genetic resistance to V. dahliae exists and has been incorporated into several potato cultivars, the commercial potato industry is still dominated by cultivars susceptible to the pathogen. As a result, soil fumigation with metam sodium remains an important means by which Verticillium wilt is controlled, despite its expense and potentially negative environmental impact. Recent restrictions on metam sodium use by the Environmental Protection Agency directed at reducing exposure to vapor emissions have increased the need to improve shank injection of the soil fumigant. In studies reported here, the application of metam sodium reduced the severity of Verticillium wilt, however, soil temperature at the time of injection, metam sodium injection depth, and application rate had little overall effect. In 2011, temperature at the time of metam sodium injection did not result in significant differences in any parameter evaluated. However, in 2012, soil populations of V. dahliae, wilt severity and host colonization were significantly reduced when metam sodium was applied at 4 °C compared to 13 or 15 °C. No significant differences were observed between a single or two metam sodium injection depths in any parameter evaluated across the 2 years the study was conducted. While all rates of metam sodium significantly reduced soil populations of V. dahliae compared to the non-treated control, significant differences across rates were rarely observed. Improved control of Verticillium wilt and increased yield can be achieved as a result of these studies. The effective control of Verticillium wilt can be obtained by using metam sodium at a comparatively low rate of 373 l/ha, particularly when applied at a relatively cold soil temperature of 4 °C using a single injection depth of 25 cm. The potential impact of these application modifications of metam sodium in reducing emissions and non-target exposure is discussed.     

Latent infection of potato tubers byPseudomonas solanacearum

Strains ofPseudomonas solanacearum differed in their ability to infect tubers of different resistant potato clones grown in infested soil. When eight resistant clones (Solanum phureja orS.phureja ×S. tuberosum hybrids) were grown at 24–28°C in soil infested with a race 1 or a race 3 strain of the bacterium, relatively few plants had wilt symptoms at harvest, but 26.7% and 9.2% of the tubers harvested from plants infected with the race 1 and race 3 strains, respectively, carried latent infections. Some infected clones never yielded diseased tubers, however. The development of symptoms above ground was not correlated with the incidence of tuber infection in any particular clone. No tuber infection occurred in tolerant or resistant clones grown in infested soil at cool (12–22°C) temperatures. Tubers were inoculated directly in an attempt to evaluate the ability of bacteria to multiply in these tissues at different temperatures. Highly virulent strains ofP. solanacearum survived in susceptible tubers in higher numbers and for longer periods than in resistant ones. Low temperature (4°C) had a deleterious effect on survival of the bacterium in tubers, but did not completely eliminate the pathogen even after 40 days.