The role of weeds in the epidemiology of pospiviroids

Many weeds that are closely associated with horticultural activities are known as natural reservoirs of plant viruses. However, whether these weeds can also serve as hosts of pospiviroids is not well known. Pospiviroids are naked, non‐coding RNA pathogens that cause severe economic damage in many solanaceous crops. In this study, we examined the overall risk of pospiviroid spreading from weeds to economically important crops, by combining the results from previous inoculation studies with new results coming from a survey, a contact experiment and an inoculation experiment. A survey of commercial ornamental glasshouses revealed that ornamental plants mainly belonging to the Solanaceae harbour pospiviroids, in contrast to weed species sampled in the same places. No new weed hosts could be identified after testing weeds that grew in contact with Tomato apical stunt viroid (TASVd)‐infected plants of tomato (Solanum lycopersicum) and jasmine nightshade (Solanum jasminoides) in an experimental glasshouse. Finally, in mechanical inoculation experiments with TASVd, none of the six tested weed species were determined to be a host at 6 weeks after inoculation. Commonly occurring weed species therefore do not appear to play a significant role as reservoir hosts for pospiviroids. This does not rule out other potential weed hosts that have not yet been tested. Inoculation studies should include rigorous experimental protocols with a sufficient number of replicated as well as adequate positive controls. The information gained through this study may prove useful in future risk assessments for the pospiviroid group.     

Weed interference in maize, cowpea and maize/cowpea intercrop in a subhumid tropical environment. I. Influence of cropping season

Field experiments were conducted in the early and late cropping seasons of 1979 on a loamysand Oxic Ustropept in a subhumid environment in Nigeria, using 40000, 50000 and 30000 + 40000 plants ha^?1 of maize (Zea mays L. cv. TZB), cowpea (Vigna unguiculata (L.) Walp. cv. VITA-5) and maize/cowpea intercrop respectively. These indicated that weed interference effects on crops under no-tillage depended on cropping season, cropping pattern and crop species. In the early and late seasons respectively, thirty-five and twenty-nine different weed species were recorded and weed dry weights of approximately 10·4 and 5·7 t ha^?1 from the plots kept weedy throughout the season reduced corresponding food energy yields by 60 and 82%. Except for the intercrop, which in the early season showed significant yield reduction when exposed to 4 weeks’ weed interference after sowing, all cropping patterns needed more than 4 weeks’ interference to show significant yield reductions, regardless of cropping season. In the early season, weed interference accounted more for the yield reductions in monocultures than it did for those in the intercrop, but in the late season all cropping patterns were equally sensitive to weed association. Maize, which performed much better in the early season, showed greater yield reductions than cowpea under early weed interference but less under full-season interference irrespective of cropping pattern and season. Cowpea seed quality was more reduced by intercropping than by weed interference in the early season but neither of these factors affected seed quality significantly in the late season.     

The role of oxalic acid and polygalacturonase in the pathogenicity ofPythium aphanidermatum on different cowpea varieties

The amounts of oxalic acid and polygalacturonase (PG) produced in the tissues of cowpea (Vigna unguiculata Walp.) plants infected byPythium aphanidermatum were higher in vars. IT81D-1020 and VITA 5 than in vars. IT82E-32 and TVX3236. Oxalic acid accumulated early at the infective stage of the disease but its production decreased as the plants became older or as the disease developed. At the peak of oxalic acid and PG production (8–10 days after infection) the pH of the tissue fell from 7.2 to 3.1 and thereafter rose to 4.3 (within 18 days). It seems, therefore, that the combination of oxalic acid and PG and the accompanying reduced pH of infected tissue play an important role in the pathogenesis of susceptible varieties of cowpea byP. aphanidermatum. In the two varieties found to be resistant in this study, oxalic acid and PG production were lower than in the susceptible varieties and the pH did not fall as low. Early accumulation of oxalic acid in cowpea tissue during pathogenesis may be a useful tool for monitoring disease severity, and hence susceptibility or resistance toP. aphanidermatum, when there is a compatible interaction between host and pathogen.     

Effect of recent cropping history and herbicide use on the degradation rates of isoproturon in soils

Five soil samples were taken from each of five fields with different crop management histories. Three of the fields were in an arable rotation, the fourth field was temporary grassland, and the final field was under permanent grass. Of the three arable fields, two had been cropped with winter wheat in three of the preceding 6 years, and the third had last been cropped with winter wheat once only, 6 years previously. With one exception, the winter wheat had been sprayed with the herbicide isoproturon. The rate of isoproturon degradation in laboratory incubations was strongly related to the previous management practices. In the five soils from the field that had been treated most regularly with isoproturon in recent years, <2.5% of the initial dose remained after 14 days, indicating considerable enhancement of degradation. In the soils from the field with two applications of the herbicide in the past 6 years, residues after 27 days varied from 5% to 37% of the amount applied. In soils from the other three sites, residue levels were less variable, and were inversely related to microbial biomass. In studies with selected soils from the field that had received three applications of isoproturon in the previous 6 years, kinetics of degradation were not first‐order but were indicative of microbial adaptation, and the average time to 50% loss of the herbicide (DT₅₀) was 7.5 days. In selected soils from the field that had received just one application of isoproturon, degradation followed first‐order kinetics, indicative of cometabolism. Pre‐incubation of isoproturon in soil from the five fields led to significant enhancement of degradation only in the samples from the two fields that had a recent history of isoproturon application.     

The role of Poa annua in the epidemiology of barley yellow dwarf virus in autumn-sown cereals

Studies of cereal aphids and barley yellow dwarf virus (BYDV) from 1989 to 1992 revealed that Poa annua is an abundant weed of commercial winter barley crops during the summer months. P. annua was frequently infected with BYDV, and there were usually similarities with the BYDV infection of the surrounding barley crop. These P. annua weeds were often infested by cereal aphids both in July (pre-harvest) and in September (in cereal stubble fields). Poa -infested cereal stubbles may be major local sources of viruliferous aphids, increasing the risk of BYDV in nearby winter cereals. P. annua plays an important role in the epidemiology of S. avenae -transmitted BYDV.     

The effect of cropping systems and irrigation management on development of potato early blight

Crop and soil management may modify canopy and belowground microclimate, but their effects on potential development and control of early blight are not well documented. Several management systems (Status Quo, Soil Conserving, Soil Improving (SI), Disease Suppressive, and Continuous Potato) were evaluated for their effects on early blight potential under irrigated and rainfed conditions. In 2006 and 2007, microclimatic data at the canopy level were recorded with a data logger. Early blight incidence and severity was determined by visually assessing symptoms. Disease incidence and lesion numbers varied among cropping systems and between years. Disease incidence ranged from 31 to 64% (2006) and 12 to 43% (2007), and was significantly higher with the Continuous Potato system than with Disease Suppressive, Status Quo, Soil Conserving, and SI systems. The relationships of incidence and disease severity with microclimate varied and were mostly non-significant, suggesting that the chosen variables were not reflective of pathogen development. Incidence was significantly associated with cropping systems. Disease prediction based on the Tom-Cast model was not correlated with observed disease levels. This research demonstrated that early blight disease is enhanced through continuous potato production.     

轮作小麦消减胡麻连作障碍的效应研究

为探讨轮作小麦对胡麻连作障碍的消减作用,通过田间试验研究了轮作小麦对胡麻株高和产量的影响,并通过测定土壤酶活性和土壤水提液化感作用,探寻消减连作障碍的机制。结果表明:重茬种植胡麻导致连作障碍现象突出,表现为连作3 a时株高、出苗率、千粒重和单株产量分别降低14.0%、7.75%、33.8%和43.2%,而第二年轮作小麦可以消减连作障碍,使下茬胡麻株高和产量保持在胡麻连作1 a水平,分别为69.7 cm和1.43 g·株~(-1)。轮作小麦后土壤过氧化氢酶、脲酶和碱性磷酸酶活性分别为2.41 mL·g~(-1)·h~(-1)、2.32 mg·g~(-1)·d~(-1)和9.04 mg·g~(-1)·d~(-1),与连作1 a胡麻地土壤酶活性无显著性差异,但连作将使部分土壤酶活性发生较大变化,表现为连作2a后土壤过氧化氢酶、土壤脲酶、碱性磷酸酶的活性分别降低至2.16 mL·g~(-1)·h~(-1)、8.18 mg·g~(-1)·d~(-1)和2.01 mg·g~(-1)·d~(-1),表明轮作小麦可通过保持部分土壤酶活性消减连作障碍,从而利于下茬胡麻生长。与胡麻连作相比,轮作小麦使土壤水提液对胡麻种子萌发和幼苗生长的化感自毒作用减弱,并表现出综合化感效应为0.21%的促进作用,使发芽指数(46.0)、发芽势(92.0%)、活力指数(3.36)、根长(8.35 cm)及根重(23.17 mg)等指标与CK和TC1处理下无显著性差异,而连作加剧土壤水提液自毒作用,对胡麻种子萌发和幼苗生长的抑制作用增强,且综合化感效应随连作年限增加分别降低至-8.61%和-17.01%,表明轮作小麦可以通过影响土壤自毒作用消减胡麻连作障碍。综上所述,胡麻重茬种植将导致明显的连作障碍,合理轮作小麦有利于维持胡麻地土壤酶活性、降低土壤自毒作用,从而消减胡麻连作障碍的发生。     

The role of models for multicriteria evaluation and multiobjective design of cropping systems for managing weeds

Weeds are both harmful for crop production and important for biodiversity, while herbicides can pollute the environment. We thus need new cropping systems optimising all cultural techniques, reconciling agricultural production, herbicide reduction and biodiversity conservation. Here, we show how to (i) develop models quantifying the effects of cropping systems on weed dynamics, (ii) integrate interactions between weeds and other organisms, (iii) predict the impact on production and biodiversity and (iv) use the model for multicriteria evaluation and multiobjective design of cropping systems. Among the existing weed dynamics models, we chose the one closest to our requirements to illustrate these different steps, that is, FlorSys which predicts multispecific weed dynamics as a function of cultural techniques and pedoclimate. We have illustrated the development of interaction submodels with the example of a crop pathogen whose propagation is increased when infecting grass weeds. To evaluate the weed flora impact, predicted weed densities were translated into indicators of harmfulness (crop yield loss, technical harvest problems, harvest pollution, field infestation, crop disease increase) and biodiversity (weed species richness and equitability, trophic resources for birds, insects and pollinators). Simulations were run over several years and with different weather scenarios (i) to optimise cultural techniques to control harmful weeds, (ii) to analyse the impact of changing agricultural practices (e.g. simplified tillage and rotations, no‐till, temporary crops) on weed density, species and trait composition and (iii) to evaluate cropping systems for their ability to reconcile agricultural production and biodiversity, thus identifying levers for designing sustainable cropping systems.     

进境日本豇豆中黑眼豇豆花叶病毒的检测与鉴定

从进口日本豇豆中随机挑选种子在隔离温室内种植。出苗后,发现有典型花叶症状的植株。对该病株进行电镜观测,发现有线条形病毒粒体,大小约为750nm×13nm。设计特异性引物(BL-5/BL-6),对该样品进行黑眼豇豆花叶病毒的反转录(RT)PCR分子检测。电泳检测表明,扩增出一条特异性的目标条带,大小为338bp。对该样品的RT-PCR产物进行测序,结果表明该序列与黑眼豇豆花叶病毒(GENEBANK登录号:AY575773)的序列有4个碱基差异,同源性为98.8%。鉴定该病毒为黑眼豇豆花叶病毒(Blackeye cowpea mosaicvirus)。     

苹果黑星病的药剂防治

苹果黑星病Venturia inaequalis是黑龙江省对內检疫对象之一。一般发病率为30—40％,严重时可达90％以上。主要为害小苹果树的叶和果实,造成早期落叶,削弱树势生长,花芽形成不良,影响果实品质和产量,并成为影响果树安全越冬的主要原因之一。 1963—1964年間,我們用120倍波尔多液和代森鋅分別进行了防治时期和浓度試驗,結果見     

Etiology of and effect of environmental factors on damping-off and stem rot of cowpea in Benin

Damping-off and stem rot are two types of diseases affecting cowpea (Vigna unguiculata (L.) Walp.) in the Quémé Valley, Benin. Of the fungal species isolated from diseased plants in the field during a 2-year experiment (2001 and 2002),Sclerotium rolfsii Sacc. was found to be solely responsible for these diseases. The disease incidence decreased with increasing distance of the field from the river. Measurement ofS. rolfsii initial inoculum, soil moisture and disease incidence in cowpea field plots revealed a positive correlation among these parameters. The multiple regression analysis showed that the disease incidence increase was 0.4% for one unit increase in soil moisture percent, whereas the disease incidence increase was 19.8% for one unit increase of the density of initial inoculum of the pathogen. This is the first comprehensive study of the effects of environmental factors on the incidence of cowpea damping-off and stem rot caused byS. rolfsii in Benin, and shows that the density of the initial inoculum is the main contributing factor of the disease in the field in the Quémé Valley. http://www.phytoparasitica.org posting Dec. 19, 2004.     

Effects of cropping history and origin of seed potatoes on population structure of Phytophthora infestans

The effects of origin of seed potatoes and the cropping history on the phenotypic structure of Phytophthora infestans populations was studied in northern Hessia, central Germany, from 2000 to 2002. Populations originating from fields with a history of potato cropping with only short or no rotation (old fields) were compared with populations from new fields, i.e., where no potatoes had been grown for at least 30 years and seed potatoes were either imported from breeders or produced on-farm (certified). The main goal was to determine the importance of seed potato infection in the establishment of new P. infestans populations. Isolates were characterized for mating type, virulences and rep- (repetitive extragenic palindromic) PCR fingerprints. Among a total of 639 isolates sampled from 31 sites, mating types A1 and A2 co-existed in all three years in 60–92% of the sites. Over all three years, 53 pathotypes were detected in a subsample of 272 isolates. Isolates originating from the new fields had significantly higher frequencies of the virulences v1, v2, v3, v6 and v7, indicating general effects of seed introduction into a new region. Thirty-six fingerprints were detected in a subsample of 281 isolates of which 22 were unique while four occurred in all three years and in many sites. Pathogen populations from potato fields that were grown from seed tubers of geographically different origin differed significantly based on χ ² tests. While the Nei genetic distances were less than .1 among the local populations, distances to the US lineages US-1, US-6, US-7 and US-8 ranged from .22 to .47; however, the bootstrap values were not significant. Populations from old fields were more diverse and 14 of the 22 rep-PCR types occurred there among 132 isolates tested in comparison to six in the new fields (n = 140 isolates) and two among six isolates from volunteers. The results also suggest that both sexual and asexual reproduction play a role.     

The radio warning service for apple and pear scab in the Netherlands in 1961 and 1962

Samenvatting De organisatie van de radio-waarschuwingsdients voor appel- en pereschurft in 1961 en 1962 wordt beschreven. Door een landelijke centrale post (L.C.P.), die in de Plantenziektenkundige Dienst (P.D.) was gevestigd, werden tijdens de periode van ascosporen-uitstotingen van 15 regionale centrale posten (R.C.P.'s) gegevens verzameld over de duur van de bladnatperioden en de temperatuur tijdens deze bladnatperioden. De waarnemingen van de 15 R.C.P.'s waren op hun beurt afkomstig van 19 primaire en 57 secundaire waarnemingsposten, verspreid over het land. De uitrusting en de taak van de verschillende waarnemingsposten worden vermeld.Door de landelijke centrale post werden vijf soorten berichten uitgegeven. De eerste drie soorten hebben betrekking op het begin van de ascosporen-uitstotingen; het laatste bericht geeft het einde van de ascosporen-uitstotingen aan. Daartussen vinden meldingen van het optreden van infectieperioden ergens in het land plaats. De betekenis van alle typen berichten wordt besproken.Een vergelijking van de kosten van uitrusting van waarnemingsposten bij gebruik van verschillende bladnat-registrerende apparatuur valt uit ten gunste van de in Nederland ontworpen en gebruikte de Wit-bladnatschrijver.De radio-waarschuwingsdients voor appel- en pereschurft wordt, ondanks de daaraan verbonden en vermelde bezwaren, door vele fruittelers in Nederland beschouwd als een belangrijke steun bij de bestrijding van appel- en pereschurft.     

4种药剂对豇豆根结线虫病的防治效果

为了更好地防治豇豆根结线虫病,对4种杀线虫剂进行了田间防效评价试验。结果表明,供试的4种药剂均对豇豆根结线虫有一定的防效,能控制土壤中２龄幼虫的数量和抑制根结的形成,其中10％噻唑膦颗粒剂对豇豆根结线虫的防效最好,具有低残留、持效期长等优点,可作为防治豇豆根结线虫的首选药剂; 其次为５％阿维菌素颗粒剂。同时供试的4种药剂在试验剂量范围内均对豇豆安全,建议在生产上推广应用10％噻唑膦颗粒剂和５％阿维菌素颗粒剂来防治豇豆根结线虫病。     

The distribution of peach scab lesions on the surface of diseased peaches

The aim of the study was to quantify peach scab (Fusicladosporium carpophilum) lesion distribution relative to the point of maximum lesion number on the fruit surface, the relationship between lesion count and distance from the point of maximum lesion density, and establish whether the distribution of lesions was consistent with a splash dispersed pathogen, and to assess the effect of lesion number on fruit size. Fruit of four cultivars, Jerseyqueen, Jefferson, BY07-6428r and Dixiland were collected and the fruit (assumed spherical) sliced taking three horizontal planes across the axis from the point of maximum disease, such that each horizontal zone (Z1-Z4) had the same vertical height, and thus equal surface areas. Lesion counts were analysed using general linear modeling with a Poisson distribution and a log-link function. Zones on the fruit had different numbers of lesions (P < 0.0001), with most lesions found on Z1. Cvs differed in the number of lesions per fruit (P = 0.0042–<0.0001). An analysis of covariance showed that although fruit size varied among most cvs (P = 0.1614–<0.0001), the number of lesions on a fruit did not affect fruit size (P = 0.5654). Measurements of the point of maximum disease relative to the peduncle-flower scar axis of the fruit suggest that fruit are not always held upright when infection occurs, such that up to 40% of fruit showed maximum infection at an angle >90° to the peduncle. This pattern of disease is consistent with observations of the splash-borne nature of conidia, with the most exposed, easily wetted, uppermost portion of fruit developing most disease.     

连作对马铃薯生长和土壤健康的影响及机制研究

以连作马铃薯土壤及不同连作年限马铃薯为材料,通过分析不同连作年限(分别连作0、3、6 a)马铃薯生长发育及土壤健康各因素的变化,对连作马铃薯生长发育及土壤健康的变化及机制进行了探讨。结果表明,随连作年限增加,土壤有机质、速效磷含量以及土壤pH值逐渐降低,在连作6 a时,土壤有机质含量、速效磷含量和土壤pH值分别比对照下降了50.72%、34.10%和8.68%;碱解氮含量上升,在连作3 a和6 a时,碱解氮分别比对照升高了84.62%、169.23%;土壤肥力相关酶活性下降,在连作6 a时,土壤中碱性磷酸酶、脲酶、蔗糖酶和过氧化氢酶活性分别比对照下降了36.34%、35.72%、29.83%和74.16%;酚酸类化感物质含量升高,在连作6 a时,土壤中羟基苯甲酸、香草酸、阿魏酸和总酚酸的含量比对照升高了33.61%、31.30%、51.64%、40.57%;细菌和放线菌数量下降,真菌数量升高,在连作6 a时,细菌和放线菌数量比对照降低了88.59%和84.21%,真菌数量在连作6 a时比对照升高了253.85%,说明连作造成土壤健康状况下降。研究还发现随着连作年限增加,马铃薯叶片MDA含量升高,连作6 a时MDA含量比对照增加了142.47%,说明马铃薯叶片遭受了一定程度的脂质过氧化;马铃薯叶片相对叶绿素含量、净光合速率和气孔导度下降,连作6 a时分别比对照降低了13.30%、13.98%和50.00%;株高、茎粗、地上生物量和块茎产量逐渐下降,连作6 a时分别比对照下降了42.49%、54.40%、58.35%和61.79%,说明连作严重影响了马铃薯的光合能力和生长发育。可见,马铃薯连作导致了土壤理化性质恶化,代谢活力降低,养分失去平衡,土壤酚酸类物质大量累积,最终导致微生物群系发生变化,从而从整体上降低了土壤的健康状况,严重影响马铃薯生长发育。     

两种喷雾助剂对噻虫嗪防治豇豆上蓟马的减施增效作用

为探索有机硅助剂Silwet stik和植物油助剂迈丝对噻虫嗪防治豇豆上蓟马Megalurothrips usitatus的效果及其残留行为的影响,通过田间试验,比较了25％噻虫嗪水分散粒剂(WG)在登记剂量和减量10％、20％、30％条件下分别添加两种助剂后5 d和7 d的防效,以及施药后噻虫嗪及其代谢物噻虫胺在豇豆...     

甘肃马铃薯疮痂病病原初步鉴定

对甘肃不同地区马铃薯疮痂病病原进行了分离鉴定.采用盆栽方法进行致病性测定、形态特征、生理生化特性测定和16S rDNA序列分析.结果表明:共有6株菌能使马铃薯块茎出现疮痂症,分别为GP-1、GP-2、GH-1、GH-2、JB-1和JB-2.经鉴定菌株GP-1、JB-2的形态特征、生理生化特性及16S rDNA序列与Streptomyces scabies 87 22菌株均一致;GP-2、JB-1的16S rDNA序列与S.scabies菌株相似性为99％.菌株GH-2和GH-1与S.griseus的16S rDNA序列相似性分别为100％和99％,形态特征一致,但不能以棉籽糖和肌醇为单一碳源,暂定为S griseus.     

Identification of blackeye cowpea mosaic virus from germplasm of yard-long bean and from soybean,and the relationships between blackeye cowpea mosaic virus and cowpea aphid-borne mosaic virus

Two potyvirus isolates, one from germplasm of yard-long bean (Vigna unguiculata ssp.sesquipedalis) introduced into the Netherlands, and another one from soybean plants (Glycine max) in Indonesia, were compared with two virus isolates of blackeye cowpea mosaic virus (BICMV) from the USA and a Moroccan isolate of cowpea aphid-borne mosaic virus (CAMV). It is proposed that all five isolates be now considered BICMV on the basis of host ranges, symptoms and serology. From our results, and a reassessment of the literature it is suggested to drop the name CAMV in favour of BICMV.Samenvatting Twee potyvirussen, de een in Nederland ingevoerd met genenmateriaal vanVigna unguiculata ssp.sesquipedalis en de ander uit planten van sojaboon (Glycine max) in Indonesië, werden vergeleken met twee isolaten van blackeye cowpea mosiac virus (BICMV) en een Marokkaans isolaat van cowpea aphid-borne mosaic virus (CAMV). Op grond van waardplantenreeksen, symptomen en serologie stellen de auteurs voor om alle vijf isolaten te beschouwen als BICMV. Gebaseerd op de verkregen resultaten en een kritische beschouwing van de literatuur wordt de aanbeveling gedaan om de naam CAMV te laten vallen ten gunste van BICMV.     

The threat of wild habitat to scab resistant apple cultivars

Evaluations of plant resistance to pathogens are rarely made using isolates from wild habitats, although the heterogeneity of such habitats may generate pathogen diversity which could be a source of new virulence in cultivated habitats. The aim of this study was to investigate whether scab resistance factors, identified and characterized in apples using isolates of Venturia inaequalis from a cultivated habitat, remained effective against isolates from a wild habitat. Three V. inaequalis core collections originating from the cultivated apple Malus × domestica and from two wild species, M. sieversii and M. sylvestris, were established to maximize pathogen diversity. For each core collection, 10 isolates were inoculated in mixtures onto 51 genotypes from an apple progeny segregating for two qualitative resistance genes and six quantitative resistance loci (QRL). On each apple genotype, isolates that contributed to the scab symptoms were identified within the mixture using microsatellite markers. The most frequently detected isolates were inoculated singly to compare their aggressiveness according to their host origin. The results showed that isolates from a wild habitat were able to infect the susceptible apple genotypes. However, these isolates were never more aggressive than isolates from the cultivated habitat on the resistance factors tested. It can therefore be concluded that the resistance factors used in this study, identified with V. inaequalis isolates from a cultivated habitat, remained effective against isolates from M. sylvestris and M. sieversii.