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1.
由于花椒树枝伸展长、带刺以及果实小,现阶段仍以人工采收为主,采摘效率低下。为提高花椒采收效率和质量,现设计出一种齿梳-气吸式采摘装置,并对采摘流场进行理论分析。为提高气吸式花椒采摘装置的作业质量,以"大红袍"和"刺椒"花椒品种为试验对象,利用自制的气吸式花椒采摘装置,以采摘头转速、气流速度、梳齿式刀片刃口角为影响因素,以采净率、损伤率以及采收净度为评价指标,进行了二次旋转正交组合试验。通过Design-Expert 6.0.10软件,建立了评价指标与诸影响因素的数学回归模型,分析了显著因素对评价指标的影响,优化试验参数。确定最优参数组合为:采摘头转速367.5 r·min~(-1),气流速度32.7 m·s~(-1),梳齿式刀片刃口角31.5°。在此参数组合下采收效果为:采净率95.2%,损伤率1.2%,采收净度96.5%(即含杂率3.5%)。加工梳齿刀片刃口角32°,调整风机流速30 m·s~(-1)、采摘头转速为350 r·min~(-1)进行验证实验,采收效果:采净率91.8%,相对误差5.3%,损伤率1.3%,相对误差8.3%,采收净度92.5%,相对误差4.1%,各指标符合设计需求。  相似文献   

2.
为了确定模袋混凝土护坡、砂砾石护底的复合断面衬砌渠道的糙率系数,本文在内蒙河套灌区什巴分干渠(0+200~2+216)和建设二分干渠(1+910~3+040)开展了模袋混凝土复合断面衬砌渠道的原型观测试验研究,得出了不同水深和流量条件下的渠道糙率系数,并建立了渠道观测断面水力测量误差与糙率系数计算误差之间的函数关系,计算分析了什巴分干渠和建设二分干渠糙率系数观测试验的测定误差。试验得出:什巴分干渠原型观测的糙率系数最小值为0.025 1,最大值为0.026 7,平均值为0.025 9;建设二分干渠原型观测的糙率系数最小值为0.0264,最大值为0.0279,平均值为0.0272;什巴分干渠原型观测的糙率系数测定最大误差为5.037%,建设二分干渠原型观测的糙率系数测定最大误差为4.305%。模袋混凝土复合断面衬砌渠道糙率系数范围为0.0251~0.0279,平均值为0.0265,原型观测糙率系数测定的最大误差为5.037%。  相似文献   

3.
为阐明胡麻脱粒物料在振动筛上实际的筛分效果,采用CFD-DEM耦合方法,对胡麻脱粒物料在胡麻联合收获机风筛式清选装置中的清选效果进行研究,探究鱼鳞筛开口角度、气流速度、清选筛振动频率以及清选筛振幅对清选效果的影响,并通过统计胡麻籽粒含杂率和清选损失率来衡量不同工作参数下分离清选装置的工作性能。仿真试验结果表明:鱼鳞筛开口角度最优为30°,鱼鳞筛透筛率为79.77%,茎秆透筛率为65.52%,籽粒透筛率为90.01%;振动筛振动幅度最优为15 mm,胡麻籽粒损失率为3.6%,籽粒含杂率为3.4%;振动筛振动频率最优为6 Hz,清选损失率为3.5%,籽粒含杂率为3.4%;风机风速最优为5.5 m·s-1,籽粒含杂率为3.2%,清选损失率为3.0%。结合优化工作参数进行大田作业性能验证试验,通过对机收后的收集物料测定试验指标可知,总清选损失率为3.58%,籽粒含杂率为3.16%,大田试验结果与仿真模拟结果基本一致。机收后的胡麻籽粒外形完整,破损现象较少,含杂率与总损失率均达到相关试验标准要求,表明优化后的参数满足胡麻联合收获标准要求。  相似文献   

4.
为降低甘肃产区沙棘加工企业沙棘枝条果脱果、筛分除杂后的纯果含杂率,在传统的ZKB型直线振动筛基础上,设计了配置3层筛片的直线振动筛,其中3层筛片筛孔直径分别为12、8、5 mm。使用离散元仿真分析软件,并以振动筛振动方向角、振幅和频率为自变量、振动筛筛分效率和筛分速度为响应值,采用综合评分法设计正交试验,对各个因素及其交互作用进行分析。结果表明:当振动方向角为45°、振幅为2 mm、振动频率为18 Hz时筛分效果最好。在此条件下进行样机试验,下层筛筛分效率、筛分速度分别为85.3%、0.33 m·s-1,上层筛筛分效率、筛分速度分别为85.9%、0.38 m·s-1,该机主要设计指标符合相关国家标准,满足企业对筛分效率的需求。样机实地试验与仿真试验对9组试验数据的4个指标差异、最佳振动参数的研究结果趋于一致。  相似文献   

5.
针对我国燕麦机械化脱粒时脱出物含杂率高、夹带损失率大等问题,本研究设计了一种横轴流柔性脱粒分离装置,通过减少茎秆破碎来降低含杂率,并通过柔性脱粒杆齿的振动来减小夹带损失。选取柔性杆齿长A、柔性杆齿直径B、柔性杆齿间距C和滚筒转速D为试验控制因素,以含杂率和损失率为试验指标,进行正交试验,得到了影响该装置脱粒性能指标的因素主次为D、B、A、C。在正交试验基础上,选取对该装置脱粒性能指标影响较强的2个因素进行回归分析,试验结果表明:当滚筒转速为1 048 r·min-1、柔性杆齿直径为7.5 mm时,本装置的脱粒性能最佳,此时的含杂率为29.41%、损失率为1.31%。对上述优化组合进行试验验证,结果为含杂率的平均值为29.50%、损失率的平均值为1.12%。在相同参数条件下,与脱粒元件全为刚性杆齿的横轴流滚筒进行对比,含杂率和损失率分别降低了2.71%和0.52%,脱粒性能明显提高。该研究可为燕麦脱粒分离装置的创新设计提供参考。  相似文献   

6.
为减少农药的使用,提升宁夏枸杞的品质,本研究在明确声波与蚜虫的作用机理基础上,开发了声压120 dB,频率范围20~1 000 Hz的低频声波装置,并探索其室内和田间对蚜虫的防效。结果表明,在室内和田间,声波强度100 dB,连续3 d,声波处理3 h/d,室内145 Hz和室外170 Hz的声波对蚜虫的趋避效果分别为83.3%和40%。该低频声波技术和装置可用于枸杞蚜虫的防控,结合机器人等运动平台,具备大面积枸杞蚜虫声波防治的可能性。  相似文献   

7.
黄土丘陵区退耕草地土壤稳定入渗率生长季变化   总被引:1,自引:0,他引:1       下载免费PDF全文
运用双环法,探讨了黄土丘陵区退耕草地土壤稳定入渗率生长季的变化。结果表明:(1)赖草地土壤稳定入渗率在生长季内呈现出"W"型显著的季节变化趋势(P0.05),紫花苜蓿地土壤稳定入渗率则无显著的生长季变化(P0.05)。在草地生长季,赖草地土壤稳定入渗率值的变化范围为1.61~4.53 mm·min~(-1),平均值为2.89 mm·min~(-1)。赖草地土壤稳定入渗率最小值出现在抽穗期(1.61 mm·min~(-1)),最大值出现在种子成熟期(4.53 mm·min~(-1))。紫花苜蓿地土壤稳定入渗率值的变化范围为2.12~2.3 mm·min~(-1),平均值为2.23 mm·min~(-1)。紫花苜蓿地土壤稳定入渗率最小值出现在种子成熟初期,在旁枝形成期、开花期和种子成熟末期出现最大值2.3mm·min~(-1)。(2)赖草地与裸地的土壤稳定入渗率具有显著性差异(P0.05),紫花苜蓿地与裸地则无显著性差异(P0.05),赖草地的平均土壤稳定入渗率最大(2.89±1.03 mm·min~(-1)),其次是紫花苜蓿地(2.23±0.09 mm·min~(-1));(3)土壤容重、总孔隙度和毛管孔隙度等土壤属性生长季的变化是影响黄土丘陵区退耕草地土壤稳定入渗率生长季变化的主要因素;(4)利用土壤容重、总孔隙度和毛管孔隙度等参数可以很好地模拟黄土丘陵区退耕草地土壤稳定入渗率生长季的变化(R20.86,NSE0.86)。  相似文献   

8.
为探索马铃薯糖苷生物碱诱导采后枸杞鲜果抗病性的效应,采用菌丝生长速率法测定了离体条件下马铃薯糖苷生物碱对枸杞鲜果采后主要致腐病原菌镰孢菌Fusarium sp.的抑菌活性;采用浸泡处理法测定了马铃薯糖苷生物碱对采后枸杞鲜果发病病情指数及对果实多酚氧化酶(PPO)、过氧化物酶(POD)、苯丙氨酸解氨酶(PAL)和超氧化物歧化酶(SOD)等相关防御酶活性的影响。结果表明:不同浓度马铃薯糖苷生物碱对镰孢菌均具有一定的抑制作用,EC50为0.11 g/mL;0.05~0.25 g/mL(提取原料)的马铃薯糖苷生物碱能显著降低采后枸杞鲜果病情指数,较对照降低了10.18%~38.51%;以0.15 g/mL(提取原料)的马铃薯糖苷生物碱处理后对枸杞鲜果抗果腐病的诱导效果最好,达45.81%;马铃薯糖苷生物碱处理枸杞鲜果后,果实中4种防御酶PPO、POD、PAL、SOD的活性均较对照有不同程度提高,分别于处理后第4、5、2、2天与对照差异达到最大,较对照提高了30.76%、21.34%、31.35%和21.91%。表明马铃薯糖苷生物碱能够诱导枸杞鲜果对采后病害的抗性效应,且采后抗病性可能与枸杞相关防御酶活性的增加有关。  相似文献   

9.
为满足旱地全膜双垄沟农艺技术要求,设计了一种玉米精量播种机。为实现播种机平稳工作、保证膜下播种深度,采用双向平行四杆仿形机构,根据初始工作角和最大上下仿形量,确定了仿形机构的各项尺寸参数,上下仿形量可达到98.35 mm,左右仿形角达到15.2°,满足仿形播种要求;为减少漏播,降低空穴率,采用凸轮-平面连杆开启式穴播轮;借助ADAMS软件对穴播器成穴过程进行仿真分析,探讨了穴播轮滑移率对穴孔形状的影响,并以此对播种机的前进速度进行优化,降低了空穴错位率。田间试验结果表明:全膜双垄沟播玉米精量播种机作业后空穴率为0.9%,穴粒数合格率为93.6%,膜下播种深度合格率为91.8%,穴位错孔率为2.5%,作业质量符合行业技术标准要求。  相似文献   

10.
苹果梨黑斑病的发生及侵染过程   总被引:6,自引:1,他引:6  
苹果梨果实的黑斑病为典型的潜伏侵染性病害,采后冷藏60天,表面光滑无任何症状,采后90天开始,皮孔或萼筒伸出黑灰色菌丝,进而其周围组织坏死形成黑斑.采后100天,黑斑病的发病率达28.86%.黑斑病是由链格孢Alternaria alternata(Fr.)Keissl.侵染引起的,链格孢在采前可经两条途径侵入苹果梨果实.一是在花朵开放时经花柱侵入,花后50天定殖于花柱的病原菌通过萼室间组织陆续进入心室,至采收时,心室中链格孢出现率可达45%;二是自果实膨大期开始侵入果皮,潜伏于皮下组织,至采收时萼端、胴部、梗端链格孢的带菌率分别为40%、24%和42.8%.  相似文献   

11.
In 1975 many tumours were observed in plants ofBegonia Schwabenland grown in Aalsmeer. Submersion of the roots ofNicotiana megalosiphon seedlings in a homogenate of tumorous tissue, induced tumours after two weeks. Short periods of submergence yielded results similar to those obtained after longer periods. Tumour homogenates lost their infectivity after ten min at 50°C. Aphids transmitted the infectious agent.Treatment with propylene oxide did not inhibit infectivity completely. Filtration through a 450 nm filter removed the infectious agent.Tobacco tumor virus or a viroid could not be isolated. Cultures ofCorynebacterium fascians, isolated from tumours ofN. megalosiphon were highly infectious and induced tumours in healthyN. megalosiphon andBegonia. Tumorous tissue homogenates ofPelargonium zonale, Dahlia sp.,Gladiolus sp., andLilium sp. also caused tumours inN. megalosiphon, from whichC. fascians was isolated. It was not possible to produce tumours inN. megalosiphon with homogenates from roses with symptoms of bud proliferation.Samenvatting In 1975 werden vele tumoren waargenomen inBegonia Schwabenland op Aalsmeerse bedrijven (Fig. 1). De infectiositeit van tumorweefsel kon goed en snel worden vastgesteld door de wortels van zaailingen vanNicotiana megalosiphon in een homogenaat van tumorweefsel te dompelen. Tumoren ontstonden na twee weken, de eindbeoordeling geschiedde na een maand (Fig. 2). Ook verschillende andereNicotiana spp.,Melilotus officinalis (Fig. 3) enPisum odoratum (Fig. 4) werden aangetast.Bij de infectiositeitstoets gaven zeer korte dompeltijden even goede resultaten als langere (Tabel 1). Infectieus sap verloor zijn infectievermogen na 10 min verhitting bij 50°C. Bladluizen brachten de smetstof over. Propyleenoxide verminderde de infectiositeit wel, doch onderdrukte deze niet totaal. Bij filtratie door een 450 nm filter bleef het infectieuse agens op het filter achter. Het tumor-inducerende agens was ook aanwezig in die delen van planten met tumoren welke gezond leken en het ging voor een gering deel over met zaad (Tabel 2).Uit tumoren konden wij geen tabakstumorvirus of een viroïde isoleren. Culturen vanCorynebacterium fascians, geïsoleerd uit tumoren vanN. megalosiphon bleken zeer infectieus en veroorzaakten tumoren inN. megalosiphon enBegonia. Homogenaten van tumorweefsel vanPelargonium zonale, dahlia (Fig. 5), gladiool (Fig. 6) enLilium Mid Century Hybrid Enchantment (Fig. 7) veroorzaakten ook tumoren opN. megalosiphon, waaruitC. fascians werd geïsoleerd. Met sap van kroeskopzieke rozen konden wijN. megalosiphon niet besmetten.  相似文献   

12.
Plant Viruses Transmitted by Whiteflies   总被引:18,自引:0,他引:18  
One-hundred and fourteen virus species are transmitted by whiteflies (family Aleyrodidae). Bemisia tabaci transmits 111 of these species while Trialeurodes vaporariorum and T. abutilonia transmit three species each. B. tabaci and T. vaporariorum are present in the European–Mediterranean region, though the former is restricted in its distribution. Of the whitefly-transmitted virus species, 90% belong to the Begomovirus genus, 6% to the Crinivirus genus and the remaining 4% are in the Closterovirus, Ipomovirus or Carlavirus genera. Other named, whitefly-transmitted viruses that have not yet been ranked as species are also documented. The names, abbreviations and synonyms of the whitefly-transmitted viruses are presented in tabulated form together with details of their whitefly vectors, natural hosts and distribution. Entries are also annotated with references. Whitefly-transmitted viruses affecting plants in the European–Mediterranean region have been highlighted in the text.  相似文献   

13.
During a survey conducted from 1998 to 2002, Fusarium proliferatum was found associated with young and adult palms belonging to the genera Chamaerops, Phoenix, Trachycarpus and Washingtonia showing symptoms of wilt and dieback. The fertility and toxicological profile of 36 strains representing different locations and hosts were studied. All of them except two, which were infertile, belonged to mating population D. Both mating types (MATD-1 and MATD-2) were isolated from the same host species, showing a high potential of genetic recombination in the field. Additionally, eight strains were fertile once crossed as female. Toxin analysis showed differences in the ability of strains to produce fumonisin B1, moniliformin, beauvericin, fusaric acid and fusaproliferin. Only 17 of them produced all the toxins analyzed. Pathogenicity tests were conducted on Phoenix dactylifera and P. canariensis using nine F. proliferatum Spanish strains and two reference strains from Saudi Arabia. Eight months after inoculation all strains caused disease, with palms showing lesions on the bases of leaves and development of wilt symptoms similar to those originally observed in affected plants. This is the first report on the occurrence of F. proliferatum on P. dactylifera in Spain and also the first report of this pathogen on C. humilis, P. canariensis, P. reclinata, T. fortunei, W. filifera and W. robusta.  相似文献   

14.
Isolates of an unidentified Rhizoctonia sp. (UR isolates) were obtained from creeping bentgrass and Kentucky bluegrass with reddish brown sheath and foliar rots. Because the UR isolates anastomosed with isolates of three varieties of Waitea circinata (var. oryzae, var. zeae, and var. circinata), colony morphology, hyphal growth rate at different temperatures, pathogenicity, sequence analysis of the internal transcribed spacers (ITS) region of ribosomal RNA genes (rDNA) were compared. The colony color of mature UR isolates was distinct from isolates of the other three varieties of W. circinata. In pathogenicity tests on creeping bentgrass, the severity of the disease caused by UR isolates was significantly higher than that caused by the three varieties of W. circinata. Sequence similarities of the rDNA-ITS region between UR isolates and between isolates within each variety were high (97–100%), but they were lower among isolates from UR and the varieties of W. circinata (88–94%). In a phylogenetic tree based on the rDNA-ITS sequences, UR isolates formed a cluster separate from each of the clusters formed by the three varieties of W. circinata. These results indicate that the UR isolates clearly differ from the three varieties of W. circinata. We therefore propose that the UR isolates be classified as new Rhizoctonia sp. that are closely related to W. circinata and that the disease on creeping bentgrass should be called Waitea reddish-brown patch disease (Sekikasshoku-hagusare-byo in Japanese).  相似文献   

15.
The epidemiology ofSitobion avenae and its natural enemies in winter wheat was studied in 1975, 1976 and 1977. Immigration was important until the end of flowering. The alate immigrants had apterous offspring. These became the driving force in population growth. Their offspring were mostly alatae which usually left the field. A model of the epidemic was developed. Quantitative relations between the aphids and their environment were obtained from literature or established in laboratory trials. The model simulated population development and population composition from the beginning of June till the population peak at the end of June or early in July. Because quantitative data on relations between aphids and their natural enemies and pathogens are scarce, and since the knowledge on wing formation is still limited, the population collapse could not be predicted. In the future, prognosis over a period of three weeks seems possible.Samenvatting De toenemende betekenis van graanbladluizen (vooralSitobion avenae) gepaard gaande met een sterke toename van het gebruik van insecticiden op granen maakte verbetering van de prognose over het schadelijk optreden wenselijk. Door gedetailleerde tellingen in het veld (Fig. 1–7) werden gegevens verkregen over het verloop van de epidemie en het optreden van natuurlijke vijanden in 1975, 1976 en 1977.Een immigratieperiode tot in de bloei kon worden vastgesteld. Daarna lijkt de aantrekkelijkheid van het gewas voor alate luizen te verminderen. De alate immigranten krijgen aptere nakomelingen. Deze vormen de stuwende kracht van de populatiegroei. De nakomelingen van apteren zijn merendeels alaat. Zij verlaten het gewas.Een model van de populatieontwikkeling gedurende de epidemie werd opgesteld. De relatiediagrammen Fig. 9 en 10 laten groei en ontwikkeling vanS. avenae en een predator (Syrphus corollae) zien. Kwantificering van de betrekkingen werd mogelijk door literatuurgegevens en laboratoriumexperimenten.Met het model kon de populatieontwikkeling vanS. avenae vanaf begin juni tot aan de populatiepiek in 1975, 1976 en 1977 vrij goed worden gesimuleerd (Fig. 12). Ook de populatieopbouw kon worden gesimuleerd (Fig. 14). De teruggang van de populatiedichtheid blijkt moeilijker te voorspellen door het ontbreken van gegevens over natuurlijke vijanden.Het lijkt waarschijnlijk dat in de toekomst met het model een prognose over de piek van de bladluispopulatie circa 3 weken tevoren mogelijk zal zijn.  相似文献   

16.
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.  相似文献   

17.
Barley yellow dwarf disease is one of the most important problems confronting cereal production in Iran. Barley yellow dwarf virus-PAV (BYDV-PAV) and Cereal yellow dwarf virus-RPV (CYDV-RPV) are the predominant viruses associated with the disease. One isolate of BYDV-PAV from wheat (PAV-IR) and one isolate of CYDV-RPV from barley (RPV-IR) were selected for molecular characterisations. A genome segment of each isolate was amplified by PCR. The PAV-IR fragment (1264 nt) covered a region containing partial genes for coat protein (CP), read through protein (RTP) and movement protein (MP). PAV-IR showed a high sequence identity to PAV isolates from USA, France and Japan (96–97%). In a phylogenetic analysis it was placed into PAV group I together with PAV isolates from barley and oats. The fragment of RPV-IR (719 nt) contained partial genes for CP, RTP and MP. The sequence information confirmed its identity as CYDV. However, RPV-IR showed 90–91% identity with both RPV and Cereal yellow dwarf virus-RPS (CYDV-RPS). Phylogenetic analyses suggested that it was more closely related to RPS. These data comprise the first attempt to characterise BYD-causing viruses in Iran and southwest Asia. The nucleotide sequence data reported appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession numbers AY450425 and AY450454  相似文献   

18.
Research on root rot pathogens of peas in the Netherlands has confirmed the prevalence ofFusarium solani, F. oxysporum, Pythium spp.,Mycosphaerella pinodes andPhoma medicaginis var.pinodella. Aphanomyces euteiches andThielaviopsis basicola were identified for the first time as pea pathogens in the Netherlands. Other pathogens such asRhizoctonia solani andCylindrocarpon destructans were also found on diseased parts of roots. F. solani existed in different degrees of pathogenicity, and was sometimes highly specific to pea, dwarf bean of field bean, depending on the cropping history of the field.A. euteiches was specific to peas, whereasT. basicola showed some degree of physiological specialization.  相似文献   

19.
Tsror  Leah  Aharon  M.  Erlich  Orly 《Phytoparasitica》1999,27(3):215-226
Potato seed tubers are imported to Israel from northern Europe and planted in spring; tubers harvested early from the spring crop are used as seed for the autumn crop. Although only seed lots registered as certified are imported, a previous survey (1984–1994) indicated that most imported lots were affected by latent or active infections caused byErwinia carotovora,Streptomyces scabies, Rhizoctonia solani, Fusarium spp. andSpongospora subterranae. The survey was extended until 1998, and included additional pathogens:Ralstonia solanacearum,Helminthosporium solani, Colletotrichum coccodes andVerticillium dahliae. Most of these pathogens were also monitored in domestic seed tubers, and are reported for the first time. Brown rot was not observed in any of the imported lots. Blackleg and soft rot caused byErwinia spp. were detected in most of the imported lots; however, less than 7% of the lots were contaminated at high levels, while approximately 65% were contaminated at moderate levels. Common scab was detected in most of the imported lots; 51% of the imported lots were contaminated at moderate or high levels, whereas only 6.5% of the domestic seed lots were contaminated at these levels. Black scurf was detected in most of the imported lots; on average, 47.3%, 44.2% and 1.4% of the lots were contaminated at low, moderate and high levels, respectively, and only 7.1% were disease-free. In contrast, most of the domestic lots were either disease-free (45.4%) or had a low disease incidence (37.3%). Only 16.7% of the lots were moderately infected and 0.2% were highly contaminated. Silver scurf was observed in most of the imported lots during all years of the survey, with no differences among the producing countries; on average, 22.7%, 66.1% and 7.5% of the lots were contaminated at low, moderate and high levels, respectively, and only 3.7% were disease-free. Most of the domestic lots (76%) were disease-free and only 6.6% were infected at moderate or high levels. Black dot was observed in a considerable portion of the shipments from Holland during all years of the survey, particularly in 1998, when 34% of the lots were infected. The shipments from France and Germany were infected at low levels, except in 1998, when 19% and 11% of the lots, respectively, arrived infected. In shipments from Scotland and Ireland low incidences of the disease were observed in 1994 and 1995. In the domestic lots, black dot incidence was low (<2.4%) except in 1996, when 11% of the lots were infected.V. dahliae was monitored only in domestic seed tubers. The incidence of disease-free lots was 56–64%, whereas in 20–30% of the lots the level of infection was <5%, and in 6–16% of the lots the level was >5%. The survey findings demonstrate transmission of seedborne pathogens; most of these pathogens can become established in the soil and eventually cause severe outbreaks of disease in potatoes grown in Israel. http://www.phytoparasitica.org posting May 16, 1999.  相似文献   

20.
Corynebacterium fascians, which causes leafy gall, has been shown to be responsible for the unusual symptoms recently found in lilies. The symptoms are described and the different bacterial isolates compared by biochemical, serological and pathogenicity experiments. No evidence could be found for the existence of specialized strains even though considerable variation in virulence could be demonstrated. Although the role of variation in susceptibility of the different lily cultivars should not be underestimated, it would appear that high inoculum levels ofC. fascians in the soil may be largely responsible for these outbreaks.Also included in this study are the results of biochemical, serological and pathogenicity experiments ofC. fascians which has been isolated fromKalanchoe, Euphorbia, Brodiaea, Hebe andVerbascum.Samenvatting Reeds een aantal jaren was in lelies een woekering in stengelbollen bekend, die echter sporadisch voorkwam en economisch van weinig betekenis was. Tijdens de zomer van 1977 echter trad de ziekte op één enkel perceel zo ernstig op dat zeer aanzienlijke oogstderving het gevolg was. Behalve de stengelbol kan ook de hoofdbol misvormd zijn. Bovendien kunnen misvormde stengelbollen lange spruiten vormen, zgn. sabeltandvorming. Soms is het wortelstelsel gereduceerd; in de kas zijn verdikte stengels waargenomen. De ziekte staat nu bekend onder de naam woekerziekte.Door de PD te Wageningen en het LBO te Lisse werd de bacterieCorynebacterium fascians (Tilford) Dows. uit het zieke materiaal geïsoleerd. In gezamenlijk onderzoek werd nagegaan of de bacterie de veroorzaker is van bovengenoemde symptomen en of hier sprake is van een op lelie gespecialiseerde stam.Biochemische en serologische vergelijkingen tussen isolaten vanC. fascians uit lelie,Kalanchoe, Euphorbia, Brodiaeea, Hebe enVerbascum laten zien dat er zeer weinig verschillen bestaan. Alle isolaten reageren op een standaard antiserum met titers variërend tussen 1: 640–1: 5120.Een oriënterende inoculatieproef werd uitgevoerd op het LBO in 1977. Daarna werden op de PD 10 van de 25 isolaten uit lelie en 8 uit andere waardplanten getoetst op lelie, chrysant en lathyrus. Uit de inoculatieproeven blijkt, dat de bacterie de veroorzaker is van de waargenomen symptomen. Tussen de isolaten blijkt een groot verschil in pathogeniteit te bestaan (12–100% aantasting), zonder dat dit aan herkomst gebonden is. Het voorkomen van op lelie of andere waardplanten gespecialiseerde stammen is daarom niet aan te nemen.In hoeverre de hevige aantasting een gevolg is van een opbouw van de bacterie-populatie door een te nauwe vruchtwisseling en mechanische rooimethoden moet worden nagegaan.  相似文献   

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