Systemic spread of Plum pox virus (PPV) in Mariana plum GF 8-1 in relation to shoot growth

Infection of Prunus spp. by Plum pox virus (PPV) is characterized by an uneven distribution of the virus within the tree and branches. In order to gain a better understanding of this distribution, a method for modelling tree growth was used. PPV spread was followed within susceptible Mariana plum clone GF 8-1 shoots for 4 months after inoculation. Shoot growth was unaffected by the presence of the virus. Symptoms appeared on leaves produced in the most actively growing parts of the shoots, i.e. at the beginning of the season. PPV was detected in leaves other than those showing symptoms. The proportion of leaves with detectable virus decreased from the zone showing symptoms, with 100% ELISA-positive responses, to the shoot tip with no detectable virus in leaves produced between 111 and 127 days after inoculation. Furthermore, a higher proportion of positive ELISA results was obtained below the zone showing symptoms (77%) compared with 50% above. PPV was detected in 95% of the most vigorous shoots 71 days after inoculation compared with 37% of slower-growing, later-produced shoots.     

Effects of aqueous extracts and decomposition of Mikania micrantha H.B.K. debris on selected agronomic crops

Laboratory and greenhouse experiments were conducted to determine the effects of aqueous extract and the debris of Mile-a-Minute ( Mikania micrantha H.B.K.) on the germination and growth of four test species, viz. tomato ( Lycopersicon esculentum Mill.), Chinese cabbage ( Brassica chinensis L.), corn ( Zea mays L.) and long bean ( Vigna sesquipedalis L.). Germination percentage, radicle length and fresh weight of two crops, Chinese cabbage and tomato, decreased progressively when plants were exposed to increasing concentrations (12.5, 25, 37.5 and 50 g L⁻¹) of aqueous extract of Mikania , but did not affect those of corn and long bean seedlings. The emergence of tomato and Chinese cabbage was greatly reduced when Mikania debris was incorporated into the soil, irrespective of the amount of debris and the decomposition period. In contrast, the emergence of corn and long bean seedlings was not affected. The application of fertilizer (NPK 15 : 15 : 15) enhanced the fresh weight of all seedlings tested as compared with those not supplied with the fertilizer. Four compounds were identified in the leaf extract of Mikania , viz. caffeic acid, p -hydroxybenzaldehyde, resorcinol and vanillic acid.     

Effects of weed control practices on surface-dwelling arthropod predators in tomato agroecosystems

Weed control, an important practice in agroecosystems to protect crop production, is usually achieved with herbicides. However, these pesticides are expensive, pose potential risks to the environment, may affect some beneficial organisms indirectly, and decrease overall arthropod biodiversity, including pests and their natural enemies, by removing weeds that might act as hosts or shelters for many organisms. The activity density response of important surface-dwelling arthropod predators (ground beetles [Coleoptera: Carabidae], ants [Hymenoptera: Formicidae] and spiders [Arachnida: Araneae]) to herbicides (trifluralin and paraquat), and to two alternative weed management practices (rye straw mulch and mechanical treatment to maintain weeds below threshold levels, in comparison with an untreated check), was assessed using pitfall traps. The mulch treatment had the greatest effect on activity density, reducing the number of predators trapped significantly (P<0.05). Herbicide use resulted in significant (P<0.05) reductions in the activity density of ground beetles. Most predators were trapped in the check plots — which had the highest weed biomass, followed in turn by numbers trapped in the threshold weed control treatment, the full herbicide application and the mulch treatment plots. http://www.phytoparasitica.org posting July 10, 2002.     

麦二叉蚜传播玉米矮花叶病毒的机制

用胶体金标记法和荧光抗体标记法研究了麦二叉蚜(Schizaphis graminum)传播玉米矮花叶病毒(Maize dwaft mosaic virus,MDMV)的机制。麦二叉蚜传播玉米矮花叶病毒需要辅助成份-蛋白酶(Helper component-proteinase,HC-Pro)的参与。在电镜下观察到HC-Pro可以与MDMV粒子结合。用FITC标记的HC-Pro抗体和MDMV抗体证明,HC-Pro可以直接结合到蚜虫口针上;而MDMV粒子不能直接结合到蚜虫口针,必须在HC-Pro的辅助下才能结合到蚜虫口针上。这为HC-Pro在蚜虫传毒过程中起桥梁作用提供了新的证据。MDMV粒子主要吸附在蚜虫口针的尖端和中间部分。     

晋南冬麦区大麦黄矮病毒流行株系监测及防治策略探讨

连续5年(1996～2000年)采集晋南冬麦区小麦黄矮病标样,采用生物学和血清学(酶联免疫吸附法)相结合的诊断方法对该地区的大麦黄矮病毒流行株系进行了鉴别。结果表明,该小麦黄矮病流行区近五年以GAV株系为主流株系,兼有少量GPV、PAV和混合株系存在。同时对小麦抗黄矮病新品种“临抗1号”进行了GPV和GAV两种株系的抗性测定,明确了该品种兼抗GPV和GAV两种株系。根据小麦黄矮病发生现状,提出了一套以选育推广抗耐病品种为主,以药剂防治为辅的综合防治措施。以期为当地小麦生产服务。     

胶体金免疫层析法快速检测烟草环斑病毒

采用柠檬酸三钠还原法制备胶体金颗粒 ,标记烟草环斑病毒的抗体 ,制成免疫层析检测试纸条。检测粗提纯病毒的灵敏度为 1 0 0 0ng/ml,病汁液稀释 1 0 0 0倍后仍可快速检出。对大豆病种子、烟草冻干病叶等不同材料进行检测也有良好的效果 ,1～ 2min即可出现结果。用 9种不同的病毒进行测试 ,未出现非特异性反应。     

25％啶菌噁唑乳油防治番茄灰霉病药效试验

田间试验表明25%啶菌唑乳油对番茄灰霉病有良好的防治效果,53.3～106.7mL/667m23次药后防效79%以上。     

北方地区小西葫芦黄花叶病毒的酶联检测和西瓜品种抗病性鉴定

应用DAS-ELISA对分别于1998年在河南、陕西和1999年在河南、陕西、河北和山西采集的葫芦科病毒病样本84份、186份进行小西葫芦黄花叶病毒的检测,表明该病毒在这些地区广泛发生,ZYMV阳性检出率分别为79.8%和57.5%熏在北京和河南临颖县ZYMV发生率较低熏≤23.1%,在其余地区即河北石家庄,河南郑州、开封、孟津,山西运城,陕西西安其阳性检出率在40.0%～92.9%之间。除冬瓜样本没有ZYMV外,西瓜、甜瓜、南瓜、丝瓜、小西葫芦、苦瓜、黄瓜和瓠子均受到ZYMV的侵染。不同地区、年份和作物之间ZYMV阳性检出率存在差异。对18份西瓜品种的抗ZYMV温室人工接种鉴定的试验表明,目前推广的一些品种对ZYMV缺乏抗病性。     

Purification and some properties of Papaya meleira virus, a novel virus infecting papayas in Brazil

'Meleira', or 'sticky disease', is currently the most damaging papaya disease in the mid-eastern Brazilian growing regions. Consistent disease transmission via latex injection, presence of similar isometric particles in the laticiferous vessels of diseased plants, and detection of double-stranded DNA in naturally and experimentally infected papaya trees suggest that a virus is the causal agent. Conclusive evidence for viral aetiology was previously lacking, mostly because every attempt to purify the putative virus from infected papayas had failed. Following the successful purification and partial characterization of the meleira virus, healthy papaya seedlings injected with purified virus particles later developed typical symptoms of the disease. Negatively stained, isometric, full and 'empty' purified virus particles measured 42 and 38 nm, respectively. The viral genome was a single dsRNA molecule of about 12 kbp. Several capsid proteins, ranging in size from 14·4 to 45 kDa, were consistently revealed by PAGE. Papaya meleira virus (PMeV) appears to represent a novel group of viruses, with no known similar counterpart among known plant-, vertebrate-, invertebrate- or prokaryote-infecting viruses.     

Association of a Geminivirus with a Leaf Curl Disease of Sunn Hemp (Crotalaria juncea) in India

Natural occurrence of a geminivirus causing severe leaf curl disease on sunn hemp (Crotalaria juncea) was recorded in India. The association of a geminivirus with the disease was demonstrated by whitefly transmission tests and polymerase chain reaction (PCR) amplification of DNA fragments of expected sizes with three pairs of degenerate geminivirus primers. The PCR-amplified viral DNA fragments were further characterized by Southern hybridization with a geminivirus probe consisting of the cloned coat protein (CP) gene of Indian tomato leaf curl virus (ITLCV). Restriction fragment length polymorphism analysis of a PCR-amplified CP fragment revealed that the geminivirus from sunn hemp was different than ITLCV.