Plum pox virus detection in dormant plum trees by PCR and ELISA

An immunocapture polymerase chain reaction (IC-PCR) protocol and ELISA were compared for their effectiveness in detecting plum pox virus (PPV) in dormant plum material. Although the IC-PCR was about one thousand times more sensitive than ELISA, PPV was detected by ELISA in 71–80% of bark samples collected in December, January and March 1996/97 from pot-grown rootstock trees inoculated with PPV the previous March, compared with 85–86% detection in the same samples by IC-PCR. In similar samples from one-year-old shoots taken from infected branches of orchard trees, 66–81% were positive by ELISA compared with 81–87% by IC-PCR. With bulked samples taken from the fibrous roots of the pot-grown trees, PPV was detected in 92–100% of samples by IC-PCR in winter compared with only 38–65% by ELISA. These results were confirmed in samples from the roots and shoots of the same trees in 1997/98. Three samples per shoot would have been sufficient to detect PPV by ELISA in 87 of the 88 infected shoots tested during the two winters. However, infected shoots are irregularly distributed in diseased trees and PCR assays of root samples offer the potential for improving the reliability of identifying trees infected with PPV.     

Resistance to Plum pox virus in plants expressing cytosolic and nuclear single‐chain antibodies against the viral RNA NIb replicase

The expression of engineered single‐chain variable fragments specific to the NIb RNA replicase of Plum pox virus (PPV) (scFv2A) in transgenic plants was successfully used as a strategy to interfere with viral infection. Different scFv2A fusion proteins were constructed to target those subcellular compartments, such as the cytosol, endoplasmic reticulum (ER) membrane structures and the nucleus, where NIb protein presumably accumulates. Several transgenic lines of Nicotiana benthamiana plants expressing the scFv2A targeted to the cytosol (2A lines), ER (6K2 lines) and nucleus (NLS lines) were obtained. The protective effect of scFv expression was determined by mechanical virus inoculation in five 2A, three 6K2 and four NLS transgenic lines. The strongest resistance was afforded with the 2A‐3 (six non‐infected plants out of 10), 6K2‐1 (17 out of 33) and NLS‐11 (16 out of 19) transgenic lines. The success of this interference with PPV infection opens new possibilities for the control of this RNA virus and could be exploited not only to confer resistance in transgenic plants, but also to elucidate the role of the non‐structural NIb protein in different cell compartments during viral infection.     

Elimination of <Emphasis Type="Italic">Plum pox virus</Emphasis> through in vitro thermotherapy and shoot tip culture compared to conventional heat treatment in apricot cultivar Bebecou

The effectiveness of in vitro thermotherapy (explants at 35–37°C for 20 days) in obtaining propagating material of apricot (Prunus armeniaca L.) cultivar Bebecou that is free of Plum pox virus (PPV) was compared to a conventional heat treatment technique (potted plants at 30–35°C for 8 weeks). An improved protocol for in vitro thermotherapy was combined with shoot tip culture. The protocol is 5.8 times more effective than conventional thermotherapy while taking half the time and is likely to have a high commercial impact for nurseries.     

ICTV第八次报告的最新植物病毒分类系统

 本文介绍了国际病毒分类委员会第八次报告中的最新植物病毒分类系统18个科、81个属,以及亚病毒感染因子的类病毒和病毒卫星。与第七次报告相比新增的3个科、9个属分别是:矮缩病毒科、芜菁黄花叶病毒科、线形病毒科、番茄伪曲顶病毒属、香蕉束顶病毒属、塞尔病毒属、内源RNA病毒属、葡萄斑点病毒属、柑橘病毒属、葡萄卷叶病毒属、温州蜜柑矮缩病毒属、樱桃锉叶病毒属。     

Further observations on variation of lettuce mosaic virus in relation to lettuce (Lactuca sativa), and a discussion of resistance terminology

Two potyvirus isolates from endive, originating from southern France (Ls252) and from the Netherlands (Ls265), that were highly and poorly pathogenic on lettuce, respectively, were compared with a common isolate (Ls1) of lettuce mosaic virus (LMV) and with two highly deviant Greek isolates fromHelminthia (Picris) echioides (Gr4) and endive (Gr5), earlier recognized as LMV. The isolates could not be distinguished by particle morphology and serology, and were all identified as LMV. Leaf curling, plant stunting and necrosis were more characteristic of the virus than mosaic. The isolates studied varied considerably on differential host species and a range of lettce cultivars including pathotype differentials of Pink et al. [1992b]. Ls1 and Ls265 reacte largely as pathotype II, including the common strain of the virus, but Ls265 was least pathogenic on lettuce. Ls252 fitted pathotype IV and was very similar to LMV-E (the Spanish strain). The Greek isolates were very similar to each other in causing very severe symptoms on some non-lettuce hosts and a number of lettuce cultuvars. In lettuce variectal reaction Gr4 resembled pathotype I, but Gr5 severely affected Salinas 88, resistant to pathotypes I, II and III, and it appears to be a novel pathotype. Genetic interaction between lettuce and LMV is not following a simple yes-or-no pattern, and it is not a mere matter of resistance versus susceptibility. Adoption of a more realistic resistance terminology is proposed. None of the lettuce cultivars tested was resistant to the most pathogenic isolate Ls252, but resistance to it was found in 2 out of 12 wildLactuca species tested (Lactuca perennis andL. tatarica) while the symptomless plants ofL. perennis clearly reacted in ELISA.     

番茄SlAGO1的表达分析及其抗番茄黄化曲叶病毒(TYLCV)功能研究

 本研究运用 MEGA 7.0 进行多序列比对并构建系统进化树,利用实时荧光定量 PCR(qRT-PCR)分析SlAGO1在番茄组织中的表达水平及接种TYLCV后的防御响应;通过沉默番茄八氢番茄红素脱氢酶基因SlPDS,建立‘矮番茄'沉默体系,采用 qRT-PCR 分析SlAGO1在沉默后对TYLCV表达的影响。系统进化树结果显示SlAGO1a/b(SlAGO1)氨基酸序列同源性极高,暗示其为同一个基因在染色体上的多个拷贝;qRT-PCR分析表明,SlAGO1在花、叶中显著表达,且受TYLCV的诱导表达;VIGS沉默SlAGO1后接种TYLCV侵染性克隆,植株表现出明显的病毒症状,qRT-PCR分析显示病毒含量显著高于对照,表明SlAGO1在番茄植株抗病毒中发挥重要作用。研究结果可为番茄抗病毒机制研究及番茄抗病毒育种奠定基础。     

Systemic resistance to bacterial leaf speck pathogen in Arabidopsis thaliana induced by the culture filtrate of a plant growth-promoting fungus (PGPF) Phoma sp. GS8-1

The culture filtrate (CF) from the plant growth-promoting fungus Phoma sp. GS8-1 was found to induce systemic resistance in Arabidopsis thaliana against the bacterial leaf speck pathogen Pseudomonas syringae pv. tomato DC3000 (Pst), and the underlying mechanism was studied. Roots of A. thaliana were treated with CF from GS8-1, and plants expressed a clear resistance to subsequent Pst infection; disease severity was reduced, and proliferation of pathogen was suppressed. Various mutants of A. thaliana were used to test whether the CF induced resistance through one of the known signaling pathways: salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). The CF was fully protective against Pst in Arabidopsis mutants jar1 and ein2 similar to wild-type plants. However, its efficacy was reduced in plants containing transgene NahG. Examination of systemic gene expression revealed that CF modulates the expression of SA-inducible PR-1, PR-2 and PR-5 genes, the JA/ET-inducible ChitB gene, and the ET-inducible Hel gene. Moreover, the expression of these genes was further enhanced upon subsequent stimulation after attack by Pst. Our data suggest that in addition to a partial requirement for SA, the signals JA and ET may also play a role in defense signaling in Arabidopsis.     

Effects of fungicide on growth of Leptosphaeria maculans and L. biglobosa in relation to development of phoma stem canker on oilseed rape (Brassica napus)

Controlled‐environment and field experiments were done to investigate effects of the fungicide Punch C (flusilazole plus carbendazim) on growth of Leptosphaeria maculans and L. biglobosa in oilseed rape. In controlled‐environment experiments, for plants inoculated with L. maculans, fungicide treatment decreased lesion size and amount of L. maculans DNA in leaves; for plants inoculated with L. biglobosa, fungicide did not affect lesion size or amount of pathogen DNA. When release of ascospores was monitored using a Burkard spore sampler, the timing and pattern of ascospore release differed between the four seasons. In 2006/2007, the majority of ascospores released were L. maculans, whilst in 2007/2008 the majority were L. biglobosa; in both seasons L. maculans ascospores were released before L. biglobosa ascospores. In field experiments in 2002/2003 and 2003/2004, fungicide treatment decreased severity of stem canker on cv. Apex, but gave no significant yield response. In 2006/2007 and 2007/2008, fungicide treatment decreased phoma leaf spot incidence in autumn and stem canker severity at harvest, and increased yield. Fungicide treatment decreased stem canker severity more on cv. Courage, with a good yield response, than on cv. Canberra. In 2002/2003 and 2003/2004, fungicide treatment decreased the frequency of spread of L. maculans into stem pith tissues and in 2006/2007 fungicide decreased the amount of L. maculans DNA in stem tissues (measured by quantitative PCR). These results are used to suggest how effects of fungicides on interactions between L. maculans and L. biglobosa might affect severity of phoma stem canker and yield response.