A multi-phasic approach reveals that apple replant disease is caused by multiple biological agents, with some agents acting synergistically

Apple replant disease (ARD) has been reported from all major fruit-growing regions of the world, and is often caused by a consortium of biological agents. The aim of this study was to investigate the etiology of ARD in South Africa in six orchard soils, using a multiphasic approach under glasshouse conditions. This approach first involved determining the ARD status of the soils by monitoring apple seedling growth responses in non-treated soil versus growth in pasteurized soil, as well as in 15% non-treated soil that was diluted into pasteurized soil. Subsequently, the potential for specific organisms to function as causal agents of ARD was investigated using (i) biocide applications, (ii) quantitative real-time PCR (qPCR) analyses of ARD ‘marker’ microbes (Pythium irregulare, Pythium sylvaticum, Pythium ultimum, Pythium vexans, Rhizoctonia solani AG-5 and the genera Cylindrocarpon and Phytophthora), (iii) nematode analyses, (iv) isolation of actinomycetes and (v) pathogenicity testing of actinomycetes individually, and when co-inoculated with P. irregulare or Cylindrocarpon macrodidymum. The analyses showed that the soils could be grouped into low, moderate and severe ARD soils, with each group containing two soils. Several lines of evidence suggested that actinomycetes are not involved in ARD in South Africa. Multiple biological agents were determined to contribute to ARD including (i) oomycetes (Phytophthora and Pythium) that are important based upon their widespread occurrence, and the fact that metalaxyl application improved seedling growth in four soils (ii) the genus Cylindrocarpon that was also widespread, and for which a synergistic interaction with P. irregulare was demonstrated and (iii) occasionally parasitic nematodes, mainly Pratylenchus penetrans, Pratylenchus scribneri and Pratylenchus delattrei, since fenamiphos application improved seedling growth in two orchards. qPCR analyses of the ARD marker microbes showed that R. solani AG-5 is absent from South African orchards, and that P. ultimum is widespread, even though the latter species could not be detected in previous isolation studies. The other marker microbes were also widespread, with the exception of P. sylvaticum. qPCR quantification of the marker microbes could not be correlated with the severity of ARD in any manner. qPCR analyses did, however, show that possible root pruning pathogens such as P. irregulare, P. sylvaticum and P. ultimum had much lower DNA concentrations in seedling roots than P. vexans and the genera Cylindrocarpon and Phytophthora.     

福建口岸进境线虫疫情分析

基于对2004~2013年福建出入境检验检疫局辖区口岸进境线虫疫情截获的统计分析,旨在掌握进境线虫截获的种类和规律,为线虫检疫监管措施完善提供理论依据。统计表明,2004~2013年福建各口岸共送检项目为线虫类样品1 550批次,样品种类共计87种,主要包括植物种子、木片、木质包装、种苗等。检出线虫疫情352批次,检出率高达22.71%。截获线虫涵盖11个属,来自美国、越南、日本等40多个国家和地区。说明进境线虫疫情复杂,应对进境植物种子、木片、木质包装等加强植物检疫监管,以防止线虫疫情随寄主携带入境。     

利用大豆分子连锁图定位大豆孢囊线虫4号生理小种抗性QTL

大豆孢囊线虫 (SCN ,HeteroderaglycinesIchinohe)是一种土传的定居性内寄生线虫 ,是引起大豆黄萎病的病原 ,是大豆生产上危害最大的病害之一。SCN的生理小种多达十几种 ,在我国大豆孢囊线虫病原主要为 4号生理小种 ,它是现有生理小种中致病力最强的小种。经典遗传学研究已经确定大豆孢囊线虫抗性基因由 1- 4对核基因控制 ,估计有 10个以上的抗性座位。近年来分子标记技术及QTL定位方法的发展为深入研究该病害的抗性遗传规律提供了有效的手段 ,这对加速我国抗大豆抗孢囊线虫新品种培育具有重要意义。本研究以晋豆 2 3×ZDD2 315组合F2 群体 (2 5 3个单株 )为试验材料 ,其中灰布支黑豆 (ZDD2 315 )是我国山西省农家品种 ,对大豆孢囊线虫 4号生理小种表现为高抗。利用塑料钵柱法进行SCN抗性鉴定 ,构建大豆孢囊线虫抗性主座位所在区域的分子图谱 ,并进行SCN的QTL定位及遗传效应分析。根据已发表的大豆A和G连锁群的分子遗传图谱 ,应用BSA法 ,获得了 8个与SCN4号生理小种抗性基因相关的SSR标记 ,它们是Satt0 38(176bp/ 182bp) ,Satt30 9(130bp/ 135bp) ,Satt6 10 (2 4 0bp/ 2 2 2bp) ,Sat_14 1(189bp/ 184bp) ,Satt187(30 0bp/ 2 5 0bp) ,Satt315 (2 5 3bp/ 2 4 8bp) ,Satt6 32 (2 86bp/ 2 90bp)和Sat_16 2(2     

施用化肥对下辽河平原稻田土壤线虫群落产生的影响

通过田间小区试验,研究了施用化肥对下辽河平原稻田土壤线虫群落组成产生的影响。结果表明,共获得15科、19属,其中绕线属、小杆属、垫刃属为优势属。线虫总数、食细菌线虫、植物寄生线虫和杂食-捕食线虫数量在不同处理之间存在极显著差别(p<0.01),三个施肥处理中的线虫总数显著高于无肥处理(对照)。在水稻收获后土壤线虫数量变化对不同种类肥料具有不同的响应。     

Evaluation and identification of potential organic nematicidal volatiles from soil bacteria

Naturally occurring volatile compounds with nematicidal activities (NAs) are of significant economical importance in agriculture and forestry. In this study, volatile organic compounds (VOCs) produced by 200 isolates of soil bacterial were evaluated in in vitro experiments. Our results identified that among the 200 bacterial isolates, 149 (74.5%) and 165 (82.5%) exhibited a greater than 20% NA against the free-living nematode Panagrellus redivivus and the pinewood nematode Bursaphelenchus xylophilus, respectively. Among them, 22 isolates showed 100% NA against P. redivivus and seven isolates showed 100% NA against B. xylophilus. When exposed to nematicidal volatiles, nematodes gradually reduced their movements within 1-12 h after treatment, and most stopped moving completely after 24 h. Our analysis indicated significant variation in nematicidal capability of the VOCs not only among bacterial species but also among isolates of the same species. Volatiles of representative isolates were extracted using solid-phase micro-extraction (SPME) and their structures identified using gas chromatography-mass spectrometry (GC-MS). The detected so volatile compounds included alcohols, aldehydes, ketones, alkenes and ethers. Of the 20 VOCs with strong NA (?80%), nine (phenol, 2-octanol, benzaldehyde, benzeneacetaldehyde, decanal, 2-nonanone, 2-undecanone, cyclohexene and dimethyl disulfide) displayed 100% NA to both model nematodes. Furthermore, five compounds (terpineol, benzeneethanol, propanone, phenyl ethanone and nonane) showed different NA to B. xylophilus (75-100%) and P. redivivus (17.02-100%).     

Fungal-feeding habits of six nematode isolates in the genus Filenchus

The family Tylenchidae is a large group of soil nematodes but their feeding habits are not fully known. We studied the fungal-feeding abilities of nematodes in the genus Filenchus. We measured population growth rates (PGRs) of six nematode isolates, representing three Filenchus species, when feeding on seven fungal species on two types of culture media. On Potato Dextrose Agar (PDA) Filenchus misellus, Filenchus discrepans and an unidentified Filenchus sp. generally showed moderate to large PGRs on saprophytic fungi (Rhizoctonia solani, Chaetomium globosum, Coprinus cinereus, Flammulina velutipes) and low PGRs on plant-pathogenic fungi (Fusarium oxysporum, Pythium ultimum). In soil medium amended with chopped soybean plant material or wheat bran, the status of most of the fungi as food for the nematodes was similar to that on PDA, although PGRs tended to be lower in the soil medium. However, C. globosum, a good food on PDA, only supported low PGR in soil for each of the three nematodes. The PGRs of F. misellus on C. globosum in soil were still low even when types and amounts of organic matter amendments were varied. A nematophagous fungus, Pleurotus ostreatus (oyster mushroom), was determined to be a food for Filenchus on PDA or in soil, based on PGR measurements corrected for extraction efficiency. To determine whether fungal species and culture media affected nematode extraction efficiencies and, consequently, the apparent PGRs, we compared efficiencies between R. solani, C. globosum and C. cinereus, and between PDA and soil. The relatively low extraction efficiencies across fungal species in soil seemed responsible for the lower nematode PGRs in soil than on PDA. On PDA generally, fungal species did not affect the assessment. In soil, effects of fungal species on extraction were significant, but not consistent, across nematode species. Nevertheless, the extraction efficiency differences in soil were considered not to affect assessment of the three fungi as food for the nematodes. The confirmation that three Filenchus species reproduce by feeding on fungi in soil suggests that fungal-feeding is not an unusual habit in the field, in this genus. We believe that in community studies, nematodes in the genus Filenchus should be considered fungal feeders or root and fungal feeders, rather than only plant feeders. Our confirmation of fungal-feeding habits in the genus Filenchus supports the hypotheses that plant-feeding nematodes evolved from those feeding on fungi.     

捕食线虫真菌酯酶同工酶谱和可溶性蛋白质谱分析

 本文对5个属14个种共33株捕食线虫真菌采用聚丙烯酰胺凝胶电泳技术进行了酯酶同工酶谱和可溶性蛋白质谱分析。结果表明,酯酶同工酶谱带少,但各属的特征谱带是明显的,在同属不同种之间,多数种都有自已的特征谱带与其它种相区别,同种不同菌株间没有明显差异;蛋白质谱带较多,在每个属中均有1~2条特征谱带,属间的谱带差异明显,同属不同种和同种不同菌株间蛋白质谱带都表现出多型性。     

嘉峪关市洋葱根际土壤线虫种类与种群密度 动态变化规律

对甘肃省嘉峪关市洋葱根际土壤线虫种类及其在洋葱生长期间的种群密度动态进行了研究，
结果表明，从洋葱根际土壤样品中共分离到植物寄生线虫2 目4 科5 属，非植物寄生线虫3 目5 科12 属。
各类线虫在洋葱移栽前数量最少，在洋葱鳞茎膨大期数量最多。燕麦真滑刃线虫（Aphelenchus avenae）
是该地区洋葱根际土壤植物寄生线虫的优势种，中杆属线虫（Mesorhabditis spp.）为该地区洋葱根际土壤
非植物寄生线虫的优势种。在洋葱的各个生长时期，洋葱根际土壤中非植物寄生线虫的密度均大于植物寄
生线虫。瓦斯乐斯卡指标（WI 值）为8.09，表明甘肃省嘉峪关市洋葱种植田土壤健康指数较高，土壤健
康状况良好。