根结线虫在中国的一新纪录种——拟禾本科根结线虫Meloidogyne graminicol

 本文描述了采自海南省三亚市葱(Allium tistulosum)上的拟禾本科根结线虫Meloidogyne graminicola。该种雌虫的会阴花纹多为上下长的卵圆形;线纹细弱,通常平滑连续,但在局部区域骤然出现将线纹截断的短线纹;侧区不明显;侧尾腺口小,相隔很近。雄虫的头冠与头区等宽,头区很低、光滑或有2条不明显的环纹。二龄幼虫的尾相当长,尾透明末端的界限通常明显,尾端细长,末端呈细棍棒状。拟禾本科根结线虫在中国属首次报道,其寄主葱及其所属的百合科为拟禾本科根结线虫寄主植物的新纪录种和新纪录科。     

寄生在柑桔根上的根结线虫新种——简阳根结线虫

 简阳根结线虫Meloidogyne jianyangensis n.sp.采自四川简阳县柑桔园的柑桔根上。雌虫的会阴花纹近圆形,线纹平滑、纤细,背腹线纹通常连贯。以尾尖处向两侧有脊状放射形条纹,条纹数目不定、在阴肛区的背侧有半圈脊状条纹。在放射状的条纹间,线纹有时不连贯,有如许多小刻点。尾觉器距离很近。雄虫头冠高,唇盘和中唇融合,无侧唇。口针长19.1-26.0(21.8μm)。口针基球和杆部界限明显。背食道腺开口距口针基部2.5-3.5(3.0μm)。侧带处有4条侧线,两边两条间有横纹,中间两条侧线间无横纹。二龄幼虫长387.6-483.3(423.2)μm。头冠高,唇盘和中唇融合成哑铃状。口针长13.0-16.8(15.1)μm。背食道腺开口距口针基部2.1-3.7(2.5)μm。尾部渐细,尾尖钝圆。简阳根结线虫雌虫的主要酯酶带Rf=0.41、0.45和0.48。     

福建省毛豆根结线虫种类鉴定及初侵染来源

福建省漳州市一基地毛豆(品种:‘毛豆64’)苗期发生严重根结线虫病, 发病株率为78%。为明确其病原的种类及其初侵染来源, 通过形态学、分子生物学方法进行了种类鉴定。研究结果表明, 该线虫雌虫、雄虫、2龄幼虫(J2)的形态学特征与测量值和拟禾本科根结线虫Meloidogyne graminicola相吻合;基于线虫rDNA-ITS序列和28S rDNA D2D3序列构建的系统发育树进一步确定其为拟禾本科根结线虫;室内接种试验确定了其致病性。这是首次在福建省毛豆上发现拟禾本科根结线虫。在毛豆基地畦地残留的前作水稻稻茬根内和根际土壤中均分离到大量J2s, 经特异性引物扩增确定为拟禾本科根结线虫, 研究认为前作水稻根系受拟禾本科根结线虫侵染, 在灌溉淹水状态下线虫2龄幼虫和卵在根内与土壤中长期存活, 成为轮作毛豆根结线虫病的初侵染源。     

日本鸡爪槭中苹果根结线虫的鉴定

宁波口岸连续从来自日本的鸡爪槭根和根围介质中截获一种根结线虫,经形态学和分子生物学方法鉴定为苹果根结线虫。其主要鉴定特征是:雌虫会阴花纹卵圆形,线纹平滑细密,背弓和腹弓均低平,侧尾腺口大,侧尾腺间距大于阴门裂宽;雄虫背食道腺开口到口针基部球的距离较大,平均8μm;2龄幼虫体长和尾长均较短,分别为362～466μm和29.2～39.3μm,c=11.6～15.3。所截获的苹果根结线虫18S rDNA序列与已在GenBank登录的2个苹果根结线虫株系(登录号为EU669948和EU669949)最接近,相似度达99.4%和99.6%。这是我国首次报道截获该种线虫。     

水稻拟禾本科根结线虫发生与防治

拟禾本科根结线虫是严重影响水稻产量的植物寄生线虫之一,已成为制约中国及亚洲地区水稻产量的重大问题。拟禾本科根结线虫寄主范围广泛,可危害高地、低洼地和深水水稻;通过巨细胞从水稻根中摄取营养物质,从而在根系上形成许多弯钩状根结;其食道腺分泌物可以直接对水稻产生危害,影响水稻细胞代谢和免疫,从而影响水稻产量。目前水稻抗根结线虫病的品种较少,主要通过化学药剂在苗床进行防治。本文对拟禾本科根结线虫的寄主范围、危害特性、侵染特点、致病机制及防治方法等进行了综述,并对将来通过基因编辑等遗传工程技术提高水稻品种抗性的策略进行了展望,以期为我国水稻拟禾本科根结线虫的防治提供理论依据。     

中国南方稻田及其周边环境根结线虫种类鉴定

为了解根结线虫在中国南方稻区的分布和种类, 从15个省(直辖市/自治区)采集1 181份土样, 经生物测定发现312份土样中种植的水稻或番茄幼苗根系会产生根结, 阳性总检出率为26.42%。利用线虫特异性引物从171份阳性样品中鉴定出6种根结线虫:拟禾本科根结线虫Meloidogyne graminicola、北方根结线虫M.hapla、花生根结线虫M.arenaria、爪哇根结线虫M.javanica、象耳豆根结线虫M.enterolobii和南方根结线虫M.incognita, 分别占鉴定总样品数的88.89%、41.52%、29.82%、10.53%、4.09%和3.51%。被1、2、3、4、5、6种根结线虫混合侵染的土样比例分别为42.11%、41.52%、12.87%、2.92%、0.58%和0, 其中最常见的为拟禾本科根结线虫单独侵染(34.50%)、拟禾本科根结线虫与北方根结线虫(22.81%)或花生根结线虫(13.45%)混合侵染。本研究结果将为制定相应的传播阻断策略和防控措施提供参考。     

甘肃河西地区番茄根结线虫病病原鉴定

利用形态特征对甘肃省河西地区番茄根结线虫病病原线虫进行鉴定,其重要的形态特征如下：雌虫体长L=599.0（510.0～690.0）μm,体宽W=439.0（409.0～473.0）μm,口针长ST=15.4(15.0～16.0)μm,背食道腺开口到口针基部球的距离DGO=3.6(2.0～4.3)μm。雌虫梨形,排泄孔位于口针基球处,会阴花纹背弓明显高,线纹由平滑到波浪状,有些线纹向侧面分叉,但无明显的侧线;2龄幼虫L=376.0（360.0～393.0）μm,W=14.8（14.2～15.2）μm,ST=11.7(11.2～12.5)μm,DGO=3.6(2.1～4.0)μm,头部前端平,口针基部球明显,半月体邻近分泌和排泄孔,尾透明且纤细,尾尖尖圆;雄虫L=1 411.0（532.0～1 720.0）μm,W=32.0（28.0～38.0）μm,ST=24.5(23.0～26.0)μm,DGO=3.2(2.0～4.1)μm,头区不缢缩,有不完全的头环,没有侧唇,口针基球圆形至扁圆形。综合以上雌虫、2龄幼虫和雄虫的形态特征,确定了该地区的番茄根结线虫病病原线虫为南方根结线虫（Meloidogyne incognita）。     

水稻拟禾本科根结线虫生防细菌的分离鉴定与防治效果评价

为获得对水稻拟禾本科根结线虫具有较高杀线虫活性的生防细菌,初筛以马铃薯腐烂茎线虫、复筛以拟禾本科根结线虫2龄幼虫为靶标线虫,采用直接触杀法对土壤分离细菌进行筛选。获得8株具有较高杀线虫活性的菌株,其中D45菌株发酵液的杀虫活性最好。其发酵液上清5倍稀释液处理24、48 h后,马铃薯腐烂茎线虫和拟禾本科根结线虫2龄幼虫的死亡率分别为69.8%、72.1%和60.9%、70.4%。盆栽试验和田间试验表明,在拟禾本科根结线虫侵染前采用D45菌株发酵液进行土壤处理,可显著减少水稻根结数。D45高活性菌株产生的杀线虫物质对蛋白酶稳定,但不耐热和酸。经生理生化测定结合16S rRNA基因序列分析,D45菌株为巨大芽胞杆菌Bacillus megaterium。D45菌株对防治水稻拟禾本科根结线虫具有应用潜力。     

一年蓬根结线虫病的病原线虫鉴定

2021年11月在陕西省汉中市佛坪县采集到有明显根结症状的一年蓬植株样品,从其根部分离得到根结线虫雌虫,观察会阴花纹,并利用特异性引物扩增和ITS序列系统进化分析进行分子生物学鉴定。结果显示,根结线虫雌虫的会阴具有较为明显侧线,尾端具有刻点,与北方根结线虫相似。利用北方根结线虫特异性引物对分离到的线虫DNA进行扩增,能够得到610bp的特异性扩增条带。系统进化分析显示分离到的线虫ITS序列与NCBI数据库中已报道的北方根结线虫相应序列聚为一支。一年蓬根结线虫病在我国为首次报道,而侵染佛坪县一年蓬的根结线虫为北方根结线虫。     

成都平原水旱轮作田常见根结线虫调查

调查四川省成都平原地区水旱轮作田根结线虫发生情况及种类分布,为水旱轮作田根结线虫的防治提供依据。对成都平原15个县(市、区)28个乡(镇)共159块水旱轮作田的土样进行根结线虫普遍率调查,利用线虫ITS通用引物和8对根结线虫特异性引物对其中检出率高的地区重新采集的土样进行根结线虫种类分子鉴定。结果表明,成都平原水旱轮作田根结线虫平均检出率为40.25%。重新采集的土样共鉴定出5种根结线虫:拟禾谷根结线虫Meloidogyne graminicola、花生根结线虫M. arenaria、南方根结线虫M. incognita、北方根结线虫M. hapla和爪哇根结线虫M. javanica,各线虫的检出率分别为40.91%、34.09%、13.64%、13.64%和2.27%,其中29.55%的样品由2种以上根结线虫混合侵染。拟禾谷根结线虫和花生根结线虫为该地区优势种群。     

根结线虫在中国的新纪录种——西班牙根结线虫(Meloidogyne hispanica Hirschmann)

 A root-knot nematode, Meloidogyne hispanica Hirschmann, was first described and illustrated from roots of papaya in Danzhou, Hainan province in China. The perineal pattern of female was characterized by oval shaped to rectangular with a low dorsal arch; dorsal striae varied from fine and wavy to coarse; lateral lines forked with fringe-like striae between lines and phasmidial ducts distinctly appeared. Male had high and rounded head region with labial disc and medial lips fused to form elongate lip structures. Second-stage juve-nile had distinct body annules and stylet with rounded, posteriorly sloping knobs, and the tail terminus was slender with indistinct hyaline. This Chinese new record of M. hispanica had a unique esterase phenotype (S2-M1) which was different from that of other Meloidogyne species.     

Frequency of Sexual Reproduction by Mycosphaerella graminicola on Partially Resistant Wheat Cultivars

ABSTRACT The frequency of sexual reproduction has a profound effect on the population structure and the adaptive potential of a facultatively sexual parasite. Little is known about the relationship of quantitative host resistance to the frequency of sex in pathogens. We sampled over 5,000 fungal fruiting bodies from eight different wheat cultivars over a 3-year period. The cultivars possessed varying degrees of susceptibility to Mycosphaerella graminicola, a facultatively sexual pathogen that is hetero-thallic and bipolar. The fruiting bodies were classified as M. graminicola pycnidia or ascocarps (asexual and sexual fruiting bodies, respectively), other identifiable fungi, or unidentified. In all 3 years, area under the disease progress curve (AUDPC) explained a significant proportion of the variation in ascocarps as a percentage of M. graminicola fruiting bodies (P < 0.0005). The mean percentage of M. graminicola ascocarps from all cultivars was 63% in 1998, when the epidemic was intense, and 14% in 1999, a year of low disease levels. In 2000, samples were taken at 7-day intervals from 6 June to 27 June from two cultivars with substantially different AUDPCs (788 and 2,185 percentage-days). The less diseased cultivar yielded its first M. graminicola ascocarps 1 week later than the more diseased cultivar, and respective means of ascocarps as a percentage of M. graminicola fruiting bodies across sampling dates were 20.2 and 59.3%. The ratio of sexual to asexual reproduction by M. graminicola is likely to be strongly conditioned by infection density.     

Effects of Infection by Mycosphaerella graminicola on Translocation of Fluquinconazole in Wheat Seedlings

ABSTRACT Translocation of (14)C-labeled fluquinconazole was measured using combustion analysis and radio thin-layer-chromatographic analysis in seedling wheat leaves uninfected and infected with Mycosphaerella graminicola. Two isolates were used with differing sensitivity to demethylation inhibitor fungicides. Fluquinconazole was translocated acropetally, but not basipetally. Fluquinconazole accumulated around infection sites within 6 days after treatment. Accumulation occurred before M. graminicola hyphae had colonized the host mesophyll further than one host cell around the invasion site. This suggested that the accumulation was caused by a host response to infection. Infrared gas analysis showed that rates of transpiration and stomatal conductance in inoculated leaves were significantly increased very soon after inoculation but net photosynthesis was decreased. The actual mechanism of fungicide accumulation was not determined.     

Genetic Variation for Virulence and Resistance in the Wheat-Mycosphaerella graminicola Pathosystem III. Comparative Seedling and Adult Plant Experiments

ABSTRACT Fourteen Dutch Mycosphaerella graminicola isolates were studied for their virulence to 22 wheat cultivars in the seedling stage in an experiment set up as a completely randomized block design with three repetitions. Isolate x cultivar interactions were highly significant. Cluster analyses were applied to select three isolates with significantly different virulence characteristics for both disease parameters. These were retested in the seedling stage and used to inoculate two field experiments that were planted according to a split plot design in 1992 and 1995. Overhead inoculations were conducted after flowering to avoid the effects of plant height; hence, these experiments were intended as monocyclic tests for virulence differences between the isolates. Significant isolate x cultivar interactions were detected in each experiment, demonstrating specificity in the wheat-M. graminicola pathosystem in the adult plant stage under field conditions. The reproducibility of the adult plant data was high. Genetic differences among the isolates were additionally demonstrated by randomly amplified polymorphic DNA (RAPD) patterns, which also showed that no significant contamination of the inoculated plots with the natural M. graminicola population had occurred. Rank correlations between seedling and adult plant data were significant for M. graminicola isolates IPO323 and IPO290, but not for isolate IPO001. Hence, evaluation of resistance and virulence may require seedling, as well as adult plant, tests.     

Substantial reductions in winter wheat diseases caused by addition of straw but not manure to soil

Over a period of 3 years, five agronomically distinct crops of winter wheat were grown in plots in which straw (1 kg m⁻²), manure (4 kg m⁻²) or nothing were incorporated into the soil. Plant establishment and height, but not leaf area per tiller, were lower in straw-treated plots. Fertilizer regimes differed between years. Soil and leaf nitrogen were recorded; there was no obvious link between N and any disease or soil amendment. The numbers of leaf layers scorable for disease were similar in all treatments. At the end of the season, plants from straw-treated plots had consistently reduced septoria tritici blotch (caused by Mycosphaerella graminicola ), powdery mildew [caused by Erysiphe ( Blumeria ) graminis ], brown rust (caused by Puccinia recondita ) and foot rot (caused by Fusarium spp.). Early on, M. graminicola was worse in straw-treated plots. In manure-treated plots, P. recondita was reduced but effects on other diseases were inconsistent and slight. A fungicide, chlorothalonil, was applied in one crop; its effects did not interact with those of other treatments. Mycosphaerella graminicola was not suppressed by straw in outdoor pot experiments. Late in the season, straw-treated plants had significantly higher leaf silica ( P  < 0·01). In a glasshouse experiment, plants supplied with silicon had less E. graminis infection ( P  < 0·001) and higher leaf silica, but effects on M. graminicola were inconsistent. A prior inoculation of M. graminicola primed plant defences against a subsequent attack of E. graminis , but only in the presence of adequate Si. It is postulated that straw acts in the field by increasing Si availability.     

Quantitative PCR monitoring of the effect of azoxystrobin treatments on Mycosphaerella graminicola epidemics in the field

Quantitative PCR and visual monitoring of Mycosphaerella graminicola epidemics were performed to investigate the effect of curative and preventative applications of azoxystrobin in wheat field crops. A non-systemic protectant and a systemic curative fungicide, chlorothalonil and epoxiconazole, respectively, were used as references. PCR diagnosis detected leaf infection by M graminicola 3 weeks before symptom appearance, thereby allowing a clear distinction between curative and preventative treatments. When applied 1 week after the beginning of infection, azoxystrobin curative activity was intermediate between chlorothalonil (low effect) and epoxiconazole. When applied preventatively, none of the fungicides completely prevented leaf infection. There was some indication that azoxystrobin preventative treatments may delay fungal DNA increase more than epoxiconazole at the beginning of leaf infection. Both curative and preventative treatments increased the time lapse between the earliest PCR detection and the measurement of a 10% necrotic leaf area. Azoxystrobin only slightly decreased the speed of necrotic area increase compared with epoxiconazole. Hence, azoxystrobin activity toward M graminicola mainly resides in lengthening the time lapse between the earliest PCR detection and the measurement of a 10% necrotic leaf area. Information generated in this way is useful for optimal positioning of azoxystrobin treatments on M graminicola.