Emerging Hazelnut Cultivation and the Severe Threat of Bacterial Blight in Chile

Severe attacks of bacterial blight were observed on young plants throughout the hazelnut growing areas in Chile. The incidence of the disease in nurseries and fields ranged from 60–90%. The causal agent was identified as Xanthomonas arboricola pv. corylina, based on phenotypic and genetic tests.     

Extensive Field Survey,Laboratory and Greenhouse Studies Reveal Complex Nature of Pseudomonas syringae-Associated Hazelnut Decline in Central Italy

Pseudomonas avellanae (Pav) has been reported as the causal agent of bacterial decline and bacterial canker of hazelnut in Italy and Greece, respectively. Both hazelnut diseases were reported to be similar in terms of symptoms, severity and persistence. In this study, we found that both symptomatic and asymptomatic trees in the field were colonized by Pav. Multilocus Sequence Typing (MLST) analysis showed that Pav strains isolated during this study in Italy belong to the P. syringae phylogroup 1 and they are closely related to Pav strains previously isolated in Greece from hazelnut bacterial canker. On the other hand, strains isolated in earlier studies from hazelnut decline in Italy belong to both phylogroup 1 and 2 of P. syringae. Both phylogroup 1 strains of P. syringae from Greece and Italy are different than strains isolated in this study in terms of their capacity to excrete fluorescent pigments on different media. Despite the same plant genotype and cropping practices adopted, the incidence of hazelnut decline ranged from nearly 0 to 91% across our study sites. No disease developed on plants inoculated with Pav through wounding while leaf scar inoculations produced only mild disease symptoms. Based on our results and the previously reported correlation between pedo-climatic conditions and hazelnut decline, we conclude that hazelnut decline in central Italy could be incited by a combination of predisposing (adverse pedo-climatic conditions) and contributing factors (Pav). Because this is a true decline different from “bacterial canker” described in Greece, we refer to it as hazelnut decline (HD).     

我国小麦赤霉病成灾原因分析及防控策略探讨

小麦是世界上三大粮食作物之一,是全球30亿以上人口的主粮。近年来,由于各种病虫害危害,全球小麦生产和粮食安全受到严重威胁,其中由禾谷镰刀菌引起的小麦赤霉病是小麦生产上重要的病害之一。此外,病菌会产生多种真菌毒素对人畜生命健康构成严重威胁。化学药剂的使用以及抗病品种的种植可以有效地控制小麦赤霉病的发生。但是,由于高产优质抗病品种匮乏、气候变暖等因素影响,小麦赤霉病在我国小麦主产区频繁暴发;同时,赤霉病菌抗药性产生致使化学农药的防控效果大大降低。从气候变化、耕作制度改变、小麦品种抗性及病菌抗药性等方面,分析了赤霉病暴发成灾的主要原因。在此基础上,结合当前赤霉病防控研究进展以及存在的科学问题,探讨该病害持续绿色防控的对策建议,以期为我国小麦赤霉病的防控研究提供参考。     

Cassava Bacterial Blight: Using Genomics for the Elucidation and Management of an Old Problem

Bacterial Blight is an important disease of cassava, causing losses that have resulted in historical famines in certain growing zones. The disease is caused by Xanthomonas axonopodis pv. manihotis, a gram-negative rod that belongs to the gammaproteobacteria. In this review, we describe the pathosystem and the recent studies that have been undertaken to elucidate both susceptibility and resistance mechanisms in cassava, with the hope of generating resistant plants using biotechnology. We first describe studies of the pathogen, including pathogen population changes through time as well as genomic tools that have recently been generated to determine pathogenicity factors. Secondly, we discuss mechanisms of disease resistance that have been elucidated in recent years and how these mechanisms could be used for the generation of improved plants resistant to CBB.     

Severe Outbreak of Pseudomonas syringae pv. avellanae on Hazelnut in Italy

Pseudomonas syringae pv. avellanae , the causal agent of bacterial canker of hazelnut, has been isolated for the first time in Italy. Biochemical tests were consistant with the type-strain of the microorganism and whole-cell protein profiles of the studied isolates were similar to those of the type-strain. When artifically inoculated, either in summer or in autumn, the isolates incited the same symptoms as those observed in the field.
The main symptoms are the failure of the buds to swell or their withering after breaking in spring; the chlorosis of the foliage and rapid withering of the leaves that remain attached on the twigs during summer; dark brown discolouration of the bark and cambium, necrosis in the primary roots and the final dieback of the plant. The pathogen killed more than 1,800 adult hazelnut plants in one orchard within a period of five years. The main differences of the symptomatology between bacterial canker and bacterial blight of hazelnut, caused by Xanthomonas campestris pv. corylina , and the "seccume" of the hazelnut are briefly discussed.     

应用RAPD分析技术研究生姜青枯病的土壤防治

利用随机扩增多态性技术(RAPD)研究生姜连作地、施加有机肥后的生姜连作地及新开地中土壤微生物多样性与生姜青枯病的关系, 结果发现, 连作地的青枯病发病率为100%, 新开地没有发病, 而施加有机肥的连作地生姜青枯病发病率降至37%。发现施加有机肥连作地的真菌、放线菌数量增加, 平板上不同菌落形态的真菌、细菌、放线菌增加明显。多样性指数分析发现Shannon指数、Simpson指数等均显著增加。随机扩增条带出现连作地的条带丰富度较少、新开地的条带最多、施加有机肥连作地的RAPD条带明显多于连作地, 接近新开地, 并出现了一些连作地没有的特异条带。结果表明, 施加有机肥可以改善土壤微生物群落结构。     

水稻花粉株系白叶枯病抗性遗传

本文研究了粳稻感病品种沈农1033分别与7个抗白叶枯病的品种（其中汕稻有75－34,辛尼斯,1R20;粳稻有早生爱国3号,邳早15,蚌珠芒,爪哇14）杂交,F花粉培养并观察了花粉株系第二代（H2）的抗性转移及遗传表现和花粉株系第三代,第四代抗性稳定性,572个株系的性状是整齐一致的,占95．5％,其中抗病（高抗和中抗）株系有376个,占62．9％,感病系有196个,占32．7％,表现有分离的杂合系约4．5％,不同组合的H2与F2群体中抗,感反应变异幅度不同,对同一组合不同熟期花粉株系其生育日数与抗病性间存在着极显著相关性,生育期长的株系抗性较强。花粉再生植株后代H2在生育期,株高,穗长,粒重等性状上十分多样,白叶枯病抗性遗传分析结果表明,在4个组合中抗性均由1个显性上位基因控制,抗病性广义遗传力在80％以上。杂种花粉植株第二,第三,第四代的农艺性状以及白叶枯病的抗性持续地稳定,不因世代的增加其性状的整齐度不降,抗性减弱。     

水稻白叶枯病候选抗性基因SHNLR的RGAs克隆及分析

旨在从含有疣粒野生稻抗白叶枯病基因的新种质SH5、SH76基因组中克隆抗病基因。利用RGAs法得到1个NBS-LRR类同源基因,暂命名为SHNLR(登录号为JF934724)。结果表明,SHNLR的开放阅读框长度为3 105 bp,编码1 034个氨基酸,含有CC、NB-ARC与LRR结构域,具备CC-NBS-LRR类植物抗病基因的结构特征。BLASTn和BLASTp比对显示SHNLR是单拷贝基因,未发现同源性较高且功能已知的基因,仅NBS保守域序列与番茄Prf基因的相似度最高。对SHNLR基因电子定位,发现其位于水稻第11号染色体的长臂末端,但与11号染色体上已定位或克隆的8个白叶枯病抗性基因具有不同序列或处于不同的位置。半定量RT-PCR分析表明,SHNLR在抗病新种质叶片中的表达明显受到白叶枯病菌Zhe173的诱导。因此推测SHNLR可能是1个与抗白叶枯病相关的R基因。     

New Multilocus Variable-Number Tandem-Repeat Analysis Tool for Surveillance and Local Epidemiology of Bacterial Leaf Blight and Bacterial Leaf Streak of Rice Caused by Xanthomonas oryzae

Multilocus variable-number tandem-repeat analysis (MLVA) is efficient for routine typing and for investigating the genetic structures of natural microbial populations. Two distinct pathovars of Xanthomonas oryzae can cause significant crop losses in tropical and temperate rice-growing countries. Bacterial leaf streak is caused by X. oryzae pv. oryzicola, and bacterial leaf blight is caused by X. oryzae pv. oryzae. For the latter, two genetic lineages have been described in the literature. We developed a universal MLVA typing tool both for the identification of the three X. oryzae genetic lineages and for epidemiological analyses. Sixteen candidate variable-number tandem-repeat (VNTR) loci were selected according to their presence and polymorphism in 10 draft or complete genome sequences of the three X. oryzae lineages and by VNTR sequencing of a subset of loci of interest in 20 strains per lineage. The MLVA-16 scheme was then applied to 338 strains of X. oryzae representing different pathovars and geographical locations. Linkage disequilibrium between MLVA loci was calculated by index association on different scales, and the 16 loci showed linear Mantel correlation with MLSA data on 56 X. oryzae strains, suggesting that they provide a good phylogenetic signal. Furthermore, analyses of sets of strains for different lineages indicated the possibility of using the scheme for deeper epidemiological investigation on small spatial scales.     

水稻抗白叶枯病基因及其应用研究进展

由黄单胞菌水稻变种Xanthomonas oryzae pv.Oryzae（Xoo）引起的白叶枯病是水稻重要病害之一。目前,已有37个水稻白叶枯抗性基因被鉴定并报道,其中28个被定位到染色体上,7个被克隆。本文简要综述了水稻白叶枯抗性基因的鉴定、定位和克隆的进展,并讨论了合理利用抗性基因防治白叶枯病的前景。     

Diagrammatic Scale for Assessment of Bacterial Blight in Coffee Leaves

Due to the lack of a standardized visual method for assessing bacterial blight (Pseudomonas syringae pv. garcae) in coffee leaves, a diagrammatic scale was developed and validated to quantify the disease. Leaves were collected in crops and nursery with different intensity of symptoms, and the true severity was determined electronically. Based on the frequency distribution of severity values and according to the Weber–Fechner's law of visual stimulus, the minimum and maximum limits and the intermediate levels in the scale were determined. Validation was performed by ten evaluators who estimated the severity of 50 leaves with different intensity of symptoms. One evaluation was performed without diagrammatic scale and two evaluations with the scale at 7‐day intervals. The accuracy, precision, repeatability and reproducibility of the estimates were evaluated. The scale had nine levels: 0 (0%), 1 (0.1–0.99%), 2 (1–2%), 3 (2.01–4%), 4 (4.01–8%), 5 (8.01–16%), 6 (16.01–25%), 7 (25.01–45%) and 8 (≥45.1%). Using the scale, the evaluators were able to improve accuracy, precision, reproducibility and repeatability of estimates, compared to evaluators without scale. The scale was appropriate to visual estimation of severity of bacterial blight in coffee leaves.     

Sources of Resistance to Cowpea Bacterial Blight Disease in Nigeria

The development of resistant crop varieties depends on the reliability of the method of screening for resistance. One of the techniques widely used in evaluating field resistance is the field screening method. However, most cowpea varieties regarded as having field resistance are often found to be susceptible in farmers’ fields, where the inoculum density can be higher. This study rescreened 96 cowpea varieties, evaluated earlier in breeders’ fields as resistant to Xanthomonas campestris pv. vignicola, in field and greenhouse under high inoculum pressure. There were significant differences (P ≤ 0.05) in the reactions of cowpea varieties to bacterial blight in terms of disease incidence and severity. Results from the field screening showed that there were 69 susceptible, 25 moderately susceptible, and 2 resistant varieties. In artificial inoculation in the greenhouse IT81D‐1228‐14, IT82E‐16, IT93K‐2271‐2‐2, TVu 1235, and TVu 4630, which were moderately susceptible in the field showed a susceptible reaction. Tvu 12349 and Tvu 15549 gave consistent reactions in the field and in the greenhouse and are therefore good sources of stable resistance to bacterial blight pathogen. Stem canker incidence also varied significantly (P ≤ 0.05) among the cowpea varieties. Seventeen varieties did not manifest canker symptoms.     

云南“大粒水稻”对稻白叶枯病的抗性遗传

云南地方品种——云南大粒抗水稻白叶枯病菌“江陵691”,其抗性由2对具重叠作用的隐性抗性基因控制,与IR28、南粳15的显性抗病基因不等位;也与已命名的xa-5、xa-8、xa-9和xa-13 4个抗性基因也不等位。     

Reduction of Bacterial Blight Infestation of Cotton Seeds by Treatment with Sodium Hypochlorite

The efficacy of sodium hypochlorite (NaOCl) for restraining cotton seed infestation by Xanthomonas campestris pv. malvacearum was studied. Seeds of three cotton cultivars were artificially inoculated by soaking in suspensions (ca. 5.10 ⁸ CFU/ml) of different strains of Xcm. Twelve h after soaking (at 30°C) various dilutions of NaOCl were added to the soaking suspensions and incubated for another 12 h. The infestation rate of cotyledons and effect on germination were determined 14 and 21 days after treatment under the standardized conditions of a growth chamber (12 h 20,000 Lux at plant height, 30/20 °C day/night, ca. 100 % relative humidity). Cbncentrations below 0.15 % of active chlorine in the soaking-water had no marked effect on reduction of the disease. Goncentrations between 0.45 % to 0.60 % appeared to be most effective without reducing germination rate. Seed germination was affected, however, by concentration of active chlorine above 0.6 %. Seed quality during sodium hypochlorite treatment obviously influenced the effectivity of this measure.     

Epidemiological and linkage studies on Huntington's disease in Italy

Summary The results of an epidemiological survey on Huntington's disease in the Lazio Region, Central Italy, and of linkage studies in a subset of families are reported. From a total of 99 ascertained families and 491 patients, a prevalence of 25.6 × 10–6 was obtained, with distributions of age at onset and age at death similar to those described in the literature. No relationship with the sex of the transmitting parent was observed. Analysis of 10 chromosome 4 restriction fragment length polymorphisms in 11 families showed consistent linkage between the genetic loci D4S10, D4S43 and D4S95, and the disease. A recombination rate of 0.08 for D4S10 markers was obtained in this sample. Allelic frequencies of DNA markers in the general population are also reported.     

浙江省早籼稻区试品种(系)白叶枯病抗性稳定性研究

本文对浙江省早籼稻区域试验中多品系、多年、多点、非平衡、无重复的白叶枯病抗性鉴定数据,作了统计分析。分析结果表明,浙江省近年早籼稻区域试验,品种抗病性效应的方差最大,其次为地点×年份、品种×地点、品种×地点×年份互作效应。杭820显著比对照广陆矮4号抗白叶枯病,而G90-316、G90—280、杭8820白叶枯病抗性显著高于对照浙852。本文还进行了各参试品种抗性分析。