Relationship between severity of blackleg (Leptosphaeria maculans/L. biglobosa species complex) and subsequent primary inoculum production on oilseed rape stubble

The relationship between severity of blackleg, or phoma stem canker ( Leptosphaeria maculans/L. biglobosa ), and subsequent primary inoculum production on oilseed rape ( Brassica napus ) stubble was investigated at two sites in France over 3 years. The quantity of primary inoculum produced in the following year increased with canker severity, from 1·9 to 10·8 pseudothecia cm⁻² on stubble with the least and most severe cankers, respectively. Stubble incubated at Le Rheu (cooler, more rain) had 1·7 times more pseudothecia than stubble incubated at Grignon. Stubble collected at Grignon had 2·7 times more pseudothecia than that collected at Le Rheu. The use of Darmor, a cultivar with a good level of quantitative resistance, reduced the severity of canker in the field, but not the subsequent inoculum production for stubble of the same canker severity class. At both sites, maturation of pseudothecia occurred after 63–75 days of incubation and increased with canker severity with a mean of 0·5 and 3% mature pseudothecia appearing per favourable day, on stubble with the least and most severe cankers, respectively. A simplified procedure for pseudothecial quantification proved satisfactory: for all three observers, most (91–96%) of the fructifications counted as pseudothecia were real pseudothecia. Only a few (4–14%) of the fructifications considered as non-pseudothecia were in fact pseudothecia of L. maculans . The total area occupied by pseudothecia, which was simpler and faster to evaluate, was correlated (coefficient of determination, R ² = 71%) with the number of counted pseudothecia. The results presented here make it possible to forecast the quantity of available primary inoculum for a given disease severity.     

The Leptosphaeria maculans – Leptosphaeria biglobosa species complex in the American continent

Stem canker of oilseed rape (canola, Brassica napus ) is associated with a species complex of two closely related fungal species, Leptosphaeria maculans and L. biglobosa . Of these, L. maculans is the most damaging and develops gene-for-gene relationships with the host . Here, a wide scale analysis of the L. maculans - L. biglobosa species complex was performed throughout the American continent (23 locations from Chile to Canada) plus several locations in Western Australia for comparison purposes, based on a collection of 1132 isolates from infected tissues of a susceptible cultivar. Fungal species were discriminated on the basis of morphological, phytopathological and molecular criteria and showed that L. biglobosa was closely associated with L. maculans in most of the locations. Multiple gene phylogeny using sequences of ITS, actin and β-tubulin confirmed the prevalence of the L. biglobosa 'canadensis' sub-clade in Canada, whereas up to three different sub-clades of L. biglobosa were found in Georgia (USA). Race structure of L. maculans was investigated using a combination of pathogenicity tests and PCR amplification of avirulence alleles AvrLm1 , AvrLm4 and AvrLm6 . Three contrasting situations were observed: (i) race structure in Ontario, Chile and Georgia was related to that of European and Western Australian populations, with a low race diversity; (ii) only one race was found in Mexico, and not found outside of this country; (iii) a large diversity of races was observed in central Canada (Manitoba, Alberta and Saskatchewan) with very specific features including maintenance of avirulence alleles absent from Europe, absence of the AvrLm7 allele common in Europe (or eastern Canada) and wide location-to-location variability.     

Detection of citrus canker in citrus plants using laser induced fluorescence spectroscopy

Citrus canker is a serious disease caused by Xanthomonas citri subsp. citri bacteria, which infects citrus plants (Citrus spp.) leading to a large economic loss in citrus production worldwide. In Brazil citrus canker control is done by an official eradication campaign, therefore early detection of such disease is important to prevent greater economic losses. However, detection is difficult and so far it has been done by visual inspection of each tree. Suspicious leaves from citrus plants in the field are sent to the laboratory to confirm the infection by laboratory analysis, which is a time consuming. Our goal was to develop a new optical technique to detect and diagnose citrus canker in citrus plants with a portable field spectrometer unit. In this paper, we review two experiments on laser induced fluorescence spectroscopy (LIF) applied to detect citrus canker. We also present new data to show that the length of time a leaf has been detached is an important variable in our studies. Our results show that LIF has the potential to be applied to citrus plants.     

柑橘溃疡病田间消长规律及药剂防治技术

多年田间系统观察表明 ,柑橘溃疡病的消长 ,在春梢期 ,主要影响因子为气温。 4月下旬平均气温 2 0℃持续 1 0～ 1 5d ,田间始病 ;平均气温 2 5℃连续 3d ,田间进入病情激增期。在夏、秋梢期 ,主要影响因子为湿度和降雨。相对湿度低于 70 % ,不利于发病 ;持续阴雨或短时大雨极有利于流行。溃疡病的药剂防治应掌握在春梢展叶后 7d用药 ,夏、秋梢则萌芽后即用药。药剂品种以可杀得和百菌清最理想 ,喷药次数以 3次为好。     

我国杨树溃疡病研究进展

杨树溃疡病主要由真菌侵染所致,该真菌是一类世界性分布的真菌,寄主范围十分广泛,可危害多种林木和果树的树干及果实,引起枯枝、溃疡、流胶和果腐等。另外,还可以引起根腐,导致整株树的枯死。发生病害的林木,用材林材性降低,经济林产量降低,造成严重危害和经济损失。文中对其病害分布、致病机理、抗病机制以及抗病育种等进行了综述。     

几种树皮腐烂病菌的分子鉴定

一些引起树皮腐烂病的病原菌往往不产孢,利用传统形态学方法很难对病原菌进行准确鉴定,因此,本研究拟通过ITS序列分析对引起几种腐烂病菌进行分子鉴定。本试验对采自河北省5个不同县市的苹果树、杨树、柳树、槐树和杏树等5种树木上的腐烂病菌进行了分离和致病性测定。通过测定的ITS序列与GenBank中的同源序列的分析对其进行分子鉴定,从5种寄主植物上共鉴定出Valsa mali var. mali、Valsa sordida、Botry-osphaeri dothidea和Botryosphaeria rhodina等4种树皮腐烂病菌,结果表明,通过ITS序列分析,可对树皮腐烂病菌进行准确鉴定,并对系统发育树上代表不同病原菌种类的每个分支上序列的名称、寄主范围以及地理来源进行了详细地讨论。     

七叶树溃疡病病原真菌的分离与鉴别

【目的】分离和鉴别引起七叶树溃疡病的病原菌,为制定合理的防治技术提供依据。【方法】采用组织分离培养、人工接种、形态观察及核糖体转录间隔区序列(ITS-rDNA)分析,对引起七叶树溃疡病的水渍型溃疡病病原菌NW397和干腐型溃疡病病原菌NW3362种真菌进行鉴别与比较。【结果】引起七叶树溃疡病的病原为2种不同的真菌,并表现出不同的危害特征。水渍型溃疡病菌NW397 ITS-rDNA序列与多主葡萄座腔菌(Botryosphaeria dothidea Sacc.)等的序列同源性高达99%;干腐型溃疡病菌NW336ITS-rDNA序列与乌饭树拟茎点菌(Phomopsisvaccinii)等的同源性高达95%以上。【结论】七叶树水渍型溃疡病菌定名为多主葡萄座腔菌(Botryosphaeria do-thidea Sacc.),干腐型溃疡病菌定名为梨干枯拟茎点菌(Phompsis fukushii Tanaka et Mill)。     

陕西关中地区猕猴桃溃疡病调查初报

通过对陕西关中(杨凌、周至、眉县)地区13个村65个猕猴桃园的猕猴桃溃疡病发病特点调查分析,发现树龄、品种与猕猴桃溃疡病的发生直接相关,表现为随着树龄的增大溃疡病危害逐渐加重(3～14 a生);3个主栽品种(秦美、亚特和海沃德)中海沃德最感病.地区之间猕猴桃溃疡病严重程度存在着不同程度的差异,除地区间小气候外,管理水平和灌溉水平均为影响溃疡病发生的重要因素.     

球毛壳中抗真菌物质对树皮腐烂病菌的抑制作用

[目的]阐明球毛壳中抗真菌物质对树皮腐烂病菌的抑制作用机制。[方法]通过平板对峙培养、发酵液萃取、薄层层析分离和抑菌活性测定等方法,研究毛白杨内生真菌球毛壳ND35产生的抗真菌物质对树皮腐烂病菌的抑制作用。[结果]球毛壳ND35的抗真菌物质粗提物对杨树和苹果树腐烂病菌有较强的抑制作用,对2种病菌的菌丝生长抑制率分别是66.4%和72.6%。对分生孢子萌发的抑制率分别是92.2%和80.4%。薄层层析分离和活性测定结果证明,抗真菌物质2号组分在对树皮腐烂病菌的抑菌过程中起主要作用。[结论]球毛壳中抗真菌物质对于树皮腐烂病有生物防治潜力。     

杨树烂皮病生防链霉菌的筛选及鉴定

为明确能有效抑制杨树烂皮病菌的拮抗放线菌F58的生防效果及分类地位,采用平板对峙法、杯碟法和人工接种法分别测定了其活菌及发酵液的抑菌活性;并通过形态学、生理生化特征、16S rRNA及全细胞脂肪酸分析等方法研究了其分类地位。结果表明,拮抗放线菌F58对杨树烂皮病菌、杨树溃疡病菌、苹果斑点落叶病菌等13种供试植物病原菌均有抑制作用,抑菌谱广,其中对杨树烂皮病菌和杨树溃疡病菌抑制作用最强,抑菌带达30.2 mm以上,菌株F58发酵液对这2种病菌也有很强的抑制作用,抑菌圈直径分别为56.4 mm和42.7 mm;发酵液的无菌滤液对杨树烂皮病的保护效果和治疗效果分别达88.7%和73.4%。根据菌株形态、生理生化特性、16S rRNA序列比对及全细胞脂肪酸分析,鉴定拮抗放线菌F58为盐屋链霉菌Streptomyces sioyaensis。