甜瓜黑点根腐病菌Monosporascus cannonballus在中国大陆的首次报道

2005年夏季,在甘肃省中部的半干旱种植区的一块甜瓜品种试验田中,一些甜瓜植株在收获前2周突然凋萎,从病根上分离得到3株生长速度快的高温型子囊菌,对其中2个菌株进行了形态特征、生物学特性及致病性研究,根据其独特的、每个子囊内仅产生一个黑色子囊孢子的主要形态特征和对甜瓜及西瓜的致病性,将其鉴定为Monosporascus cannonballus PollackUecker。这是该菌在我国大陆的首次报道。     

Potential for Biocontrol of Monosporascus Root Rot/vine Decline Under Greenhouse Conditions using Hypovirulent Isolates of Monosporascus cannonballus

Monosporascus root rot/vine decline (MRR/VD) causes root necrosis and severe stunting of muskmelon and watermelon plants in several countries around the world. MRR/VD is caused by the soilborne ascomycete fungus, Monosporascus cannonballus. Currently, there are few options available for control of MRR/VD. This research describes experiments to test the possibility of using naturally occurring M. cannonballus isolates containing double-stranded RNA (dsRNA) for the biological control of MRR/VD. These isolates often develop a degenerate phenotype characterized by slow growth and reduced ascospore production. In addition, these degenerate isolates are hypovirulent on muskmelon. Plants co-inoculated with a hypovirulent, dsRNA⁺ isolate (Tx93-449⁺) and a virulent, dsRNA^- isolate (Az90-33^-) at an inoculum ratio of 10:1 (hypovirulent:virulent) were indistinguishable from the uninoculated plants in greenhouse pathogenicity trials. In vitro infection assays using fluorescence microscopy on aniline-stained muskmelon roots suggested that although the hypovirulent dsRNA⁺ isolate Tx93-449⁺ penetrated and partially colonized roots of the seedlings, it was not as efficient in colonizing the roots as the virulent, dsRNA^- isolate Az90-33^-. While more extensive experiments are needed, these data suggest that hypovirulent dsRNA⁺ isolates of M. cannonballus have potential for development as biological control agents to reduce disease pressure associated with MRR/VD.     

Host range of Acremonium cucurbitacearum, cause of Acremonium collapse of muskmelon

The pathogenicity of Acremonium cucurbitacearum to 31 cucurbits, 18 crop plant species, and 15 weed species was evaluated under greenhouse conditions. This study demonstrates that many other cucurbits in addition to muskmelon and watermelon can potentially serve as hosts of A. cucurbitacearum . Using a disease severity index (DSI), all muskmelon and watermelon cultivars were ranked as susceptible or highly susceptible, with the exception of honeydew cultivar TAM Dew Improved, which ranked resistant in one study. Highly resistant cucurbits included Cucurbita maxima (autumn squash), Luffa acutangula , L. aegyptiaca (sponge gourd) and Benincasa hispida (ash gourd). Cyclanthera pedata and Cucumis miriocarpus were rated as resistant. The percentage recovery of A. cucurbitacearum ranged from 8% to 100% and tended to be higher in plants with a higher DSI. Other crops and weed species common to muskmelon production fields are not likely to be involved in the perpetuation or propagation of the fungus.     

Development of Specific PCR Primers for Identification and Detection of Rhizopycnis vagum

Rhizopycnis vagum is a recently described coelomycete known to belong to the complex of root rot pathogens contributing to vine decline of cucurbits in several parts of the world. However, the fungus has also been reported to infect tomato, and as an endophytic associate of mycorrhizal roots of wild, asymptomatic Pinus halepensis and Rosmarinus officinalis plants in Italy. To accelerate epidemiological and ecological investigations on this fungus, a PCR primer pair was developed. Primers Rv1-F and Rv1-R were designed, based on alignment of internal transcribed spacer (ITS) sequences (ITS1-5.8S-ITS2), which amplified a 396-bp fragment from all R. vagum isolates tested, including isolates pathogenic to melons and endophytic isolates from mycorrhizae. Specificity of the primer pair was verified both in silico (BLAST searches using each primer string as a query) and in PCR assays, where the primers failed to amplify DNA from any isolate of fungi taxonomically related to R. vagum (e.g. Massarina walkeri and Stagonospora spp.) and other vine decline and common soilborne pathogens (e.g. Monasporascus cannonballus, Acremonium cucurbitacearum, Fusarium spp. and Rhizoctonia solani). Under optimum conditions, detectable amplification of the specific sequence required 0.05 pg of target DNA. Amplification of the expected 369-bp fragment was also obtained from DNA root extracts of nearly asymptomatic Cucumis melo plants inoculated with R. vagum under greenhouse conditions.     

Crop residue destruction strategies that enhance rather than inhibit reproduction of Monosporascus cannonballus

Destruction of infected crop residue is a management strategy commonly recommended for the control of many plant diseases. Based upon knowledge of the biology of the root-infecting fungus Monosporascus cannonballus , this strategy is a likely candidate for use in the management of vine decline of melons caused by this pathogen. Specifically, ascospores, the primary survival structure and inoculum for root infection, are produced on infected melon roots primarily after crop termination. Thus, destruction of infected roots prior to reproduction would be a very practical method of preventing inoculum build-up in soil. Results from this study demonstrated that two plant residue destruction methods commonly used by growers at crop termination [i.e. foliar application of a herbicide (glyphosate) and mechanical destruction of vines] significantly enhanced, relative to untreated controls, the rapidity and extent of pathogen reproduction on infected roots left in field after harvest.     

Population Dynamics of <Emphasis Type="Italic">Monosporascus</Emphasis><Emphasis Type="Italic">cannonballus</Emphasis> Ascospores in Marsh Soils in Eastern Spain

The population dynamics of Monosporascus cannonballus ascospores in the soils of four muskmelon fields located in a marsh area in Castellón province (eastern Spain) was studied for a 3 year period. Two of these fields were cropped to muskmelon with fallow periods between muskmelon cropping, and the others were in fallow and had extensive flooding periods. Muskmelon cultivation resulted in a progressive increase of the number of ascospores in soil, reaching a maximum 7 months after muskmelon planting (2–4 months after plant death), and a subsequent decline during fallow periods between muskmelon crops. During muskmelon cropping, in-bed and between-bed ascospore numbers were compared and, in general, there were no statistical differences between them. In the fields which were in fallow and flooded, the dynamics found was a progressive decline of the population of ascospores. Soilborne inoculum was viable and capable of infecting muskmelon at the end of the 3 year period in all fields, demonstrating that ascospores of M.␣cannonballus are able to survive for this period of time in the absence of muskmelon cultivation and also that this fungus seems to be well adapted to survive in soils which maintain a high water table during the crop or under flooding conditions.     

Fungi associated with root rot and collapse of melon in Italy

Melon represents the most widespread cucurbit in Italy. In recent years melon has been subjected to significant losses in yield and quality due to an increasing number of soil-borne fungal diseases. The collapse of melon, caused by a complex of fungal pathogens, including Monosporascus cannonballus , Acremonium cucurbitacearum , Plectosporium tabacinum and Rhizopycnis vagum , represents one of most destructive diseases worldwide. The purpose of this study was to determine the occurrence of collapse throughout melon-producing areas in Italy in recent years, to verify the identification of isolates collected, and to test their pathogenicity on melon and other cucurbits. Several fungi were isolated from symptomatic roots of melons in the Italian production areas. The identification was supported by PCR with a species-specific primer and DNA sequence data. RFLP and sequence analyses showed the existence of a substantial homogeneity among Italian M. cannonballus isolates. Given the self-incompatibility of these isolates it is impossible to ascertain vegetative compatibility groups (VGC) and consequently genetic relatedness cannot be studied. The frequency of isolation of fungal species varied with geographic locations, M. cannonballus being present mainly in Central Italy, while A. cucurbitacearum and P. tabacinum were most common in Apulia. In pathogenicity tests under greenhouse conditions M. cannonballus , A. cucurbitacearum and P. tabacinum caused collapse symptoms and root rots, whereas R. vagum was found to be a weak pathogen.     

New South Wales Department of Agriculture,Entomology Branch,Annual Report 1966-7 (extracts)

Abstract

Damage to tea plants due to a root infection was observed on an estate in southern Malawi. Initial symptoms on plants in the infected areas varied from yellowing of leaves on individual branches followed by dieback to a more frequent rapid wilting of the leaves of entire bushes. The bark surface of superficial roots and collar region was covered by a loose mat of coarse fungal mycelium varying from white or cream to pale or bright yellow in colour. Infection was well developed on a large proportion of roots of affected plants before foliage symptoms appeared. The causal agent was identified as Pseudophaeolus baudonii (Pat.) Ryv.; this is the first record of the fungus in Malawi and the first record of its occurrence anywhere on tea. The fungus is widely distributed in Africa on a range of hosts. It is not yet known how the fungus is transmitted and definite control methods cannot be recommended although it is suggested that entire tea crops in diseased areas be removed and the land used for tobacco production. It is unlikely thatP. baudonii will have serious economic effects on tea crops in the area.     

Induction of Terpenoid Synthesis in Cotton Roots and Control of Rhizoctonia solani by Seed Treatment with Trichoderma virens

ABSTRACT Research on the mechanisms employed by the biocontrol agent Trichoderma virens to suppress cotton (Gossypium hirsutum) seedling disease incited by Rhizoctonia solani has shown that mycoparasitism and antibiotic production are not major contributors to successful biological control. In this study, we examined the possibility that seed treatment with T. virens stimulates defense responses, as indicated by the synthesis of terpenoids in cotton roots. We also examined the role of these terpenoid compounds in disease control. Analysis of extracts of cotton roots and hypocotyls grown from T. virens-treated seed showed that terpenoid synthesis and peroxidase activity were increased in the roots of treated plants, but not in the hypocotyls of these plants or in the untreated controls. Bioassay of the terpenoids for toxicity to R. solani showed that the pathway intermediates desoxyhemigossypol (dHG) and hemigossypol (HG) were strongly inhibitory to the pathogen, while the final product gossypol (G) was toxic only at a much higher concentration. Strains of T. virens and T. koningii were much more resistant to HG than was R. solani, and they thoroughly colonized the cotton roots. A comparison of biocontrol efficacy and induction of terpenoid synthesis in cotton roots by strains of T. virens, T. koningii, T. harzianum, and protoplast fusants indicated that there was a strong correlation (+0.89) between these two phenomena. It, therefore, appears that induction of defense response, particularly terpenoid synthesis, in cotton roots by T. virens may be an important mechanism in the biological control by this fungus of R. solani-incited cotton seedling disease.     

山东局地甜瓜细菌性茎软腐病病原菌的分离与鉴定

<正>果胶杆菌(Pectobacterium)可引起马铃薯、黄瓜等多种作物的软腐病,具有十分广泛的寄主范围。近年来,随着甜瓜种植规模的不断扩大,山东、河北、辽宁等多个甜瓜种植区出现茎秆严重腐烂的现象,发病初期甜瓜茎秆出现褐色病斑,然后逐渐腐烂,导致植株整株死亡,造成了严重的经济损失。本研究对山东寿光、昌乐和莱西疑似甜瓜茎软腐病的病株进行调查采样(图1-A、B),通过病原菌分离鉴定和致病性测定,为该地区细菌病害的病原分析提供实验参考。     

Comparison of conventional and molecular methods for the detection of Rosellinia necatrix in avocado orchards in southern Spain

White root rot, caused by Rosellinia necatrix , is one of the most important diseases in avocado orchards and is particularly widespread on the Mediterranean seaboard of southern Spain. In this study, the presence of the pathogen in soil samples collected from the base of 47 plants showing different symptoms of canopy decline was assessed with a molecular detection method based on real-time Scorpion PCR. Results were compared with symptoms in the canopy and with the traditional method of isolation of R. necatrix from roots and/or bark. The fungus was isolated from 24 samples by the traditional method and from 37 soil samples by the molecular method (cycle threshold values 25·8 to 47·1), demonstrating the higher sensitivity and reliability of the molecular method. A single real-time PCR amplification was sufficient to detect R. necatrix in naturally infested soils. The avoidance of nested PCR has important practical implications because of the reduced costs and risk of cross contamination. Also, it enables faster sample analysis and is more appropriate for quantitative detection. A modified molecular method was also developed to detect R. necatrix in roots and in soils with very low populations of the pathogen.     

The classification of isolates of Gaeumannomyces graminis from wheat, rye and oats using restriction fragment length polymorphisms in families of repeated DNA sequences

Isolates of the take-all fungus, Gaeumannomyces graminis var. avenae , which affects oats, wheat and other grasses, and of G.g. var. tritici , which preferentially affects wheat, rye and barley, contain a high proportion of repeated sequences. Total DNA from 57 fungal isolates collected from many locations and different cereal hosts, and scored for virulence on wheat, rye and oats, revealed many restriction fragment length polymorphisms. These RFLP s were observed either by staining the DNA directly, by hybridization to radioactively labelled total fungal DNA , or by hybridization with labelled wheat ribosomal DNA . With only a few exceptions, the isolates with the same preferred cereal hosts showed more similar patterns of restriction fragments than isolates that had different pathogenicity properties on cereal hosts, irrespective of the geographical origins of the isolates. This was even the case for R isolates of G.g. var. tritici that were virulent on wheat and rye compared with N isolates that were virulent only on wheat. Isolates were identified by hybridizing DNA from infected root samples with ³²P-labelled total fungal DNA . The restriction fragment polymorphisms involving families of repeated sequence can therefore be used as a predictive assay for host preference of an isolate, and have probably arisen by host selection of fungal lineages. The variation between isolates in different pathogenicity groups suggests that there is little gene flow between isolates that can infect different hosts, even though they can coexist in the same field.     

Colonisation and histological changes in muskmelon and autumn squash tissues infected by <Emphasis Type="Italic">Acremonium cucurbitacearum</Emphasis> or <Emphasis Type="Italic">Monosporascus cannonballus</Emphasis>

Muskmelon (Cucumis melo cv. Temprano Rochet) and autumn squash (Cucurbita maxima) seedlings were inoculated either with Acremonium cucurbitacearum or Monosporascus cannonballus, two of the soil-borne fungi implicated in ‘melon collapse’. Inoculation was achieved in two different ways: by growing the plants in pots containing infested soil to study the histological changes produced in the infected tissues using light microscopy and by growing seedlings in Petri dishes together with fungal colonies in order to observe the colonisation of the plant tissues using scanning electron microscopy. Both muskmelon and autumn squash roots infected with A. cucurbitacearum showed a suberised layer in the epidermis and the outermost layers of the parenchymatic cortex, but these symptoms developed earlier in the muskmelon plants. Muskmelon plants infected by this fungus also presented hypertrophy and hyperplasia, which led to a progressive separation of the vascular bundles in the lower stems of the affected plants. This response was not observed in autumn squash during the study. On the other hand, few histological changes were observed in tissues infected with M. cannonballus and only a slight increase in the size of cortical intercellular spaces was noted in the lower stems of muskmelon plants, and infected autumn squash tissues remained free of these symptoms throughout the study. The scanning electron microscope observations revealed that both fungi were able to colonise the tissues of the two host plants which were studied. A. cucurbitacearum colonised the epidermis and cortex of both muskmelon and autumn squash. The hyphae grew both inter- and intracellularly, and the density of the colonisation decreased within the endodermis. The same colonisation of host plants was observed as a result of M. cannonballus infection. The xylem vessel lumina of both muskmelon and autumn squash showed hyphae and tylose formation as a result of both fungal infections. However, non-fungal structures were detected in the hypocotyl vascular tissues. The present study demonstrates that both fungi are capable of infecting the tissues of a species which is resistant (autumn squash) and a species which is susceptible (muskmelon) to melon collapse.     

Genetic diversity, aggressiveness and metalaxyl sensitivity of Pythium aphanidermatum populations infecting cucumber in Oman

Seventy three isolates of Pythium aphanidermatum obtained from cucumber from four different regions of Oman and 16 isolates of muskmelon from the Batinah region in Oman were characterized for aggressiveness, sensitivity to metalaxyl and genetic diversity using AFLP fingerprinting. Twenty isolates of P. aphanidermatum from diverse hosts from different countries were also included in the study. Most isolates from Oman were found to be aggressive on cucumber seedlings and all were highly sensitive to metalaxyl (EC₅₀ < 0·80 µg mL^?1). Isolates from cucumber and muskmelon were as aggressive as each other on both hosts (P > 0·05), which implies a lack of host specialization in P. aphanidermatum on these two hosts in Oman. AFLP analysis of all isolates using four primer–pair combinations resolved 152 bands, of which 61 (~40%) were polymorphic. Isolates of P. aphanidermatum from Oman and other countries exhibited high genetic similarity (mean = 94·1%) and produced 59 different AFLP profiles. Analysis of molecular variance indicated that most AFLP variation among populations of P. aphanidermatum in Oman was associated with geographical regions (F_ST = 0·118; P < 0·0001), not hosts (F_ST = –0·004; P = 0·4323). These data were supported by the high rate of recovery (24%) of identical phenotypes between cucumber and muskmelon fields in the same region as compared to the low recovery (10%) across regions in Oman, which suggests more frequent movement of Pythium inoculum among muskmelon and cucumber fields in the same region compared to movement across geographically separated regions. However, recovering clones among regions and different countries may imply circulation of Pythium inoculum via common sources in Oman and also intercontinental spread of isolates.     

Isolation, Selection, and Efficacy of Pochonia chlamydosporia for Control of Rotylenchulus reniformis on Cotton

ABSTRACT The reniform nematode, Rotylenchulus reniformis, is a serious threat to cotton (Gossypium hirsutum) production in the United States, causing an annual loss of about $80 million. The objective of this study was to isolate fungi from eggs of R. reniformis and select potential biocontrol agents for R. reniformis on cotton. We focused on the fungus Pochonia chlamydosporia because it suppresses root-knot and cyst nematodes and because preliminary data indicated that it was present in Arkansas cotton fields. Soil samples were collected from six cotton fields in Jefferson County, Arkansas. A total of 117 isolates of the nematophagous fungus P. chlamydosporia were obtained. In an in vitro test, 105 of the 117 isolates parasitized fewer than 15% of R. reniformis eggs, but 12 isolates parasitized between 16 and 35% of the eggs. These 12 isolates produced from 6.8 x 10(4) to 6.9 x 10(5) chlamydospores per gram of medium in vitro, and chlamydospore production was similar on rice grain and corn grain media. In two greenhouse experiments, a single application of isolate 37 (5,000 chlamydospores per gram of soil) significantly reduced the numbers of R. reniformis on cotton roots and in soil. The three isolates (37, 26, and 14) that parasitized the most eggs in vitro were also the most effective in suppressing numbers of R. reniformis and in increasing cotton growth in the greenhouse.     

Pink root rot of squash caused by Setophoma terrestris in Japan

Pink root rot of squash (Cucurbita moschata) caused by Setophoma terrestris was found in Maebashi, Gunma Prefecture, Japan in July 2007. Cucumber grafted on the squash first developed wilt and finally blight. These symptoms followed a severe pink root rot of the squash rootstock. The fungal isolates from diseased roots were identified as S. terrestris based on morphological characteristics and nucleotide sequences. One isolate induced a similar pink root rot but not entire wilting of the cucumber vine. We propose the name “pink root rot” (koshoku-negusare-byo in Japanese) of squash for the new disease.     

Clostridium bifermentans and C. subterminale are associated with kiwifruit vine decline,known as moria,in Italy

Since 2012, a new pathogenic syndrome has frequently been observed in many areas of kiwifruit cultivation in Italy. The main symptoms include an initial withering of the leaves followed by a total and sudden collapse of plants, mainly occurring during summer. The withered leaves fall and the main and secondary feeder roots appear rotten, sometimes showing a reddish-brown discoloration. The disease, that affects both the green and yellow-fleshed cultivars, has been called kiwifruit vine decline and is locally known as moria. The syndrome has been found consistently associated with soil waterlogging, which frequently occurs either after the traditional agronomical practice of irrigating orchards through surface irrigation or after very heavy rainfall. So far, the role played by bacteria in this syndrome has not been investigated. In the present study, Clostridium spp. were isolated from both rotten roots and soils obtained from Italian kiwifruit orchards affected by the syndrome, indicating for the first time that anaerobic bacteria are able to cause damage to woody crops. C. bifermentans and C. subterminale incited symptoms in kiwifruit in both in vivo and in vitro pathogenicity tests. Soil waterlogging seems to potentially favour colonization of kiwifruit roots by anaerobic bacteria, probably because saturation of the soil can facilitate proliferation and persistence of these bacteria during long periods of the vegetative growth of the crop. The occurrence of anaerobic bacteria does not exclude the possibility that other microorganisms can play additional/synergic role(s) in causing the kiwifruit vine decline.     

Association of a novel DNA virus with the grapevine vein-clearing and vine decline syndrome

A severe vein-clearing and vine decline syndrome has emerged on grapevines (Vitis vinifera) and hybrid grape cultivars in the Midwest region of the United States. The typical symptoms are translucent vein-clearing on young leaves, short internodes and decline of vine vigor. Known viral pathogens of grapevines were not closely associated with the syndrome. To obtain a comprehensive profile of viruses in a diseased grapevine, small RNAs were enriched and two cDNA libraries were constructed from a symptomatic grapevine and a symptomless grapevine, respectively. Deep sequencing of the two cDNA libraries showed that the most abundant viral small RNAs align with the genomes of viruses in the genus Badnavirus, the family Caulimoviridae. Amplification of the viral DNA by polymerase chain reaction allowed the assembly of the whole genome sequence of a grapevine DNA virus, which shared the highest homology with the Badnavirus sequences. This is the first report of a DNA virus in grapevines. The new DNA virus is closely associated with the vein-clearing symptom, and thus has been given a provisional name Grapevine vein clearing virus (GVCV). GVCV was detected in six grapevine cultivars showing vein-clearing and vine decline syndrome in Missouri, Illinois, and Indiana, suggesting its wide distribution in the Midwest region of the United States. Discovery of DNA viruses in grapevines merits further studies on their epidemics and economic impact on grape production worldwide.     

Identification of a bacterium isolated from galls on carrot and weeds

In 2004, bacterial galls were found on the roots of carrots in Shizuoka Prefecture, Japan. Galls were about 0.1–2 cm in diameter, light brown in color and had rough surfaces. In 2005, similar galls were found on the roots of three weeds: henbit (Lamium amplexicaule L.), Persian speedwell (Veronica persica Poir.) and leaf mustard (Brassica juncea L.). A bacterium that forms white, rough colonies was isolated from the carrot and weeds galls. The bacterial isolates had properties identical with Rhizobacter dauci Goto and Kuwata. Phylogenetic analysis based on 16S rDNA sequences showed that the carrot isolate had the highest homology (similarity of 100%) with that of the type strain of R. dauci. Rep-PCR genomic fingerprinting using BOX A1R primer showed that the carrot and weeds isolates were nearly identical. Pathogenicity of the isolates was confirmed by inoculating the roots of carrots and the weeds. After 2–5 weeks, they formed galls on the roots of the original host species and on other plant species tested. The galls were indistinguishable from those formed naturally, and the inoculated bacterium was reisolated. Thus, the causal bacterium of carrot and weeds gall was identified as R. dauci, and the bacterium was found to have a wider host range than previously known. These weed hosts may serve as inoculum sources for carrot bacterial gall disease.     

宁夏乌拉尔甘草内生菌鉴定及甜瓜采后病害病原拮抗菌的筛选

采用组织分离法从宁夏地区乌拉尔甘草的根、茎、叶中分离内生菌,依据形态进行初步鉴定;以甜瓜采后病害病原菌为供试菌株,测定甘草内生细菌抑菌活性.结果显示:从宁夏地区乌拉尔甘草的根、茎、叶中共分离出内生菌287株,根中分离出142株,茎中分离出78株,叶中分离出67株,136株属内生真菌,151株属内生细菌.对产孢的53株内...