甜瓜种子携带的镰刀菌种类鉴定及其致病性研究

 采用洗涤检验法和马铃薯葡萄糖琼脂培养基法,从甜瓜种子上分离得到23个镰刀菌分离物。采用形态观察和分子生物学方法对其进行鉴定,并研究其致病性以及对甜瓜种子发芽的影响。通过观察菌落形态和色素颜色,以及大型分生孢子、小型分生孢子和厚垣孢子形态,同时分析ITS-rDNA序列和翻译延伸因子-1α(TEF-1α)基因序列,以确定真菌分离物的分类属性。结果表明,4个分离物为尖孢镰刀菌(Fusarium oxysporum),5个分离物为层生镰刀菌(F. proliferatum),5个分离物为木贼镰刀菌(F. equiseti),9个分离物为轮枝样镰刀菌(F. verticillioides)。这4种镰刀菌均对甜瓜幼苗有致病性,其分生孢子悬浮液对甜瓜种子发芽有抑制作用。这是我国首例开展甜瓜种子携带致病性镰刀菌的研究报道。     

甜瓜种子携带的镰刀菌种类鉴定及其致病性研究

 采用洗涤检验法和马铃薯葡萄糖琼脂培养基法,从甜瓜种子上分离得到23个镰刀菌分离物。采用形态观察和分子生物学方法对其进行鉴定,并研究其致病性以及对甜瓜种子发芽的影响。通过观察菌落形态和色素颜色,以及大型分生孢子、小型分生孢子和厚垣孢子形态,同时分析ITS-rDNA序列和翻译延伸因子-1α(TEF-1α)基因序列,以确定真菌分离物的分类属性。结果表明,4个分离物为尖孢镰刀菌(Fusarium oxysporum),5个分离物为层生镰刀菌(F. proliferatum),5个分离物为木贼镰刀菌(F. equiseti),9个分离物为轮枝样镰刀菌(F. verticillioides)。这4种镰刀菌均对甜瓜幼苗有致病性,其分生孢子悬浮液对甜瓜种子发芽有抑制作用。这是我国首例开展甜瓜种子携带致病性镰刀菌的研究报道。     

甜瓜种子携带的链格孢菌种类鉴定及其致病性研究

采用洗涤检验法和马铃薯葡萄糖琼脂培养基法,从甜瓜种子上分离得到14个链格孢菌分离物。通过菌落形态、产孢表型、分生孢子以及分生孢子梗等形态学观察,结合分析ITS-rDNA和histone 3基因序列,对链格孢菌分离物的种类进行鉴定;甜瓜种子携带的链格孢菌种类分别为细极链格孢(Alternaria tenuissima)、交链格孢(A.alternata)和倒果链格孢(A.obovoidea)。还研究了这些链格孢菌分离物对甜瓜离体叶片的致病性及其对种子发芽的影响;结果表明,除A.obovoidea外,另外两种链格孢菌均对甜瓜离体叶片具有致病性;A.tenuissima和A.alternata的孢子悬浮液对甜瓜种子发芽均有一定的抑制作用。这是国内首次围绕甜瓜种子传带链格孢菌的种类及其致病性开展详细的研究。     

大棚甜瓜三种主要真菌病害拮抗细菌的筛选与鉴定

从甜瓜根际土壤、牦牛粪、蚯蚓粪等样品中分离出245株细菌,用平板对峙法筛选出14株对甜瓜枯萎病菌具有良好抑制作用的菌株,分别采用管碟法和凹玻片法测定拮抗细菌发酵液对甜瓜枯萎病的抑制效果和对甜瓜白粉病菌、甜瓜霜霉病菌孢子囊萌发的抑制效果。抑菌试验结果显示,菌株FCJ2发酵液对甜瓜枯萎病菌的抑制率为64.7%,对甜瓜白粉病菌、甜瓜霜霉病菌孢子萌发抑制率为62.3%、49.2%。盆栽试验结果显示,FCJ2对甜瓜枯萎病、甜瓜白粉病和甜瓜霜霉病的防效分别为88.5%、93.6%和82.6%,与农药对照组相比均具有显著差异(P0.05)。经形态特征鉴定、生理生化特征鉴定及16S rDNA序列分析,确定FCJ2为芽孢杆菌属枯草芽孢杆菌Bacillus subtilis。     

甜瓜种子携带的链格孢菌种类鉴定及其致病性研究

 采用洗涤检验法和马铃薯葡萄糖琼脂培养基法,从甜瓜种子上分离得到14个链格孢菌分离物。通过菌落形态、产孢表型、分生孢子以及分生孢子梗等形态学观察,结合分析ITS-rDNA和histone 3基因序列,对链格孢菌分离物的种类进行鉴定;甜瓜种子携带的链格孢菌种类分别为细极链格孢(Alternaria tenuissima)、交链格孢(A. alternata)和倒果链格孢(A. obovoidea)。还研究了这些链格孢菌分离物对甜瓜离体叶片的致病性及其对种子发芽的影响;结果表明,除A. obovoidea外,另外两种链格孢菌均对甜瓜离体叶片具有致病性;A. tenuissima和A. alternata的孢子悬浮液对甜瓜种子发芽均有一定的抑制作用。这是国内首次围绕甜瓜种子传带链格孢菌的种类及其致病性开展详细的研究。     

大豆炭疽病菌Colletotrichum chlorophyti的鉴定

从进口的乌拉圭大豆的残留茎秆上分离到一种新的大豆炭疽病菌,根据菌落形态、分生孢子形态、ITS序列及ACT序列特征以及对大豆的致病性,将其鉴定为Colletotrichum chlorophyti,这是我国口岸首次截获该菌。     

甘肃省马铃薯坏疽病病原鉴定

本文通过Koch’s法则以及形态学和分子生物学方法对甘肃省兰州市马铃薯坏疽病进行病原鉴定。从马铃薯坏疽病标样中分离得到5株形态特征一致的产生分生孢子器的腔孢纲真菌,其代表菌株GSAA-0232对马铃薯块茎具有强的致病性,用该菌接种马铃薯块茎,可引起与自然发病相同的坏疽病症状。该菌的培养物生成代谢物"E"(NaOH斑反应显示出特有的紫红色)。利用引物Phoma-2/Phoma-7可扩增出474bp的Phoma foveata特异条带。根据其形态特征、生物学特性、致病性及分子生物学鉴定结果 (GenBank登录号:JQ963624),将菌株GSAA-0232鉴定为Boeremia foveata(Foister)Aveskamp,Gruyter&Verkley。这是Boeremia foveata引起马铃薯坏疽病在我国的首次报道。     

浅析致病性镰刀菌的生物防治方法

描述了致病性尖孢镰刀菌的形态特征及其引起枯萎病的植株症状,阐述了防治致病性镰刀菌侵害植物的策略和措施。从生物防治的角度,简要介绍了目前防治致病性镰刀菌的生防因子和措施。     

甜瓜细菌性果斑病生防菌株BW-6的筛选和鉴定

甜瓜细菌性果斑病是由西瓜嗜酸菌（Acidovorax citrulliSchaad et al.）引起的一种毁灭性病害。本研究以西瓜嗜酸菌为指示菌,采集97个土样,采用土壤稀释平板法和对峙培养进行拮抗菌的分离和筛选,获得19株细菌可以抑制西瓜嗜酸菌生长。通过离体叶片、盆栽试验进行生测,BW-6菌株对甜瓜果斑病的生防效果最好,且比较稳定,防效达80.3%。在甜瓜叶面进行室外定殖试验表明,BW-6菌株可以在甜瓜叶面上大量定殖,但随着时间的推移菌数逐渐减少。根据菌株BW-6的形态特征、生理生化特性以及16S rDNA序列分析综合考察,鉴定其为枯草芽胞杆菌(Bacillus subtilis Cohn)。     

苹果干腐病和轮纹病的发生及防治

苹果干腐病和轮纹病均为害枝干,并为害果实。在苹果主产区,历年因干腐和轮纹烂果遭受损失严重。近年来,随着富士品种栽培面积的扩大,其枝干轮纹病问题日益引起人们的关注。1 病原菌苹果干腐病菌和苹果轮纹病菌都是子囊菌。于腐病菌(Botryosphaeria berengerianade Not.)属于葡萄腔菌属。轮纹病菌(E.berengeriand de Not.f.sp.piricola(Nose)Koganezawa et Sakuma)原属于囊孢壳属。近年来,日本对干腐病菌和轮纹病菌的形态、培养性状和致病性进行了比较研究,于1984年提出轮纹病菌有性阶段的形态结构与干腐     

Sanitation practices that inhibit reproduction of Monosporascus cannonballus in melon roots left in the field after crop termination

Ascospores of Monosporascus cannonballus function as primary inoculum for infection of melon roots. Previous studies demonstrated that pathogen reproduction (i.e. ascospore production) occurs on infected melon roots primarily after the crop has been terminated. Therefore, the key to maintaining low soil population densities of the pathogen is to destroy the hyphae of the pathogen in infected roots as soon as possible after crop termination, thereby inhibiting ascospore production. Results from a 3-year field study demonstrated that, relative to the nontreated controls, an immediate postharvest application of metam sodium (applied via the drip irrigation system at 187 L ha⁻¹) or cultivation (which lifts roots onto the surface of the soil for rapid desiccation) significantly inhibited pathogen reproduction in infected melon roots, as shown by the number of roots subsequently bearing perithecia. Additionally, ascospore populations in plots that received either the metam sodium or cultivation treatment were significantly lower ( P  < 0·05) than populations in the nontreated control plots at the end of the 3-year study. These results demonstrated the efficacy of these postharvest treatments in the inhibition of pathogen reproduction and retardation of inoculum build-up in soil.     

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.     

Effect of soil temperature on disease development in melon plants infected by Monosporascus cannonballus

The effect of soil temperature on melon collapse induced by Monosporascus cannonballus was studied in the laboratory and in the field. In the laboratory, ascospore germination and hyphal penetration into melon roots were enhanced by increasing the temperature from 20 to 32°C. The optimum temperature for mycelial growth of five isolates of M. cannonballus was 30°C. In the field, the effect of temperature was studied in experiments conducted during the winter and autumn cropping seasons from 1995 to 1998. Disease progress was much faster in the autumn than in the winter crop seasons. Disease incidence reached 100% in the three consecutive autumn seasons studied. In the winter seasons, however, planting date influenced disease incidence. Early planting, at the beginning of January, resulted in a low disease incidence (6–26%, 125 days after planting), whereas planting at the end of January resulted in higher disease incidence (72–88%, 95–119 days after planting). In plots in which the soil was artificially heated to 35°C during the winter season, disease incidence reached 85%, as in the autumn season. Plants grown during the winter in unheated soil, or in artificially heated soil disinfected with methyl bromide, did not collapse. Root colonization by the pathogen was higher in the autumn and in heated soil than in the winter season in nonheated soil. Fifty per cent of root segments were colonized 35, 42 and 67 days after planting in the winter-heated, autumn and winter-unheated plots, respectively. A high correlation was found between soil temperatures above 20°C during the first 30 days after planting and disease severity. It is suggested that soil temperature during the early stages of plant development is an important factor in disease development and the expression of melon collapse caused by M. cannonballus.     

Effect of water potential on mycelial growth and perithecial production of Monosporascus cannonballus in vitro

The effects of osmotic water potential (Ψ_s) on mycelial growth and perithecial production of Monosporascus cannonballus , the cause of root rot and vine decline of melons, were examined at 25°C on potato dextrose agar (PDA) amended with KCl, NaCl or sucrose. Patterns of the growth responses of four isolates to decreasing Ψ_s were similar for each of the osmotica. Compared with growth on nonamended PDA (−0·3 MPa), growth of all isolates increased as Ψ_s was reduced to −0·8 MPa. Maximum growth occurred at Ψ_s values of −0·6 to −0·8 MPa. Growth was not reduced below that on nonamended PDA until Ψ_s was reduced to −1·8 MPa, and a 50% reduction in growth did not occur until Ψ_s was reduced to < −2·5 MPa. Reproduction was much more sensitive to reduced Ψ_s than was mycelial growth, and perithecia were produced only at Ψ_s ≥ −0·7 or −0·8 MPa on PDA amended with KCl or NaCl, respectively. Three isolates produced perithecia on PDA amended with sucrose only at Ψ_s ≥ −0·6 MPa, but the fourth isolate produced perithecia at ≥ −1·9 MPa. Colonization of the xylem early in disease development may provide an essential source of water for subsequent reproduction in the root cortex during plant senescence. Postharvest cultivation to expose and desiccate roots may prevent reproduction even when temperatures lethal to hyphae are not attained.     

Microbe-Mediated Germination of Ascospores of Monosporascus cannonballus

ABSTRACT Ascospores of Monosporascus cannonballus germinated readily in the rhizosphere of cantaloupe plants growing in field soil. However, little or no germination occurred in the rhizosphere of melon plants growing in field soil that was autoclaved prior to infestation with ascospores. The latter data suggested that root exudates alone do not stimulate ascospore germination and that the soil microflora may be involved in the induction of ascospore germination. Amending field soil with streptomycin (which inhibits gram-negative microorganisms) did not suppress ascospore germination in the rhizosphere of cantaloupe plants. However, amending the soil with penicillin (which inhibits gram-positive microorganisms) did suppress ascospore germination. Pentachloronitrobenzene (PCNB), which inhibits the gram-positive actinomycetes but does not inhibit gram-positive or gram-negative bacteria, also suppressed ascospore germination. These results suggest that actinomycetes, either directly or indirectly, are involved in the induction of ascospore germination in field soil in the presence of exudates from cantaloupe roots. Optimum germination occurred at temperatures ranging from 25 to 35 degrees C, and data indicate that a high percentage (>/=72%) of the ascospore population within 500 mum of a root are capable of germination and subsequent penetration of cantaloupe roots.     

Olpidium bornovanus-mediated germination of ascospores of Monosporascus cannonballus: a host-specific rhizosphere interaction

Monosporascus cannonballus, a host-specific root-infecting ascomycete, is the causal agent of a destructive disease of melon (Cucumis melo L.) known as vine decline. Ascospores germinate only in the rhizosphere of melon plants growing in field soil. However, no germination occurs in the rhizosphere of melon plants if the field soil is heated to temperatures >50°C prior to infestation with ascospores. This observation suggested that germination is mediated by one or more heat-sensitive members of the soil microflora. Although bacteria or actinomycetes were heretofore suspected as the germination-inducing microbes, our data demonstrate that Olpidium bornovanus, an obligate, host-specific, root-infecting zoosporic fungus, is responsible. In four experiments conducted in autoclaved field soil amended with various population densities of culturally produced ascospores, significant ascospore germination was recorded only in the rhizosphere of cantaloupe seedlings colonized by O. bornovanus.     

稻曲病菌的形态学观察研究

 利用光学和电子显微镜对稻曲病菌的有性子座和不同来源的繁殖体进行了形态学观察。子囊壳单层环状埋生于子座外层,顶端突出子座表面而形成许多乳突结构。子囊发育成熟后,子囊壳壁的顶端可自行消解,露出里面的子囊。子囊孢子无色单胞,线状。厚垣孢子圆形或稍椭圆,黄褐色至黑褐色,胞壁厚密,外表有许多疣状突起。子囊孢子和厚垣孢子萌发都产生次生分生孢子。这些次生分生孢子与液体培养获得的分生孢子在大小和形态特征上是一样的,它们都是薄壁分生孢子。薄壁分生孢子卵圆形或长圆形,大小为2.6~8μm×2~5μm,无色透明,外表光滑。薄壁分生孢子萌发直接形成新一代薄壁分生孢子,此繁殖过程可不断重复进行。     

Techniques for isolatinghelminthosporium pedicellatum from infected corn roots

In a comparison of potato dextrose agar (PDA) and Czapek’s Dox broth (CDB) agar with and without benomyl, aa growth media forHelminthosporium pedicellatum Henry (Trichometasphaeria pedicellatum Nelson), PDA was 1.5 times more efficient than CDB under all conditions. Growth rate was negatively correlated with benomyl concentration, and was inhibited 11% and 74% at benomyl concentrations of 10 μg and 200 μar, respectively, on both media. Pure isolates of the fungus were recovered from corn roots only where roots had been sterilized with 10% sodium hypochlorite. Root sterilization may thus be more important than medium amendment in isolating pure cultures ofedicellatum from plant roots.     

Preliminary studies of<Emphasis Type="Italic">in vitro</Emphasis> stimulation of sexual mating among isolates of<Emphasis Type="Italic">Mycosphaerella fijiensis</Emphasis>, causal agent of black sigatoka disease in bananas and plantains

Single-ascospore-derived isolates ofMycosphaerella fijiensis Morelet from false horn ‘Agbagba’ plantain leaves obtained from five different villages in southern Nigeria were stimulated to mate under artificial conditions. Pairs of isolates were incubated under blacklight on potato dextrose agar (PDA) with surface-sterilized plantain leaves or on PDA with autoclaved plantain leaves. Some isolates were observed to be sexually compatible by their ability to produce spherical to bulb-shaped fruiting body structures (FBS) and ascospores on pairing. FBS were observed to measure between 39–65 μm (smallest diameter) and 39–104 μm (largest diameter; mean 55.3×71.1 μm) in diameter, whereas ascospore lengths measured between 13.0 and 14.9 μm. Length of incubation time required for FBS production was dependent on the pair of isolates involved, the average being 40.1 days. With some pairs, ascospores were observed after 35 days of incubation. http://www.phytoparasitica.org posting Dec. 16, 2002.     

Spatio-temporal development of pycnidia and perithecia and dissemination of spores of Mycosphaerella pinodes on pea (Pisum sativum)

The pattern of development of pycnidia and perithecia of Mycosphaerella pinodes was studied in the glasshouse on pea plants (cv. Solara) sprayed with a pycnospore suspension and in field plots inoculated with barley grains colonized by the fungus. The numbers of pycnidia and perithecia were estimated on each stipule and internode of infected plants, and were related to ratings of disease severity (0–5 scale). Pycnidia were produced on both green and senescent organs, whereas perithecia only appeared on senescent organs. The development and quantity of pycnidia were related to initial inoculum concentration and the physiological stage of the plants. The formation of fruiting bodies progressed from the bottoms to the tops of plants during crop development. Spore trapping showed that both pycnospore dispersal and ascospore discharge were initiated by rainfall or dew. Pycnospores were principally trapped in the first 20 cm above the soil surface while ascospores were also trapped above the crop canopy. Pycnospores and ascospores were dispersed throughout the growing season, suggesting that ascospores also play an important role in secondary infections.