Polysaccharide production benefits dry storage survival of the biocontrol agent Pseudomonas fluorescens S11:P:12 effective against several maladies of stored potatoes

Pseudomonas fluorescens S11:P:12 (NRRL B-21133) is a biological control agent able to suppress several potato diseases and sprouting. Notably, it produces a polysaccharide during liquid cultivation, and the objective of this work was to determine the role of this material in the bio-control process. First, the polysaccharide was isolated, purified and identified as marginalan, which accumulated to ~3.3 g/L in cultures. The bioactivity of isolated marginalan applied alone or in combination with washed cells of strain S11:P:12 was tested in potato bioassays of dry rot and pink rot suppressiveness and sprout inhibition. Since the formulation and storage of a dried biocontrol product is preferred for commercial use, the impact of marginalan on cell survival during drying and storage was also studied. Washed bacteria formulated with 0–6.6 g/L polysaccharide were either applied to Hyflo granules, then slowly dried for 24 h with airflow at 50–60% relative humidity, or in 1-µL droplets placed in replicate wells of a micro-plate, then quickly dried for 1 h in a biohazard hood. Both Hyflo and micro-plate dry storage results indicated that marginalan significantly reduced cell death after drying, such that the final stable viable cell density was 2.5–5 orders of magnitude greater, respectively, than if no marginalan were included with cells. Marginalan had no significant impact on disease or sprout suppression by strain S11:P:12, and its main benefit to biocontrol was viable cell preservation during drying and storage. When marginalan was formulated with other selected P. fluorescens strains, its benefits to drying and storage survival were again evident (especially after 4°C instead of 25°C storage), but its effects were more subtle than for strain S11:P:12, and dry rot suppression was not impacted.     

Biological control of post-harvest late blight of potatoes

Introduction of US-8 genotypes of Phytophthora infestans has coincided with an increase in severity of potato late blight in North America. As alternatives to chemical fungicides, 18 bacterial strains patented as biological control agents (BCA) of both sprouting and Fusarium dry rot were cultivated in three liquid media and screened in wounded potato bioassays for their ability to suppress late blight incited by P. infestans (US-8, mating type A2). Washed or unwashed stationary-phase bacteria were mixed with fungal zoospores to inoculate potato wounds with 5µL containing ～10⁸ bacterial CFU/mL and 2×10⁴ zoospore count/mL. Disease suppressiveness was evaluated after tubers were stored a week at 15°C, 90% relative humidity. One-fifth of the 108 BCA treatments screened, reduced late blight by 25–60%, including among other strains Pseudomonas fluorescens S22:T:04 (showing most consistency), P22:Y:05, S11:P:12 and Enterobacter cloacae S11:T:07. Small-scale pilot testing of these four strains, alone and in combination, was conducted under conditions simulating a commercial application. Suspensions of 4×10⁴ P. infestans sporangia/mL were sprayed at a rate of 1.6 mL followed by 0.8 mL of bacteria treatment at ～5×10⁹ CFU/mL per each of 90 unwounded potatoes. Three replicate boxes per treatment (30 tubers per box) were randomized in storage and maintained 4 weeks at 7.2°C, 95% relative humidity. All BCA treatments significantly reduced disease; and unwashed bacteria outperformed those washed free of culture broth. Disease suppression ranged from 35% up to 86% the first test year and from 35 to 91% the second year. Highest overall performance rankings significantly above the control were achieved by the following strains in culture broth: four-strain mix > P. fluorescens S22:T:04> P. fluorescens S11:P:12. Combined with previous demonstrations of dry rot and sprout suppression, the consistent late blight control by these strains and strain mixtures suggests the commercial feasibility of a single treatment for broad spectrum suppression of post-harvest potato diseases and sprouting.     

Antifungal and sprout regulatory bioactivities of phenylacetic acid, indole-3-acetic acid, and tyrosol isolated from the potato dry rot suppressive bacterium Enterobacter cloacae S11:T:07

Enterobacter cloacae S11: T:07 (NRRL B-21050) is a promising biological control agent that has significantly reduced both fungal dry rot disease and sprouting in laboratory and pilot potato storages. The metabolites phenylacetic acid (PAA), indole-3-acetic acid (IAA), and tyrosol (TSL) were isolated from S11:T:07 liquid cultures provided with three different growth media. The bioactivities of these metabolites were investigated via thin-layer chromatography bioautography of antifungal activity, wounded potato assays of dry rot suppressiveness, and cored potato eye assays of sprout inhibition. Relative accumulations of PAA, IAA, and TSL in cultures were nutrient dependent. For the first time, IAA, TSL, and PAA were shown to have antifungal activity against the dry rot causative pathogen Gibberella pulicaris, and to suppress dry rot infection of wounded potatoes. Disease suppression was optimal when all three metabolites were applied in combination. Dosages of IAA that resulted in disease suppression also resulted in sprout inhibition. These results suggest the potential for designing culture production and formulation conditions to achieve a dual purpose biological control agent able to suppress both dry rot and sprouting of stored potatoes.     

一株马铃薯干腐病拮抗菌的筛选、鉴定及其生物防效

【背景】马铃薯干腐病是一种由镰刀菌引起的田间和储藏期都普遍发生的病害,主要引起块茎腐烂,致使马铃薯品质和产量降低,严重影响其食用价值和经济价值。【目的】发掘有效的生防菌株以控制马铃薯干腐病,并探究其抑菌作用。【方法】从甘肃定西地区马铃薯根际土壤中分离到109株细菌,以硫色镰刀菌(Fusarium sulphureum)为靶标菌,采用平板对峙法筛选拮抗菌,并通过形态学、生理生化特征及16S r RNA基因序列分析对拮抗菌株进行鉴定。检测拮抗菌无菌发酵液对F.sulphureum菌丝生长、孢子萌发、马铃薯块茎损伤接种病斑直径、干腐病发病率及对绿豆种子发芽的影响。【结果】筛选到一株对马铃薯干腐病有较强抑制作用的菌株YL11,经鉴定其为假单胞菌属(Pseudomonas sp.)菌株。YL11菌株无菌发酵液对F.sulphureum菌丝生长、孢子萌发、马铃薯块茎病斑扩展、干腐病发病率、毒素活性均有显著抑制作用。20%无菌发酵液对F.sulphureum菌落生长的抑制率达到87.3%;75%无菌发酵液可完全抑制孢子萌发;无菌发酵液浸泡能有效抑制马铃薯干腐病病斑的扩展,14 d时对病斑扩展的抑制率达到67.1%;90 d后干腐病的发生率降低了68.4%;同时降低了F.sulphureum毒素的活性。【结论】拮抗菌株YL11能显著抑制F.sulphureum的生长,对马铃薯干腐病有较强的生物防治效果,具有潜在的应用价值。     

Fungal decomposition of oat straw during liquid and solid state fermentation

White rot fungi (Coriolus hirsutus, Coriolus zonatus, and Cerrena maxima from the collection of the Komarov Botanical Institute of the Russian Academy of Sciences) and filamentous fungi (Mycelia sterilia INBI 2-26 and Trichoderma reesei 6/16) were grown on oat straw-based liquid and solid media, as well as in a bench-scale reactor, either individually or as co-cultures. All fungi grew well on solid agar medium supplemented with powdered oat straw as the sole carbon source. Under these conditions, the mould Trichoderma reesei fully suppressed the growth of all basidiomycetes studied; conversely, Mycelia sterilia neither affected the development of any of the cultures, nor did it show any substantial susceptibility to suppression by their presence. Pure solid cultures of basidiomycetes, as well as the co-culture of Coriolus hirsutus and Cerrena maxima caused a notable bleaching of the oat straw during its consumption. When grown on the surface of oat straw-based liquid medium, the basidiomycetes consumed up to 40% polysaccharides without measurable lignin degradation (a concomitant process). Under these conditions, Mycelia sterilia decomposed no more than 25% lignin in 60 days, but this was observed only after polysaccharide exhaustion and biomass accumulation. In contrast, during solid state straw fermentation, white rot fungi consumed up to 75% cellulose and 55% lignin in 83 days (C. zonarus), whereas the corresponding consumption levels for co-cultures of Mycelia sterilia and Trichoderma reesei equaled 70 and 45%, respectively (total loss of dry weight ranged from 55 to 60%). Carbon dioxide-monitored solid-state fermentation of oat straw by the co-culture of filamentous fungi was successfully performed in an aerated bench-scale reactor.     

Suppression of root rot of mung bean (Vigna radiata L.) by Streptomyces sp. is associated with induction of peroxidase and polyphenol oxidase

Five strains of Streptomyces sp. were evaluated in vitro for their ability of inhibiting the mycelial growth of Macrophomina phaseolina, the causal agent of root rot of mung bean (Vigna radiata L.). Among the Streptomyces sp. strains tested, PDK showed the maximum in vitro inhibition of mycelial growth of M. phaseolina and recorded an inhibition zone of 21?mm. The strains CBE, MDU, SA and ANR recorded inhibition zones of 18, 16, 13 and 11?mm, respectively. These Streptomyces sp. strains were tested for their growth-promoting efficiency on mung bean seedlings. Among them, CBE and PDK recorded the maximum increase in shoot length, root length and seedling vigour compared with control, followed by MDU. Three Streptomyces sp. strains (CBE, MDU and PDK) that showed higher levels of inhibition of growth of M. phaseolina in dual culture assay and plant growth-promoting activity were tested for their biocontrol activity against root rot under greenhouse and field conditions. Seed treatment or soil application with powder formulation of Streptomyces sp. strains CBE, MDU and PDK was effective in controlling root rot disease; but, combined application through seed and soil increased the efficacy in both the greenhouse and field trials. Among the treatments, seed treatment plus soil application with powder formulation of Streptomyces sp. strain CBE proved to be most effective, which reduced the root rot incidence from 26.8% (with non-bacterised seeds) to 4.0% in Trial I and from 32.0 to 4.9% in Trial II. The above treatment recorded the highest yield in both the field trials, and the yield increase was 78 and 74% over control in Trial I and Trial II, respectively. Isozyme analysis of the Streptomyces sp.-treated plants indicates that seed treatment plus soil application strongly induce the activities of peroxidase (PO-1 and PO-2) and polyphenol oxidase (PPO-2 and PPO-3) in mung bean. Among the three strains tested, Streptomyces sp. strain MDU- treated plants showed higher levels of activities of PO and PPO. Based on the above findings, it can be concluded that both the direct inhibition of pathogen and induced resistance might be involved in the control of root rot of mung bean by Streptomyces sp.     

甘露寡糖对纯培养和共培养的乳酸杆菌体外生长的影响

三株(S、L和M)猪源乳酸杆菌以甘露寡糖(mannan-oligosaccharide, MOS)为碳源体外纯培养或与猪源致病性大肠杆菌共培养, 研究MOS对乳酸杆菌的选择性生长作用。结果表明, 纯培养时, 三株菌MOS组的OD值和乳酸浓度均高于对照, pH均低于对照, 但菌株之间存在差异。共培养时, 乳酸杆菌和大肠杆菌都可利用MOS进行生长, 但乳酸杆菌的生长强于大肠杆菌, 产生较多的乳酸、显著降低pH(P＜0.05) , 这种促生长作用在最初的12 h较明显。     

Isolation and evaluation of a Bacillus methylotrophicus strain for control of corn stalk rot

Bacteria were isolated from corn plants and efficacy of a selected isolate for control of corn stalk rot caused by Fusarium graminearum was evaluated. The bacterial isolate provided the greatest suppression of F. graminearum in lab studies and reduced corn stalk rot significantly in 2013 and 2014 field experiments.     

甘蔗赤腐病内生拮抗菌YC89的筛选及鉴定

【目的】筛选防治甘蔗赤腐病(sugarcane red rot)的生防菌株。【方法】实验以前期分离获得的甘蔗内生细菌为目标菌,以甘蔗赤腐病的病原真菌镰孢炭疽菌(Colletotrichum falcatum Went.)为指示菌,采用平板对峙法筛选对该病菌有较强抑制作用的菌株,然后通过琼脂扩散法测定菌株代谢产物对抑菌活性的影响,并对具有较好拮抗效果的高效菌株进行抑菌广谱性分析并对其进行鉴定。最后通过形态学、生理生化特征以及16SrDNA和gyrA序列分析对高效菌株YC89进行鉴定。【结果】经初筛筛选到抑菌带均大于1.60 cm的5株拮抗细菌,其中X22、W2、YC89抑菌带均高达1.87 cm。对初筛得到的5株内生菌进行复筛,结果所示菌株YC89、H1、X22、W2、YT93对镰孢炭疽菌的抑菌率都在75%以上,其中菌株YC89对该病菌的抑菌效果最好,其抑菌率为78%。菌株YC89的发酵液、上清液、过滤液及粗蛋白提取液对镰孢炭疽菌的生长有较强的抑制作用,且菌株YC89对玉米大斑病、甘蔗梢腐病、草莓灰霉病等7种病原菌也有较好的抑制效果。通过菌株鉴定结果,初步将YC89菌株鉴定为贝莱斯芽孢杆...     

Involvement of phenazines and lipopeptides in interactions between Pseudomonas species and Sclerotium rolfsii, causal agent of stem rot disease on groundnut

Aims: To determine the role of phenazines (PHZ) and lipopeptide surfactants (LPs) produced by Pseudomonas in suppression of stem rot disease of groundnut, caused by the fungal pathogen Sclerotium rolfsii. Methods and Results: In vitro assays showed that PHZ‐producing Pseudomonas chlororaphis strain Phz24 significantly inhibited hyphal growth of S. rolfsii and suppressed stem rot disease of groundnut under field conditions. Biosynthesis and regulatory mutants of Phz24 deficient in PHZ production were less effective in pathogen suppression. Pseudomonas strains SS101, SBW25 and 267, producing viscosin or putisolvin‐like LPs, only marginally inhibited hyphal growth of S. rolfsii and did not suppress stem rot disease. In contrast, Pseudomonas strain SH‐C52, producing the chlorinated LP thanamycin, inhibited hyphal growth of S. rolfsii and significantly reduced stem rot disease of groundnut in nethouse and field experiments, whereas its thanamycin‐deficient mutant was less effective. Conclusions: Phenazines and specific lipopeptides play an important role in suppression of stem rot disease of groundnut by root‐colonizing Pseudomonas strains. Significance and Impact of the Study: Pseudomonas strains Phz24 and SH‐C52 showed significant control of stem rot disease. Treatment of seeds or soil with these strains provides a promising supplementary strategy to control stem rot disease of groundnut.     

In vitro and in vivo antagonism of actinomycetes isolated from Moroccan rhizospherical soils against Sclerotium rolfsii: a causal agent of root rot on sugar beet (Beta vulgaris L.)

Aims:  To evaluate the ability of the isolated actinomycetes to inhibit in vitro plant pathogenic fungi and the efficacy of promising antagonistic isolates to reduce in vivo the incidence of root rot induced by Sclerotium rolfsii on sugar beet.
Methods and Results:  Actinomycetes isolated from rhizosphere soil of sugar beet were screened for antagonistic activity against a number of plant pathogens, including S.   rolfsii . Ten actinomycetes out of 195 screened in vitro were strongly inhibitory to S. rolfsii . These isolates were subsequently tested for their ability to inhibit sclerotial germination and hyphal growth of S. roflsii . The most important inhibitions were obtained by the culture filtrate from the isolates J-2 and B-11, including 100% inhibition of sclerotial germination and 80% inhibition of hyphal growth. These two isolates (J-2 and B-11) were then screened for their ability to protect sugar beet against infection of S. rolfsii induced root rot in a pot trial. The treatment of S. rolfsii infested soil with a biomass and culture filtrate mixture of the selected antagonists reduced significantly ( P  ≤ 0·05) the incidence of root rot on sugar beet. Isolate J-2 was most effective and allowed a high fresh weight of sugar beet roots to be obtained. Both antagonists J-2 and B-11 were classified as belonging to the genus Streptomyces species through morphological and chemical characteristics as well as 16S rDNA analysis.
Conclusion:  Streptomyces isolates J-2 and B-11 showed a potential for controlling root rot on sugar beet and could be useful in integrated control against diverse soil borne plant pathogens.
Significance and Impact of the Study:  This investigation showed the role, which actinomycete bacteria can play to control root rot caused by S.   rolfsii , in the objective to reduce treatments with chemical fungicides.     

Application of actinomycetes as biocontrol agents in the management of onion bacterial rot diseases

This study was conducted to achieve biological control for the post-harvest onion bacterial rot diseases with the aid of Egyptian isolates of actinomycetes. In this respect, 45 actinomycetes strains were isolated from Egyptian soils and screened for their antagonistic effect against onion bacterial rot pathogens; Erwinia carotovora subsp. carotovora and Burkholderia cepacia. The most two active strains were identified based on their cultural, morphological and molecular properties as Streptomyces lavendulae HHFA1 and Streptomyces coelicolor HHFA2, the latter was most potent and so was used in vivo (pots and field) for controlling onion bacterial rot. S. coelicolor HHFA2 application resulted in enhancement in the photosynthetic pigments and some foliar growth parameters of onion plants confirming its growth promoting effect. The results of the post-harvest estimation of the disease incidence (DI) of the onion bacterial rot throughout storage revealed that, the application of S. coelicolor HHFA2 reduced the DI pronouncedly comparing with the untreated control and confirm its successful role in the biological control of onion bacterial rot diseases.     

Srinivasan’s coagulation test in taxonomically classified streptomycetes

Srinivasan’s coagulation test was performed in 18 strains of the genusStreptomyces and one strain of the genusActinoplanes. The highest coagulation activity was detected in strains systematically classified in a series of streptomycetes with pink or red aerial mycelium:S. erythreus, Streptomyces sp. AJ/22,S. roseo-luteus andS. griseofuscus. With the exception ofS. griseofuscus these three cultures also exhibited the highest inhibitory activity againstB. subtilis. When using hemoglobin as substrate it was possible to detect acid, neutral and alkaline proteinases with the highest proteolytic activity at pH 3.0 to 4.0 in the most active strain ofS. erythreus.     

Novel Chlamydiales strains isolated from a water treatment plant

Chlamydiae are obligate intracellular bacteria infecting free-living amoebae, vertebrates and some invertebrates. Novel members are regularly discovered, and there is accumulating evidence supporting a very important diversity of chlamydiae in the environment. In this study, we investigated the presence of chlamydiae in a drinking water treatment plant. Samples were used to inoculate Acanthamoeba monolayers ( Acanthamoeba co-culture), and to recover autochthonous amoebae onto non-nutritive agar. Chlamydiae were searched for by a pan-chlamydia 16S rRNA gene PCR from both Acanthamoeba co-cultures and autochthonous amoebae, and phylotypes determined by 16S rRNA gene sequencing. Autochthonous amoebae also were identified by 18S rRNA gene amplification and sequencing. From a total of 79 samples, we recovered eight chlamydial strains by Acanthamoeba co-culture, but only one of 28 amoebae harboured a chlamydia. Sequencing results and phylogenetic analysis showed our strains belonging to four distinct chlamydial lineages. Four strains, including the strain recovered within its natural host, belonged to the Parachlamydiaceae ; two closely related strains belonged to the Criblamydiaceae ; two distinct strains clustered with Rhabdochlamydia spp.; one strain clustered only with uncultured environmental clones. Our results confirmed the usefulness of amoeba co-culture to recover novel chlamydial strains from complex samples and demonstrated the huge diversity of chlamydiae in the environment, by identifying several new species including one representing the first strain of a new family.     

Quorum quenching by Bacillus cereus U92: a double-edged sword in biological control of plant diseases

In the present survey, quorum quenching activity was examined from a biocontrol point of view. Acyl-homoserine lactone (AHL) degrading bacteria were isolated from tomato rhizosphere using two standard bioreporter strains and different synthetic AHLs and then identified according to 16S rDNA sequences. Five isolates capable of inactivating both short and long 3oxo-substituted AHLs showed high similarity with the genera Bacillus, Microbacterium and Arthrobacter, and thereby Bacillus cereus U92 was determined as the most efficient quorum quencher strain. In the quantitative experiments, this strain remarkably inactivated all synthetic AHLs up to 80%. In the laboratory co-cultures, B. cereus U92 efficiently quenched QS-regulated phenotypes in Agrobacterium tumefaciens, Pseudomonas aeruginosa, Pseudomonas chlororaphis and Chromobacterium violaceum. The strain successfully reduced the frequency of Ti-plasmid conjugal transfer in A. tumefaciens by about 99% in the binary cultures. Meanwhile, in a more natural environment, this strain acted as a biocontrol agent, efficient in alleviating QS-regulated crown gall incidence on tomato roots (up to 90%) as well as attenuating Pectobacterium soft rot on potato tubers (up to 60%). On the other hand, reducing phenazine production in P. chlororaphis operated as a suppressor of its QS-regulated biocontrol activity and also inhibited pyocyanin production in P. aeruginosa, a plant growth-promoting bacterium, by 75%. In general, B. cereus U92 seems very promising in the biological control of pathogenic bacteria; however, its broad AHL-degrading activity has a detrimental role on beneficial microbes which should not be neglected.     

The degradation and utilization of wheat-straw cell-wall monosaccharide components by defined ruminal cellulolytic bacteria

Cell walls (CW) of untreated wheat straw and sulphur-dioxide (SO₂)-treated wheat straw were used as model substrates for the hydrolysis and utilization of CW carbohydrates by pure cultures or pair-combinations of defined rumen bacterial strains. Fibrobacter succinogenes S85 and BL2 strains and their co-cultures with D1 were the best degraders of CW among ruminal cultures, solubilizing 37.2–39.6% of CW carbohydrates of untreated straw and 62.2–74.5% of SO₂-treated straw. Complementary action between Butyrivibrio fibrisolvens D1 and the F. succinogenes strains was identified with respect to co-culture growth and carbohydrate utilization. However, the extent of CW solubilization was determined mainly by the F. succinogenes strains. In both substrates, utilization of solubilized cellulose by F. succinogenes S85 and BL2 monocultures was higher than that of xylan and hemicellulose: 96.5–98.3%, 34.4–40.5% and 33.5–36.2%, respectively. Under scanning electron microscopy visualization, S85 and BL2 cells of the co-cultures comprised the most dense layer of bacterial cell mass attached to and colonized on straw stems and leaves, whereas D1 cells were always nearby. Stems and leaves of the untreated straw were less crowded by attached bacteria than that of the SO₂-treated straw. In both materials, the cell surface topography of S85 and BL2 bacteria attached to CW particles was specified by a coat of characteristic protuberant structures, polycellulosome complexes.     

Susceptibility of eight potato cultivars to tuber infection by Phytophthora erythroseptica and Pythium ultimum and its relationship to mefenoxam-mediated control of pink rot and leak

In addition to cultural practices, the application of the fungicide mefenoxam is an important disease management tactic used to control both pink rot and leak on potato tubers grown in the USA. Mefenoxam resistance has been identified in many of the potato growing regions, and therefore resistance management strategies are very important for retaining this fungicide as a tool to manage these storage rot diseases. The relationship between mefenoxam efficacy and cultivar susceptibility to pink rot and leak was assessed in post‐harvest inoculation studies. Mefenoxam was applied to potato (Solanum tuberosum) cultivars known to express varying levels of susceptibility to pink rot and leak caused by Phytophthora erythroseptica and Pythium ultimum, respectfully. Tubers harvested from plants treated with in‐furrow and foliar applications of mefenoxam were inoculated with isolates sensitive to the fungicide. Incidence and severity of both diseases ranged widely among cultivars. Russet Norkotah was the most susceptible to infection by P. erythroseptica, while cvs Pike and Atlantic were the most resistant. Cultivars Dark Red Norland, Russet Norkotah, Goldrush and Russet Burbank were most susceptible to infection by P. ultimum whereas Snowden was most resistant. Control of pink rot differed significantly among cultivars following mefenoxam treatment, ranging from 28% (cv. Goldrush) to 67% (cv. Snowden) and generally provided the greatest level of disease control on susceptible and moderately susceptible cultivars such as Russet Norkotah and Snowden, respectively. In contrast, the impact of mefenoxam on leak development was minimal and disease control did not differ significantly among the cultivars. The fungicide failed to control leak in the susceptible cvs Atlantic and Pike and control ranged from 1.7% to 5.2% in cvs Goldrush, Russet Norkotah, Dark Red Norland, Russet Burbank and Kennebec. The greatest level of leak control was achieved with the moderately resistant cv., Snowden, at 12.7%. Cultivars most likely to benefit from mefenoxam treatments should be targeted as part of a pink rot management programme. Judicious use of the fungicide, when matched with the level of cultivar susceptibility, may prove to be an efficient and effective approach to reduce infection rates and possibly manage mefenoxam resistance thereby maintaining longevity of the compound.     

地黄内生放线菌的分离及地黄轮纹病拮抗菌Streptomyces folium leaf-16的新种鉴定

药用植物内生放线菌具有合成天然活性化合物的潜力,放线菌新种是寻找新型抗生素先导化合物的一个重要来源。【目的】挖掘药用植物地黄内生放线菌资源,并对地黄轮纹病拮抗菌株leaf-16进行新种鉴定。【方法】本研究采用五步消毒法分离河南道地药材地黄的内生放线菌,以地黄轮纹病原真菌草茎点霉(Phoma herbarum)为指示菌,采用平板对峙法筛选对该病菌有抑制作用的菌株,16S rRNA基因测序发现一株抗地黄轮纹病的放线菌新种leaf-16。通过形态、生理生化、细胞壁化学组分和分子生物学等特征对菌株leaf-16进行多相分类学鉴定。【结果】经平板对峙实验得到8株抗地黄轮纹病的放线菌,其中菌株leaf-16经16S rRNA基因测序、形态比较、生理生化、化学组分和分子生物学以及DNA-DNA杂交分析,确定菌株leaf-16为1株链霉菌新种,并命名为Streptomyces folium。【结论】菌株leaf-16为1株链霉菌新种,具有抑制地黄轮纹病原真菌的活性,为进一步分离新型抗地黄轮纹病的生物制剂奠定物质基础。     

Biological Control of Black Rot (Xanthomonas campestris pv. campestris) of Cabbage in Tanzania with Bacillus strains

We evaluated the biocontrol efficacy of strains of Bacillus from Tanzania against the black rot pathogen, Xanthomonas campestris pv. campestris, in cabbage and the influence of the method of application under field conditions. The incidence and severity of black rot in the foliage, stems and heads of the highly susceptible cultivar, Copenhagen Market, were significantly reduced, especially when antagonists were applied through the roots as compared to application through the seeds or foliage (cotyledons). Promising antagonists included strains of B. cereus, B. lentimorbus and B. pumilus.