Production of a proteinaceous phytotoxin by Ascochyta rabiei grown in expressed chickpea sap

Production of the solanapyrone toxins by Ascochyta rabiei is nutrient dependent. When grown on a medium consisting entirely of expressed sap from the aerial parts of young chickpea plants (PSM). only low concentrations of the solanapyrones were produced (< 24 μM). However, toxicity of 4-day-old culture filtrates to isolated cells of chickpea leaflets was comparable with that obtained from 12-day-oId culture filtrates on Czapek Dox nutrients supplemented with chickpea seed extract or cations—media that are conducive to solanapyrone production. The additional toxic component which peaked at 4 days in culture was heat labile, losing about 50% of its activity on boiling for 10 min. Affinity for solid-phase extraction media, precipitation with ammonium sulphate and acetone, ionization properties and UV absorption characteristics suggested that the toxin was a polypeptide. The toxin was purified by solid-phase extraction, acetone precipitation and high performance liquid chromatography (HPLC) on a C2 column. Hydrolysis of the purified toxin yielded 14 amino acids, and calculation of the numbers of residues of each amino acid suggested a molecular mass of 7, 551 Da, A band corresponding to this molecular mass was present on SDS-PAGE gels. However, both the native peptide and its hydrolysate contained a compound that reacted with p -anisaldehyde suggesting the possibility of a glycosidic moiety.     

Production of the phytotoxins, solanapyrones A and C and cytochalasin D among nine isolates of Ascochyta rabiei

Nine isolates of Ascochyta rabiei from Pakistan were grown in still culture on Czapek Dox liquid medium supplemented with aqueous extracts of the seed of one of two cultivars, a desi (6153) or a kabuli (Cypressa). Toxicity of the culture filtrates from both media was assayed with cells isolated from the leaves of both cultivars and concentrations of the phytotoxins. solanapyrone A and solanapyrone C, in the filtrates were determined by high-performance liquid chromatography (HPLC). For eight of the fungal isolates, toxicity and solanapyrone concentration were correlated, r varying from 0·383 to 0·859 according to medium and assay cultivar, but culture filtrates of another isolate, which was the most active by more than an order of magnitude, contained cytochalasin D but neither of the solanapyrones.     

COMPLEX FORMATION AS AN ADSORPTION MECHANISM FOR LINURON AND ATRAZINE

Summary. Measurements were made of the effect of exchangeable cations on the adsorption of linuron and atrazine by an ion-exchange resin, cellulose phosphate powder, bentonite and a peat soil. The cations studied were Ca²⁺, Ni²⁺, Cu²⁺, Fe³⁺ and Ce⁴⁺. The results with linuron were consistent with the hypothesis that complex formation with exchangeable cations is a possible mechanism of adsorption. This was not so with atrazine due to complications arising from pH effects, and it seems unlikely that adsorption of atrazine by this process is significant.     

Application of a flowing solution culture technique to study the parasitic fitness of the nematode Radopholus similis on banana plantlets under two different nitrogen nutrient regimes

A flowing solution culture technique was used to study the effects of N nutrition on banana root infestation by the burrowing nematode Radopholus similis . Paired groups of banana plants were grown in separate compartments containing coarse sand (2–5 mm diameter). Input nutrient solutions had fixed compositions and identical total N concentrations. The two compartments differed in their NH₄⁺/total N concentrations, one receiving 0% NH₄⁺/total N (100% NO₃⁻/total N) and the other 60% NH₄⁺/total N (40% NO₃⁻/total N). The compartments were connected by a inverted T-shaped tube containing fine sand (200–250  μ m diameter) through which nematodes were inoculated. The pH and N concentrations of the output solution were determined at regular intervals. The pH of the output solution differed markedly between the two compartments, with values of 6.8 and 3.6 in the 0% and 60% NH₄⁺ compartments, respectively. In the compartment receiving 0% NH₄⁺, the number of nematodes in the roots and the growth of banana plants was significantly higher than in the compartment receiving 60% NH₄⁺. Even though they were more infested by nematodes, banana plants receiving 100% NO₃⁻ developed better than the less infested plants grown in the medium containing 40% NO₃⁻.     

Effect of the fungal pathogen Bipolaris sorokiniana toxin prehelminthosporol on barley root plasma membrane vesicles

The effects of the phytotoxin prehelminthosporol from the fungal pathogen Bipolaris sorokiniana on the activities of the plasma membrane H⁺-ATPase, Ca²⁺- ATPase, and 1, 3-β-glucan synthase in barley roots were investigated in vitro. Plasma membranes were isolated by aqueous polymer two-phase partitioning. Proton pumping by the H⁺-ATPase was drastically reduced in a dose-dependent manner, with complete inhibition at 500 μM prehelminthosporol, while inhibition of ATP hydrolysis was less drastic, with a 35% inhibition at 500 μM toxin. Ca²⁺ uptake was also reduced, although to a lesser extent than proton pumping, with a maximal inhibition of 60% at 500 μM toxin. The 1, 3-β-glucan synthase activity was weakly stimulated at toxin concentrations below 100 μM, with higher concentrations being inhibitory. Taken together, our results indicate that prehelminthosporol exerts its effect in at least two ways. First, it appears to disrupt the membrane barrier and thus seriously interfere with establishment of the proton gradient that drives ion and nutrient uptake and affect the efflux of Ca²⁺ to maintain the low cytoplasmic concentration of Ca²⁺ essential for the function of Ca²⁺ as a messenger in signal transduction. Secondly, it appears to inhibit the enzyme activities. The 1, 3-β-glucan synthase is activated by Ca²⁺ and can operate in the presence of low concentrations of prehelminthosporol (which may induce Ca²⁺ leakage into the cytoplasm and hence activate the enzyme), to produce callose to seal leaky membranes.     

Variation of soil physical-chemical characteristics in salt-affected soil in the Qarhan Salt Lake,Qaidam Basin

Soil salinization has adverse effects on the soil physical-chemical characteristics.However,little is known about the changes in soil salt ion concentrations and other soil physical-chemical characteristics within the Qarhan Salt Lake and at different soil depths in the surrounding areas.Here,we selected five sampling sites(S1,S2,S3,S4,and S5)alongside the Qarhan Salt Lake and in the Xidatan segment of the Kunlun Mountains to investigate the relationship among soil salt ion concentrations,soil physical-chemical characteristics,and environmental variables in April 2019.The results indicated that most sites had strongly saline and very strongly saline conditions.The main salt ions present in the soil were Na⁺,K⁺,and Cl^-.Soil nutrients and soil microbial biomass(SMB)were significantly affected by the salinity(P<0.05).Moreover,soil salt ions(Na⁺,K⁺,Ca2+,Mg²⁺,Cl^-,CO₃^2-,SO₄^2-,and HCO₃^-)were positively correlated with electrical conductivity(EC)and soil water content(SWC),but negatively related to altitude and soil depth.Unlike soil salt ions,soil nutrients and SMB were positively correlated with altitude,but negatively related to EC and SWC.Moreover,soil nutrients and SMB were negatively correlated with soil salt ions.In conclusion,soil nutrients and SMB were mainly influenced by salinity,and were related to altitude,soil depth,and SWC in the areas from the Qarhan Salt Lake to the Xidatan segment.These results imply that the soil quality(mainly evaluated by soil physical-chemical characteristics)is mainly influenced by soil salt ions in the areas surrounding the Qarhan Salt Lake.Our results provide an accurate prediction of how the soil salt ions,soil nutrients,and SMB respond to the changes along a salt gradient.The underlying mechanisms controlling the soil salt ion distribution,soil nutrients,and SMB in an extremely arid desert climate playa should be studied in greater detail in the future.     

一株抗马铃薯坏疽病生防细菌B-401产抑菌物质条件优化及稳定性

以马铃薯坏疽病菌为靶标菌株,采用含药平板法对高寒草地禾草内生细菌B-401产抑菌物质条件及抑菌物质的稳定性进行了研究。结果表明,生防菌株B-401产抑菌物质的最佳培养基配方为牛肉膏8g、酵母浸膏5.0g、葡萄糖10g、水1000mL,最适温度为23.4℃,最适pH值为7,最佳装液量为35.2mL/150mL三角瓶,最佳培养方式为光照条件下振荡培养24h,最适发酵时间为96h,优化验证试验结果表明,其对马铃薯坏疽病菌的EC₅₀＝0.111μL/mL,是优化前EC₅₀＝3.196μL/mL的3.47%。菌株B-401所产抑菌物质在25~90℃具有较好稳定性,抑菌活性均大于75%,在100℃及以上高温处理后抑菌物质活性降低;对酸碱性和紫外照射稳定,相对活性分别在77.45%和98%以上;对金属离子Na⁺、Mg²⁺和Mn²⁺稳定,相对活性达99%以上,而对Ag⁺、Cu²⁺、Zn²⁺和Fe³⁺较不稳定。     

Biocontrol of seedborne Botrytis cinerea in chickpea with Gliocladium roseum

An isolate of Gliocladium roseum proved highly antagonistic to Botrytis cinerea . Sporulation of B. cinerea on chickpea seed naturally infected or inoculated with B. cinerea was suppressed by seed treatment with conidial suspensions of G. roseum at 10⁷ and 10⁸ conidia/mL, respectively. Establishment of healthy seedlings in punnets (small trays) 5 weeks after sowing with inoculated seed was increased from 29.2% to 59.7% by treatment with G. roseum at 3×10⁷ conidia/mL, and from 1.4% to 69.4% with G. roseum at 3×10⁸ conidia/mL, the latter being equivalent to disease control by Thiram. There was no significant effect of Rhizobium on disease suppression by G. roseum , and treatment with G. roseum at 10⁸ conidia/mL did not reduce nodulation. Amendment with culture filtrates of G. roseum did not affect the growth rate of B. cinerea on potato dextrose agar, indicating that constitutive production of an antibiotic is not involved in biocontrol. A selective medium was developed to enumerate propagules of G. roseum on seed recovered from soil. There was no significant change in the population of G. roseum on seed after incubation for 4 weeks in soil to which the isolate of G. roseum was indigenous.     

Virulence for faba bean and production of ascochitine by Ascochyta fabae

The production of ascochitine by seven isolates of Ascochyta fabae accounted for the toxicity of culture filtrates of the fungus to cells isolated from leaves of Vicia faba. The LD₅₀ value for cells from cultivars that were susceptible, tolerant or resistant to the fungus was similar i.e. 3·0 × 10⁻⁵ m , 3·8 × 10⁻⁵ m and 2·9 × 10⁻⁵ M, respectively. Ascochitine affected neither the germination of seeds nor the growth of mature plants at 5·17 × 10⁻⁴ m but caused necrosis and wilting of plant cuttings at 2·5 × 10⁻⁴ m and 5·10⁻⁴ m . There was no association between virulence of 16 isolates of A. fabae for three cultivars of V.faba and the production of ascochitine in vitro. One isolate produced no ascochitine in vitro and yet was the most virulent for two of three cultivars. The toxin could not be extracted from infected plants.     

Phosphonate transport in Phytophthora capsici

Phosphate was shown to reverse the in vitro activity of phosphonate ions against P. capsici (strain 375) more efficiently in liquid than in solid media. Phosphonate transport by mycelia incubated in aqueous solutions was enhanced by a previous phosphate starvation and the presence of K⁺ cations. The intracellular phosphonate concentration reached a constant level and this concentration, which is a function of the external concentration, fits a hyperbolic relationship. Phosphonate transport was greatly stimulated when mycelia were incubated in modified Ribeiro's medium. In the absence of any phosphorus source in the growth medium, the phosphate content of mycelia at stationary phase of growth decreased. This sign of phosphate deficiency was intensified in the presence of phosphonate.     

Fusaric acid: phytotoxicity and in vitro production by Fusarium oxysporum f.sp. lilii,the causal agent of basal rot in lilies

The production of phytotoxins byFusarium oxysporum f.sp.lilii, a pathogen causing bulb and scale rot in lilies, was investigated. To determine the toxic activity of culture filtrate, a bioassay with in vitro grown scale bulblets or with callus was set up. The fungus produces toxic components in different culture media. The highest toxicity was observed in Czapek Dox medium. HPLC and GC/MS analyses revealed the presence of fusaric acid at toxic concentrations in this medium. The production of fusaric acid in time coincides with the increase of toxic activity in the culture filtrate. It is concluded that at least part of this toxicity is due to fusaric acid.     

Nematicidal activity of essential oils and organic amendments from Asteraceae against root-knot nematodes

The essential oil of Chrysanthemum coronarium flowerheads showed strong nematicidal activity in vitro and in growth-chamber experiments. Essential oil concentrations of 2, 4, 8 and 16  µ L mL⁻¹, significantly reduced hatch, J ₂ survival (determined by final value and area under curves of cumulative percentage hatch or mortality) and reproduction rate of Meloidogyne artiellia in vitro , with the lowest values occurring at 16  µ L mL⁻¹. In pot trials with chickpea cv. PV 61, essential oil concentrations of 10–40  µ L per 500 cm³ soil, applied on sterile cotton pellets, also significantly reduced the nematode's reproduction rate. The biological processes of mortality and hatching/reproduction were adequately described by the monomolecular and expanded negative exponential models, respectively. Effectiveness of soil amendment with either flowers, leaves, roots or seeds of C. coronarium , and flowers from several species of Asteraceae ( Chrysanthemum segetum , Calendula maritima , Calendula officinalis and Calendula suffruticosa ) at 5 g per 500 cm³ soil was tested for suppression of M. artiellia and growth of chickpea cv. PV 61 under growth-chamber conditions. In these tests, flowers of all five Asteraceae species and various parts of C. coronarium significantly reduced reproduction rates of M. artiellia , by 83·0–95·9%, with the minimum rates occurring in infected chickpea plants amended with flowers of C. officinalis and C. suffruticosa . The in vitro and in planta results suggest that the essential oil of C. coronarium and organic amendments from Asteraceae species may serve as nematicides.     

利用马铃薯全粉加工废水培养解淀粉芽胞杆菌产抗菌脂肽条件优化

为实现马铃薯全粉加工废水资源高值化利用,以马铃薯全粉加工废水为基础培养基,采用Plackett-Burman设计和Box-Behnken响应面设计,对解淀粉芽胞杆菌Bacillus amyloliquefaciens PC2利用马铃薯全粉加工废水发酵产抗菌脂肽的培养基进行优化。结果表明,马铃薯全粉加工废水蛋白质、游离氨基酸、游离淀粉和还原糖含量分别为16.0、2.11、0.18和1.29 mg/mL,钾、钙和镁含量分别为1.07、0.05和0.10 mg/mL,铁、锌、锰和铜含量分别为7.10、2.34、0.25和0.09 μg/mL。蔗糖、谷氨酸钠和硫酸铵是影响菌株PC2发酵抗菌脂肽的3个主要因素。菌株PC2以马铃薯全粉废水为基础培养基无抗菌脂肽产生,采用响应面法优化获得了产抗菌脂肽的最佳培养基配方为：蔗糖30.2 g,谷氨酸钠3.96 g,硫酸铵6.0 g,马铃薯全粉加工废水1000 mL,所得抗菌脂肽粗提物对金黄色葡萄球菌的抑菌圈直径为21.74 mm。采用单因素试验结合响应面法,获得最适发酵条件为：接种量6.0%,装液量50 mL/250 mL,初始pH 6.8,发酵温度31℃,摇床转速170 r/min,发酵时间35 h。获得的抗菌脂肽粗提物抑菌圈直径可达22.81 mm,较优化前增加了1.08 mm,发酵液活菌数由优化前的2.6×10⁸ CFU/mL提高至3.2×10¹⁰ CFU/mL。试验结果为马铃薯全粉加工废水资源化利用奠定了基础。     

Effects of salt stress on ion accumulation and antioxidative enzyme activities of Oryza sativa L. and Echinochloa oryzicola Vasing

The effects of salt stress on physiological factors, such as inorganic ion absorption and antioxidative enzyme activities, of rice ( Oryza sativa L. cv. Anapurna) and Echinochloa oryzicola Vasing were investigated. Although having similar morphology, rice and E. oryzicola possessed considerably different salt-tolerance mechanisms. Echinochloa oryzicola was more salt-tolerant than rice. When exposed to salt stress (100 mmol L⁻¹ sodium chloride, NaCl; six days), E. oryzicola had the ability to limit the accumulation of sodium ions (Na⁺), maintained high potassium ion (K⁺) content and had a constantly higher K⁺/Na⁺ ratio than rice. Rice was not effective in limiting Na⁺ absorption but had a higher antioxidative capacity than E. oryzicola . The constitutive activities of superoxide dismutase (SOD) and catalase of rice were three and five times higher than that of E. oryzicola, respectively. Induced activities of SOD, ascorbate peroxidase and glutathione reductase were also higher in rice than in E. oryzicola . The high antioxidative capacity was one of the tolerance mechanisms used by rice to cope with salt stress. Therefore, the salt tolerant-mechanisms are different between the two plants.     

Genetic characteristics of Fusarium verticillioides isolates from maize in Costa Rica

Thirty-nine isolates of Fusarium verticillioides from maize seeds from three regions of Costa Rica were classified on fertility, fumonisin production, vegetative compatibility and pathogenicity. The identity of the isolates was verified by sexual crosses with standard tester strains and by isozyme analysis. Twenty-three isolates (59%) were mating type A⁻ and 16 (41%) were A⁺; 29 (74%) were female fertile. The isolates produced high amounts of fumonisin B₁ when grown on sterilized maize grits, 32 isolates producing more than 1000 μg g⁻¹, as determined by TLC, and 7 less than 1000 μg g⁻¹. Vegetative compatibility tests by pairing nit mutants identified 34 vegetative compatibility groups (VCGs), of which 29 had one member and 5 had two members. Isolates belonging to the same VCG were obtained from the same seed sample. Two pathogenicity tests with different inoculation methods were performed: on toothpick inoculation of 7-week-old maize stalks, 71% of the isolates were pathogenic according to the length of the necrosis formed in the stalk, and on sand inoculation of maize seedlings all the isolates were pathogenic, according to shoot length and dry weight production. Differences in aggressiveness between some of the isolates were recorded. It is concluded that natural populations of F. verticillioides in Costa Rica consist of genetically diverse, highly fertile and pathogenic isolates that represent a potential risk for disease development and fumonisin accumulation in maize crops.     

武夷菌素高产基因工程菌发酵培养基的优化

为进一步提高武夷菌素的产量,以基因工程菌Streptomyces ahygroscopicus var. wuyiensis W273为试验菌株,采用单因子试验确定发酵培养基的最适6种营养成分为玉米粉、葡萄糖、黄豆面、氯化铵、碳酸钙和氯化镁;应用SAS软件中的Plackett-Burman设计法,对影响菌株发酵生产武夷菌素的6个因素进行了筛选,确定葡萄糖和碳酸钙为影响摇瓶发酵生产武夷菌素的主要因素。利用响应面分析法对2个主要因素的最佳水平及其交互作用进行研究,建立了二次回归方程,Y=218.18+270.28X₁+1274.74X₂-3.28X₁²-5.4X₁X₂-200.98X₂²,并最终确定最佳培养基配方为玉米粉20 g/L、葡萄糖39 g/L、黄豆面20 g/L、氯化铵4 g/L、碳酸钙2.65 g/L、氯化镁0.4 g/L。以新配方在28℃、220 r/min进行摇瓶发酵60 h后,武夷菌素效价平均值为7215 μg/mL,较原始培养基发酵后武夷菌素效价提高了26.5%。     

Chemical characteristics of precipitation and the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain,northwestern China

Precipitation chemistry analysis is essential to evaluate the atmospheric environmental quality and identify the sources of atmospheric pollutants. In this study, we collected a total of 480 precipitation samples at 6 sampling sites in the northern and southern slopes of Wushaoling Mountain from May 2013 to July 2014 to analyze the chemical characteristics of precipitation and to identify the main sources of ions in precipitation. Furthermore, we also explored the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain based on the precipitation chemistry analysis.During the sampling period(from May 2013 to July 2014), the p H values, EC(electrical conductivity)values and concentrations of cations(Ca~(2+), Mg~(2+), Na~+, K~+ and NH_4~+) and anions(SO_4~(2–), NO_3~–, Cl~–, NO_2~– and F~–) in precipitation were different in the northern and southern slopes at daily and seasonal time scales, with most of the values being higher in the northern slope than in the southern slope. The chemical type of precipitation in the southern and northern slopes was the same, i.e.,SO_4~(2–)-Ca~(2+)-NO_3~–-Na~+. The concentrations of ions in precipitation were mainly controlled by terrigenous material and anthropogenic activities(with an exception of Cl~–). The concentration of Cl~– in precipitation was mainly controlled by the sea salt fraction. The concentrations of Na+ and Cl~– showed an increasing trend after the occurrence of sand dust events both in the northern and southern slopes. In addition, after the occurrence of sand dust events, the concentrations of K~+, Mg~(2+), SO_4~(2–), NO_3~– and Ca~(2+) showed an increasing trend in the southern slope and a decreasing trend in the northern slope. It is our hope that the results may be helpful to further understand the atmospheric pollution caused by sand dust events in the Wushaoling Mountain and can also provide a scientific basis for the effective prevention of atmospheric pollution.     

阳离子对黄瓜苗期猝倒病菌果胶酶活性的影响

 本文首次从寄主-寄生物相互关系角度系统研究了阳离子对黄瓜苗期猝倒病菌Pythium aphanidermatum产生的果胶酶活性的影响,胚轴胞壁Ca²⁺含量很大,而且随苗龄增加,其含量也有规律的增加。细胞壁Ca³⁺含量变化与胚轴抗病菌果胶酶能力密切相关。不同阳离子对病菌在寄主体内、外产生的PG活性有明显影响,并随反应时间而变化。病菌在寄主体内和体外合成的PG对阳离子敏感程度不同。低浓度Ca²⁺有激活PG的作用,高浓度Ca²⁺则抑制PG活性。Na⁺超过一定浓度时有抑制PG活性的作用。PGTE比PMTE对Ca³⁺抑制作用敏感。     

Survival of Didymella rabiei in chickpea straw debris in Spain

Didymella rabiei grew saprophytically on pieces of infested chickpea stems and pods, and formed pycnidia and pseudothecia. The extent of saprophytic growth and production of viable spores were determined by the incubation conditions. On debris left on the soil surface under natural conditions, the fungus rapidly colonized the tissues, formed abundant pseudothecia and pycnidia, and remained viable throughout the 2 years of the study. When plant debris was buried, D, rabiei was restricted to the original lesions, in which it formed new pycnidia and was viable for 2 to 5 months. Under controlled conditions in the laboratory, D. rabiei extensively colonized plant debris spread over the soil surface. On the other hand, the fungus did not grow on buried debris, or showed only very limited development when the artificially infested debris was buried between two layers of sterilized soil. Incubation temperature was the principal factor associated with the production of conidia and especially ascospores.     

A semiselective medium for the isolation of Acidovorax valerianellae from soil and plant debris

Bacterial black spot of corn-salad ( Valerianella locusta ) caused by Acidovorax valerianellae appeared in France in the beginning of the 1990s. The disease is now widespread in the main area of corn-salad production and is responsible for high depreciation and significant economic losses every year. A semiselective medium is described for the detection of the bacterium in various environments and to identify primary sources of inoculum. The medium TSAV (tryptic soy broth, 3 g L⁻¹, agar 15 g L⁻¹, 5-fluorouracyl 5 mg L⁻¹, novobiocin 5 mg L⁻¹, propiconazole 5 mg L⁻¹) increased chances of obtaining cultures of A. valerianellae from naturally infested soil and from root-debris. Using TSAV, the pathogen was detected in root-debris up to 39 days after the harvest of a diseased crop. As only a few days usually separates harvest from the next sowing date, soil is likely to be an important source of inoculum for the next crop.