Dominant Colonisation of Wheat Roots by Pseudomonas fluorescens Pf29A and Selection of the Indigenous Microflora in the Presence of the Take-all Fungus

Increases in populations of fluorescent pseudomonads on wheat roots are usually associated with take-all decline, natural control of take-all, a disease caused by the fungus Gaeumannomyces graminis var. tritici (Ggt). Colonisation by Pseudomonas fluorescens strain Pf29A was assessed on the roots of healthy plants and of plants with take-all, and the effect of this bacterium on indigenous populations of fluorescent pseudomonads was studied. The efficacy of Pf29A as an agent for the biocontrol of take-all on five-week-old wheat seedlings was tested in non-sterile conducive soil in a growth chamber. RAPD (random amplification of polymorphic DNA) fingerprinting with a decamer primer was used to monitor strain Pf29A and culturable indigenous rhizoplane populations of fluorescent pseudomonad. Pf29A decreased disease severity and accounted for 44.6% of the culturable fluorescent pseudomonads on healthy plant rhizoplane and 75.8% on diseased plant rhizoplane. Fewer RAPD patterns were obtained when Pf29A was introduced into the soil with Ggt. In the presence of Ggt and necrotic roots, Pf29A became the dominant root coloniser and dramatically changed the diversity and the structure of indigenous fluorescent pseudomonad populations. The results show that Ggt and reduced lesion size on roots can trigger a specific increase in antagonist populations and that the introduction of a biocontrol agent in soil influences the structure of indigenous bacterial populations.     

Direct and Specific Assessment of Colonisation of Wheat Rhizoplane by Pseudomonas fluorescens Pf29A

The efficacy of fluorescent pseudomonads as suppressors of soil-borne diseases is linked to their ability to colonise plant roots. Monitoring the dynamics of biocontrol agents in the rhizosphere should improve the irreliability. We designed a pair of Sequenced Characterised Amplified Region (SCAR) primers specific to Pseudomonas fluorescens Pf29A, based on a specific 700 bp RAPD product selected in a previous work. Primer specificity was tested with DNA samples extracted from rhizospheric soil and rhizoplane of wheat plants grown in two different non-sterile soils. We assessed the total population of Pf29A by PCR and the culturable population by counting a tetracycline-resistant Pf29A transformant producing Green Fluorescent Protein (GFP), on selective medium 5 days after inoculation of non-sterile soil. SCAR primers were specific for Pf29A in both soils. We evaluated the limit of detection to 14.2 fg of target DNA, equivalent to 242 Pf29A cells per cm of wheat root. Culturable populations of Pf29A transformant accounted for 13% and 4% of the total populations 5 days after treatment with 10³ and 10⁷ CFU of transformed Pf29A per gram of soil. The SCAR derived sequence is a good candidate to develop a strain specific and sensitive PCR-quantification of Pf29A available for population dynamic studies in fields. We confirm that only a small proportion of the total Pf29A rhizosphere population is culturable.     

A case study of infection of rice roots by deleterious fungi and minor pathogenic<Emphasis Type="Italic"> Pythium</Emphasis> species in a paddy field

Roots of rice plants grown in paddy fields in a transplant culture system were collected seven times between 8 and 22 weeks after transplanting, for two crop seasons. Rice seedlings grown in a potting medium amended with the collected roots were significantly shorter than those grown in the same medium either without the addition of the roots or amended with pasteurized, collected roots indicating that seedlings were inhibited by heat-labile microorganisms on the collected rice roots. Ninety-five and 172 pure cultures of Pythium spp. and fungi, respectively, were isolated from the rice roots collected 5 or 7.5 weeks after transplanting in the fields. Among these microorganisms, Pythium aristosporum inhibited seedling growth in greenhouse experiments, and Acremonium sp., Alternaria sp., Epicoccum nigrum, Fusarium sp., Massarina sp., Penicillium spp., Rhinocladiella sp., Stemphylium sp., Trichocladium sp., and several unidentified fungi inhibited seminal root growth in in vitro experiments. These microorganisms might be involved in the inhibition of seedling growth in soils amended with the rice roots collected from the paddy field. Thus, roots of rice plants at the middle stage of growth transplanted into paddy fields can harbor pathogenic or deleterious fungi or Pythium sp(p). The effects of these microorganisms on rice growth in paddy fields are discussed.     

Dynamics of the root/soil pathogens and antagonists in organic and integrated production of potato

Microbial communities in the root, rhizoplane, and rhizosphere and non-rhizosphere soil in potato, in organic and integrated production systems, were compared at the emergence and flowering phases of plant development. Microorganisms were identified on the basis of their morphology. The dominant groups included Clonostachys + Gliocladium + Trichoderma, Fusarium + Gibberella + Haematonectria + Neonectria, Paecilomyces, Penicillium and Phoma. Microbial density at the flowering phase was often significantly greater in roots and non-rhizosphere soil than in the rhizoplane and rhizosphere. Diversity of the communities often remained stable or was greater at the emergence phase. The density of bacteria changed with time. The density of Pseudomonas often decreased while Streptomyces significantly increased with time. Changes in densities of pathogens and antagonists decreased the suppressiveness of the habitat towards soil-borne potato pathogens at the flowering phase. The study contributes information that will help to: (a) understand the epidemiology of some potato diseases, (b) make decisions on the economic and ecological aspects of chemical control in potato, (c) develop strategies for manipulation of the soil microbial environment as a viable crop management technique, and (d) develop prognosis models for potato diseases in central Europe.     

Analysis of nematodes and soil-borne fungi fromAmmophila arenaria (Marram grass) in Dutch coastal foredunes by multivariate techniques

A survey was carried out at nine locations in the Dutch coastal foredunes to identify the species of soil borne fungi and nematodes associated withAmmophila arenaria (Marram grass).Ammophila arenaria is a sand binding grass that is very important for the stabilization of coastal foredunes. Degeneration of the plants occurs at stabilized sites and is supposed to be caused by a combination of soil-borne fungi and nematodes. Canonical correspondence analysis (CCA) and two-way indicator species analysis (TWINSPAN) were used to examine which fungal and nematode species usually coexist in the rhizosphere of vigorous and early declining stands ofA. arenaria. In total, 47 species of fungi and 10 genera of plant-parasitic nematodes were found. According to CCA, the community of soil organisms of stands that were more than 10 years old was significantly different from recently established stands of 3 years old. Also, the community of soil organisms isolated from calcareous locations differed significantly from that of lime-poor locations. No relationship between the vigour of the plants (vigorous vs. early declining) and the soil borne species composition was found, although in roots of vigorous stands, the number of nematodes was higher than that of early declining stands. A relatively large group of soil organisms occurred generally. This group possibly contains an ubiquitous pathocomplex that cause the growth reducing effects of biotic origin which generally occur inA. arenaria. Analysis of this group of nematodes and fungi by TWINSPAN resulted in 9 different combinations of concurring soil organisms of which 5 combinations were present at all investigated locations. Two of the latter combinations contained both nematodes and fungi. The first contained three endoparasitic nematodes (Meloidogyne maritima, Heterodera spp. andPratylenchus sp.) that concurred with the fungusMucor hiemalis. The second group containedHeterodera spp.,Telotylenchus ventralis, Filenchus sp. together with the potentially plant-pathogenic fungiMicrodochium bolleyi and Fusarium culmorum, as well as the fungiMortierella sp. andTrichoderma harzianum, all in relatively high numbers.It is concluded that both CCA and TWINSPAN are valuable exploratory techniques, especially when used in combination, to detect possible combinations of soil organisms which may be involved in the degeneration ofA. arenaria. Further identifications of harmful organisms should be obtained from experiments.     

刺五加根际效应和土壤环境因子对土壤跳虫群落结构的影响

为明确刺五加根际效应和土壤环境因子对土壤跳虫的影响,于2019年6-8月在中国科学院辽河源农业生态研究与示范基地调查刺五加根际和非根际土壤的跳虫总属数、个体数、功能性状参数以及群落特征参数,同时利用Pearson分析法和冗余分析法研究刺五加根系分泌物和土壤环境因子对跳虫群落结构的影响。结果表明,6-8月在根际土壤中捕获棘?属跳虫176头,所占比例为34.37%,为优势属,捕获钩圆?属、球角?属、长脚?属、德?属跳虫分别为26、37、32和31头,所占比例分别为5.08%、7.23%、6.25%和6.05%,均为常见属;在非根际土壤中,捕获棘?属跳虫91头,所占比例为17.77%,为优势属,捕获钩圆?属、球角?属、长脚?属、德?属跳虫分别为28、33、19和39头,所占比例分别为5.47%、6.45%、3.71%和7.62%,均为常见属;6月,刺五加根际土壤的跳虫总属数、个体数、Pielou均匀度指数分别为3.50、14.92和0.72,非根际土壤的跳虫总属数、个体数、Pielou均匀度指数分别为2.83、8.83和0.87,与根际土壤的差异显著;根际土壤跳虫的体宽、体长、触角与体长的比值、栖息环境功能性状值分别为0.73 mm、4.4 mm、0.19和0.18,显著低于非根际土壤跳虫的0.79 mm、5.58 mm、0.32和0.40;根际土壤pH与土壤跳虫群落的总属数、个体数呈正相关,与Pielou均匀度指数呈负相关,非根际土壤pH与土壤跳虫的个体数呈正相关;德?属、球角?属跳虫与土壤丁香酸含量、水杨酸含量、没食子酸含量呈负相关,长?属跳虫与土壤丁香酸含量、水杨酸含量和没食子酸含量呈正相关,棘?属和钩圆?属跳虫与土壤丁香酸含量呈负相关。表明土壤环境因子和刺五加根际效应对土壤跳虫群落有影响。     

玉米矮化病株及其根际土壤内线虫的分离与分子鉴定

为探究玉米矮化病的病原,采用Ludox TM悬浮法对从吉林和辽宁采集的玉米矮化病株及其根际土壤和健康株根际土壤分离的线虫进行了鉴定和种群比较,并对矮化病株茎基组织PCR产物进行测序分析。结果表明:玉米健康株根际土壤分离出29属线虫,特有线虫是角咽线虫属Actinolaimus和木盾移线虫属Peltamigratus,矮化玉米病株根际土壤分离出28属线虫,特有线虫为锥线虫属Dolichorus,二者相同的线虫属有27个。矮化玉米病株根际土壤中植物线虫种类和数量明显比健康株根际土壤中高,线虫种群数量差异明显的主要是矮化线虫属Tylenchorhynchus、短体线虫属Pratylenchus和刺线虫属Belonolaimus,病株根际土壤中这3个属线虫总数约占病株土壤分离线虫总数的20.23%、11.27%和10.40%。玉米矮化病株茎基组织中短体线虫属和矮化线虫属数量占优势,2个属的线虫数量分别占测序总数的22%、14%(吉林长岭)和16%、20%(辽宁黑山)。表明玉米矮化病的发生与植物线虫相关,很可能是多种线虫共同引起的病害。     

Rhizosphere Competence of Pythium oligandrum

ABSTRACT The associations of Pythium oligandrum with the root cortex, rhizoplane, and rhizosphere were measured with 11 crop species. This work was expedited by the use of a semiselective technique for isolation of P. oligandrum from soil and plant material. Cortical colonization of roots by P. oligandrum was not detected, and the rhizoplanes of the roots of most crops were free of the fungus. However, P. oligandrum was detected in large quantities with every crop tested when roots with adhering soil (rhizosphere soil) were assayed. Different crop species and cultivars of cantaloupe, cauliflower, and tomato varied in rhizosphere densities of P. oligandrum, but rhizosphere population densities of the fungus were consistently higher than in nonrhizosphere soils with plants grown in P. oligandrum-infested sterilized potting mix or an unsterilized mineral soil. After transplanting tomatoes into potting mix infested with P. oligandrum, increases in CFU occurred over time in the rhizosphere but not in the nonrhizosphere soil. In trials on delivery methods of inoculum of P. oligandrum, the rhizosphere populations of tomato plants grown in potting mix were about sixfold higher compared to seed-coat treatments when ground, alginate pelleted oospores were applied to seedlings growing in plug containers prior to transplanting or to pots containing potting mix before direct seeding.     

Fungal infestation of seeds from seven populations of wild oats (Avena fatua L.) with different dormancy and viability characteristics

Seeds from seven genetically inbred pure lines of wild oats (Avena fatua L.) with different levels of dormancy and viability were analysed for seed-borne fungi. All lines had fungi on the seeds. The predominating fungi were Alternaria alternata and Cladosporium herbarum, of which the latter was non-pathogenic and the former only weakly pathogenic on seedlings of wild oats. Drechslera avenacea, Cochliobulus sativus and Fusarium spp., frequently isolated, were pathogenic on A. fatua. Only D. avenacea was host specific to A. fatua and cultivated oats Avena sativa. Cochliobolus sativus and Fusarium spp, were equal or more pathogenic on seedlings of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), oats and rye (Secale cereale L.) than on seedlings of A. fatua. Drechslera avenacea occurred on a significantly higher percentage of seeds from A. fatua lines, AN 51 and AN 474, than from the other lines. Other fungi isolated occurred randomly on all A. fatua lines. There was no relationship between low viability of seeds and fungi carried on the seeds.     

Genetic diversity and identification of race 3 of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">lactucae</Emphasis> in Taiwan

Sorghum is an important drought tolerant crop cultivated for food and fodder purposes. Anthracnose disease caused by Colletotrichum graminicola is a major constraint in sorghum productivity in India. Certain antagonistic fungi, that were isolated in the previous study from the rhizosphere and rhizoplane of perennial grasses in India, were studied for their antagonism in vitro to C. graminicola, root colonization ability and rhizosphere competence. Out of 138 isolates tested, 89 were antagonistic. Fifteen fungal isolates with greater than 70 % in vitro inhibition zone to the pathogen tested positive for root and rhizosphere colonization abilities. Three isolates – Chaetomium globosum isolate 57, Trichoderma harzianum isolate 184 and Fusarium oxysporum (NSF isolate 9) with prominent biocontrol potentials were tested for the control of sorghum anthracnose in greenhouse and field. Chaetomium globosum, Trichoderma harzianum and Fusarium oxysporum isolates decreased seedling mortality, and incidence and severity of disease at different growing stages. They promoted plant growth (dry biomass- 45.3, 40.0 and 46.7 %) and increased yield (grain biomass- 33.3, 23.8 and 49.2 %) respectively, over control in field. The population of the above fungi in soil was moderately high at harvest stage. The present investigation revealed that fungal isolates from rhizosphere and rhizoplane of perennial grasses could be employed to manage anthracnose and enhance plant growth and yield potentialities in sorghum, at the same time.     

解淀粉芽孢杆菌LJ1诱导黄瓜抗白粉病的研究

解淀粉芽孢杆菌LJ1是从土壤中分离得到的一株对黄瓜白粉病具有较好防效的生防细菌。田间试验发现,用LJ1发酵上清100倍稀释液喷施黄瓜幼苗,在施药后14 d时其对黄瓜白粉病的防效可达83.45%。为研究LJ1防治病害的作用机制,用LJ1发酵上清100倍稀释液喷施黄瓜幼苗,测定黄瓜叶片中的超氧化物歧化酶(SOD)、多酚氧化酶(PPO)、苯丙氨酸解氨酶(PAL)等与诱导抗病性相关的酶活性和信号分子水杨酸含量的变化,并检测了苗期根围土壤中真菌的动态。结果显示,经过LJ1发酵液处理后3种酶的活性和水杨酸的含量在不同时间点均有一个骤增的过程,其活性显著高于对照,并且7 d后土壤中的可培养真菌数量急剧减少。说明LJ1发酵液中有诱导黄瓜产生抗病性的物质,并且诱导后分泌的抗性物质对真菌具有广谱性。     

Quantitative relationships between the weed flora after cultivation and the seed population in the soil

Eighty comparisons were made between the numbers of weed seedlings emerging after seedbed preparation and the numbers of apparently viable seeds extracted by sieving and flotation from samples of the top 10 cm of soil. When soil moisture was adequate, the total seedling numbers represented 3–6% of the numbers of seeds; when dry weather followed cultivation, the percentages were lower than this. The percentages were relatively high for Poa annua L. and Stellaria media (L.) Vill. but low for Chenopodium album L. and Papaver spp. Relatively high numbers of seeds of Potygonum aviculare L. gave rise to seedlings in early spring but few appeared on seedbeds prepared after mid-May; the reverse was true for Aphanes arvehsis L. It is suggested that data of this kind could provide a basis for predicting weed floras following cultivation at any time of year from determinations of seed numbers made at the start of the year.     

Germination of chlamydospores of Fusarium oxysporum f. sp. pisi race 1 in the rhizosphere,and penetration of the pathogen into roots of a susceptible and a resistant pea cultivar

Germination of chlamydospores ofFusarium oxysporum f. sp.pisi race 1 in the rhizosphere of pea seedlings and red clover seedlings grown in natural soil heavily infested with the pathogen, was highest in percentage along the actively growing parts of the roots. At these sites, exudation of ninhydrinpositive substances and reducing sugars was most intense with seedlings grown in vitro.No significant difference in the percentage of germinating chlamydospores ofFusarium oxysporum f. sp.pisi race 1 were observed in the rhizosphere soil and on the root surface of homologous parts of roots of seedlings and mature plants of a susceptible Rondo and a resistant Rovar pea cultivar grown in natural soil heavily infested with the pathogen. Differences in the growth of mycelium of the pathogen on the root surface, or in the attachment of the mycelium to the root surface of both cultivars were not observed. Epidermis and cortex cells of roots of both cultivars reacted on penetration by the pathogen by producing a cellulose thickening of the cell wall, which later became infiltrated with a ligning-like material. A selective effect on the activities of the pathogen in the rhizosphere, on the root surface and in the epidermis and cortex in relation to resistance thus could not be demonstrated. Formation of new chlamydospores from germ tubes of germinating chlamydospores was frequently observed in the rhizosphere of the susceptible and resistant pea cultivar and in the rhizosphere of red clover seedlings.     

Interactions between the biocontrol agent Pseudomonas fluorescens CHA0 and Thielaviopsis basicola in tobacco roots observed by immunofluorescence microscopy

Pseudomonas fluorescens CHA0 protects plants from damage caused by several soilborne fungi. In this work, immunofluorescence microscopy was used to investigate the colonization of tobacco roots by CHA0 and its physical relationship with the black root rot fungus Thielaviopsis basicola . The pseudomonad colonized the rhizoplane shortly after planting of tobacco seedlings in sterile soil microcosms, in which it had been introduced as soil inoculant. CHA0 was found between and inside cells in the epidermis and the cortex, as well as in the xylem vessels, within 4–7 days after planting of seedlings. The presence of CHA0 delayed the colonization of the interior of tobacco roots by T. basicola compared with the treatment in which only the fungus had been inoculated. Likewise, the pseudomonad reduced the extent of black root rot from 82% to 28%. However, CHA0 was seldom found in contact with the mycelium of T. basicola or in its vicinity, indicating that direct colonization of the mycelium of T. basicola by CHA0 was not required for protection of tobacco against black root rot. Overall, the results suggest that the interior of the root is a key site for implementation of the strain's biocontrol activity against soilborne plant-pathogenic fungi.     

Effects of sodium azide and methyl bromide on soil bacterial populations,enzymic activities and other biological variables

The application of a granular formulation of sodium azide (Smite 8G), to pine nursery beds at rates of 0, 22.4, 67.2 and 134.5 kg active ingredient ha^?1 under water seal or plastic seal, was compared over a 1-year period with methyl bromide, applied at a rate of 650 kg ha^?1, to determine the effects of soil bacterial populations, soil enzymic activities, development of mycorrhizal roots, weed population and incidence of root diseases. Bacterial populations at 24 days after treatment had increased in proportion to the amount of sodium azide added; however, highest numbers of bacteria were recorded from the methyl bromide-treated plot. At the last sampling date no significant differences were observed in bacterial populations among treatments. Neither sodium azide nor methyl bromide caused permanent changes in soil enzymic activities or adversely affected mycorrhizal root development on pine seedlings. Sodium azide at 134.5 kg ha^?1 and methyl bromide both significantly decreased the number of Cyperus spp. plants in plots; however, the number of pine seedlings exhibiting a root disease was highest in plots receiving these treatments.     

Pratylenchus species of soybean in Croatia1

The numbers and species of phytoparasitic nematodes on soybean were studied over several years in Croatia, especially in the regions of Slavonija and Baranja. 19 phytoparasitic species were found, and of these Pratylenchus spp. predominated. These nematodes were found in mixed populations and their numbers were, at times, enormous. The average number per 100 ml of soil was about 100 individuals, with a maximum of 3348. The relationship between the number of nematodes and yield of soybean was calculated by a single regression equation. The soybean cultivars Sava and OS-88 apparently possess tolerance to relatively high numbers of Pratylenchus spp. in the rhizosphere.     

Antagonistic Pythium against pathogenic Pythium on cucumber roots1

Antagonistic microorganisms introduced into the growing medium, the seed or the root, have been shown to reduce the attack of many soil-borne plant pathogenic fungi. In 1983, three experiments with Pythium oligandrum were carried out using cucumber seedlings artificially inoculated with Pythium splendens. The seedlings cv. Ideal Nova were grown in shallow boxes containing granulated rockwool fibre (Grodania). The plants were grown at a minimum temperature of 20°C in a glasshouse. Plants were treated with the antagonist either by coating the seeds, or by applying a disc of a PDA-culture to 9-day old seedlings. The pathogen was introduced 9 or 5 days later, respectively, by adding PDA culture discs to the rockwool; 15 and 38 days later, the area with attacked roots was calculated as a percentage of the box-bottom area. The experiments showed that it is possible to control P. splendens by either method of application. P. oligandrum was able to colonize the seed and rhizosphere and suppress P. splendens for at least 38 days. If future experiments are similarly positive, the methods for use in commercial horticulture should be worked out as soon as possible.     

生防荧光假单胞菌CPF-10对西瓜根围土壤真菌群落的影响

探讨了生防菌荧光假单胞菌Pseudomonas fluorescens CPF-10对西瓜根围土壤真菌群落结构的影响。采用传统分离培养法,结合变性梯度凝胶电泳(DGGE)分析,研究了施用CPF-10后不同生育期西瓜根围土壤真菌群落结构的变化。结果表明:施入生防菌CPF-10后2周,其对土壤真菌有一定的促进作用;第3～7周时,CPF-10对土壤真菌尤其是部分病原菌有较强的抑制作用;CPF-10对丛枝菌根真菌(AMF)有一定的促进作用,可维持3周左右;收获期后则检测不到CPF-10对土壤真菌群落的影响。生防菌CPF-10对西瓜根围土壤真菌群落产生的短暂影响不会对土壤生态系统构成长期威胁。对比土著真菌及丛枝菌根真菌的DGGE图谱和切胶条带测序结果,发现DGGE技术更适用于分析小范围特定菌属如丛枝菌根真菌的变化。     

连续施用不同氮量对半干旱地区马铃薯根际真菌群落结构的影响

针对马铃薯生产中因氮肥过量施用导致的土壤微生物群落结构失衡和多样性下降等问题,在始于2013年的不同氮肥用量(N0:不施氮,对照;N75:施氮量75 kg·hm~(-2);N150:施氮量150 kg·hm~(-2);N225:施氮量225 kg·hm~(-2);N300:施氮量300 kg·hm~(-2);N375:施氮量375 kg·hm~(-2))田间定位试验中,于2017年马铃薯成熟期采集根际土壤,应用Illumina PE250测序等分子生物学手段,研究连续5 a施用不同氮量对半干旱地区马铃薯根际真菌群落结构的影响。结果表明:不同施氮量对马铃薯根际真菌群落物种组成造成了显著影响,子囊菌门、Mucoromycota和担子菌门是3个优势门类真菌(相对丰度1.0%),以子囊菌门的相对丰度最大,占总序列的75.48%～83.95%,其优势属是Plectosphaerella(29.92%)和镰刀菌属(13.54%);马铃薯干腐病和枯萎病的病原菌——镰刀菌属的相对丰度随施氮量增加呈增大的趋势。马铃薯根际真菌Alpha多样性随施氮量的增加而降低。连续5 a超量施氮导致了0～20 cm表层土壤中NO~-_3-N含量显著增加,N375处理的NO~-_3-N含量是N0处理的3.76倍。连续5 a超量施氮也显著降低了根际pH值和速效磷含量,N375处理比N0处理pH值和速效磷含量分别降低了0.17个单位和32.10%。RDA及相关性分析结果表明,土壤硝态氮含量是影响马铃薯根际真菌群落结构变化的主要因素(F=1.571,P=0.043~*)。连续大量施用氮肥显著降低了马铃薯块茎产量,连续施氮5 a后,由于土壤剖面中NO~-_3-N的积累,最高产量施肥量由2013—2014年的N225减低为N75,其它施氮处理较N75分别减产了3.46%、22.81%、26.05%和25.32%。长期过量施用氮肥使马铃薯根际硝态氮大量累积,导致pH值降低,进而使根际真菌多样性降低;同时过量氮肥施用会使根际中土壤真菌病原菌相对丰度增加,不利于土壤的健康和马铃薯的高产。     

Mitigation of vanillic acid-promoted faba bean Fusarium wilt by faba bean–wheat intercropping

Long-term continuous monocropping of faba beans increases the incidence of faba bean wilt, while faba bean–wheat intercropping can effectively control it. This study aimed to understand the underlying mechanism of faba bean–wheat intercropping for the control of Fusarium oxysporum and vanillic acid (VA)-promoted occurrence of faba bean wilt. The occurrence of faba bean wilt was investigated among the monocropped and intercropped plants of faba beans in a field experiment. The contents and types of phenolic acids were examined in the rhizosphere soil. Monocropped and intercropped faba beans were examined under the dual stress of F. oxysporum and different concentrations of VA (0, 50, 100, 200 mg/L) to understand the alleviating mechanism of faba bean–wheat intercropping. Exogenous addition of high concentrations of VA significantly inhibited the growth and reproduction of F. oxysporum, but under the dual stress of F. oxysporum and different concentrations of VA, it significantly inhibited the defence enzymes of faba bean roots, stems, and leaves, and rhizosphere soil enzymes. Interestingly, faba bean–wheat intercropping alleviated VA stress and thereby the incidence and disease index of faba bean Fusarium wilt by improving plant resistance and soil enzyme activity. The dual stress of F. oxysporum and VA promotes the occurrence of Fusarium wilt by damaging the defence system of the faba bean root system and rhizosphere soil environment. However, faba bean–wheat intercropping effectively alleviates the autotoxicity of VA by improving the physiological and biochemical resistance of faba beans and soil enzyme activities, and thus controls the occurrence of Fusarium wilt.