Damping-off of cabbage plug seedlings caused by Pythium ultimum var. ultimum in Japan

In October 2004, Pythium ultimum var. ultimum was isolated from rotten stems of cabbage plug seedlings in a commercial nursery in Mie Prefecture (Japan). The isolated fungus was then used to inoculate seedlings and subsequently reisolated from the seedlings with the damping-off disease, showing that P. ultimum var. ultimum is a new pathogen causing cabbage seedling disease.     

Substrate Colonization, Strain Competition, Enzyme Production In Vitro, and Biocontrol of Pythium ultimum by Trichoderma spp. Isolates P1 and T3

The antagonistic Trichoderma spp. isolates P1 and T3 differed in their ability to colonize and to compete in sphagnum peat moss and on wood chips. In peat supplemented with straw, isolate T3 produced twice as many colony forming units (cfu) as isolate P1. On wood chips, the two isolates formed a similar number of cfu. When the two Trichoderma isolates were cultivated together approximately 85–90% of the cfu were from T3 on both substrates. The presence of Pythium ultimum in peat amended with straw did not influence the number of Trichoderma cfu formed. The two Trichoderma isolates produced different amounts of hydrolytic enzymes both in liquid cultures and in peat. Seven different enzyme activities were tested. Enzyme production by T. harzianum isolate T3 was less influenced by the type of carbon source amendment than that of isolate T. atroviride P1. Culture filtrates of isolate P1 grown on complex carbon sources were high in endochitinase activity, whereas cellulase and endo-1,3--glucanase activities were more pronounced in filtrates of isolate T3. There was no significant difference between the two isolates in their ability to protect cucumber seedlings against P. ultimum while the combination of the two fungi resulted in significantly less biocontrol than each isolate alone.     

Aggressiveness and production of cell-wall degrading enzymes by Pythium violae, Pythium sulcatum and Pythium ultimum, responsible for cavity spot on carrots

This study investigated the relationships between pathogenesis, types of symptoms and in vitro production of cell-wall degrading enzymes by P. violae, P. sulcatum and P. ultimum. The three pathogens, considered as the three Pythium species principally responsible for cavity spot on carrot roots, secreted only low levels of fatty acid esterases activity, suggesting they have limited ability to degrade suberin in the walls of the outer cell layers of carrot tissues. Among the enzymes that degrade cell-wall polysaccharides, only pectate lyases and cellulases were produced by P. violae, and these were produced late and in small amounts: the symptoms caused by P. violae were limited and typical of cavity spot. Conversely, P. ultimum caused maceration of tissues, and secreted polygalacturonases and -1,4-glucanases earlier and in larger amounts than P. violae. P. ultimum also produced a large diversity of proteins and cellulase isoenzymes. Although secreting all the monitored enzymes in higher quantity than the two previous species, P. sulcatum was responsible for only typical limited symptoms of cavity spot, with a brown colouring. The role of plant reactions induced in response to early pectinolytic enzyme production by P. sulcatum may account for this apparent inconsistency.Died on April 11, 1997     

Production of Indole-3-acetic Acid and Tryptophol by Pythium ultimum and Pythium Group F: Possible Role in Pathogenesis

Pythium group F is a minor pathogen which induces symptomless infections that occur frequently and results in yield losses in tomato soilless cultures. To elucidate the mode of action of this microorganism, the influence of culture filtrates of Pythium group F on tomato growth was investigated and compared to that of the pathogen Pythium ultimum. Depending on metabolite production by the fungus, marked differences were observed in plant response. Pythium group F crude culture filtrates or low molecular weight fractions (< 500) caused swelling behind the root tip and reduced root growth; the cohesion and adherence of cells within the cortical area were also affected. These symptoms were similar to those observed on plants treated with indole-3-acetic acid. By contrast, P. ultimum filtrates caused a marked distortion of cell shape accompanied with folding of host cell walls, particularly in the cortical area. These symptoms were characteristic of the activity of toxic compound(s) on host cells. Chemical analysis of the filtrates demonstrated that indole-3-acetic acid and tryptophol were produced by Pythium group F and P. ultimum. However, Pythium group F took up and metabolized more indole-3-acetic acid precursors, especially tryptophan, a key amino acid in the pathways leading to indole-3-acetic acid synthesis. The fact that Pythium group F and P. ultimum transformed tryptamine and indole-3-acetaldehyde into indole-3-acetic acid and tryptophol confirms the existence of a tryptamine pathway within both fungi. These results support the hypothesis that auxins facilitate Pythium group F infections. On the other hand, toxin(s) and hydrolytic enzymes are likely involved in P. ultimum pathogenesis.     

哈茨木霉菌(Trichoderma harzianum)和终极腐霉菌(Pythium ultimum)对玉米蛋白质组的影响(I)

 哈茨木霉(Trichoderma harzianum) T22菌株已普遍用于防治包括由终极腐霉(Pythium ultimum)引起的苗病或根腐病在内的各种病害。玉米自交系Mo17种子经T22处理后播种在接种腐霉或未接种的田间土壤内,5 d后取幼苗的根系或幼茎提取蛋白。结果表明:在接种腐霉菌的土壤内,未进行T22处理的5 d龄幼苗长势明显比对照差,而经T22处理的幼苗长势明显比对照好。T22和腐霉菌复合处理及T22单独处理对幼苗生长影响基本相同。本研究建立了蛋白质提取和双向电泳分离技术。通过双向电泳及相应的分析软件(PDQuest^TM 2-D softw are)可将不同处理的幼苗自交系蛋白进行分离。T22菌株处理的根系产生104种上游调控蛋白和164种下游调控蛋白,T22与腐霉菌复合处理可产生97种上游调控蛋白和150种下游调控蛋白,而用腐霉菌单一处理诱导的上游或下游蛋白的数量明显少于上述2个处理。T22或腐霉菌单一或复合处理的根系蛋白质组图谱与空白对照相比差异显著,它们与对照的蛋白质组图谱相似系数分别为0.72、0.51和0.49;T22与腐霉菌分别处理的蛋白质组图谱间也相差明显,两者的相似系数仅为0.65。进一步研究发现,T22菌体蛋白质组图谱与上述各种处理的蛋白质组图谱相似系数均很低,说明各种处理诱导后的幼苗根系蛋白质组组分主要来自植物本身,其变化主要因T22或腐霉菌的诱导所致。腐霉菌的侵染对寄主根系蛋白组图谱影响明显高于T22的作用。蛋白质组中各种蛋白质的质谱分析(M ALDI-TOF)与鉴定将另文发表。     

Infection of Norway spruce (Picea abies (L.) Karst.) seedlings with Pythium irregulare Buism. and Pythium ultimum Trow.: histological and biochemical responses

We have studied the reaction of Picea abies seedlings to infection with Pythium. The highly virulent species Pythium ultimum and the less virulent species Pythium irregulare germinated on the root and hypocotyl surface, formed appressoria and penetrated through the stomata as well as through the epidermis. No major differences in the growth of both fungal species were observed during the early events of colonization. The less virulent species formed about 25% more appressoria suggesting that the fungus experienced difficulties with penetration. Differences were observed in the response of the host plant to infection. Autofluorescence, possibly related to deposition of lignin or lignin-like materials increased more in cortical and endodermal tissue colonized with the highly virulent P. ultimum than with the less virulent P. irregulare. Chitinase activity was highest in the tissues most extensively colonized by the fungus. In addition, a systemic increase of chitinase activity was also detected. Interestingly, chitinase activity increased systemically in cotyledons which were never in contact with the pathogen, indicating the translocation of a systemic signal. Salicylic acid was also detected in spruce seedlings; its level increased in roots during infection with the less virulent P. irregulare.     

Influence of electrical conductivity on biological activity of Pythium ultimum and Binab T in a closed soilless system

Journal of Plant Diseases and Protection - The effects of electrical conductivity (EC) of the nutrient solution on the performance of the commercial biocontrol product Binab T against the root...     

Suppression of Seedling Damping-Off Caused by Pythium ultimum, P. irregulare, and Rhizoctonia solani in Container Media Amended with a Diverse Range of Pacific Northwest Compost Sources

ABSTRACT Suppression of seedling damping-off disease caused by Pythium spp. and Rhizoctonia solani is a potential benefit of formulating soilless container media with compost. Thirty-six compost samples from Pacific Northwest commercial composting facilities were analyzed for a number of physical, chemical, and biological properties, including suppression of damping-off caused by Pythium ultimum, P. irregulare, and R. solani. The samples were produced from diverse feedstocks and composting technol ogies; this was reflected in a large degree of variability in the measured properties. When mixed with sphagnum peat moss and inorganic aggregates, 67% of the compost samples significantly suppressed P. irregulare damping-off of cucumber, 64% suppressed P. ultimum damping-off of cucumber, and 17% suppressed damping-off of cabbage caused by R. solani. Suppression of Pythium damping-off was related to the potential of compost to support microbial activity and a qualitative index of ammonia volatilization. Suppression of Rhizoctonia damping-off was not related to any one compost factor. Currently available compost products potentially could provide commercially acceptable control of damping-off caused by Pythium spp., but it is necessary to fortify composts with microbial antagonists for the control of R. solani.     

小麦全蚀病生防细菌的筛选和鉴定

为获得对小麦全蚀病菌有良好拮抗效果的生防菌株,分别从河南省商丘市及驻马店市小麦全蚀病发生田块中采集小麦根际土样,采用稀释平板涂布法共分离到1051株细菌,通过与全蚀病菌G1037菌株进行平板对峙筛选,最终获得9株具有明显拮抗效果且生长状况良好的菌株。16S rDNA序列比对及生理生化性状分析结果表明：菌株P155、P154、P16及P147为荧光假单胞菌Pseudomonas fluorescens,菌株P188和P97为恶臭假单胞菌Pseudomonas putida,菌株LY3为产酶溶杆菌Lysobacter enzymogenes,菌株S38为嗜根寡养单胞菌Stenotrophomonas rhizophila,菌株B20为洋葱伯克霍尔德Burkholderia cepacia。产抗生素相关基因的检测结果发现,菌株P147含吩嗪和硝吡咯菌素合成基因,菌株B20含硝吡咯菌素合成基因。除B20、LY3、S38和P147外,其余菌株均可产生嗜铁素。9株细菌都产蛋白酶。除P97、B20和S38外,其余菌株均可产脂肽类物质。盆栽试验结果表明,9株生防菌对小麦全蚀病都具有较好的防治效果,菌株P155和P154的防治效果最好,相对防效分别为67.11%和63.82%,略高于3%的苯醚甲环唑种衣剂的防治效果。研究结果表明这些细菌具有作为小麦全蚀病生防菌的潜力。     

两株荧光假单胞杆菌菌株对烟草黑胫病病原菌的抑制作用

烟草黑胫病是一种典型的土传病害，在我国，除个别较寒冷的地区，各主要产烟省均有不同程度的发生。其中安徽、河南、山东为历史上的重病区；云南、贵州、福建、广东、湖南、四川等烟区发生也相当普遍，且多与烟草青枯病混合发生，危害更为严重。根际细菌防治土传病害是     

Influence of a Fungus-Feeding Nematode on Growth and Biocontrol Efficacy of Trichoderma harzianum

ABSTRACT A fungivorous nematode, Aphelenchoides sp., was isolated from field soil by baiting with mycelium of the biocontrol fungus Trichoderma harzianum ThzID1, and subsequently was maintained on agar cultures of the fungus. Interactions between the nematode and the green fluorescent protein-producing transformant, T. harzianum ThzID1-M3, were investigated in both heat-treated (80 degrees C, 30 min) and untreated field soil. ThzID1-M3 was identified in soil by epifluorescence microscopy. When ThzID1-M3 was added to soil as an alginate pellet formulation, addition of the nematode (10 per gram of soil) significantly reduced radial growth and recoverable populations of the fungus, and the effect was greater in heat-treated soil than in untreated soil. Addition of ThzID1-M3 to soil pretreated with the nematode (10 per gram of soil) stimulated nematode population growth for approximately 10 to 20 days, whereas nematode populations decreased in the absence of added Trichoderma sp. When sclerotia of Sclerotinia sclerotiorum were added to soil (10 per 200 g of soil) with ThzID1-M3 (40 pellets per 200 g of soil), addition of Aphe-lenchoides sp. (2,000 per 200 g of soil) reduced the number of sclerotia colonized by ThzID1-M3. These results suggest that fungivorous nematodes may be a significant biotic constraint on activity of biocontrol fungi in the field.     

Interactions Between Trichoderma harzianum Strain T22 and Maize Inbred Line Mo17 and Effects of These Interactions on Diseases Caused by Pythium ultimum and Colletotrichum graminicola

ABSTRACT Seed treatment with Trichoderma harzianum strain T22, which results in colonization of plant roots but little or no colonization of shoots or leaves, had substantial effects on growth of and disease expression in maize inbred line Mo17. Shoots and roots of 10-day-old seedlings grown in a sandy loam field soil were larger (roots were nearly twice as long) in the presence of T22 than in its absence. Both main and secondary roots were increased in size and area and the root hair area was greater with T22. However, root hair area per unit of root length was greater in control plants. Increased growth probably was due to direct stimulation of plant growth in addition to effects from biological control of deleterious microflora. Seedlings of Mo17 grown in autoclaved or mefenoxamtreated sandy loam field soil were larger than those produced in untreated soil. However, seedlings grown in the presence of T22, either in treated or untreated soil, were larger than those produced in its absence. Infestation of soil with Pythium ultimum had little effect upon growth of Mo17. The presence of T22 increased protein levels and activities of beta-1,3 glucanase, exochitinase, and endochitinase in both roots and shoots, even though T22 colonized roots well but colonized shoots hardly at all. With some enzymes, the combination of T22 plus P. ultimum gave the greatest activity. Plants grown from T22-treated seed had reduced symptoms of anthracnose following inoculation of leaves with Colletotrichum graminicola, which indicates that root colonization by T22 induces systemic resistance in maize.     

Pythium rot of chingensai ( Brassica campestris L. chinensis group) caused by Pythium ultimum var. ultimum and Pythium aphanidermatum

Severe rot was found at the base of leaves and stems of chingensai (Brassica campestris L. chinensis group) in Okayama Prefecture in 2000. The causal fungi were morphologically identified as Pythium ultimum Trow var. ultimum and P. aphanidermatum (Edson) Fitzpatrick. This is the first report of rot caused by Pythium species on chingensai. We named this disease Pythium rot of chingensai.     

Identification and Quantification of Pathogenic Pythium spp. from Soils in Eastern Washington Using Real-Time Polymerase Chain Reaction

ABSTRACT Traditional methods of quantifying Pythium spp. rely on the use of selective media and dilution plating. However, high variability is inherent in this type of enumeration and counts may not be representative of the pathogenic population of Pythium spp. Variable regions of the internal transcribed spacer of the rDNA were used to design species-specific primers for detection and quantification of nine Pythium spp. from soils in eastern Washington. Primer pairs were designed for Pythium abappressorium, P. attrantheridium, P. heterothallicum, P. irregulare group I, P. irregulare group IV, P. paroecandrum, P. rostratifingens, P. sylvaticum, and P. ultimum and used with real-time polymerase chain reaction. Standard curves were generated for each of the species using SYBR Green I fluorescent dye for detection of amplification. Seventy-seven isolates of Pythium were screened to confirm specificity of each primer set. DNA was extracted from soil and standard curves were generated for P. irregulare group I, P. irregulare group IV, and P. ultimum to correlate populations of each species in the soil with quantities of DNA amplified from the same soil. Examination of raw field soils revealed results similar to those observed in previous studies. This new technique for the quantification of Pythium spp. is rapid and accurate, and will be a useful tool in the future study of these pathogenic Pythium spp.     

Net Carbon Gain and Growth of Bell Peppers, Capsicum annuum 'Cubico', Following Root Infection by Pythium aphanidermatum

ABSTRACT The first characterization of alterations in whole-plant photosynthetic rate and carbon assimilation of bell peppers associated with infection by Pythium aphanidermatum is described. Relationships of root disease caused by P. aphanidermatum to whole-plant net carbon exchange rate (NCER), total carbon accumulation, dark respiration rates, water loss, and destructive growth parameters were quantified in vegetative, hydroponically grown pepper plants (Capsicum annuum 'Cubico'). Inoculated plants displayed lower whole-plant NCER. This translated into a loss of 28% in cumulative C gain during 7 days after inoculation and occurred before visible shoot symptoms developed. Leaf area and dry weight of shoots and roots were significantly decreased and the shoot/root ratio was higher in inoculated plants than in noninoculated plants. We propose that reduced NCER in inoculated plants was mainly due to restricted development of leaf area, because no differences in NCER and evapotranspiration were observed between control and inoculated plants when expressed based on leaf area and root dry mass, respectively. These findings indicate that Pythium infection did not affect the photosynthetic apparatus directly and that the reductions in photosynthesis and growth were not caused by inefficient water transport by diseased roots. These results enlarge on the understanding of physiological responses of host plants to early stages of root disease.