Effects of ethrel on the formation and responses to VA mycorrhiza in Medicago and Triticum

Summary Ethrel, a compound which readily releases ethylene, depressed VA mycorrhiza formation inMedicago sativa andTriticum vulgare when it was either applied to the rooting medium or sprayed to the foliage. The axenic germination ofGlomus mosseae spores was found to be sensitive to ethrel suggesting that at least part of the effect of ethrel on mycorrhization could come from its effect on fungal development. The possible ecological significance of these findings is discussed.     

丛枝菌根真菌促进南美蟛蜞菊生长及对难溶磷的吸收

为了解2种丛枝菌根真菌(AMF)摩西管柄囊霉(Funneliformis mosseae, FM)和地表球囊霉(Glomus versiforme, GV)对入侵植物南美蟛蜞菊(Wedelia trilobata)的生长和对难溶性磷酸盐利用的影响,采用沙培盆栽方式,研究了南美蟛蜞菊在接种AMF与添加难溶性磷酸盐的生长和磷含量的变化。结果表明,在磷限制环境下FM对南美蟛蜞菊的侵染率达55%～69%,GV的侵染率达到63%～80%。添加难溶性磷酸盐后,2种AMF均促进了南美蟛蜞菊茎的伸长(FM:+46%; GV:+65%)、总生物量的增加(FM:+27.2%; GV:+40%)和磷含量的增加(FM:+36.6%; GV:+40.7%)。对比FM,GV对植物利用难溶性磷有更显著的促进作用。因此,南美蟛蜞菊与2种AMF形成的共生体系可以促进植物生长和对营养资源的利用,提高对难溶性磷的吸收效率可能使得南美蟛蜞菊在营养贫乏的环境中更好地建立种群。     

Direct effect of biocontrol agents on wilt and root-rot diseases of sesame

In Egypt, sesame cultivation is subject to attack by wilt and root-rot diseases caused by Fusarium oxysporum f.sp. sesami (Zap) Cast. and Macrophomina phaseolina (Maubl) Ashby causing losses in quality and quantity of sesame seed yield. Bacillus subtilis and Trichoderma viride isolates which were isolated from sesame rhizosphere were the most effective to antagonise fungal pathogens, causing high reduction of hyphal fungal growth. Trichoderma viride was found to be mycoparasitic on Fusarium oxysporum f.sp. sesami and M. phaseolina causing morphological atternation of fungal cells and sclerotial formation. In general, Bacillus subtilis, T. viride, avirulent Fusarium oxysporum isolate and Glomus spp. (Amycorrhizae) significantly reduced wilt and root-rot incidence of sesame plants at artificially infested potted soil by each one or two pathogens. Data obtained indicate that Glomus spp significantly reduced wilt and disease severity development on sesame plants followed by T. viride. Meanwhile, avirulent Fusarium oxysporum isolate followed by Glomus spp. were effective against root-rot disease incidence caused by M. phaseolina. Glomus spp. followed by B. subtilis significantly reduced wilt and root-rot disease of sesame plants. All biotic agents significantly reduced F. oxysporum f.sp. sesami and M. phaseolina counts in sesame rhizosphere at the lowest level. Glomus spp. and the avirulent isolate of F. oxysporum eliminated M. phaseolina in sesame rhizosphere. Meanwhile T. viride was the best agent at reducing F. oxysporum at a lower level than other treatments. Application of VA mycorrhizae (Glomus spp.) in fields naturally infested by pathogens significantly reduced wilt and root-rot incidence and it significantly colonised sesame root systems and rhizospheres compared to untreated sesame transplantings.     

Fungal genes related to calcium homeostasis and signalling are upregulated in symbiotic arbuscular mycorrhiza interactions

Fluctuations in intracellular calcium levels generate signalling events and regulate different cellular processes. Whilst the implication of Ca²⁺ in plant responses during arbuscular mycorrhiza (AM) interactions is well documented, nothing is known about the regulation or role of this secondary messenger in the fungal symbiont. The spatio-temporal expression pattern of putatively Ca²⁺-related genes of Glomus intraradices BEG141 encoding five proteins involved in membrane transport and one nuclear protein kinase, was investigated during the AM symbiosis. Expression profiles related to successful colonization of host roots were observed in interactions of G. intraradices with roots of wild-type Medicago truncatula (line J5) compared to the mycorrhiza-defective mutant dmi3/Mtsym13. Symbiotic fungal activity was monitored using stearoyl-CoA desaturase and phosphate transporter genes. Laser microdissection based-mapping of fungal gene expression in mycorrhizal root tissues indicated that the Ca²⁺-related genes were differentially upregulated in arbuscules and/or in intercellular hyphae. The spatio-temporal variations in gene expression suggest that the encoded proteins may have different functions in fungal development or function during symbiosis development. Full-length cDNA obtained for two genes with interesting expression profiles confirmed a close similarity with an endoplasmic reticulum P-type ATPase and a Vcx1-like vacuolar Ca²⁺ ion transporter functionally characterized in other fungi and involved in the regulation of cell calcium pools. Possible mechanisms are discussed in which Ca²⁺-related proteins G. intraradices BEG141 may play a role in mobilization and perception of the intracellular messenger by the AM fungus during symbiotic interactions with host roots.     

丛枝菌根真菌延长百合切花观赏期作用机制的初步研究

为初步探究丛枝菌根(arbuscularmycorrhizal,AM)真菌促进百合生长并延长瓶插过程中切花观赏期的作用机制,于温室盆栽条件下对百合Lilium brownii进行摩西斗管囊霉Funneliformis mosseae和变形球囊霉Glomusversiforme单一接种或者共同双接种处理。结果表明,共同接种F.mosseae和G.versiforme的百合地上部干重和地下部干重均显著高于不接种对照,分别增加了60%和58%。与不接种对照相比,接种F. mosseae和G. versiforme处理的百合根尖数、根系长度、分叉数、表面积和根系体积分别比对照增加123%、128%、182%、118%和232%。切花瓶插期间,接种AM真菌处理的百合切花水分平衡值和鲜重变化率显著高于对照处理;乙烯释放速率和呼吸速率显著低于对照,瓶插5d时达到乙烯峰值5.4μL/*g·h (FW)+,共同接种F. mosseae和G. versiforme处理的百合切花乙烯释放速率比对照降低30%;呼吸速率则在瓶插1d时达到峰值0.7μL/*g·h (FW)+,共同接种比对照降低37%;百合花瓣内超氧化物歧化酶(SOD)活性、过氧化氢酶(CAT)活性、可溶性糖含量和可溶性蛋白含量比对照分别提高19%、32%、52%和26%。百合花瓣内N、P、K、Mg、Ca、Fe和Zn含量均显著高于不接种对照处理,Mn和Cr含量则低于对照;共同接种处理的百合瓶插寿命增加了3d,最佳观赏时间比对照延长2d。结论认为共同接种F. mosseae和G. versiforme处理更加有效地改善切花花枝的水分平衡、营养状况与生理代谢,控制衰老激素的合成,从而延长百合切花的瓶插寿命和最佳观赏期。     

Response of Three Arbuscular Mycorrhizal Fungi to Simulated Acid Rain and Aluminium Stress

Simulated acid rain (SAR) combined with higher concentration of aluminium (SAR+Al) influenced the ecophysiology of three arbuscular mycorrhizal fungi (AMF) in both the germination and symbiotic phases of their life cycle. Acaulospora tuberculata, an isolate from the soil with low pH, exhibited a higher tolerance to environmental stress as compared to Glomus mosseae and G. fistulosum. This higher tolerance may be related to the edaphic conditions of soil of the isolate origin. The histochemical staining of the alkaline phosphatase and NADH-diaphorase activities in the extraradical mycelium (ERM) of the AMF proved to be more sensitive indication of negative effects of the SAR or SAR+Al stress compared to commonly measured parameters of the AMF such as mycorrhizal colonisation or growth of the ERM. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth of arbuscular mycorrhizal mycelium in calcareous dune sand and its interaction with other soil microorganisms as estimated by measurement of specific fatty acids

Fatty acid analysis was used for determining the extent of the development of the external mycelium of AM fungi (mixed inoculum from a sand dune) growing from roots of Festuca rubra and Plantago lanceolata in calcareous dune sand. The plants were raised in chambers specially designed to permit the growth of AM mycelium in root-free compartments. In two separate experiments, growth of external mycelium in the root-free compartments was detected and the amount of mycelium was estimated using the indicator of AM fungal biomass, phospholipid fatty acid (PLFA) 16:15. The results showed that the PLFA 16:15 was suitable for estimating the mycelium emerging from the mixed inoculum obtained from the field roots of F. rubra and P. lanceolata.The PLFA 16:15 showed external mycelium to become established in the root-free compartments within a period of 3 weeks and the amount of mycelium to continue to increase at 6 and 9 weeks. Increases in neutral lipid fatty acid (NLFA) 16:15 (indicator of storage lipids) over time were inconsistent between the two experiments, but appeared to follow patterns of sporulation in each experiment.In both experiments, the root-free compartment was colonised by saprophytic fungi to a greater extent in the case of non-mycorrhizal than of AM treatment, as indicated by an increase in PLFA 18:26,9 (indicator of saprophytic fungi). The absence of an increase in the case of AM treatment indicates that AM fungal mycelium can negatively affect the growth of saprophytic fungi in this soil type. This result was, however, only weakly supported by measurements of ergosterol content. The analysis of bacteria specific PLFAs showed that bacterial biomass was not affected by the AM mycelium.     

A comparison of the development and metabolic activity of mycorrhizas formed by arbuscular mycorrhizal fungi from different genera on two tropical forage legumes

 Two glasshouse experiments were done to assess the development and metabolic activity of mycorrhizas formed by isolates of arbuscular mycorrhizal fungi (AMF) from three different genera, Acaulospora, Gigaspora and Glomus on either Pueraria phaseoloides L. or Desmodium ovalifolium L. plants. The second of the two experiments included three levels of a localised phosphate source in the pots. Alkaline phosphatase (ALP), stained histochemically in the intra-radical mycelium (IRM) of AMF over sequential harvests, did not provide a direct marker for the efficiency of AMF in mobilising phosphorus (P) for plant growth and development. The ability of the extra-radical mycelium (ERM) to scavenge a localised phosphate source, determined by its extraction from buried 35-μm mesh pouches, was dependent on the species of AMF tested. This work indicates that AMF from different genera have unique patterns of mycelial development when forming mycorrhizas with tropical hosts in the presence of a localised phosphate source. AMF also appear to have different mechanisms for the control of P transfer, within the mycelium, to the host. The significance of the architecture of the ERM is discussed as well as the localisation of ALP in the IRM in determining the efficiency of AMF in terms of P accumulation in planta and subsequent growth of plants. Accepted: 19 August 1998     

龙胆VA菌根真菌的分离和鉴定

采用湿筛法和单孢接种技术,从东北龙胆根际土壤中分离到能在东北龙胆组培苗上形成VA菌根的真菌孢子和孢子果呆,依其显微形态特征对部分菌株进行鉴定,大多属于球囊霉属（Glomus）中的漏斗孢球囊霉（Glomusmosseae）和地球囊霉（G．geosporum）     

我国东南沿海地区的AM真菌Ⅳ.四个我国新记录种

本文报道了采自我国山东、福建、广西和海南四省土壤中的四种ＡＭ真菌新记录种：１．两型球囊霉ＧｌｏｍｕｓｄｉｍｏｒｐｈｉｃｕｍＢｏｙｅｔｃｈｋｏ＆Ｔｅｗａｒｉ;２．多产球囊霉ＧｌｏｍｕｓｆｅｃｕｎｄｉｓｐｏｒｕｍＳｃｈｅｎｃｋ＆Ｓｍｉｔｈ;３．亮色盾巨孢囊霉ＳｃｕｔｅｌｏｓｐｏｒａｆｕｌｇｉｄａＫｏｓｋｅ＆Ｗａｌｋｅｒ;４．网纹盾巨孢囊霉Ｓｃｕｔｅｌｏｓｐｏｒａｒｅｔｉｃｕｌａｔａ（Ｋｏｓｋｅ,Ｍｉｌｅｒ＆Ｗａｌｋｅｒ）Ｗａｌｋｅｒ＆Ｓａｎｄｅｒｓ。文中详细描述了其形态特征和生境状况。