丛枝菌根真菌对入侵植物南美蟛蜞菊生长及竞争力的影响

【背景】丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)能促进植物的养分吸收及生长发育。入侵中国华南地区的外来入侵植物南美蟛蜞菊(Wedelia trilobata)常分布于养分匮乏的荒地,却能迅速生长并排挤本地植物而快速扩张领地。【目的】探究丛枝菌根真菌是否促进南美蟛蜞菊的生长与竞争能力。【方法】采用南美蟛蜞菊及其同属本地植物蟛蜞菊(Wedelia chinensis)的盆栽对比控制试验,并设置接种及不接种AMF变形球囊霉(Glomus versiforme)、不同磷营养水平以及单种或混种的种植方式3种处理对两种植物的生长及竞争能力进行比较。【结果】AMF均能侵染上述两种植物,并且AMF对南美蟛蜞菊根系的侵染率显著高于其对蟛蜞菊根系的侵染,尤其是在低磷水平下南美蟛蜞菊的菌根侵染率更高,而且AMF的侵染显著促进了低磷水平下南美蟛蜞菊的生长及其对蟛蜞菊的竞争能力。【结论】丛枝菌根真菌能够促进南美蟛蜞菊的生长,增强其对本地植物的竞争优势,该效应很可能对外来植物南美蟛蜞菊的成功入侵产生一定的作用。     

南美蟛蜞菊霜霉病病原鉴定及系统发育分析

[目的]为从天敌病原生物方面探索外来入侵植物南美蟛蜞菊的生物防治,对新发现的南美蟛蜞菊霜霉病进行病原鉴定和系统发育分析。[方法]在广东省广州市对南美蟛蜞菊霜霉病的发生及危害情况进行调查,并通过病害症状识别、病原显微形态记录与比较、病原菌及其近似种ITS序列结构比较、LSU序列和ITS序列系统发育分析,对南美蟛蜞菊霜霉病病原进行鉴定和系统发育分析。[结果]南美蟛蜞菊霜霉病在广州零星发生,但该病害在华南农业大学校园内发生较严重,发病率达50%~70%,病情指数为30~35。经鉴定,其病原菌为南美蟛蜞菊单轴霉,是国内一新记录种。基于病原菌LSU序列和ITS序列的系统发育分析显示,侵染菊科植物的单轴霉属菌种聚在一个分枝,亲缘关系密切,与侵染其他不同科寄主植物的单轴霉亲缘关系较远。ITS序列结构比较显示,寄生于菊科向日葵族植物的单轴霉属菌种的ITS2区包含多个重复序列,不同菌种间的ITS2区重复序列相似度不同,说明侵染菊科向日葵簇植物的单轴霉属菌物可细分成多个种,而不是只有向日葵单轴霉。[结论]广州发生的南美蟛蜞菊霜霉病是该寄主上首次正式报道的病害,鉴定的病原菌也是国内一新记录种;寄生在菊科植物上的单轴霉属种类不尽相同,但亲缘关系紧密。     

土施糖类对丛枝菌根真菌侵染率和产孢的影响

丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)不能进行光合作用,需要宿主植物提供碳水化合物供其完成整个生命周期,添加外源物质调控AMF和宿主植物的关系被认为是一种可行的措施。通过盆栽实验种植番茄,探索土施不同糖类对摩西球囊霉Glomus mosseae的侵染率、产孢能力和功能(宿主植物生长和养分)的影响。结果表明,添加葡萄糖和蔗糖可提高接种了摩西球囊霉的番茄的地上部生物量以及磷、钾吸收量,但对地上部氮吸收量影响不显著;添加麦芽糖和淀粉对地上部生物量及氮磷钾养分吸收量的影响均不显著。添加糖类处理,土壤碱解氮均有下降趋势;土壤速效磷、速效钾随着地上部磷和钾吸收量增加有下降趋势。糖类添加对土壤有机质没有影响。添加不同糖类均提高了AMF的侵染率,其中添加蔗糖处理的侵染率较单独施用摩西球囊霉菌处理增加了114%。单独施用摩西球囊霉菌剂处理土壤孢子数为10个/g,添加葡萄糖和淀粉处理的孢子数均为8个/g,添加蔗糖和麦芽糖处理的孢子数均为11个/g,添加糖类均对AMF产孢无显著影响。     

丛枝菌根真菌对小麦生长的影响

为了促进经济作物小麦的生长,提高土壤氮磷循环与转化效率,选择两种优良丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)——摩西球囊霉(GM,Glomus mosseae)、根内球囊霉(GI,Glomus intraradices),研究AMF在小麦整个营养生长阶段中对其生长以及对土壤中植物生长需求的大量元素——氮、磷的作用及影响。结果表明:人工施加菌剂可显著提高AMF对小麦的侵染率,施加GM菌剂时,小麦侵染率提高24.54%,同时,株高提高14.08%,小麦地上生物量提高24.05%。GM效果优于GI。施加菌剂后,小麦侵染率与土壤中水解性氮呈显著正相关;植物地上生物量与土壤中总氮,水解性氮呈显著负相关。表明AMF可活化土壤中的氮元素,同时促进作物生长,强化对土壤中氮元素的利用。     

土壤因子对府谷清水川流域砒砂岩区刺槐和沙棘AMF的影响

应用相关性分析和通径分析研究了府谷清水川流域砒砂岩区土壤因子对刺槐(Robinia pseudoacacia)和沙棘(Hippophae rhamnoides)根际丛枝菌根真菌(AMF)的影响.结果表明:AMF可以与刺槐和沙棘形成良好的共生关系;从两种植物根际土中共分离鉴定出AMF 13种,其中摩西囊霉(Glomus mosseae)、地球囊霉(Glomus geospo-rum)和缩球囊霉(Glomus constrictum)为优势种;AMF平均侵染率为90.6%,平均孢子密度为559.1个?100 g-1干土;AMF的孢子密度、侵染率和种类之间没有显著的相关性;刺槐和沙棘根际AMF侵染率均与pH呈显著正相关,在刺槐根际,pH和有效氮通过直接作用影响侵染率,有机质和有效磷通过间接作用影响侵染率;在沙棘根际,pH和有效磷通过直接作用影响侵染率,有机质和有效氮通过间接作用影响侵染率;在沙棘根际,有机质和pH主要是通过直接作用影响AMF种类,有效氮主要通过有效磷的间接作用影响AMF种类.     

低pH影响丛枝菌根真菌丛枝发育和磷的吸收

以番茄Solanum lycopersicum为寄主植物,在pH 3.7、pH 4.5、pH 5.5和pH 6.5条件下接种根内根孢囊霉Rhizophagus intraradices,分别在培养4周和7周取样测定低pH对丛枝菌根真菌(AMF)丛枝发育和磷吸收利用的影响。结果表明,当pH低于5.5时,低pH显著抑制AMF对根系的侵染和丛枝的形成,且抑制效应随pH的降低而增强;与侵染率相比,丛枝丰度随土壤pH的降低而降低的幅度更大;低pH显著降低了植株生物量;与不接种处理相比,接种AMF显著提高植株生物量;相关分析表明,在菌根侵染指标中丛枝丰度与植株生长相关性最高;方差分解分析表明,pH对植株生物量的贡献率(88%和77%,两次取样)大于AMF的贡献率(5%和8%,两次取样);低pH对碱性磷酸酶活性的影响与根系侵染有相似的趋势;AMF能显著提高地上部P浓度,而低pH显著降低地上部P浓度以及根系中LePT3、LePT4和LePT5的表达。这些结果表明,低pH对AMF与植物的共生关系有显著的抑制作用,其中对丛枝的形成与功能的抑制效应最大。     

南方红豆杉丛枝菌根(AM)的研究

研究了南方红豆杉根部丛枝菌根真菌(AMF)侵染情况、菌根形态结构以及根际土中AMF孢子的种类与数量.结果显示:南方红豆杉可与AMF形成典型的丛枝-泡囊型菌根,侵染率在71.2%~94.4%,但是历山、蟒河自然保护区的侵染强度优于人工栽培区;在南方红豆杉根际土中共分离鉴定出5种AMF,无梗囊霉属1种、球囊霉属4种,分别是:光壁无梗囊霉、地表球囊霉、地球囊霉、缩球囊霉、明球囊霉,其中光壁无梗囊霉为优势种;南方红豆杉的根由表皮、外皮层、内皮层、中柱组成,AMF只侵染表皮层、内皮层,不能侵染中柱.这为将来利用AMF接种技术进行南方红豆杉的繁殖、移植栽培以及紫杉醇的积累等研究提供了理论依据.     

黑麦对难溶性磷酸盐的吸收及活化机制研究

以2个黑麦品种冬牧70和King为材料,研究了植物对难溶性磷酸盐的吸收及活化,以揭示植物抵御酸性土壤逆境的机制.结果显示,(1)在活性铝含量高的赤红壤中施用磷酸铝、磷酸铁、磷酸钙等难溶性磷酸盐后,植株的生物产量和磷的积累量分别增加了0.84~6.38倍和0.60~20.5倍,且施用难溶性磷酸盐后冬牧70的生物产量和磷的积累量的增加量明显高于King.(2)铝胁迫下2种黑麦根系分泌物中的阴离子组分均能溶解难溶性磷酸盐,而在中性或阳离子组分中的难溶性磷酸盐溶解不显著;HPLC图谱显示,阴离子组分中含有柠檬酸和苹果酸.(3)铝胁迫下根系有机酸分泌量随铝处理浓度(10、30、50μmol/L AlCl3)的增加而增加,而且在柠檬酸或苹果酸溶液中难溶性磷酸盐的溶解度显著增加,其溶解的磷随有机酸浓度的增加而增加.(4)黑麦冬牧70品种对难溶性磷酸盐的吸收、阴离子组分对难溶性磷酸盐的溶解及有机酸分泌作用均较King强.结果表明,在铝胁迫下根系分泌的有机酸是黑麦活化、吸收土壤中难溶性磷的有效机制.     

番茄对不同养分水平下南美蟛蜞菊和蟛蜞菊化感作用的响应

外来入侵植物分泌的化感物质能够影响本地植物的生长生理特性,养分水平对入侵植物的化感潜力有重要影响。该文通过将番茄植株分别与同种番茄、南美蟛蜞菊、蟛蜞菊植株相邻原位种植,以15%、25%、50%、75%的Hoagland培养液模拟不同养分水平开展温室控制实验,探究在不同养分水平下入侵植物南美蟛蜞菊及其亲缘植物蟛蜞菊的化感作用对本地植物番茄叶绿素荧光参数及生物量的影响。结果表明:(1)番茄在75%养分水平下的叶绿素荧光参数和生物量显著优于其余3个养分水平。(2)随着养分水平降低,番茄叶片的PSⅡ最大光化学效率(F_v/F_m)、PSⅡ实际光合量子产量[Y(Ⅱ)]、光化学淬灭系数(qp)及植株的总生物量显著减少,非光化学淬灭系数(NPQ)和植株根系生物量的分配比例增加。(3)在25% Hoagland培养液处理下,与南美蟛蜞菊混植番茄的F_v/F_m、Y(Ⅱ)、qp和总生物量显著低于与蟛蜞菊混植番茄,NPQ和根系生物量的分配比例显著高于与蟛蜞菊混植番茄。综上结果说明南美蟛蜞菊和蟛蜞菊可能通过根系分泌化感物质抑制番茄的生长发育,且南美蟛蜞菊的化感作用强于蟛蜞菊,而增加栽培基质中的养分水平可以显著降低南美蟛蜞菊和蟛蜞菊对番茄的化感胁迫作用。     

盐胁迫下外源褪黑素和从枝菌根真菌对月季幼苗生理特性及光合荧光参数的影响

本试验旨在探究100mol/L盐胁迫下根际施用褪黑素(MT)、接种近明球囊霉属AMF幼套近明球囊霉(Claroideoglomus etunicatum)及其复合处理对月季幼苗生长、叶绿素荧光参数、激素代谢及抗氧化系统的影响,以探明两者缓解月季盐胁迫的机制。结果发现,盐胁迫下月季幼苗生长受到抑制,株高、茎粗以及生物量等显著下降;施用MT可以促进AMF侵染,提高侵染率、丛枝着生率、泡囊数和侵入点数。100mol/L盐处理下,与对照(CK)处理相比,AMF+MT处理的叶绿素总量、叶绿素a/b分别增加46.2%和67.2%;叶绿素荧光参数中PSⅡ最大光化学效率(Fv/Fm)、PSⅡ潜在活性(Fv/Fo)、PSⅡ实际光化学效率(φPSⅡ)、PSII有效光化学量子效率(Fv’/ Fm’)、光化学猝灭系数(qP)分别增加4.9%、51.0%、175.0%、168.7%和92.5%,NPQ的下降幅度为42.7%;此外,盐胁迫下,月季叶片中玉米素核苷(ZR)、赤霉素(GA)、生长素(IAA)含量下降,而脱落酸含量(ABA)增加,AMF+MT处理后ZR、GA、IAA分别增加146.9%、116.9%、35.7%,ABA下降21.1%;同时AMF+MT处理能够激活抗氧化酶SOD、CAT活性,降低超氧阴离子(O2-)产生速率和H2O2累积。结论认为,接种AMF、添加MT或者AMF+MT处理均可以提高叶绿素含量,保护叶绿素荧光系统,维持植物内源激素的平衡,激活SOD、CAT等抗氧化酶活性以及降低脂质过氧化和H2O2累积,以减轻盐胁迫对月季幼苗的伤害,促进月季生长,其中以AMF+MT处理下月季幼苗的抗盐性效果更佳。     

Life history plasticity and fitness in a caddisfly in response to proximate cues of pond-drying

The majority of plants are involved in symbioses with arbuscular mycorrhizal fungi (AMF), and these associations are known to have a strong influence on the performance of both plants and insect herbivores. Little is known about the impact of AMF on complex trophic chains, although such effects are conceivable. In a greenhouse study we examined the effects of two AMF species, Glomus intraradices and G. mosseae on trophic interactions between the grass Phleum pratense, the aphid Rhopalosiphum padi, and the parasitic wasp Aphidius rhopalosiphi. Inoculation with AMF in our study system generally enhanced plant biomass (+5.2%) and decreased aphid population growth (−47%), but there were no fungal species-specific effects. When plants were infested with G. intraradices, the rate of parasitism in aphids increased by 140% relative to the G. mosseae and control treatment. When plants were associated with AMF, the developmental time of the parasitoids decreased by 4.3% and weight at eclosion increased by 23.8%. There were no clear effects of AMF on the concentration of nitrogen and phosphorus in plant foliage. Our study demonstrates that the effects of AMF go beyond a simple amelioration of the plants’ nutritional status and involve rather more complex species-specific cascading effects of AMF in the food chain that have a strong impact not only on the performance of plants but also on higher trophic levels, such as herbivores and parasitoids.     

Field response of chickpea to inoculation withGlomus versiforme

The response ofCicer arietinum to inoculation withGlomus versiforme under field conditions was investigated in a phosphorus deficient sandy loam soil. Inoculation with the mycorrhizal fungusGlomus versiforme increased the rate of VAM development in chickpea. The weight of nodules and the number of nodules per plant were higher in inoculated than in uninoculated plants. The phosphorus content of the shoots and its total uptake, were increased by either the application of single super-phosphate, or by inoculation withG. versiforme. Inoculation increased shoot dry weights and grain yields by 12% and 25% respectively, as compared with the 33% and 60% increases respectively produced by P-treated plants.     

Phosphorus Acquisition Strategies within Arbuscular Mycorrhizal Fungal Community of a Single Field Site

Diversity in phosphorus (P) acquisition strategies was assessed among eight isolates of arbuscular mycorrhizal fungi (AMF) belonging to three Glomus species, all obtained from the same field site. Maize (Zea mays L. cv. Corso) was used as a test plant. Compartmented cultivation containers coupled with ³³P radioisotope labeling of soil P were employed to estimate (1) the distance from the roots that AMF were able to acquire soil P from, (2) the rate of soil colonization, (3) the efficiency of uptake of soil P by AMF, (4) benefits provided to maize in terms of P acquisition and growth. Glomus mosseae and G. intraradices took up P 10 cm from roots, whereas G. claroideum only up to 6 cm from the roots. G. mosseae most rapidly colonized the available soil volume and transported significant amounts of P to maize from a distance, but provided no net P uptake benefit to the plants. On the other hand, both G. intraradices and three out of four G. claroideum isolates significantly improved net P uptake by maize. These effects seem to be related to variability between and to a limited extent also within AMF species, in mycelium development, efficiency of hyphal P uptake and effects on plant P acquisition via the root pathway. In spite of absence of maize growth responses to inoculation with any of the AMF isolates, this study indicates remarkable functional diversity in the underground component of the studied field site.     

Interactions Between Plant Growth Promoting Fungi and Arbuscular Mycorrhizal Fungus Glomus Mosseae and Induction of Systemic Resistance to Anthracnose Disease in Cucumber

Cucumber plants were treated with plant growth promoting fungi (PGPF), Phoma sp. (isolates GS8-2 and GS8-3) and Penicillium simplicissimum (isolate GP17-2) with or without the arbuscular mycorrhizal fungus (AMF) Glomus mosseae. Induction of systemic resistance in cucumber against the anthracnose disease caused by Colletotrichum orbiculare was tested to evaluate the nature of the interaction between the PGPF and AMF. Root colonizing ability of each fungal species as influenced by their interaction was also evaluated. Plant roots were pre-inoculated with each PGPF isolate and/or G. mosseae for four weeks and leaves were then challenge inoculated with the pathogen C. orbiculare. Plants treated with each PGPF isolate showed considerable protection against the disease, but the treatment of G. mosseae had no significant effect on disease development. However, combined inoculation of Phoma GS8-2 or GS8-3 with G. mosseae reduced the level of disease protection induced by single inoculation of each Phoma isolate. In contrast, the high levels of protection induced by the P. simplicissimum GP17-2 were not altered by combining it with G. mosseae. Root colonization of both Phoma sp. isolates was also suppressed by the presence of the G. mosseae, but such an effect was not found on the population development of P. simplicissimum. The percent cucumber root length colonized by G. mosseae was not affected by any of the PGPF isolates tested.     

Growth and yield of lentil and wheat inoculated with three Glomus isolates from Saskatchewan soils

The vesicular-arbuscular mycorrhizal fungi (VAMF) Glomus clarum (Nicol. and Schenck) isolate NT4, G. mosseae (Nicol. and Gerd.) Gerd. and Trappe isolate NT6 and G. versiforme (Karst.) Berch isolate NT7 coexist in wheat field soils in Saskatchewan. This study assessed the response of lentil (Lens esculenta L.) and wheat (Triticum aestivum L.) to monospecific and mixed cultures of these VAMF isolates. Seedlings were inoculated with 100 spores of a VAMF isolate, or an equal mixture of spores of two isolates, and grown in a sterile soil mix in a growth chamber. Both crops responded differently to these different VAMF isolates. In the case of lentil, G. clarum NT4 was more effective than G. mosseae NT6 and G. versiforme NT7, and significantly increased (P<0.05) the shoot dry weight (43%) and grain yield (57%) compared with the uninoculated control. There was a significant positive correlation between the percentage of VAMF colonized roots and shoot dry weight (r=0.672^***) and shoot phosphorus concentration (r=0.608^***) of lentil. In the case of wheat, G. clarum NT4 had no effect on shoot dry weight, but produced significant (P<0.08) increases in grain yield (12%) and the phosphorus concentration of the shoot and grain. Although G. clarum NT4 and G. mosseae NT6 both produced similar levels of VAM colonization in wheat, the only response of wheat to isolate NT6 was an increase in plant height at harvest. The efficacy of G. clarum NT4 on both crops appeared to be related to its ability to produce more arbuscular colonization than G. mosseae NT6. Dual inoculation of seedlings with G. clarum NT4 and G. mosseae NT6 resulted in competition between these two isolates. This was evident from a comparison of plant shoot dry weight and grain yield, and VAMF spore production on the two crops inoculated either with isolate NT4 alone or in combination with NT6. G. mosseae NT6 reduced the efficacy of G. clarum NT4 by 16% when dual inoculated on lentil, but had no effect when the host was wheat. Based on spore production, it was found that G. clarum NT4 was more competitive than G. mosseae NT6 when dual inoculated on lentil or wheat. Isolate NT4 produced ca. 2000 and 500 spores/ 100 g substrate, respectively, in the lentil and wheat pots, which was approximately 2–3 times more spores than those produced by isolate NT6 with either crop. When the plants were dual inoculated, there was a 15–19% reduction in spore production by G. clarum NT4 and a 50–70% decrease in spore production by G. mosseae NT6. Our results show that G. clarum NT4 was more competitive and effective in its ability to colonize and increase the growth and yield of lentil and wheat than G. mosseae NT6 or G. versiforme NT7. The relative performance of isolate NT4 with different host plants suggests that this VAMF isolate exhibits a host preference for lentil.     

Flavonoids in roots of white clover: interaction of arbuscular mycorrhizal fungi and a pathogenic fungus

The effects of two arbuscular mycorrhizal fungi (AMF) (Glomus mosseae and G. claroideum) and a pathogenic fungus (Pythium ultimum) on the production of eight flavonoids in roots of two white clover (Trifolium repens L.) cultivars were evaluated. Quantification of AM and pathogenic fungi in the roots showed that the AM symbiosis significantly reduced P. ultimum biomass and in some cases prevented infection. The flavonoid productions in clover roots varied depending on the presence of beneficial and/or pathogenic fungi, fungal isolate or plant cultivar. Only plants colonized with G. claroideum showed detectable concentrations of either coumestrol or kaempferol (cultivar-dependant). In addition, inoculation with G. claroideum resulted in significantly higher concentrations of coumestrol in cv. Sonja and medicarpin in cv. Milo. A low production of coumestrol and kaempferol in mycorrhizal plants may be G. mosseae-specific. Only the concentrations of formononetin and daidzein increased in clover roots in response to infection with P. ultimum. These flavonoids are supposedly stress metabolites, synthesized or produced from glycosides in response to pathogen infection. However, the presence of one or both AMF significantly lowered the formononetin and daidzein concentrations, and overruled the inductive effect of P. ultimum. Therefore the antagonistic action of AM against the pathogen must take place through another mechanism.     

Effectiveness of three Glomus species in protecting pepper (Capsicum annuum L.) against verticillium wilt

The objective of this work was to study the influence of three Glomus species—Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, Glomus intraradices (Schenck and Smith) and Glomus deserticola (Trappe, Bloss, and Menge)—on the development of Verticillium-induced wilt in Capsicum annuum cv. Piquillo. Results showed that the effectiveness of arbuscular mycorrhizal fungi (AMF) as biocontrol agents varied among different Glomus species. In pepper colonized by G. intraradices the severity of the disease was even higher than that observed in non-mycorrhizal plants in terms of plant growth and pepper yield. On the other hand, the high effectiveness exhibited by G. mosseae in improving plant growth and the early beginning of the reproductive stage in these plants was not associated with great plant protection and high pepper yield in diseased plants. Only plants associated with G. deserticola had greater yield than non-mycorrhizal ones despite the lower P fertilization applied to the mycorrhizal treatment and this fact was observed in both healthy and diseased plants. It is suggested that the higher specific phosphorus uptake in Verticillium-inoculated plants associated with G. deserticola could contribute to diminish the deleterious effect of pathogen on yield. On the other hand, the possible influence of endogenous phenolics in roots on the tolerance or resistance of pepper against wilt induced by Verticillium dahliae remains unclear.     

Impact of two fluorescent pseudomonads and an arbuscular mycorrhizal fungus on tomato plant growth,root architecture and P acquisition

The ability of fluorescent pseudomonads and arbuscular mycorrhizal fungi (AMF) to promote plant growth is well documented but knowledge of the impact of pseudomonad-mycorrhiza mixed inocula on root architecture is scanty. In the present work, growth and root architecture of tomato plants (Lycopersicon esculentum Mill. cv. Guadalete), inoculated or not with Pseudomonas fluorescens 92rk and P190r and/or the AMF Glomus mosseae BEG12, were evaluated by measuring shoot and root fresh weight and by analysing morphometric parameters of the root system. The influence of the microorganisms on phosphorus (P) acquisition was assayed as total P accumulated in leaves of plants inoculated or not with the three microorganisms. The two bacterial strains and the AMF, alone or in combination, promoted plant growth. P. fluorescens 92rk and G. mosseae BEG12 when co-inoculated had a synergistic effect on root fresh weight. Moreover, co-inoculation of the three microorganisms synergistically increased plant growth compared with singly inoculated plants. Both the fluorescent pseudomonads and the myco-symbiont, depending on the inoculum combination, strongly affected root architecture. P. fluorescens 92rk increased mycorrhizal colonization, suggesting that this strain is a mycorrhization helper bacterium. Finally, the bacterial strains and the AMF, alone or in combination, improved plant mineral nutrition by increasing leaf P content. These results support the potential use of fluorescent pseudomonads and AMF as mixed inoculants for tomato and suggest that improved tomato growth could be related to the increase in P acquisition.     

Arbuscular mycorrhizal fungi can alter some root characters and physiological status in trifoliate orange (<Emphasis Type="Italic">Poncirus trifoliata</Emphasis> L. Raf.) seedlings

Citrus plants strongly depend on mycorrhizal symbiosis because of less or no root hairs, but few reports have studied if their root traits and physiological status could be altered by different arbuscular mycorrhizal fungi (AMF). In a pot experiment we evaluated the effects of three AMF species, Glomus mosseae, G. versiforme and Paraglomus occultum on the root traits and physiological variables of the trifoliate orange (Poncirus trifoliata L. Raf.) seedlings. Root mycorrhizal colonization was 58–76% after 180 days of inoculation. AMF association significantly increased plant height, stem diameter, leaf number per plant, shoot and root biomass. Mycorrhizal seedlings also had higher total root length, total root projected area, total root surface area and total root volume but thinner root diameter. Among the three AMFs, greater positive effects on aboveground growth generally ranked as G. mosseae > P. occultum > G. versiforme, whilst on root traits as G. mosseae ≈ P. occultum > G. versiforme. Compared to the non-mycorrhizal seedlings, contents of chlorophyll, leaf glucose and sucrose, root soluble protein were significantly increased in the mycorrhizal seedlings. In contrast, root glucose and sucrose, leaf soluble protein, and activity of peroxidase (POD) in both leaves and roots were significantly decreased in the mycorrhizal seedlings. It suggested that the improvement of root traits could be dependent on AMF species and be related to the AMF-induced alteration of carbohydrates and POD.     

Interaction between arbuscular mycorrhizal fungus Glomus mosseae and plant growth promoting fungus Phoma sp. on their root colonization and growth promotion of cucumber (Cucumis sativus L.)

Interaction between arbuscular mycorrhizal fungus Glomus mosseae and plant growth promoting fungus Phoma sp. was studied for its effect on their root colonization and plant growth of cucumber. Two isolates of Phoma sp. (GS8-2 and GS8-3) were tested with G. mosseae. The percent root length colonized by G. mosseae was not adversely affected by the presence of Phoma isolates. In contrast, the root colonization of both isolates GS8-2 and GS8-3 in 4-week-old plants was significantly reduced (80.7% and 84.3%, respectively) by added G. mosseae. Inoculating plants with each Phoma isolate significantly increased the shoot dry weight. However, dual inoculation of each Phoma isolate with G. mosseae had no significant effect on growth enhancement.