The relative importance of host vigor and hormonal response to pathogens in controlling the development of arbuscular mycorrhizal fungi

Plants are routinely colonized by both beneficial and detrimental microorganisms. These two microbial guilds may indirectly interact with each other via their host, either by modifying its vigor, or by altering its hormonal/defense status. Here, we studied indirect interactions between arbuscular mycorrhizal (AM) fungi and three plant pathogens. We show that AM fungal sporulation was only triggered by the least aggressive fungal pathogen, which is known to induce a jasmonate-based hormonal response by the host without affecting its vegetative growth and vigor. Conversely, the most aggressive fungal pathogen considerably reduced host vigor but did not alter AM fungal growth and sporulation. Our results thus suggest that the plant hormonal system is an important component of indirect interactions between AM fungi and plant pathogens.     

芸苔链格孢产孢基物与光照条件的选择

在小麦、燕麦、玉米、高粱四种谷物培养基上进行芸苔链格孢[Alternariabrassicae(Berk.)Sacc]孢子产生的试验表明,小麦粒及玉米粒培养基是很好的产孢基物.在16天的产孢过程中,每克基物可分别得到166.75、156.65万个孢子.获得孢子期分别为达8及14天,共可诱发出4至7次.按产孢量来看,小麦粒培养基最大,但不及在玉米粒培养基产孢期长而稳定.玉米粒培养基是更合适的芸苔链格孢产孢培养基.用紫外线光灯及日光灯对培养9天的小麦粒产孢基物照射1小时以上即可明显地提高其产孢量.紫外光灯下照射2小时,日光灯下照射2～12小时产孢能力最强.用日光灯照射其产孢总量要高于紫外光灯照射.本项研究为进行白菜种质材料抗芸苔链格孢筛选提供了诱发孢子的可靠方法.     

烟草赤星病菌(Alternaria alternata)营养生理研究

研究了6种碳源和6种氮源对烟草赤星病菌[Alternaria alternata(Fr)Keissler]菌丝生长和产孢量的影响。结果表明,不同的碳源和氮源对该病菌菌丝生长和产孢量均有显著影响。病菌在以淀粉为碳源的培养基上菌丝生长最快,乳糖次之;菌丝干重以果糖培养基上最大,乳糖、葡萄糖、麦芽糖、蔗糖、淀粉次之,无碳对照最低;产孢量以在麦芽糖为碳源的培养基上最高,乳糖次之,无碳对照最低。病菌在以蛋白胨为氮源的培养基上菌丝生长最快,菌丝干重最大,硝酸铵次之,脲最慢;产孢量以在蛋白胨为氮源的培养基上最高,硝酸铵、硫酸铵上次之,脲最低。脲和氯化铵对病菌生长和孢子形成均有抑制作用。     

Spore production by the vesicular-arbuscular mycorrhizal fungus Glomus monosporum as related to host species,root colonization and plant growth enhancement

Summary The vesicular-arbuscular mycorrhizal fungus Glomus monosporum was inoculated on grapevine (Vitis vinifera), red clover (Trifolium pratense), meadow grass (Poa pratensis) and onion (Allium cepa) as hosts in two experiments carried out in different environments. Grapevine and clover showed the largest growth response and spore production. Mycorrhizal infection was lowest in meadow grass. Very poor correlations were observed, on an overall basis, between spore production and per cent root infection or infected root length. Spore production per unit infected root length for each host species was a comparatively stable parameter; it was largest for grapevine and smallest for meadow grass in both experiments. Sporulation was positively correlated with growth enhancement by mycorrhizal plants, and growth increments per unit infected root followed the same trend as spore numbers per unit infected root, i.e. largest for grapevine and lowest for meadow-grass. It is concluded that the ability of G. monosporum to produce spores and to enhance plant growth per unit infected root length depends on the host plant species.     

Mechanisms of production of soil protease by proteolytic Bacillus subtilis in wetland rice soil

In sterile soil inoculated with proteolytic Bacillus subtilis, the correlation between variations in protease activity and cell numbers was investigated during incubation, and the results were compared with those obtained in different growth media. In sterile soil inoculated with B. subtilis, the extracted soil z-FLase activity (hydrolytic activity towards benzyloxycarbonyl-L-phenylalanyl-L-leucine extracted with 0.1 M phosphate buffer) was correlated with the extracted soil protein content (r=0.95; P<0.01) and the number of vegetative cells (r=0.88, P<0.05), while the extracted soil caseinase activity was well correlated with the number of spores (r=0.82, P<0.05) and not with the number of vegetative cells. Extracellular z-FLase activity in different growth media, inoculated with the proteolytic B. subtilis, was correlated with the extracellular protein concentration (r=0.73, P<0.01) and the number of cells (r=0.73, P<0.01), but extracellular caseinase activity was not correlated with either of these measurements. From these results, we concluded that soil z-FLase production might relate to vegetative growth of the proteolytic B. subtilis and soil caseinase might relate to B. subtilis sporulation.     

大豆紫斑病菌（Cercospora kikuchii）生物学特性研究

大豆紫斑病菌在ＰＤＡ培养基上生长速率最快，在大豆叶葡萄糖琼脂培养基和番茄培养基瞳孢量经在ＰＤＡ上高２倍，比病菌生长发育最适温度为２５－２８℃，低于１５℃或高于３７℃均不适宜，在连续黑暗条件下有利于生长，ＰＨ４－９之间，均能生长和产孢以ＰＨ－＝７生长最适，ＰＨ＝７－８产孢最多，分生孢子在葡萄糖液中萌发最好，在１５－４０℃之间均能萌发，最适温度为３０－３３℃，ＰＨ＝３－９之间均能萌发，ＰＨ＝７－８萌发     

Selection and orchard testing of antagonists suppressing conidial production by the apple scab pathogen <Emphasis Type="Italic">Venturia inaequalis</Emphasis>

Apple scab caused by Venturia inaequalis is a major disease in apple production. Epidemics in spring are initiated by ascospores produced on overwintering leaves whereas epidemics during summer are driven by conidia produced on apple leaves by biotrophic mycelium. Fungal colonisers of sporulating colonies of V. inaequalis were isolated and their potential to reduce the production of conidia of V. inaequalis was evaluated on apple seedlings under controlled conditions. The four most effective isolates of the 63 screened isolates were tested subsequently under Dutch orchard conditions in 2006. Repeated applications of conidial suspensions of Cladosporium cladosporioides H39 resulted in an average reduction of conidial production by V. inaequalis of approximately 40%. In 2007, applications of conidial suspensions of C. cladosporioides H39 reduced conidial production by V. inaequalis by 69% on August 6 and by 51% on August 16, but no effect was found on August 20. However, viability of available conidia of C. cladosporioides H39 was low at the end of the experiment. Epiphytic and endophytic colonisation by Cladosporium spp. of leaves treated during the experiment with C. cladosporioides H39 was significantly higher than on control leaves sampled 6 weeks after the last application. It is concluded that C. cladosporioides H39 has promising potential as a biological control agent for apple scab control. More information is needed on the effect of C. cladosporioides H39 on apple scab epidemics as well as on mass production, formulation and shelf life of conidia of the antagonist.     

绿色木霉菌株Tv04-2固体发酵条件研究

以产孢量为测定指标,通过单因子和正交试验对人参根部病害拮抗绿色木霉菌株Tv04-2固体发酵条件进行了筛选,获得了以玉米粉、麦麸等廉价农产品及其副产物为碳、氮源的最佳固体发酵培养基,其配方为:在250 mL三角瓶中装入20 g固体基质,其中玉米粉∶麦麸按1∶1比例混合,FeSO4含量0.1 g,水7 mL,接种量4 mL;最佳发酵条件为:25,20和28℃下依次发酵2 d。利用优化培养基及发酵条件进行发酵试验,可以获得高达4×109cfu/g的产孢量,为人参根部病害高拮抗活性木霉菌剂的生产和应用奠定了基础。     

两步控制策略优化生防菌B579芽孢生成条件

[目的]优化生防菌-枯草芽孢杆菌B579芽孢生成的发酵条件,提高芽孢浓度。[方法]采用2步控制策略,即发酵的第1阶段（菌体生长阶段,0~10 h）促进细胞生长,发酵的第2阶段（菌体对数生长后期,芽孢生成阶段,10~30 h）促进芽孢生成,分别考察了培养基初始葡萄糖浓度、发酵pH、第2阶段摇床转速、第2阶段发酵温度对芽孢生成的影响。通过单因素试验确定其水平,在单因素试验基础上进行正交试验优化,确定获得高浓度芽孢的最佳发酵条件。[结果]培养基初始葡萄糖浓度是影响芽孢生成的显著因素,芽孢生成的最佳发酵条件为培养基初始葡萄糖浓度5 g/L,发酵pH7.0,第1阶段的发酵温度37℃,摇床转速180 r/min,约10 h后进入第2阶段,发酵温度提高到40℃,摇床转速调节为200 r/min。发酵30 h,最终获得的芽孢浓度为（9.43±0.15）×108CFU/ml,芽孢生成率为90.99%,分别是优化前的6.70和2.43倍。[结论]利用两步控制发酵策略可提高生防菌B579芽孢浓度,建立的发酵工艺为生防菌剂的大规模生产奠定了基础。     

大豆灰斑病菌生长和产孢高效培养方法探讨

为明确大豆灰斑病菌菌丝生长和产孢的有效方法,探讨了V8培养基组分中V8蔬菜汁和碳酸钙含量对大豆灰斑病菌菌丝生长速率和产孢量的影响及最佳组分配比。利用5种不同浓度V8蔬菜汁和5种浓度碳酸钙组成25种不同组分处理,以广泛使用的PDA培养基为对照培养基,接种大豆灰斑病7号生理小种进行暗培养,每2 d测量其菌落生长情况和产孢子量并进行对比分析。结果表明:25种不同组分V8培养基的菌落直径、生长速率、生长面积及产孢子量均大于PDA培养基的菌落。V8培养基菌落直径生长最快为3.47 mm·d^-1;孢子产量最多达每皿9.87×106个。培养第5天时,病原菌的生长活力最大。最适宜培养时间为11~13 d,其产孢量达到高峰。培养基组合A4b4碳酸钙含量为1.5 g·L^-1、V8蔬菜汁浓度为15%时,最适合菌落直径生长,菌落生长面积最大。培养基组合A4b3碳酸钙含量为1.5 g·L^-1、V8蔬菜汁浓度为12%时,产孢子量最多。