Effect of culture medium on spore production and germination of races of Colletotrichum lindemuthianum

Spore production on the media neopeptone glucose agar (PGA), malt extract agar (MEA), Czapek Dox agar (CDA) and bean pod extract agar (BEA) was determined for 10 races ofColletotrichum lindemuthianum, as well as the aftereffects on spore germination on water agar.Clear race-medium interactions were found for spore production. PGA was a universal medium for races of this fungus, but five races gave a much higher production on MEA. CDA and BEA were less effective for spore production. There was no clear aftereffect of the four media on spore germination. The 10 races could be divided into good, moderate and bad germinators, independent of the medium on which they had been developed.Samenvatting Onderzoek in vitro werd gedaan naar de invloed van vier cultuurmedia op de sporenproduktie van 10 fysio's vanC. lindemuthianum. Bovendien werd nagegaan of de kieming van de sporen op water-agar afhankelijk was van het medium waarop de sporen waren gevormd.Er bleken voor sporenproduktie inderdaad aanwijsbare fysio/medium interacties te zijn. De beste algemene gechiktheid had neopepton-glucose-agar (PGA). Op moutextract-agar (MEA) werden echter met verschillende fysio's veel hogere sporenprodukties verkregen, terwijl de sporenproduktie van andere fysio's duidelijk lager lag dan op PGA. De resultaten met Czapek-Dox-agar (CDA) en bonepeul-extract-agar (BEA) waren minder goed. Voor de 10 fysio's kan derhalve met PGA en MEA worden volstaan. Media met natuurlijke extracten (mout, bonepeulen) of met pepton, waren beter voor sporenproduktie dan het synthetische medium Czapek-Dox-agar.De media hadden geen na-effect op de sporenkieming op water-agar. De fysio's konden echter worden ingedeeld in goede, matige en slechte kiemers.     

Dose-response relationships between phytopathogenic bacteria and their hosts

Theories on the relationships between the challenge dose of phytopathogenic bacteria and the quantal response of the host plant are discussed and applied to experimental results. In a number of cases the extent of disease was directly proportional to the dose, which is an indication of independent action. Departures from linearity in the relationships were ascribed tointer alia a shortage of multiplication sites, antagonism amongst the cells of the pathogen and heterogeneity of the tested host plants with respect to susceptibility. In a few host-pathogen combinations, dose-response relationships showing an upward curve were found; this is probably an indication of facultative synergism. The relationships found in homologous and heterologous host-pathogen combinations were similar. The implications of the above findings for the quantitative study of factors affecting the susceptibility of plants to bacterial infection are discussed.Samenvatting Na een bespreking van de theorieën over de relatie tussen het aantal fytopathogene bacteriën per inoculatie en de al-of-niet respons — waarbij dus de grootte van de individuele respons niet in acht genomen wordt — worden deze theorieën getoetst aan de resultaten van proeven die in de literatuur beschreven zijn. Onderschied wordt gemaakt tussen proeven waarin de proporties en die waarin de aantallen geslaagde inoculaties bepaald zijn. Verder is een vergelijking gemaakt tussen homologe en heterologe combinaties van waardplant en pathogeen.Waar de proporties geslaagde inoculaties werden gemeten, vond ik in een aantal gevallen evenredigheid tussen dosis en respons, mits een transformatie werd toegepast voor veelvoudige infectie. Dit is een aanduiding dat de cellen van het pathogeen elkaar niet beïnvloeden. Afwijkingen van dit rechtlijnig verband kunnen o.a. worden toegeschreven aan antagonisme tussen de cellen van het pathogeen, aan heterogeniteit in vatbaarheid van de waardplanten of aan een beperkt aantal vermeerderingsloci.In drie gevallen werd een naar boven gekromde lijn gevonden, hetgeen waarschijnlijk wijst op facultatief synergisme.In proeven waarin de aantallen geslaagde inoculaties gemeten werden, vond ik in de literatuur evenredige en dus rechtlijnige verbanden met afbuigingen naar rechts voor responses tot te hogere doses. De afwijkingen van rechtlijnigheid kunnen hier worden toegeschreven aan een beperkt aantal vermeerderingsloci of aan antagonisme tussen de cellen van het pathogeen.Geen essentieel verschil in dosis-respons verhoudingen werd gevonden tussen homologen en heterologe waardplant-pathogeen combinaties.De implicaties van bovengenoemde resultaten voor de kwantitatieve studie van factoren die de vatbaarheid van planten voor infectie door bacteriën bepalen, worden besproken.     

Oxidative stress and antioxidative responses in plant–virus interactions

During plant–virus interactions, defence responses are linked to the accumulation of reactive oxygen species (ROS). Importantly, ROS play a dual role by (1) eliciting pathogen restriction and often localized death of host plant cells at infection sites and (2) as a diffusible signal that induces antioxidant and pathogenesis-related defence responses in adjacent plant cells. The outcome of these defences largely depends on the speed of host responses including early ROS accumulation at virus infection sites. Rapid host reactions may result in early virus elimination without any oxidative stress (i.e. a symptomless, extreme resistance). A slower host response allows a certain degree of virus replication and movement resulting in oxidative stress and programmed death of affected plant cells before conferring pathogen arrest (hypersensitive response, HR). On the other hand, delayed host attempts to elicit virus resistance result in an imbalance of antioxidative metabolism and massively stressed systemic plant tissues (e.g. systemic chlorotic or necrotic symptoms). The final consequence of these processes is a partial or almost complete loss of control over virus invasion (compatible infections).     

稻梨孢菌与其他寄主梨孢菌在水稻植株上的交互作用

作者研究了1个稻梨孢菌株与4个稻以外寄主梨孢菌株在混合接种和间隔接种条件下,在水稻植株上的交互作用。结果表明:弱致病菌与强致病菌间交互作用较强,非致病菌与强致病菌间较弱。弱致病菌可明显降低强致病菌的致病性,非致病菌对强致病菌的作用,多数组合表现为减轻病害,但有少数组合表现为促进发病。弱致病菌先接种;2天后接种强致病菌,比两者混合接种具有更强烈的互作效应,病斑数减少达35.7％—38.1％。先接种菌的孢子浓度对后接种菌的致病性也有影响。     

Combining Fluorescent Pseudomonas spp. Strains to Enhance Suppression of Fusarium Wilt of Radish

Fusarium wilt diseases, caused by the fungus Fusarium oxysporum, lead to significant yield losses of crops. One strategy to control fusarium wilt is the use of antagonistic, root-colonizing Pseudomonas spp. It has been demonstrated that different strains of these bacteria suppress disease by different mechanisms. Therefore, application of a mixture of these biocontrol strains, and thus of several suppressive mechanisms, may represent a viable control strategy. A prerequisite for biocontrol by combinations of biocontrol agents can be the compatibility of the co-inoculated micro-organisms. Hence, compatibility between several Pseudomonas spp. strains, that have the ability to suppress fusarium wilt of radish, was tested in vitro on KB agar plates. Growth of P. fluorescens strain RS111 was strongly inhibited by Pseudomonas spp. strains RE8, RS13, RS56 and RS158, whereas a mutant of strain RS111 (RS111-a) was insensitive to inhibition by these strains. Strains RS111 and RS111-a only slightly inhibited some other strains. Suppression of fusarium wilt of radish in a potting soil bioassay by the incompatible combination of RE8 and RS111 was comparable to the effects of the single strains. However, disease suppression by the compatible combination of RE8 and RS111-a was significantly better as compared to the single strains. In contrast, the incompatible combination of RS56 with RS111 resulted in enhanced disease suppression as compared to the single strains. Increased disease suppression by combinations of RS13 or RS158 with RS111 or RS111-a was not observed. This indicates that specific interactions between biocontrol strains influence disease suppression by combinations of these strains.     

咪唑啉酮类簇合物的合成及其除草活性

在生物体系中,二效价配体比单效价配体对受体有更强的亲和力。根据乙酰乳酸合成酶与咪唑啉酮类复合物的3D结构信息特点,设计并合成了8个对称的双甲基咪草烟类化合物,其结构经红外、核磁及元素分析等确证。初步生物活性测定结果表明:咪唑啉酮二效价簇合物对乙酰乳酸合成酶的亲和力没有增加,在100 μg/mL浓度下,对油菜Brassica campestris L. 根长抑制率与单效价化合物相当。     

寄生蜂畸形细胞特性及与蜂幼虫生长发育的关系

本文综述寄生蜂畸形细胞特性及其功能研究的最新进展。一些进化高等的膜翅目内寄生蜂,在胚胎发育过程中,包裹在胚胎周围的浆膜会随着蜂卵的孵化,以游离的细胞团或单个细胞的形式释放到寄主昆虫的血淋巴中。这些源自浆膜被称作畸形细胞(Teratocyte)的特殊类群,在伴随蜂幼虫的生长发育过程中,自身也经历一系列结构和功能的改变。它们主要通过分泌蛋白质或酶类,改变寄主的物质代谢途径等方式为发育中的蜂幼虫提供营养和能量。对寄生蜂重要的调控因子-畸形细胞的特性及与蜂幼虫相互关系的揭示,可以阐明寄生蜂-寄主昆虫协同进化的内在机理,也可为开发害虫生物防治新策略提供新的思路和途径。     

Plant—pathogen Interactions: Genetic and Comparative Analyses

The interactions between plants and pathogens can be shifted to favor either plant of pathogen by small changes in the environment, primarily temperature and plant nutrition, and it leaves a quandary as to whether the plant on pathogen is most affected by the change in the environment. The stage of development of a plant can affect the resistance or susceptibility to a pathogen. A plant may be susceptible to a given pathogen a one stage of development but resistant at another stage of development. The view of the gene-for-gene hypotheses as a one-for-one relationship is not supported by experiments that ask whether avirulence genes and resistance genes function alone. The term genomics has been intemreted several different ways, but its most useful impact on studies of host-pathogen interactions will, most likely, be to find all the pieces to the puzzle of how plants and pathogens communicate.     

Positive plant–soil feedbacks of the invasive Impatiens glandulifera and their effects on above‐ground microbial communities

Impatiens glandulifera is one of the most widespread invasive plant species in the UK. Although aspects of its biology are known, there is little information about its association with microbial communities, both above ground and below ground. Furthermore, it is unknown whether this species exhibits any form of plant–soil feedback (PSF), commonly seen in other invasive weeds. We conducted a PSF experiment, in which plants of I. glandulifera were grown in soil that supported the species and compared with plants grown in a control soil from the same locality. Soil nutrients were measured, and the soil and foliar microbial communities were assessed. Impatiens glandulifera grew larger and faster in conditioned soil compared with the control. Higher levels of phosphate were also found in conditioned soils. Arbuscular mycorrhizal fungal (AMF) colonisation was lower in conditioned soils, suggesting that I. glandulifera may rapidly alter AMF communities in invaded areas. PSFs had a significant effect on the foliar endophyte community, with clear separation of species between conditioned and control soils. These results show that I. glandulifera displayed a positive PSF and the PSF mechanism extended beyond the soil microbial community to affect foliar endophytes. The observed increase in endophytes in plants grown in conditioned soil could enhance resistance to herbivory, thus further accentuating the invasive properties of this species.     

种间相互作用对牧草间作体系生产力的影响

为了揭示种间相互作用对柱花草/黑籽雀稗间作体系生产力的影响,试验设计三个处理,分别是单作柱花草、单作黑籽雀稗、柱花草/黑籽雀稗间作,观测了三个不同种植模式作物整个生育的物候期、整个植株生长量、生物量、生物量的当量比及不同种植体系土壤有机质、全氮和全磷的差异。结果表明:1种植牧草270天后,间作体系地上部和地下部生物量的当量比分别是3.05和3.52,土地当量比大于1,表明柱花草/黑籽雀稗间种具有间作优势。2与单作相比,间作体系黑籽雀稗物候期推迟5天;其生长量、生物量均高于单作,株高、根长、干草产量和根系产量分别高于单作9.67 cm、7.33 cm、345.50 g·株~(-1)、131.67 g·株~(-1)。与柱花草单作对比,间作的分枝期、现蕾期、花期比单作分别推迟5天、15天、5~15天;其生长量和生物量低于单作,柱花草株高、根系深、根冠比、根瘤量、干草产量和根系产量分别低于单作10.64 cm、0.54 cm、0.08、0.84粒·株~(-1)、14.29 g·株~(-1)和1.48 g·株~(-1);3间作体系土壤养分有机质、全氮、全磷比种植前增加的量分别为0.039%、0.003%、0.001%。单作柱花草样地有机质、全氮比种植前增加的量分别为0.063%、0.006%,磷比种植前减少0.001%;单作黑籽雀稗样地有机质、全氮比种植前减少0.017%、0.002%。表明,柱花草的间作提高了样地土壤有机质、全氮和全磷含量;柱花草在生物固氮过程中,以磷固氮,消耗磷素致使单作柱花草样地全磷量减少,全氮量增加。     

Stability of partial resistance in potato cultivars exposed to aggressive strains of Phytophthora infestans

Potato cultivars were evaluated for their resistance responses to aggressive strains of Phytophthora infestans in field and laboratory experiments. Analysis of variance revealed differential cultivar-by-isolate interactions for both foliar and tuber blight resistance. Differential responses occur as revealed by specific susceptibilities of cultivars to certain pathogen genotypes and changing rank order. In general, severity of late blight epidemics as observed in the haulms did not correlate well with foliar blight resistance ratings as presented in the National List of Recommended Potato Varieties. No significant correlation was found between tuber blight incidence under field conditions and the tuber blight rating in the National List. Also, there was no relation between the field and laboratory tuber blight resistance assessments. A significant association was demonstrated between late blight infection in the foliage and tuber blight incidence under field conditions. The presence of differential interaction, independent of R-gene-based resistance, indicates some adaptation of P. infestans to partial resistance and consequently adverse effects on the stability and durability of partial resistance to potato late blight.     

Mutations in ams genes of Erwinia amylovora affect the interactions with host plants

A large region for exopolysaccharide (EPS) production that is involved in the pathogenicity of Erwinia amylovora strain CFBP1430, cloned previously, was further characterized in this study. An 8.4 Kb-long sub-cloned fragment from that ams (amylovoran synthesis) region was mutagenized in vitro by Tn3Gus insertion. Several new chromosomal mutants were obtained by marker exchange. The phenotype of those mutants was determined with regard to pathogenicity, EPS production, and growth in planta. It appeared that alteration in EPS synthesis was correlated with altered pathogenicity and poor (or no) growth in planta. Altogether these data argue for a direct role of EPS in bacterial multiplication in planta, and/or for an indirect role by protecting the bacteria against host defence reactions.     

Growth traits of the exotic plant Hydrocotyle vulgaris and the evenness of resident plant communities are mediated by community age,not species diversity

Biological invasions are determined by interactions between resident plant communities and exotic plants. Time of invasion and species diversity of resident plant communities may greatly affect exotic plant invasions. We assembled low‐ and high‐diversity resident plant communities by sowing seeds of four and eight grassland species, respectively, and at each of three time periods (1, 4 and 7 weeks after sowing), the resident communities were invaded by Hydrocotyle vulgaris or not. We also constructed a plant community with H. vulgaris alone. Presence of H. vulgaris had no effect on biomass of the resident communities or biomass of each component species. Community age significantly affected biomass and evenness of the resident communities, and their competition with H. vulgaris, but the priority effect of the resident communities was slight. Increasing species richness did not change the interaction between H. vulgaris and the resident plant communities. These findings suggest a weaker competitive exclusionary effect of H. vulgaris on the resident communities with early germination, and H. vulgaris tended to have no significant impact on intact resident terrestrial plant communities. Thus, the potential risk of H. vulgaris invasion is low, especially in the communities with young age.     

Disease complexes involving plant parasitic nematodes and soilborne pathogens

This review discusses the mechanisms underlying synergistic interactions between phytophagous nematodes and soilborne pathogens, and identifies biotic and abiotic factors affecting these interactions. Approaches towards the resolution and management of nematode–pathogen complexes are considered and discussed.     

叶霉菌非亲和小种对番茄系统抗性的诱导及植株内水杨酸动态

 番茄叶霉菌小种4是番茄Cf5品系的非亲和小种,接种Cf5植株第3叶后,经不同诱导间隔期以亲和小种5接种第3叶和第4叶,15 d后检查叶霉病发病情况。试验表明,在诱导间隔期为3 d和5 d时,小种4诱导接种的第3叶和未经诱导接种的上位第4叶发病面积比不接种或接种小种5的对照显著降低,以5 d间隔期处理效果最好。上述2个叶位的发病分别比对照降低90%和85%。小种4接种第3叶后该叶位和上部未接种第4叶内水杨酸含量迅速增加,以接种后3 d含量最高,分别达4.02 μg/g鲜重和3.21μg/g鲜重,比对照分别高2倍和1.8倍。接种后5 d内始终保持较高水平。接种8 d后逐渐下降,但仍高于对照。水杨酸含量的增加早于抗性表现,因而可能在该系统的抗性诱导中起作用。     

乌桕对南方根结线虫与地上不同食性昆虫互作的光合生理响应

本文通过比较乌桕对两种地上不同食性昆虫(专食性癞皮夜蛾、广食性斜纹夜蛾)与南方根结线虫互作的光合生理响应,分析不同空间植食性生物间的互作关系及植物的响应机制。结果表明:无南方根结线虫胁迫下,2种地上不同食性昆虫对乌桕的净光合速率(P_n)、气孔导度(G_s)及胞间CO_2浓度(C_i)的影响与对照组无显著差异;而南方根结线虫胁迫下,2种地上昆虫显著降低了乌桕G_s及C_i。其中,与对照组及癞皮夜蛾处理组相比,南方根结线虫与斜纹夜蛾的共同胁迫显著降低了乌桕P_n、G_s及C_i。此外,斜纹夜蛾为害增加了乌桕叶绿素含量,南方根结线虫胁迫降低了叶绿素含量。因此,南方根结线虫与斜纹夜蛾间形成一种加性效应,并对乌桕光合生理产生了拮抗效应,而这种效应在南方根结线虫与癞皮夜蛾间并不显著。由此可见,乌桕对地上-地下植食性生物胁迫形成不足补偿机制,且具体的响应机制与植食性生物的食性相关。     

Virulence of Verticillium lecanii (Z.) against cereal aphids; does timing of infection affect the performance of parasitoids and predators?

BACKGROUND: Entomopathogenic fungi such as Verticillium lecanii (Z.) (Mycotal^®) are used for pest control as an alternative to chemical control. In this study, the effect of V. lecanii on cereal aphids is assessed. In addition, an investigation is carried out to determine whether the use of V. lecanii affects the performance of two natural enemies of aphids, the predator Harmonia axyridis (P.) and the parasitoid Aphidius colemani (V.), in no‐choice experiments under laboratory conditions. RESULTS: The number of Rhopalosiphum padi (L.) and Sitobion avenae (F.) killed was increased by increasing the concentration of V. lecanii. The timing of application of fungus to aphids affected the efficacy of other biocontrol agents, a parasitoid and a predator. Parasitation by A. colemani (V.) in both cereal aphids (S. avenae and R. padi) was not affected by V. lecanii when aphids were first treated with V. lecanii and then exposed to A. colemani. The emergence of adults from parasitised mummies was, however, lower in infected aphids than in uninfected aphids when the aphids were first exposed to the parasitoids and then treated with fungus. The female sex ratio in the emerging adults was lower in V. lecanii‐treated aphids in both species. When aphids were first treated with V. lecanii, 72 h before predation, fewer aphids of both species were consumed by H. axyridis (P.). CONCLUSION: Use of entomopathogenic fungus as a biological control agent could be a complementary strategy in an integrated pest management programme against cereal aphids, but it can reduce the efficiency of other biocontrol agents (parasitoids and predators) when applied simultaneously. © 2012 Society of Chemical Industry     

Phytobiome metabolism: beneficial soil microbes steer crop plants' secondary metabolism

Crops are negatively affected by abiotic and biotic stresses, however, plant‐microbe cooperation allows prompt buffering of these environmental changes. Microorganisms exhibit an extensive metabolic capability to assist plants in reducing these burdens. Interestingly, beneficial microbes may also trigger, at the host side, a sequence of events from signal perception to metabolic responses leading to stress tolerance or protection against biotic threats. Although plants are well known for their vast chemical diversity, plant‐microbial interactions often stimulate the production of a rich and different repertoire of metabolites in plants. The targeted microbial‐plant interactions reprogramming plant metabolism represent potential means to foster various pest managements. However, the molecular mechanisms of microbial modulation of plant metabolic plasticity are still poorly understood. Here, we review an increasing amount of reports providing evidence for alterations to plant metabolism caused by beneficial microbial colonization. In addition, we highlight the vital importance of these metabolic reprograms for plants under stress erratic conditions. © 2019 Society of Chemical Industry     

Pyramiding of partial disease resistance genes has a predictable,but diminishing,benefit to efficacy

Partial resistance genes often need to be ‘pyramided’ into a crop cultivar to obtain commercially acceptable levels of disease resistance. Analysis of data from four different wheat mapping populations, segregating for partial resistance to four contrasting foliar pathogens, showed a diminishing benefit to disease control from increasing the numbers of resistance loci in wheat lines. To test whether a general function could describe the efficacy benefit from pyramiding, a simple multiplicative survival model (MSM) was used to predict disease severities on mapping population lines carrying various combinations of two, three or four resistance loci. The effectiveness of each resistance locus was expressed as the disease severity in lines carrying resistance alleles at one locus, as a proportion of the severity in lines carrying no detectable resistance alleles. The predicted severity from any given combination of multiple resistance loci was calculated as the product of the proportional severities for the relevant single loci. A regression line fitted to transformed observed against predicted values explained 93% of the variation, with a slope and intercept not significantly different from 1 and 0, respectively. MSM may therefore provide a simple method to test contrasting types of partial resistance and search for synergistic combinations. The analysis suggests that diminishing returns are a general feature of partial resistance to foliar pathogens in wheat, a finding that is likely to apply to other crop pathosystems. Identifying and combining ever more QTL is likely to provide limited gains. The consequences of these findings for QTL analysis are described.