Effects of induced resistance on infection efficiency and sporulation of Puccinia striiformis on seedlings in varietal mixtures and on field epidemics in pure stands

An inducer race ofPuccinia striiformis inoculated two days before a challenger race on wheat seedlings of cv. Clement, reduced infection efficiency by 44% and lesion expansion by 7.7%; there was no effect on sporulation rate. In field epidemics, induced resistance restricted the disease intensity on cvs. Clement and Austerlitz in pure stands by 44% and 57% respectively. In the glasshouse at the seedling stage, disease intensity in a varietal mixture was reduced by 82% compared to the susceptible pure stands; one third of the total disease reduction was attributable to induced resistance.     

Effect of humidity on epidemiological patterns of the powdery mildew (sphaerotheca fuliginea) on squash

Epidemics ofSphaerotheca fuliginea on squash in growth chambers developed somewhat better under dry than under humid conditions. The reason appeared to be the differing effects of humidity on the various stages of disease development: dryness favored processes of colonization, sporulation and dispersal, while high humidity favored infection and conidial survival. However, all these processes will occur under conditions of humidity far from their respective optima, thus enabling the development ofS. fuliginea under widely dissimilar conditions. Information is presented on the effects of temperature on colonization and sporulation.     

稻瘟菌水平抗性稳定性的研究——品种与小种适合度的分析

在温室条件下,对9个无垂直抗性基因粳稻品种×8个日本标准稻瘟菌株组合测定了侵染几率(IP)、病斑型比例(PB)、病斑扩展速率(LR)和产孢能力(SPC)组分,并据此确定了品种与小种的适合度。方差分析结果表明,除SPC的互作项外,其它组分及类型,方差均达到显著或极显著水平。但品种和小种主效应所占方差更大,从而证实了品种的抗性类型为水平抗性。某些品种在IP、PB及LR组分上反映了小种的专化作用,但因为不同品种在各组分上的抗性反应不同,因此,品种水平抗性的稳定性不能由组分的小种专化作用确定,而须由各组分组成的适合度的小种专化性确定。对品种X小种的适合度进行了互作的多重比较,未发现专化性互作,说明供试品种的水平抗性是稳定的。     

Sensitivity ofFusarium graminearum to fungicide JS399-19:In vitro determination of baseline sensitivity and the risk of developing fungicide resistance

The baseline sensitivity ofFusarium graminearum Schwade [teleomorph =Gibberella zeae (Schweinitz) Petch] to the fungicide JS399-19 (development code no.) [2-cyano-3-amino-3-phenylacrylic acetate] and the assessment of risk to JS399-19 resistancein vitro are presented. The mean EC₅₀ values for JS399-19 inhibiting mycelial growth of three populations of wild-typeF. graminearum isolates were 0.102±0.048, 0.113±0.035 and 0.110±0.036 μg ml⁻¹, respectively. Through UV irradiation and selection for resistance to the fungicide, we obtained a total of 76 resistant mutants derived from five wild-type isolates ofF. graminearum with an average frequency of 1.71 × 10⁻⁷% and 3.5%, respectively. These mutants could be divided into three categories of resistant phenotypes with low (LR), moderate (MR) and high (HR) level of resistance, determined by the EC₅₀ values of 1.5–15.0 μg ml⁻¹, 15.1–75.0 μg ml⁻¹ and more than 75.0 μg ml⁻¹, respectively. There was no positive cross-resistance between JS399-19 and fungicides belonging to other chemical classes, such as benzimidazoles, ergosterol biosynthesis inhibitors and strobilurins, suggesting that JS399-19 presumably has a new biochemical mode of action. Although the resistant mutants appeared to have comparable pathogenicity to their wild-type parental isolates, they showed decreased mycelial growth on potato-sucrose-agar plates and decreased sporulation capacity in mung bean broth. Nevertheless, most of the resistant mutants possessed fitness levels comparable to their parents and had MR or HR levels of resistance. As these studies yielded a high frequency of laboratory resistance inF. graminearum, appropriate precautions against resistance development in natural populations should be taken into account. http://www.phytoparasitica.org posting August 7, 2008.     

The influence of silicon on components of resistance to blast in susceptible, partially resistant, and resistant cultivars of rice

ABSTRACT The application of silicon (Si) fertilizers reduces the severity of blast, caused by Magnaporthe grisea, in irrigated and upland rice; however, little research has been conducted to examine the epidemiological and etiological components of this reduction. Four cultivars of rice with differential susceptibilities to race IB-49 of M. grisea were fertilized with three rates of a calcium silicate fertilizer and inoculated with the pathogen to test the effects of Si on the following components of resistance to blast: incubation period, latent period, infection efficiency, lesion size, rate of lesion expansion, sporulation per lesion, and diseased leaf area. For each cultivar, the incubation period was lengthened by increased rates of Si, and the numbers of sporulating lesions, lesion size, rate of lesion expansion, diseased leaf area, and number of spores per lesion were reduced. Lesion size and sporulation per lesion were lowered by 30 to 45%, and the number of sporulating lesions per leaf and diseased leaf area were significantly reduced at the highest rate of Si. The net effect of Si on these components of resistance is an overall reduction in the production of conidia on plants infected with M. grisea, thereby slowing the epidemic rate of blast.     

小麦慢白粉品种的抗性组分研究

 2003~2004年度和2004~2005年度在田间测定了16个小麦品种(系)对小麦白粉菌E20菌株的抗性组分,包括潜育期、侵染几率、产孢量、病斑扩展和传染期。结果表明,小麦慢白粉品种(系)与高感对照品种相比,表现为潜育期长、侵染几率低、产孢量低、病斑扩展慢的特点,且这4个抗性组分与对照的差异都达到了显著和极显著水平,但慢白粉品种的传染期变化无一定规律。参试慢白粉品种的抗性组分参数与病情曲线下面积(AUDPC)的相关分析表明,潜育期与AUDPC呈负相关,但相关性不显著;产孢量和病斑扩展与AUDPC呈正相关,两年数据相关性均达到显著水平;侵染几率与AUDPC呈正相关,但2003-2004年度相关性不显著,而2004~2005年度相关性显著;传染期与AUDPC相关关系不明显。由此可见,在慢白粉品种的病害流行中起主要作用的是产孢量、病斑扩展,而侵染几率、潜育期和传染期作用相对较小。     

Solanum dulcamara L. (Bitterzoet) als mogelijke bron voor bladrolvirus

Summary Dijkstra (1933) demonstrated thatSolanum dulcamara (Bittersweet, Woody Nightshade) can be a host plant of potato leaf-roll virus. It was, however, not known whether this wild growing plant in nature contains the virus. AsS. dulcamara is the only common perennial Solanacea in the Netherlands its role as a virus reseroir was investigated.At 25 localities plants ofS. dulcamara were collected, and tested for the presence of leaf-roll virus by transferring virus-freeMyzus persicae (Sulz.) after 24 hrs feeding to groups ofPhysalis floridana, where they fed for 24 hrs before being killed. All plants ofS. dulcamara appeared to contain leafroll virus, though they did not show symptoms. Also seedlings ofS. dulcamara from seed of a leafroll infested plant showed no symptoms before or after infection with leafroll bij transmission withMyzus persicae (Sulz.).The virus could be transmitted fromS. dulcamara to potato (var. Bintje) byMyzus persicae (Sulz.) and by graftingS. dulcamara on potato.Seedlings, grown from seed obtained from a plant which was shown to have leaf-roll, all appeared to be infected with leaf-roll. As so far no plants were found or obtained which had no leaf-roll virus, it is possible that inS. dulcamara leaf-roll virus is invariably transmitted with seed. But as the virus does not appear to be pathogenic inS. dulcamara, one might assume that what in potatoes and other plants is called leaf-roll virus, inS. dulcamara is an integral, natural component of the organism.     

Components of partial resistance to Erysiphe graminis in spring barley

The development of powdery mildew on seven spring barley varieties lacking effective major resistance factors was compared in a small-plot field trial. Differences were observed at later growth stages indicating partial resistance in some varieties. Latent period and sporulation capacity were examined on the fifth or sixth leaf of these varieties plus several known to be susceptible, using plants raised under spore-free conditions. Latent period was extended in most partially resistant varieties compared with susceptible controls, more so at 5°C than at 10°C. Cumulative total spore production per colony over the 16-day sporulation period differed markedly between varieties, the most resistant yielding one-third as many spores as the susceptible controls. There was evidence that these resistance components were correlated with each other and with previous estimates of infection frequency. The significance of this finding, in relation to selection for improved levels of partial resistance, is discussed.     

Involvement of phenolic compounds in the resistance of grapevine callus to downy mildew (Plasmopara viticola)

Callus tissue of different grapevines (Vitis spp.) was inoculated withPlasmopara viticola. Short, highly-branched hyphae with necrosis, and long hyphae with heavy sporulation were observed on resistant and susceptible callus respectively. Thin-layer chromatography and spectrophotometric analysis showed that resistant callus contained greater quantities of gallocatechin derivatives than susceptible callus. Regression analysis between the field disease rating of each variety and its gallocatechin derivatives content indicated 92.2% correlation. Histochemical studies showed that, after infection withP. viticola, flavonoids appeared in the superficial cell walls of the callus, to a lesser degree on susceptible callus than on resistant callus. At a late stage of infection, the superficial cells of resistant callus were suberized, which did not occur in susceptible callus. This study showed that the preformed gallocatechin derivatives, the induced flavonoids and suberized superficial cells might play a role in the resistance of grapevine callus tissue to this fungus.Abbreviations CallusI Callus ofV. riparia var. Gloire de Montpellier - CallusV Callus ofV. vinifera var. Grenache - TLC Thin Layer Chromatography - var. variety - GAD Gallic acid derivatives - GD gallocatechin derivatives - RC resistant callus - SC susceptible callus     

Mechanisms involved in the biological control ofBotrytis cinerea incited diseases

Mechanisms involved in the biological suppression of infection and inoculum potential ofBotrytis cinerea are numerous and variable and the involvement of two or more mechanisms has been demonstrated in several systems. Reported combinations include antibiosis with enzyme degradation ofB. cinerea cell walls; competition for nutrients followed by interference with pathogenicity enzymes of the pathogen or with induced resistance; and alteration of plant surface wettability combined with antibiosis. Since germinatingB. cinerea conidia are dependent on the presence of nutrients, competition for nutrients is regarded as important in systems where biocontrol is involved. Conidial viability and germination capacity are also potentially affected by the presence of antibiotics produced by biocontrol agents and present in the phyllosphere. Slower in action are mechanisms involving induced resistance in the host plant and production of hydrolytic enzymes that degradeB. cinerea cell walls. The latter has been demonstrated much more convincinglyin vitro than in the phyllosphere. Biocontrol in established lesions and reduction of sporulation on necrotic plant tissues is a means to minimize the pathogen inoculum.Abbreviations BCA bio-control agent - Bc Botrytis cinerea - PG polygalacturonase - PL Pectin lyase - PME Pectin methyl esterase - PR pathogenesis related - VPD vapour pressure deficit     

Simulation studies on epidemics of wheat stripe rust (Puccinia striiformis) on slow-rusting cultivars and analysis of effects of resistance components

Simulation studies were conducted to analyse the effects of components of slow-rusting resistance to stripe rust ( Puccinia striiformis ) on wheat varieties using the Slow-Rusting Epidemic Simulation Model (SRESM). Five components, infection efficiency (IE), sporulation capacity (SC), lesion expansion rate (LE), latent period (LP) and infectious period (IP) were studied for their importance in epidemics under various weather and pathogen inoculum conditions. Simulation outputs were analysed statistically. The LE, IE and SC were found to be the most important components. However, final disease was more strongly influenced by weather and initial disease. The Integrated Resistance Index (IRJ), which combines the effects of resistance components, was used to predict the effects of various combinations of components in different types of weather and at different levels of initial disease intensity. These predictions provide guidelines for plant breeders and are useful in selecting varieties for specific regions.     

Control of infection and sporulation ofBotrytis cinerea on bean and tomato by saprophytic bacteria and fungi

Sixty isolates of saprophytic microorganisms were screened for their ability to reduce the severity of grey mould (Botrytis cinerea) infection and sporulation. Isolates of the bacteriaXanthomonas maltophilia, Bacillus pumilus, Lactobacillus sp., andPseudomonas sp. and the fungusGliocladium catenulatum reduced germination of conidia of the pathogen and controlled disease on bean and tomato plants. Their activity under growth room conditions was good, consistent, and similar to the activity of the known biocontrol agent,Trichoderma harzianum T39 (non-formulated). Although the tested isolates may for nutrients with the germinating conidia ofB. cinerea, resistance induced in the host by live or dead cells were also found to be involved. Inhibitory compounds were not detected on treated leaves. Sporulation ofB. cinerea after its establishment on leaves was also reduced by the above mentioned isolates and byPenicillium sp.,Arthrinium montagnei, Ar. phaeospermum, Sesquicillium candelabrum, Chaetomium globosum, Alternaria alternata, Ulocladium atrum, andT. viride. These sporulation-inhibiting fungi did not reduce the infection of leaves byB. cinerea. Most of these selected fungi and bacteria were capable of reducing lesion expansion.     

A review of the present status of theStemphylium complex in tomato foliage

Stemphylium solani, S. floridanum, andS. botryosum f. sp.lycopersici differ in some taxonomic details but cause similar symptoms on tomato foliage. In all three species similar genetic sources confer resistance, the host-free season is assumed to be passed in debris, and warm zones are preferred to temperate zones. The limited information available on the processes of infection and sporulation inS. solani andS. floridanum prevents a critical comparison withS. botryosum f. sp.lycopersici, for which these processes were studied in detail. Host age does not affect susceptibility toS. solani orS. floridanum, which also require short wettings for infection. Six- to eight-week-old plants are most susceptible toS. botryosum f. sp.lycopersici, which infects (and sporulates) after a long wetting period or several short wettings interspersed with dry intervals. The processes of infection and sporulation are relatively insensitive to temperature. Little is known about factors affecting epidemics ofS. solani andS. floridanum. Epidemics ofS. botryosum f. sp.lycopersici in Israel are facilitated mainly by prolonged wettings due to a combination of sprinkler irrigation and dew. Because of the slow build up of inoculum the disease reaches its peak late in the season, when host susceptibility decreases. Despite some differences among the threeStemphylium spp. but considering the similarities, and especially their possible occurrence in the same field and on the same plant, it is suggested to combine all three diseases under a common name, “TheStemphylium complex on tomatoes.”     

A comparative assessment of potential components of partial disease resistance to <Emphasis Type="Italic">Fusarium</Emphasis> head blight using a detached leaf assay of wheat,barley and oats

The relative resistance of 15 winter barley, three winter wheat and three winter oat cultivars on the UK recommended list 2003 and two spring wheat cultivars on the Irish 2003 recommended list were evaluated using Microdochium nivale in detached leaf assays to further understand components of partial disease resistance (PDR) and Fusarium head blight (FHB) resistance across cereal species. Barley cultivars showed incubation periods comparable to, and latent periods longer than the most FHB resistant Irish and UK wheat cultivars evaluated. In addition, lesions on barley differed from those on wheat as they were not visibly chlorotic when placed over a light box until sporulation occurred, in contrast to wheat cultivars where chlorosis of the infected area occurred when lesions first developed. The pattern of delayed chlorosis of the infected leaf tissue and longer latent periods indicate that resistances are expressed in barley after the incubation period is observed, and that these temporarily arrest the development of mycelium and sporulation. Incubation periods were longer for oats compared to barley or wheat cultivars. However, oat cultivars differed from both wheat and barley in that mycelial growth was observed before obvious tissue damage was detected under macroscopic examination, indicating tolerance of infection rather than inhibition of pathogen development, and morphology of sporodochia differed, appearing less well developed and being much less abundant. Longer latent periods have previously been related to greater FHB resistance in wheat. The present results suggest the longer latent periods of barley and oat cultivars, than wheat, are likely to play a role in overall FHB resistance if under the same genetic control as PDR components expressed in the head. However the limited range of incubation and latent periods observed within barley and oat cultivars evaluated was in contrast with wheat where incubation and latent periods were shorter and more variable among genotypes. The significance of the various combinations of PDR components detected in the detached leaf assay as components of FHB resistance in each crop requires further investigation, particularly with regard to the apparent tolerance of infection in oats and necrosis in barley, after the incubation period is observed, associated with retardation of mycelial growth and sporulation.     

Impact of tricyclazole and azoxystrobin on growth,sporulation and secondary infection of the rice blast fungus,Magnaporthe oryzae

BACKGROUND: Rice blast, caused by Magnaporthe oryzae B. Couch sp. nov., is one of the most destructive rice diseases worldwide, causing substantial yield losses every year. In Italy, its management is based mainly on the use of two fungicides, azoxystrobin and tricyclazole, that restrain the disease progress. The aim of this study was to investigate and compare the inhibitory effects of the two fungicides on the growth, sporulation and secondary infection of M. oryzae. RESULTS: Magnaporthe oryzae mycelium growth was inhibited at low concentrations of azoxystrobin and relatively high concentrations of tricyclazole, while sporulation was more sensitive to both fungicides and was affected at similarly low doses. Furthermore, infection efficiency of conidia obtained from mycelia exposed to tricyclazole was affected to a higher extent than for conidia produced on azoxystrobin‐amended media, even though germination of such conidia was reduced after azoxystrobin treatment. CONCLUSIONS: This study presents for the first time detailed azoxystrobin and tricyclazole growth–response curves for M. oryzae mycelium growth and sporulation. Furthermore, high efficacy of tricyclazole towards inhibition of sporulation and secondary infection indicates an additional possible mode of action of this fungicide that is different from inhibition of melanin biosynthesis. Copyright © 2012 Society of Chemical Industry     

Acquired resistance to pimaricin in Cladosporium cucumerinum and Fusarium oxysporum f.sp. narcissi associated with decreased virulence

In laboratory experiments strains ofCladosporium cucumerinum andFusarium oxysporum f.sp.narcissi were selected, which showed resistance to the fungicidal antibiotic pimaricin. Increased resistance appeared associated with decreased fitness in vitro (radial growth and sporulation on agar media) and in vivo (pathogenicity). The physiological background of a link between sensitivity to the fungicide and pathogenicity is discussed. Samenvatting In laboratoriumproeven werden stammen vanCladosporium cucumerinum enFusarium oxysporum f.sp.narcissi verkregen, die resistent waren tegen het fungicide antibioticum pimaricine. Toegenomen resistentie bleek gepaard te gaan met een verminderde vitaliteit in vitro (radiale groei en sporulatie op een agar voedingsbodem) en in vivo (pathogeniteit) (Tabel 1 en 2). Het niveau van de resistentie tegen pimaricine bleek erg beperkt (Fig. 1). De fysiologische achtergrond van een koppeling tussen gevoeligheid voor het fungicide en pathogeniteit wordt besproken.     

Responses of cucumber cultivars to induction of systemic resistance against anthracnose by plant growth promoting fungi

Initial experiment on the reactions of five Japanese cultivars of cucumber toColletotrichum orbiculare infection in the greenhouse revealed that cv Suyo and Gibai were susceptible and moderately susceptible, respectively, while cv Shogoin fushinari and Sagami hanjiro were resistant to infection byC. orbiculare; cv Ochiai fushinari was moderately resistant. The ability of 16 plant growth promoting fungi (some isolates belonged to species ofPhoma and some non-sporulating isolates) isolated from zoysiagrass rhizospheres to induce systemic resistance in the above five cucumber cultivars was tested by growing plants in potting medium infested with barley grain inocula of PGPF in the greenhouse. The second true leaves of 21-day-old plants were challenge inoculated withC. orbiculare and disease assessed. Nine, out of 16 isolates, caused significant reduction of disease caused byC. orbiculare in at least two cultivars.Phoma isolates (GS8-1 and GS8-2) and non-sporulating isolates (GU21-2, GU23-3, and GU24-3) significantly reduced the disease in all the five cultivars. The disease suppression in cucumber was due to the induction of systemic resistance, since the inducer(s) and the pathogen were separated spatially and that the inducer did not colonize aerial portions. The resistance induced by certain isolates in a susceptible cultivar was less than that in a resistant cultivar. Disease suppression caused by isolate GU21-2 was similar to theC. orbiculare induced control in certain cultivars. The average rate of expansion of lesion diameter on leaves due toC. orbiculare was slower due to induction with the selected plant growth promoting fungi compared to the uninduced control plants. Roots of four cultivars were colonized by only three isolates, however, roots of one cultivar (Suyo) was colonized by five isolates suggesting the cultivar-specific root colonization ability.Abbreviations cv cultivar(s) - PGPF plant growth promoting fungal isolates - PGPR plant growth promoting rhizobacteria     

Life-table analysis of faba bean rust

In controlled near-optimum conditions (18 °C), monocyclic sporulation capacity and spore infection efficiency were assessed for faba bean rust on the first and second leaves of field bean. After a latency period of 8–10 days, lesions sporulated duringc. 50 days. Spore production on the second leaf,c. 9×10⁴ spores per lesion, was two times as high as spore production on the first leaf. Infection efficiency was similar for both leaf layers, with a mean value of 0.11 lesion per inoculated spore. Infection efficiency decreased strongly when spores originated from mother lesions older than 20 days. Three life-table statistics (the net reproduction numberR _o , the mean generation timeT _g , and the maximum relative growth rater _max ) were calculated.R _o was larger andT _g was longer for the second than for the first leaf, butr _max was nearly the same for both leaf layers (0.31–0.33 day^–1).r _max was compared with the exponential growth rater measured in a field experiment. From the difference between the two rates, the fraction of inoculum lost in field conditions was estimated at 0.54–0.94. The life-table statistics were also compared to those of other legume rusts, and implications of life-table analysis for comparative epidemiology were discussed.     

Synthesis of six heterocyclic multifunctional alkylating agents and evaluation of their activity againstPyrenophora avenae andBlumeria graminis f.sp.hordei

Six heterocyclic alkylating agents were synthesized and examined for activity against the oat stripe pathogenPyrenophora avenae on agar plates and against the barley powdery mildew fungusBlumeria graminis f.sp.hordei on barley seedlings. Radial growth ofP. avenae was not significantly affected by any of the compounds, but four of them,α,α-bis[4,7-bis(2-chloroethyl)-1,4,7-triazacyclononane]-para-xylene[3], 1,4,8,11-tetra(2-chloroethyl)-1,4,8,11-tetraazacyclotetradecane[4], 8,11-bis(2-chloroethyl)-1,4,8,11-tetraaza-5,7-oxocyclotetradecane[5] and 7,16-bis(2-chloroethyl-1,4,10,13-tetraoxa-7,16-diazaoctadecane[6], gave significant reductions in biomass ofP. avenae grown in liquid culture and in powdery mildew infection on barley when used at 25μM. Polyamine biosynthesis was examined by following the incorporation of labeled ornithine into polyamines inP. avenae. The four compounds3–6 which reduced mildew infection all reduced the flux of label through to the polyamines inP. avenae. Whether the reductions in mildew infection caused by these compounds is related to reduced formation of polyamines is not known and awaits investigation. http://www.phytoparasitica.org posting May 22, 2005.