Pear Scab Research Articles

Acibenzolar-S-Methyl-Induced Resistance to Japanese Pear Scab Is Associated with Potentiation of Multiple Defense Responses

ABSTRACT This study reports the mode of action of acibenzolar-S-methyl (ASM) against Japanese pear scab, caused by Venturia nashicola. Pretreatment of potted Japanese pear trees with ASM reduced scab symptoms and potentiated several lines of plant defense response. This included transcripts encoding polygalacturonase-inhibiting protein (PGIP) that were highly and transiently promoted after scab inoculation of plants pretreated with ASM, suggesting a possible role for defenses involved in direct interaction with the pathogen. The activity of the key enzyme of phenylpropanoid pathway, phenylalanine ammonia lyase (PAL), was enhanced in scab-inoculated leaves pretreated with ASM only 7 days after inoculation, suggesting that it may play a minor role in induced resistance. In this work, salicylic acid (SA) accumulation was enhanced in ASM-treated leaves for the first time, according to an equivalent time course to that of PAL activity. However, a delayed induction of SA accumulation in ASM-treated leaves compared with kinetics of induction of several pathogenesis- related (PR) proteins or their encoding genes suggested that resistance triggered by ASM may be SA-independent. Among these PR proteins, PR-1, chitinase and PR-10 were promoted early by ASM after scab inoculation. Peroxidase, as well as enzymes involved in the oxidative burst such as superoxide dismutase, catalase, and ascorbate peroxidase were weakly activated with ASM treatment alone or pathogen inoculation alone and highly enhanced in ASM pretreated plants upon challenge inoculation, suggesting the occurrence of priming phenomenon during the interaction of Japanese pear-ASM-V. nashicola. An early potentiation of the activity of these enzymes after scab inoculation of leaves pretreated with ASM suggested that active oxygen species may be involved as a signal for the activation of PR proteins or genes.

Expression of potential defense responses of Asian and European pears to infection with Venturia nashicola

In order to determine if differences in timing or levels of gene and enzyme activations were likely to account for differences in resistance of pear cultivars against Japanese pear scab, time course analyses of several potential defense genes and enzymes as well as salicylic acid (SA) accumulation were carried out using leaf tissue of susceptible Japanese pear cv. ‘Kousui’ and resistant pear cvs. ‘Kinchaku’, ‘Mamenashi 12’ and ‘Flemish Beauty’ upon inoculation with the race 1 of Venturia nashicola. A phenylalanine-ammonia lyase gene ( pal) expression was not significantly affected by pathogen regardless of the compatible or incompatible interaction. Accumulation of pathogenesis-related protein 1 ( pr1) and chitinase ( chi) transcripts was early and highly elicited in the host resistant cv. ‘Kinchaku’, while in the other interactions it was delayed. In general, enhancement of SA accumulation and increase in the expression of pr1 gene in ‘Kinchaku’ are positively correlated, suggesting that this resistance is SA-dependent. The activity of four antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX)) was significantly enhanced only in resistant cultivars with a differential pattern of induction according to the cultivar. Superoxide anion ( O 2 ˙− ) was highly detected in inoculated leaves of the resistant cvs. ‘Kinchaku’ and ‘Mamenashi 12’ when compared to the susceptible cv. ‘Kousui’. The involvement of the oxidative burst as well as its relationship with the activity of the antioxidant enzymes and with resistance is discussed.

2003년 농작물 병해 발생개황

2003년은 냉해의 해였다. 3월부터 7월까지 저온이 지속되었고 생육기 내내 비가 자주 내려 강수량은 평년의 1.6배 일조시간은 평년의 68％ 수준이었다. 이 때문에 벼도 열병, 흰잎마름병이 심하게 발생하였고 강우에 의해 전반되는 역병이 대발생하여 고추의 경우 전국 재배면적의 55％가 피해를 입었다. 이외에 저온다습 조건에서 발생이 많은 잿빛곰팡이병 균핵병, 노균병이 전년에 비해 크게 증가하였고 과수의 경우 사과갈색무늬병, 배검은별무늬병이 대발생하여 큰 피해를 가져왔다. The year of 2003 was characterized as a cool humid year. Low temperature and frequent rains were continued during March to July, resulting in 1.6 times higher rainfalls and 32％ less sunshine period compared to the average yean Due to 2003's climatic condition, rice blast, and bacterial leaf blight occurred severely. Higher rainfalls caused severe epidemic of phytophthora disease and, in case of red-pepper, 55％ of cultivation acreage was devastated by the disease over the country. Besides, crop diseases which become severe under cool-humid conditions, such as gray mold, sclerotinia rot, downy mildew, increased significantly compared to the previous year. In fruit trees, brown spot of apple, and pear scab occurred severely causing much yield loss.

Effects of temperature, relative humidity and duration of wetness period on germination and infection by conidia of the pear scab pathogen (Venturia nashicola)

Experiments were conducted to determine the effects of temperature, relative humidity (RH) and duration of wetness period on in vitro germination of conidia and infection of detached pear leaves by Venturia nashicola, the causal agent of pear scab. Conidia germinated only in near‐saturation humidity (RH > 97%). The final percentage germination (24 h after inoculation) at 100% RH without free water was less than half that in free water. Conidia germinated over the range of temperatures tested (5–30°C); the optimum temperature for germination was ≈21°C. Changes in percentage germination of conidia over time were fitted by logistic models at each individual temperature. Polynomial models satisfactorily described the relationships between two (rate and time to 50% of maximum germination) of the three logistic model parameters and temperature. The minimum length of the wetness period for successful infection of detached pear leaves by conidia was observed at several temperatures. The shortest length of wetness period required for infection was 7 h at 22°C. Two polynomial models fitted well the relationship between the minimum wetness duration required for infection, and temperature.

Control of Pear Scab by Sterol Demethylation Inhibitors (DMIs)

Control of Pear Scab by Sterol Demethylation Inhibitors (DMIs)

THE JAPANESE PEAR GENOME PROGRAM II. GENETIC LINKAGE MAP IN PEAR

Pear genome research has been done using genetic linkage maps of Japanese and European pears, in the program of the National Institute of Fruit Tree Science, Japan. Two disease-related genes to black spot and pear scab diseases were identified in genetic linkage maps of 'Kinchaku' and 'Kousui'. Several RAPD markers linked to the disease resistance (or susceptibility) loci could be obtained, which will be used in marker assisted selection. The genetic linkage maps of the European pear 'Bartlett' and the Japanese pear 'Housui' were also constructed with DNA markers including AFLPs and SSRs originated from pear and apple. The former map consisted of 19 linkage groups that covered more than 1300 cM. Segregation of almost all SSR markers fitted the expected ratio of monogenic inheritance and SSR loci could be used as anchor markers to join different maps. Interestingly, SSRs developed from apple produced discrete amplified bands in pear and were mapped in pear linkage maps. Sequencing analysis showed that the nucleotide sequences of SSR alleles in pear and apple were highly homologous, and that SSR loci were presumably generated from the same origin.

Cloning and Sequence Analysis of the Eburicol 14 α‐Demethylase Encoding Gene (CYP51) from the Japanese Pear Scab Fungus Venturia nashicola

AbstractThe slow growth of many filamentous fungi in vitro prevents rapid isolation of large quantities of genomic DNA, thereby hampering molecular studies. Using a polymerase chain reaction (PCR)‐based adapter ligation cloning technique that requires only nanogram quantities of genomic DNA we have successfully cloned the complete CYP51 gene encoding the eburicol 14α‐demethylase, the target for DMI (Demethylation‐inhibiting) fungicides, from the Japanese pear scab fungus, Venturia nashicola. Analysis of predictedamino acid sequences of CYP51s from strains less sensitive to DMIs revealed no alterations when compared to the sensitive reference strain.

The use of weather and ascospore data for forecasting apple and pear scab in Victoria, Australia

The release of ascospores of Venturia inaequalis and V. pirina in the field, the apple scab infection criteria and the frequency of infection periods were investigated in Victoria. Ascospores were trapped over 3 months from green-tip in early September until late November over six years. In most seasons, the majority of ascospores from both species were trapped during the period of bloom but in years with extended dry periods (> 7 days) during bloom, ascospore release was significantly delayed. Ascospore release was triggered mainly by free moisture from rainfall and by light, but also occurred during periods of dew. In all seasons, less than 17.5% of a season’s ascospores were trapped during darkness (e.g. 1900 to 0500 h). In a field study usingpotted plants, the Mills’ criteria, itsrevised version and the Schwabe index predicted apple and pear leaf scab infections during wetting events in which leaf wetness began during day-time (0600 to 1900 h) and ascospores were trapped at the start of the wet periods. In two fruit-growing regions of Victoria, infection periods began on average 8–12 days apart and the average length of an infection period was 20 h. The use of weather information and ascospore release events is discussed in relation to the forecasting of apple and pear scab for effective scab control.

Molecular Identification of a Sexual Interloper: The Pear Pathogen, Venturia pirina, has Sex on Apple

ABSTRACT Venturia pirina (the pear scab pathogen) and V. inaequalis (the apple scab pathogen) were detected as ascospores discharged from apple leaf litter in New Zealand (spring 1998). Pseudothecia of both species were located on dead apple leaves; however, only those of V. inaequalis were associated with scab lesions. V. pirina was identified by rDNA sequence analyses, because morphological characters could not distinguish this fungus from V. asperata (a rare saprophyte on apple) and other Venturia spp. pathogenic on rosaceous fruit trees. Species-specific polymerase chain reaction primers designed to the 18S end of the internal transcribed spacer 1 region differentiated Venturia fruit tree pathogens reliably. V. pirina field isolates were pathogenic on pear, but only weak saprophytes on apple. In rare instances, when appressoria of V. pirina appeared to penetrate the cuticle of apple leaves, epidermal cells responded with a localized hypersensitive response (HR). To our knowledge, this is the first report of induction of HR-like events by V. pirina on its nonhost, apple, and also the first record of sexual reproduction of V. pirina on apple. It is assumed that V. pirina pseudothecia formed from saprophytic lesions in senescing apple leaves when active defense mechanisms such as HR were no longer induced.

Environmental factors influencing maturation and release of ascospores of Venturia pirina in Victoria, Australia

The influence of moisture, light, and temperature on Venturia pirina ascospore maturation and discharge was studied during 1992–99 in 2 pear-growing regions in Victoria. In each year and site, mature ascospores were trapped over a 3-month period beginning a few days before or at the green-tip stage of pear tree development in early September and ending in late November, with the majority of ascospores ((>80%) trapped between green-tip and petal-fall. Ascospore discharge was associated with rain and dew, with 90–98% of the season’s total number of ascospores trapped during rain events and 2–10% trapped during dew events in the 12 data sets examined. Most ascospores were trapped (82.5– 99.9%) during daytime (0600–1800 hours). The 0.1–17.5% of ascospores detected during night time (1900–0500 hours) were trapped mainly within 1–3 h of dawn or dusk. There were linear relationships between the logit of cumulative percentage of ascospore maturation and temperature accumulation (above 0 degree-days), calculated both daily and for days with >= 0.2 mm of rainfall. Six linear regression equations were formulated with 10 years of field data and using the 2 methods of accumulating degree-days, to predict the cumulative percentage of matured ascospores. Predictions were compared with additional field and laboratory observations not used in the formulation of the linear equations. The importance of the temperature-based linear equations is discussed in relation to the prediction of pear scab ascospore maturity for use in a pear scab management program.

Reduction in the Frequency of Fungicide Spray-applications to Control Japanese Pear Scab in Ibaraki Prefecture

Reduction in the Frequency of Fungicide Spray-applications to Control Japanese Pear Scab in Ibaraki Prefecture

Mapping of Disease-Related Genes in Japanese Pear using a Molecular Linkage Map with RAPD Markers.

Molecular linkage maps of disease-related genes in the Japanese pear cultivars ‘Kinchaku’ and ‘Kosui’ with RAPD markers were constructed. Using the pseudotestcross method, two separate maps were constructed from the segregation data of 82 F1 individuals. The linkage map for ‘Kinchaku’ consisted of 120 loci in 18 linkage groups spanning 768cM, while that for ‘Kosui’ contained 78 loci in 22 linkage groups extending over 508cM. The resistance allele of pear scab and the susceptibility allele of black spot were mapped in different linkage groups in ‘Kinchaku’. Compared with the reports on apple genome mapping, we estimated that these maps covered at least about a half of the total pear genome.

Pear Scab: Components of Potential Ascospore Dose and Validation of an Ascospore Maturity Model.

Variables necessary to calculate potential ascospore dose (PAD) for Venturia pirina, the causal agent of pear scab, were measured: area of individual leaves averaged 20.0 cm2, number of lesions per infected leaf ranged from 1.8 to 2.2, 13.5 to 41.7% of lesions were fertile (contained pseudothecia), number of pseudothecia per fertile lesion ranged from 15.2 to 24.4, and number of asci per pseudothecium averaged 131.5. The proportions of orchard floor covered with leaves (leaf litter density) were 0.34 and 0.67 for mowed and nonmowed orchards, respectively. Incidence of infected leaves ranged from 0.1 to 32.3%. Calculated PAD ranged from 1,114 to 708,320 ascospores per m2 in a commercial and an unsprayed orchard, respectively. For validation of a previously published model relating ascospore maturity to degree-days with a 0°C base, a linear regression equation was developed using 11 data sets collected between 1981 and 1998. The slope of the line was not different (P = 0.951) from that of the original model.

Venturia nashicola, the scab fungus of Japanese and Chinese pears: a species distinct from V. pirina

The relationship of Venturia nashicola, the scab fungus of Japanese and Chinese pears, to the European pear scab fungus, V. pirina, was reexamined. Ascospores of V. pirina were longer and wider than those of V. nashicola and the conidia of V. nashicola significantly shorter than those of V. pirina. Results from mating experiments in culture clearly showed sexual isolation between the species. V. nashicola was only pathogenic on Japanese and Chinese pears and V. pirina was only pathogenic on European pear. It is concluded that V. nashicola is distinct from V. pirina.

Purification of polygalacturonases produced by the pear scab pathogens, Venturia nashicola and Venturia pirina

An exopolygalacturonase and three endopolygalacturonases were purified from mycelia of pear scab pathogens, Venturia pirina and Venturia nashicola. The molecular weight of the isolated exoPG from V. pirina was 43kDa, and the endoPGs from V. nashicola were 42kDa as estimated by SDS–polyacrylamide gel electrophoresis. The pH optimum of the exoPG activity from V. pirina was 5.0. TheKm and Vmaxvalues of the exoPG were 0.08mgml−1and 4.44×10−3mmol reducing group min−1mg protein−1. The N-terminal amino acid sequence of the exoPG from V. pirina was similar to that of the exoPG from Fusarium oxysporum f. sp. melonis, and the N-terminal amino acid sequences of the three endoPGs fromV. nashicola races 1, 2 and 3 were similar to other fungal endoPGs with a conserved motif of ASxxxTFTxAAAxxxG.

Influence of spore dose and interrupted wet periods on the development of pear scab caused by Venturia pirina on pear (Pyrus communis) seedlings

The influence of spore dose and interrupted wet periods on pear scab infection was studied under controlled conditions by assessing disease development on pear seedlings. Under optimal conditions (20°C and continuous wetness), the severity of leaf scab (lesions/cm2) increased with conidial concentrations ranging from 102 to 105 conidia/mL. Pear seedlings inoculated with conidia were also exposed to an initial short wet period (3 and 5 h) and a final 24 h wet period which was interrupted with 1, 6, 8, 12, 24, 48 or 90 h of dryness under low ( 90%) relative humidity. The length of the dry period reduced disease severity. During interrupted wet periods under high relative humidity (>90%) at 18" and 20°C, the number of lesions per cm2 of leaf tissue decreased from 2.7 to 0.24 and 2.7 to 0.15, respectively as the dry period ranged from 1 to 90 h. In the same two experiments with similar wet/dry/wet regimes under low relative humidity (<70%), disease severity was also reduced with no scab lesions occurring if leaves were dry for more than 12 h.

Application Period and Selection of Effective Chemicals for the Japanese Pear Scab Control in Autumn

Application Period and Selection of Effective Chemicals for the Japanese Pear Scab Control in Autumn

Inheritance of Resistance to Pear Scab from European Pears to Asian Pears.

Inheritance of Resistance to Pear Scab from European Pears to Asian Pears.

Control of pear scab with hydrated lime alone or in schedules with other fungicide sprays

Hydrated lime, thiram, flusilazole and various alternating combinations of the three materials were compared in spray schedules from green tip until summer at two sites over 3 years to control pear scab caused by Venturia pirina. Six to ten sprays of 2% hydrated lime significantly ( P = 0.05) reduced the incidence of fruit scab (by up to 41%) or leaf scab (by up to 83%) when applied to trees in four trials. Hydrated lime sprays were less effective than a similar number of thiram or flusilazole sprays. In two trials, schedules of hydrated lime or flusilazole sprays were associated with increased fruit yield (up to 89%) as measured by crop weight. Some hydrated lime schedules were associated with slight phytotoxicity in the form of enlarged lenticels on fruit at harvest. No problems resulted from multiple applications of hydrated lime in commercial airblast sprayers equipped with diaphragm pumps.

Sensitivity of Japanese Pear Scab Fungus, Venturia nashicola, to DMI (Dimethylation Inhibitor) Fungicide in Ibaraki Prefecture

Sensitivity of Japanese Pear Scab Fungus, <i>Venturia nashicola</i>, to DMI (Dimethylation Inhibitor) Fungicide in Ibaraki Prefecture