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1.
ABSTRACT Berries of Vitis vinifera are reported to be susceptible to infection by Uncinula necator until soluble solids levels (brix) reach 8%, and established colonies are reported to sporulate until brix reach 15%. However, our analysis of disease progress on fruit of selected V. vinifera cultivars indicated that severity became asymptotic several weeks earlier in fruit development. When mildew-free fruit clusters of V. vinifera 'Chardonnay', 'Riesling', 'Gewürztraminer', and 'Pinot Noir' were inoculated at stages ranging from prebloom to 6 weeks postbloom, only fruit inoculated within 2 weeks of bloom developed severe powdery mildew. Substantial ontogenic resistance to infection was expressed in fruit nearly 6 weeks before fruit brix reached 8% and over 2 months before they reached 15%. Rachises of 'Chardonnay' and 'Riesling' fruit clusters developed severe powdery mildew when inoculated at bloom, and disease increased steadily over the next 60 days. The rachis of fruit clusters inoculated 31 days after bloom developed only trace levels of powdery mildew. Berry weight of all four cultivars at harvest was reduced when fruit clusters were inoculated at bloom or 16 days postbloom, primarily by splitting, rotting, and dehydration of mildewed berries, but the weight of later-inoculated berries was not reduced. Inoculation of berries just as ontogenic resistance increased markedly, approximately 3 to 4 weeks postbloom, resulted in the development of inconspicuous, diffuse, non-sporulating mildew colonies on berries, sometimes associated with a network of necrotic epidermal cells. Rather than a protracted and relatively static period of berry susceptibility lasting 3 months, fruit of V. vinifera appear to acquire ontogenic resistance rapidly after fruit set. A refocusing of disease management on this critical period of high fruit susceptibility should greatly improve the efficacy of fungicides directed against powdery mildew. 相似文献
2.
The effects of powdery mildew ( Uncinula necator ) on grape yield, juice and wine quality were quantified for cultivar Cabernet Sauvignon (CSa) in 1997 and 1999, and for Sauvignon blanc (Sa) in 1999. Analyses were carried out on batches of healthy berries to which known percentages (0–50%) of diseased berries were added, and on natural clusters that were classified into four visual classes from low (C1 ) to high (C4 ) disease severity. CSa diseased berries showed an average weight reduction of 12% (1997) and 20% (1999). The direct consequence of a higher percentage of smaller, diseased berries was a reduction in yield. The accompanying loss of weight in must from C1 to C4 clusters increased from 10 to 45%. Sugar content in diseased berries was not significantly different from disease-free berries in 1997, but was 20–21% (CSa) and 14% (Sa) higher in 1999. Severely infected batches also showed a higher total acidity than healthy ones. The total anthocyanin content of CSa was decreased by 0·91% (1997) and 0·66% (1999) per percentage mildewed berries added by weight. In Sa wines the concentration of 3-mercaptohexanol, a component of varietal aroma, was decreased by powdery mildew. Multidimensional analyses, based on all the variables studied, successfully grouped batches of CSa according to disease severity. Using directional triangular tests wine experts were able to recognize CSa wines produced from berries with ≈25% of powdery mildew; the threshold for nonexperts was 50%. CSa wines obtained from samples with more than 30% of diseased berries by weight were significantly classified as the worst according to preference order criteria, but below this value the preference was not significant. Sa wines with <50% mildewed berries could not be differentiated significantly by organoleptic tests performed by nonprofessionals. 相似文献
3.
ABSTRACT A fundamental principle of integrated pest management is that actions taken to manage disease should be commensurate with the risk of infection and loss. One of the less-studied factors that determines this risk is ontogenic, or age-related resistance of the host. Ontogenic resistance may operate at the whole plant level or in specific organs or tissues. Until recently, grape berries were thought to remain susceptible to powdery mildew (Uncinula necator) until late in their development. However, the development of ontogenic resistance is actually quite rapid in berries, and fruit become nearly immune to infection within 4 weeks after fruit set. Our objective was to determine how and at what stage the pathogen was halted in the infection process on ontogenically resistant berries. Adhesion of conidia, germination, and appressorium formation were not impeded on older berries. However, once berries were approximately 3 weeks old and older, few germlings were able to form secondary hyphae. Ontogenically resistant berries responded rapidly to infection by synthesis of a germin-like protein that had been previously shown to play a role in host defense against barley powdery mildew. On susceptible berries, cell discoloration around penetration sites indicated the oxidation of phenolic compounds; a process that was followed by localized cell death. However, the pathogen was still able to infect such cells prior to their death, continue secondary growth, and thereby colonize young berries. Formation of papillae was not involved in the differential resistance mechanism of older berries. In susceptible berries, papillae formed frequently at infection sites but did not always contain the pathogen, whereas in resistant berries, the pathogen was always halted prior to the formation of papillae. The host defense, which conditions ontogenic resistance, operates in the earliest stages of the infection process, in the absence of gross anatomical barriers, prior to the formation of a functional haustorium and prior to the development of a conspicuous penetration pore. We also found that diffuse powdery mildew colonies that were not visible in the field predisposed berries to bunch rot by Botrytis cinerea, increased the levels of infestation by spoilage microorganisms, and substantially degraded wine quality. Our improved understanding of the nature, causes, and stability of ontogenic resistance in the grapevine/ powdery mildew system has supported substantial changes in how fungicides are used to control the disease. Present applications are more focused on the period of maximum fruit susceptibility instead of following a calendar-based schedule. This has improved control, reduced losses, and in many cases reduced the number of fungicide applications required to suppress the disease. Particularly where fungicides are deployed in a programmatic fashion and ontogenic resistance is dynamic, there may be equivalent improvements to be made in other hostpathogen systems through studies of how host susceptibility changes through time. 相似文献
4.
ABSTRACT Grape berries become resistant to powdery mildew early in development and are nearly immune to infection within 4 weeks after bloom. In this study, ontogenic resistance did not reduce attachment, germination, or appressorium formation of Uncinula necator on 3- to 4-week-old berries of Vitis vinifera 'Chardonnay' or 3-week-old berries of V. labruscana 'Concord'. Pathogen ingress halted at the cuticle before formation of a penetration pore. As berries aged, hyphal elongation and colony growth slowed until finally no secondary hyphae formed on fully resistant berries. More appressoria formed per unit of hyphal length as berries aged, indicating that failure to penetrate older berries led to increased attempts to penetrate resistant fruit. Additionally, hyphae within the colonies began to die as berries aged. Finally, the number of degree-hours between germination and sporulation of the colony (latent period) increased and sporophore density decreased with berry age at time of inoculation. Thus, ontogenic resistance both slows, and eventually halts disease development on grape berries, and limits the likelihood of spread by reducing absolute supply of conidia and delaying their formation. It furthermore has a consistent, stable, and predictable impact on grape powdery mildew and operates in a similar fashion and to a similar degree in both V. labruscana and V. vinifera, although at a slightly earlier phenological stage in V. labruscana. 相似文献
5.
ABSTRACT Vitis labruscana 'Concord' is a grape cultivar widely grown in the United States for processing into juice and other grape products. Concord grapes are sporadically but sometimes severely damaged by the grape powdery mildew pathogen, Uncinula necator. Although the foliage is often reported to be moderately resistant to powdery mildew, severe fruit infection occurs in some years. We observed the seasonal development of powdery mildew on leaves, rachises, and berries of unsprayed Concord grapevines. Inoculations of flower and fruit clusters revealed a brief period of berry susceptibility and a protracted period of rachis susceptibility. The rachis remained highly susceptible to infection, and the severity of rachis infection increased throughout the growing season until the rachis formed a periderm shortly before harvest. In contrast, berries were nearly immune to infection within 2 weeks after fruit set. Rachis and berry infections were detected before the disease was observed on foliage, and the incidence of rachis and berry infection often exceeded disease incidence observed on foliage until after fruit acquired substantial ontogenic resistance. Excellent control of fruit infection, and adequate control of leaf infection, was achieved by two fungicide applications targeted at the peak period of fruit susceptibility. Although Concord is thought to be moderately resistant to powdery mildew, the rachis is highly susceptible, and may be the avenue by which prebloom infections make their way onto the developing fruit. Late-season infection of the rachis neither spread to the fruit, nor did it cause fruit to drop prematurely, and may be of little economic consequence on fruit destined for processing. Although fruit of V. vinifera cultivars have been reported to remain susceptible to infection until berry sugar levels reach 8 to 15%, Concord fruit become nearly immune to infection nearly 6 weeks before this stage of development. Because powdery mildew does not become conspicuous on foliage until late summer, it is generally regarded as a late-season problem on Concord grapes, and previous management programs have reflected this belief. However, the greatest contribution to control of fruit infection is due to fungicides applied during the peak period of fruit susceptibility, from bloom until shortly after fruit set, long before the disease is observed on foliage. 相似文献
6.
ABSTRACT Grape berries are highly susceptible to powdery mildew 1 week after bloom but acquire ontogenic resistance 2 to 3 weeks later. We recently demonstrated that germinating conidia of the grape powdery mildew pathogen (Uncinula necator) cease development before penetration of the cuticle on older resistant berries. The mechanism that halts U. necator at that particular stage was not known. Several previous studies investigated potential host barriers or cell responses to powdery mildew in berries and leaves, but none included observation of the direct effect of these factors on pathogen development. We found that cuticle thickness increased with berry age, but that ingress by the pathogen halted before formation of a visible penetration pore. Cell wall thickness remained unchanged over the first 4 weeks after bloom, the time during which berries progressed from highly susceptible to nearly immune. Autofluorescent polyphenolic compounds accumulated at a higher frequency beneath appressoria on highly susceptible berries than on highly resistant berries; and oxidation of the above phenolics, indicated by cell discoloration, developed at a significantly higher frequency on susceptible berries. Beneath the first-formed appressoria of all germinated conidia, papillae occurred at a significantly higher frequency on 2- to 5-day-old berries than on 30- to 31-day-old fruit. The relatively few papillae observed on older berries were, in most cases (82.8 to 97.3%), found beneath appressoria of conidia that had failed to produce secondary hyphae. This contrasted with the more abundantly produced papillae on younger berries, where only 35.4 to 41.0% were located beneath appressoria of conidia that had failed to produce secondary hyphae. A pathogenesis-related gene (VvPR-1) was much more highly induced in susceptible berries than in resistant berries after inoculation with U. necator. In contrast, a germin-like protein (VvGLP3) was expressed within 16 h of inoculation in resistant, but not in susceptible berries. Our results suggest that several putative barriers to infection, i.e., cuticle and cell wall thickness, antimicrobial phenolics, and two previously described pathogenesis-related proteins, are not principal causes in halting pathogen ingress on ontogenically resistant berries, but rather that infection is halted by one or more of the following: (i) a preformed physical or biochemical barrier near the cuticle surface, or (ii) the rapid synthesis of an antifungal compound in older berries during the first few hours of the infection process. 相似文献
7.
Ramming DW Gabler F Smilanick J Cadle-Davidson M Barba P Mahanil S Cadle-Davidson L 《Phytopathology》2011,101(4):502-508
In the present study we screened the progeny of Vitis vinifera × V. romanetii populations segregating for resistance to powdery mildew and determined the presence of a single, dominant locus, Ren4, conferring rapid and extreme resistance to the grapevine powdery mildew fungus Erysiphe necator. In each of nine Ren4 pseudo-backcross 2 (pBC(2)) and pBC(3) populations (1,030 progeny), resistance fit a 1:1 segregation ratio and overall segregated as 543 resistant progeny to 487 susceptible. In full-sib progeny, microscopic observations revealed the reduction of penetration success rate (as indicated by the emergence of secondary hyphae) from 86% in susceptible progeny to below 10% in resistant progeny. Similarly, extreme differences were seen macroscopically. Ratings for Ren4 pBC(2) population 03-3004 screened using natural infection in a California vineyard and greenhouse and using artificial inoculation of an aggressive New York isolate were fully consistent among all three pathogen sources and environments. From 2006 to 2010, Ren4 pBC(2) and pBC(3) vines were continuously screened in California and New York (in the center of diversity for E. necator), and no sporulating colonies were observed. For population 03-3004, severity ratings on leaves, shoots, berries, and rachises were highly correlated (R(2) = 0.875 to 0.996) in the vineyard. Together, these data document a powdery mildew resistance mechanism not previously described in the Vitaceae or elsewhere, in which a dominantly inherited resistance prevents hyphal emergence and is non-race-specific and tissue-independent. In addition to its role in breeding for durable resistance, Ren4 may provide mechanistic insights into the early events that enable powdery mildew infection. 相似文献
8.
D. H. Gent G. G. Grove M. E. Nelson S. N. Wolfenbarger J. L. Woods 《Plant pathology》2014,63(3):625-639
Powdery mildew of hop (Podosphaera macularis) may cause economic loss due to reductions in cone yield and quality. Quantitative estimates of crop damage from powdery mildew remain poorly characterized, especially the effect of late season disease management on crop yield and quality. Field studies in Washington State evaluated cone yield, bittering acid content and quality factors when fungicide applications were ceased at different stages of cone development. The incidence of cones with powdery mildew was linearly correlated with yield of cones, bittering acids and accelerated cone maturation. In cultivar Galena, the cumulative effect of every 1% increase in cones powdery mildew incidence was to reduce alpha‐acid yield by 0·33%, which was due to direct effects on cone yield but also indirect effects mediated by dry matter. In the more susceptible cultivar Zeus, alpha‐acid yield was increased 20% by controlling powdery mildew through the transition of bloom to early cone development compared to ceasing fungicide applications at bloom: additional applications provided only modest improvements in alpha‐acid yield. In both cultivars, the impact of powdery mildew on aroma characteristics and bittering acid content were less substantial than cone yield. The damage caused by powdery mildew to cone colour and alpha‐acid yield, as well as the effectiveness of fungicide applications made to manage the disease, appears inseparably linked to dry matter content of cones at harvest. Realising achievable yield potential in these cultivars requires control of the disease through early stages of cone development and harvest before maturity exceeds c. 25% dry matter. 相似文献
9.
Bud colonization and perennation of powdery mildew ( Erysiphe necator ) was studied by inoculating shoots of grapevine ( Vitis vinifera cv. Carignane) at different phenological stages. Disease incidence and severity assessments indicated that buds were most susceptible at the three- to six-unfolded-leaf stage. Incidence of powdery mildew colonies on the surface of buds collected from these shoots 7 weeks postinoculation was highest at these stages (68 and 62%, respectively), which indicates that colonization of the bud interior via the infected bud surface is likely to occur within this period. Histological analyses of buds revealed hyphae with haustoria, conidiophores and conidia on all parts of the bud interior except for the meristems. In particular, trichomes were frequently parasitized by haustoria. In total, 13·2% of all buds analysed, and 32·3% of all buds originating from shoots inoculated at the three-unfolded-leaf stage, were infected by E. necator . In the spring of the following year, buds from inoculated shoots yielded 18 flag shoots (1·6% of all emerging shoots). These primary infections caused an epidemic 28 days after the appearance of the first flag shoot. A linear regression analysis on the frequency of infections of the bud exterior, bud interior and flag shoots revealed that incidence of external bud infection in the first season is strongly correlated with flag shoot incidence in the following season ( R 2 = 0·94). Hence predictions of flag shoot incidence may be reliably based on the incidence of infection on the outer bud scales in the preceding season. 相似文献
10.
Pintye A Bereczky Z Kovács GM Nagy LG Xu X Legler SE Váczy Z Váczy KZ Caffi T Rossi V Kiss L 《Phytopathology》2012,102(7):707-716
Pycnidial fungi belonging to the genus Ampelomyces are common intracellular mycoparasites of powdery mildews worldwide. Some strains have already been developed as commercial biocontrol agents (BCAs) of Erysiphe necator and other powdery mildew species infecting important crops. One of the basic, and still debated, questions concerning the tritrophic relationships between host plants, powdery mildew fungi, and Ampelomyces mycoparasites is whether Ampelomyces strains isolated from certain species of the Erysiphales are narrowly specialized to their original mycohosts or are generalist mycoparasites of many powdery mildew fungi. This is also important for the use of Ampelomyces strains as BCAs. To understand this relationship, the nuclear ribosomal DNA internal transcribed spacer (ITS) and partial actin gene (act1) sequences of 55 Ampelomyces strains from E. necator were analyzed together with those of 47 strains isolated from other powdery mildew species. These phylogenetic analyses distinguished five major clades and strains from E. necator that were present in all but one clade. This work was supplemented with the selection of nine inter-simple sequence repeat (ISSR) markers for strain-specific identification of Ampelomyces mycoparasites to monitor the environmental fate of strains applied as BCAs. The genetic distances among strains calculated based on ISSR patterns have also highlighted the genetic diversity of Ampelomyces mycoparasites naturally occurring in grapevine powdery mildew. Overall, this work showed that Ampelomyces strains isolated from E. necator are genetically diverse and there is no indication of strict mycohost associations in these strains. However, these results cannot rule out a certain degree of quantitative association between at least some of the Ampelomyces lineages identified in this work and their original mycohosts. 相似文献
11.
The influence of increasing nitrogen supply (30, 60, 120 and 240 mg N per pot) on susceptibility was studied on seedlings of six cultivars of spring barley inoculated with virulent isolates of powdery mildew. The colony density (CD) measured as colonies per cm2 was significantly increased with increasing application of nitrogen on all cultivars, and a significant interaction was found between N and cultivar. The different reactions of the cultivars could not be ascribed to lack of N uptake. In general, increasing N application enhanced the sporulation capacity of colonies (CSC) irrespective of increased CD and the cumulative production of spores per cm2 leaf (CSCM) increased strongly with N application in all cultivars. No interaction between N and cultivar was found for the latter component. The increase in CSCM closely corresponded with the increase in N content and fresh weight of uninoculated leaves. No interaction between N treatment and powdery mildew isolates was found for infection efficiency and spore production per colony, when tested on one cultivar. The N-induced changes in infection and sporulation can explain the main part of the increasing effect of N fertilization on powdery mildew development in the field. The results indicate that it may be possible to breed for or select barley cultivars with low N impact on powdery mildew development. 相似文献
12.
A. Rügner J. Rumbolz † B. Huber G. Bleyer U. Gisi H.-H. Kassemeyer R. Guggenheim 《Plant pathology》2002,51(3):322-330
Developing shoots of grapevine ( Vitis vinifera cv. Kerner) were inoculated with conidia of the powdery mildew, Uncinula necator , at well-defined phenological stages of the host to provoke the development of flag shoots in the field and to investigate these shoots as early as possible in the following growing season for the presence of the pathogen. The disease progress was monitored and fungal growth and development on samples from a field trial were analysed by means of low-temperature scanning electron microscopy (LT–SEM). Mycelium was detected on the surface and in the interior parts of buds. The suitability of the field plot to analyse flag shoots was proven by the occurrence of such shoots in the following spring. Furthermore, early stages of cleistothecia development on berries were described for the first time. Establishment of U. necator in dormant buds of grapevine, giving rise to flag shoots in the following spring, is considered to play a significant role in overwintering of the pathogen in the vineyards of southern Germany. 相似文献
13.
14.
P. D. de Jong G. A. Hasper 《European journal of plant pathology / European Foundation for Plant Pathology》1996,102(2):205-207
To establish control thresholds for chemical control of powdery mildew (Erysiphe cruciferarum) on Brussels sprouts, mildew intensity on leaves and buds was observed on the cultivars Lunet, Tardis and Asgard during three years in unsprayed plots. Mildew infection on the leaves was observed from late August onwards, increasing to moderate or high levels. In one year light infestation of the buds was observed, but no reduction in quality occurred. These preliminary results indicate, that from late August onwards the following levels of leaf injury by powdery mildew can be tolerated: T=5+0.42*(Julian date — 235), in which T is the tolerable leaf injury in percentage leaf area covered. When sampling the crop to assess powdery mildew infection, care must be taken that leaves are sampled from all stem positions, as top leaves tend to be much less infected. 相似文献
15.
R.C. PEARSON 《EPPO Bulletin》1982,12(2):101-104
Control of gray mold in New York vineyards is difficult to achieve at the present time. Benomyl-resistant strains of Botrytis cinerea have been isolated from vineyards in all grape-growing regions of New York State. Because of this resistance and lack of governmental registration of new fungicides, growers must choose among only moderately effective fungicides such as captan, folpet, dicloran and copper. Current research indicates that either vinclozolin or iprodione at 850 g/ha to 1100 g/ha applied twice, beginning at about 5 % sugar content and two weeks later, will provide excellent control of gray mold on ripening berries, whereas sprays applied at 5 % or 90 % bloom and at berry touch are not effective. An application of gibberellic acid (GA3) (10 or 25 (µg/ml) on Aurore (S.5279) at 10–15 cm shoot growth reduced the severity of gray mold on clusters of ripe fruit, but not the incidence of it. A single application of triadimefon at 30 mg/1 sprayed on Vignoles (Ravat 51), when fruit clusters averaged 17 % surface area infected with Uncinula necator and 2.6 % sugar content, retarded the development of powdery mildew and subsequent berry splitting, and ultimately reduced the severity of gray mold by 50 % at harvest, 6 weeks later. 相似文献
16.
Falacy JS Grove GG Mahaffee WF Galloway H Glawe DA Larsen RC Vandemark GJ 《Phytopathology》2007,97(10):1290-1297
ABSTRACT A polymerase chain reaction (PCR) assay employing species-specific primers was developed to differentiate Erysiphe necator from other powdery mildews common in the northwest United States. DNA was extracted from mycelia, conidia, and/or chasmothecia that were collected from grape leaves with a Burkard cyclonic surface sampler. To differentiate E. necator from other erysiphaeceous fungi, primer pairs Uncin144 and Uncin511 were developed to select unique sequences of the internal transcribed spacer regions of E. necator. Using these primers in PCR amplifications, a 367-bp amplicon specific to E. necator was generated, but no amplicons were generated from other erysiphaceous species collected from 48 disparate hosts representing 26 vascular plant families. The PCR limit of detection was one to five conidia of E. necator placed directly into reaction mixtures or 100 to 250 conidia placed on glass rods coated with silicon grease. During field studies, this PCR assay facilitated the detection of E. necator inoculum in air samples within hours of sample rod collection and prior to disease onset. Amplification of E. necator DNA did not occur when the PCR assay was conducted on vineyard air samples collected while grapes were dormant or during periods when vine growth occurred but E. necator remained dormant. The initial PCR detection of E. necator of the season occurred during seasonal ascospore releases caused by precipitation events between bud burst and the prebloom period during the 3 years of the study. Detection ceased for 7 to 11 days following ascospore release and then resumed several days prior to the observance of microscopic symptoms and signs of powdery mildew in the field. Results of this study represent the initial step toward the goal of incorporating an inoculum availability component into current and future grapevine powdery mildew risk assessment models. 相似文献
17.
Journal of Plant Diseases and Protection - Ascospores of grape powdery mildew (Erysiphe necator Schw.) play a crucial role in the disease onset in spring in many vine-growing areas. We investigated... 相似文献
18.
Initiation of asexual sporulation in powdery mildews is preceded by a period of superficial vegetative growth of mildew colonies. We found evidence of a quorum-sensing signal in Erysiphe necator that was promulgated at the colony center and stimulated conidiation throughout the colony. Removal of the colony center after putative signal promulgation had no impact upon timing of sporulation by 48-h-old hyphae at the colony margin. However, removal of the colony center before signaling nearly doubled the latent period. A relationship between inoculum density and latent period was also observed, with latent period decreasing as the number of conidia deposited per square millimeter was increased. The effect was most pronounced at the lowest inoculum densities, with little decrease of the latent period as the density of inoculation increased above 10 spores/mm. Furthermore, light was shown to be necessary to initiate conidiation of sporulation-competent colonies. When plants were inoculated and maintained in a day-and-night cycle for 36 h but subjected to darkness after 36 h, colonies kept in darkness failed to sporulate for several days after plants kept in light had sporulated. Once returned to light, the dark-suppression was immediately reversed, and sporulation commenced within 12 h. Merging of colonies of compatible mating types resulted in near-cessation of sporulation, both in the region of merging and in more distant parts of the colonies. Colonies continued to expand but stopped producing new conidiophores once pairing of compatible mating types had occurred, and extant conidiophores stopped producing new conidia. Therefore, in addition to a quorum-sensing signal to initiate conidiation, there appears to be either signal repression or another signal that causes conidiation to cease once pairing has occurred and the pathogen has initiated the ascigerous stage for overwintering. 相似文献
19.
K. J. Evans A. K. Palmer D. A. Metcalf 《European journal of plant pathology / European Foundation for Plant Pathology》2013,135(4):661-673
Aerated compost tea (ACT), prepared from immature compost, was applied to foliage and fruit of grapevines (Vitis vinifera) to assess its potential for suppressing two important diseases: botrytis bunch rot, caused by Botrytis cinerea, and powdery mildew, caused by Erysiphe necator. An ACT applied to leaves of Cabernet Sauvignon vines in pots 7 days before inoculation with E. necator conidia reduced mean powdery mildew severity on the three youngest expanded leaves (at inoculation) to less than 1 %; mean severity on non-treated, inoculated leaves was 15 %. Multiple applications of ACTs at two vineyards in different growing seasons suppressed powdery mildew to <1 % mean severity on Chardonnay leaves (non-treated 79 % severity) and bunches (non-treated 77 % severity), and on Riesling leaves (non-treated 24 % severity). The same treatments reduced the incidence of Chardonnay bunches with latent B. cinerea and Riesling bunches with sporulating B. cinerea, although the level of botrytis bunch rot in both experiments was not economically damaging. The numbers of culturable bacteria, fungi and yeasts on Chardonnay leaves were higher than pre-treatment levels 10 days after ACT application, as were fungal numbers on Riesling leaves 21 days after treatment. Suppression by ACTs of two fruit and foliar pathogens of grapevine with different biology and epidemiology indicated potential for their use as a tactic in integrated disease management. Further testing of ACTs in a range of viticultural environments and application regimes will contribute to a better understanding of the impact of this tactic on disease, grape and wine quality. 相似文献
20.
The biotrophic fungus Erysiphe necator (formerly Uncinula necator ), for which two genetic groups have been described in European vineyards, is the causal agent of grapevine powdery mildew. By analysing the pathogen population with respect to polymorphism in the sequence of the β-tubulin gene, which distinguishes two groups of isolates, a new tool was developed for epidemiological and population studies and tested in the vineyard. As in many ascomycetes, the β-tubulin gene of E. necator ( Entub ) includes six introns and seven exons and encodes a 447-amino-acid protein. A single nucleotide polymorphism (SNP) in the intron-3 region of the Entub gene distinguished two genetic groups (A and B). This method was used to examine differences in the ratio of the two groups from a total of 289 grape powdery mildew samples collected at the beginning of the growing season from either flag shoots or leaves with sparse-spot symptoms in four different vineyards. The SNP in the intron-3 region of the β-tubulin gene, similar to SNPs in the CYP51 gene, was associated with genotypes A and B of E. necator and confirmed the existence of two sympatric populations of the pathogen in the French vineyards. Differences in the relative proportions of each group varied with the presence or absence of flag-shoot symptoms and with the region in which isolates had been collected. 相似文献