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1.
Early blight caused by Alternaria solani is a highly destructive disease of potatoes. Control of early blight mainly relies on the use of preventive fungicide treatments. Because of their high efficacy, azoxystrobin and other quinone outside inhibitors (QoIs) are commonly used to manage early blight. However, loss of sensitivity to QoIs has previously been reported for A. solani in the United States. Two hundred and three A. solani field isolates collected from 81 locations in Germany between 2005 and 2011 were screened for the presence of the F129L mutation in the cytochrome b gene; of these, 74 contained the F129L mutation. Sequence analysis revealed the occurrence of two structurally different cytb genes, which differed in the presence (genotype I) or absence (genotype II) of an intron, with genotype I being the most prevalent (63% of isolates). The F129L mutation was detected only in genotype II isolates, where it occurred in 97%. Sensitivity to azoxystrobin and pyraclostrobin was determined in conidial germination assays. All isolates possessing the F129L mutation had reduced sensitivity to azoxystrobin and, to a lesser extent, to pyraclostrobin. Early blight disease severity on plants treated with azoxystrobin was significantly higher for A. solani isolates with reduced fungicide sensitivity in the conidial germination assay compared with sensitive isolates. Data suggest an accumulation of F129L isolates in the German A. solani population over the years 2009–2011. It is assumed that the application of QoIs has selected for the occurrence of F129L mutations, which may contribute to loss of fungicide efficacy.  相似文献   

2.
Control of the potato late blight pathogen Phytophthora infestans relies heavily on chemicals. The fungicide metalaxyl‐M (Mefenoxam) has played an important role in controlling the disease, but insensitivity to the fungicide in certain isolates is now of major concern. A genetic basis for resistance to metalaxyl suggests the possibility for linking resistance phenotypes to specific population genetic markers, but in order to do this, the population genetic structure and mode of reproduction in a population must first be well described. The dynamics of metalaxyl‐M resistance in the Danish population of P. infestans was characterized over the course of the 2013 growing season, as was the population genetic structure, using simple sequence repeat (SSR) genotypes and single nucleotide polymorphism (SNP)‐based mitochondrial haplotyping of over 80 isolates. Both mating types A1 and A2 were present in most fields, but tests for recombination showed that clonal reproduction dominates in Danish populations. Genotype was not linked to haplotype and no differentiation was observed at the haplotype level, but rather between fields. Resistance phenotypes were linked to specific SSR alleles, demonstrating the potential for a more precise SNP‐based marker system for predicting resistance to metalaxyl‐M.  相似文献   

3.
The pitch canker pathogen Fusarium circinatum was first found to cause damage in nurseries and pine plantations in northern Spain in 2004. Since then, establishment of pine plantations in the region has decreased as a result of the prohibitions placed on planting Pinus spp. and Pseudotsuga menziesii in areas affected by the disease. However, although most pine species have been found to be susceptible to the pathogen under nursery conditions, little is known about how the fungus affects the trees in the field. Furthermore, it is not known whether some of the native or exotic species commonly planted in the area are also susceptible to F. circinatum. The aim of this study was to evaluate the susceptibility of several conifer species commonly planted in northern Spain to the pitch canker pathogen. For this purpose, two different trials were carried out, one under controlled laboratory conditions and the other in the field. Although most of the conifers were affected by the pathogen in the laboratory tests, only Pinus radiata, Pinus nigra, Pinus pinaster and Pinus uncinata were susceptible to the pathogen in the field.  相似文献   

4.
Although fungicide resistance in crop pathogens is a global threat to food production, surprisingly little is known about the evolutionary processes associated with the emergence and spread of fungicide resistance. Early stages in the evolution of fungicide resistance were evaluated using the wheat pathogen Zymoseptoria tritici, taking advantage of an isolate collection spanning 20 years in Oregon, USA, and including two sites with differing intensity of fungicide use. Sequences of the mitochondrial cytb protein conferring single‐mutation resistance to QoI fungicides and the nuclear CYP51 gene implicated in multiple‐mutation resistance to azole fungicides were analysed. Mutations associated with resistance to both fungicides were absent in the 1992 isolates, but frequent in the 2012 collection, with higher frequencies of resistance alleles found at the field site with more intensive fungicide use. Results suggest that the QoI resistance evolved independently in several lineages, and resulted in significant mitochondrial genome bottlenecks. In contrast, the CYP51 gene showed signatures of diversifying selection and intragenic recombination among three phylogenetic clades. The findings support a recent emergence of resistance to the two fungicide classes in Oregon, facilitated by selection for mutations in the associated resistance genes.  相似文献   

5.
Propamocarb (Previcur-N; propyl-[3-dimethylamino-propyl] carbamate-monohydrochloride) was testedin vivo against 32 field isolates ofPhytophthora infestans from six countries. Fungicide dosages required to achieve 90% control of the blight ranged between 676 and 1530 ppm a.i. in potted potato (cv. ‘Alpha’) plants and between 1135 and 2648 ppm in potato tuber slices. Isolates from Israel were less sensitive to the fungicide than isolates from Europe or North America. Toxicity of propamocarb was not related to resistance or sensitivity to phenylamide fungicides (e.g. metalaxyl). Nevertheless, most metalaxyl-resistant isolates from Israel were less sensitive to propamocarb than most metalaxyl-sensitive isolates from this country. Monocyclic epidemics conducted with the 20 Israeli isolates in the field showed that 1081–2012 ppm of the fungicide was required to achieve 90% control of the disease. Laboratory experiments revealed that the fungicide was poorly active against sporangial germination and had a limited curative efficacy. It exhibited a translaminar translocation in leaves but a poor acropetal or basipetal systemicity from foliage. Propamocarb + mancozeb mixtures (1:1, v/w) were synergistically effective in controlling the blight. Growers in Israel use tank mixtures of propamocarb (Dynone) and mancozeb to combat late blight in potato fields where phenylamide-resistant isolates ofP. infestans are prevalent.  相似文献   

6.
Field experiments, involving various fungicide strategies with pyraclostrobin and/or epoxiconazole were carried out in 2004 and 2005, with the overall purpose of monitoring the evolution of fungicide sensitivity in Mycosphaerella graminicola on different isolates per leaf, leaf levels at different points of time, and points in the field. Sensitivity was assessed on single isolates by means of epoxiconazole EC50-values, and monitoring of the G143A-mutation, which confers strobilurin resistance. In both years, fungicide application strategies did not cause any significant shifts in epoxiconazole sensitivity of the population median or variance over time compared to the starting population. In 2004, the end-population median was the same for all sprayed strategies, although compared to untreated median sensitivities were higher. In 2005, epoxiconazole sensitivity levels were similar on individual flag leaves and different points in the field. Measured on all isolates the EC50-values ranged from 0.007–1.15 mg l−1. In 2004, due to the high initial level of pyraclostrobin resistance, stabilisation of pyraclostrobin resistance was observed following the various combination treatments. No correlation between epoxiconazole sensitivities and pyraclostrobin resistance were observed. High input strategies using a mixture of epoxiconazole and pyraclostrobin resulted in the best control and yield response. A subpopulation of the isolates from 2004 was also screened for sensitivity towards five different triazoles of which tebuconazole proved to be least sensitive, and this could further be split into two subpopulations.  相似文献   

7.
Bacterial wilt, caused by Ralstonia solanacearum, is emerging as a major threat to potato production in Ethiopia, reaching epidemic proportions in the Chencha district recently, with a prevalence of 97% of potato fields in 2015. The recent disease outbreak in the district coincided with a significant introduction of seed potatoes. This research was therefore initiated to genetically characterize the pathogen so as to trace its source, identify its relationship with outbreaks in the rest of the country, and make intervention recommendations. Ralstonia solanacearum isolates were sampled both from seed and ware potato fields in Chencha and from seed potato fields in production regions suspected of being potential sources of the pathogen. Multiplex PCR and phylogenetic analysis of partial endoglucanase gene sequences identified all of the isolates as phylotype IIB sequevar 1. VNTR sequence analysis distinguished 11 different haplotypes, nine of which were unique to the Chencha district. However, one of the haplotypes was common to all seed potato producer regions of Ethiopia except for the Shashemene area. The unique and diverse VNTR haplotypes of the pathogen in Chencha indicates that it is well established in the district. When a geographical map of the VNTR haplotypes was superimposed with the main cross‐regional seed potato distribution pattern of the country, it became evident that the pathogen was being disseminated via latently infected seed from the Holeta‐Jeldu area in the Central Highlands of Ethiopia. Identification of largely uninfected highland districts and multiplication of high‐grade seed potato exclusively in those districts should be given priority.  相似文献   

8.
Since 2007, serious damage to tomato from leaf mould caused by Passalora fulva has frequently been observed in commercial greenhouses in Gifu Prefecture, Japan. One of the factors relating to this damage was suspected to be a decrease in azoxystrobin sensitivity of the pathogen. Biological and molecular studies were conducted to characterize fungicide resistance. In in vitro sensitivity tests using mycelial homogenate placed on fungicide‐amended medium, the minimum inhibitory concentrations (MIC) of azoxystrobin for mycelial growth of the isolates divided into two ranges, 0.031–0.5 mg L?1 and 8–32 mg L?1. Isolates with MICs within the two ranges were considered as sensitive and resistant, respectively, to azoxystrobin because, in in vivo tests, the percentage protection conferred by this fungicide (100 mg a.i. L?1) against these isolates was 89.7–100% and 4.5–31.1%, respectively. Resistant isolates had a replacement of phenylalanine with leucine at codon 129 (F129L) in cytochrome b. Forty‐five percent of the 271 isolates collected from 63 tomato greenhouses from 2007 to 2008 were resistant to azoxystrobin. In many greenhouses where the isolation frequency of resistant isolates was 80% or more, azoxystrobin had been used twice per crop for approximately 6 years. In 2012, 27% of the 405 isolates collected were resistant to azoxystrobin, and there was a marked difference in the frequency of occurrence of resistant isolates in the field populations between the three locations sampled. The occurrence of azoxystrobin‐resistant P. fulva isolates (F129L mutants) inflicted considerable damage on greenhouse tomatoes.  相似文献   

9.
The evolution of fungicide resistance in the cereal pathogen Zymoseptoria tritici is a serious threat to the sustainability and profitability of wheat production in Europe. Application of azole fungicides has been shown to affect fitness of Z. tritici variants differentially, so it has been hypothesized that combinations of azoles could slow the evolution of resistance. This work assessed the effects of dose, mixtures and alternations of two azoles on selection for isolates with reduced sensitivity and on disease control. Naturally infected field trials were carried out at six sites across Ireland and the sensitivity of Z. tritici isolates monitored pre‐ and post‐treatment. Epoxiconazole and metconazole were applied as solo products, in alternation with each other, and as a pre‐formulated mixture. Full and half label doses were tested. Isolates were partially cross‐resistant to the two azoles, with a common azole resistance principal component accounting for 75% of the variation between isolates. Selection for isolates with reduced azole sensitivity was correlated with disease control. Decreased doses were related to decreases in sensitivity but the effect was barely significant (P = 0·1) and control was reduced. Single applications of an active ingredient (a.i.) caused smaller decreases in sensitivity than double applications. Shifts in sensitivity to the a.i. applied to a plot were greater than to the a.i. not applied, and the decrease in sensitivity was greater to the a.i. applied at the second timing. These results confirm the need to mix a.i.s with different modes of action.  相似文献   

10.
Field trials were carried out over a 4 year period (2004–2007) to determine the effect of agronomic factors, specifically cultivar resistance, irrigation, crop duration and chemical control (in‐furrow application of azoxystrobin), on black dot development on potato tubers grown in fields where soilborne inoculum of Colletotrichum coccodes was present. In 2004, 2005 and 2006, two field trials were performed each year and in 2007, 19 mini‐field trials were carried out across Scotland and England. Cultivar resistance was clearly demonstrated to be an effective method of reducing black dot disease severity on tubers (described here as the percentage of unmarketable tubers, i.e. those with symptoms covering a surface area of >10%). In the four field trials carried out in 2004 and 2005, in irrigated and fungicide‐untreated plots, 43·8% of tubers of cv. Maris Piper were unmarketable, compared with 17·0% of tubers of cv. Sante. Assessments of disease development on underground plant parts (stems, stolons and roots) revealed that cultivar resistance acted only at the tuber level, as disease symptoms on other parts were often high irrespective of published disease resistance ratings. Irrigation increased the severity of disease on tubers in two trials (England 2004 and 2006), but its effect was less significant when rainfall was high. Delaying harvest by 2 weeks increased disease severity in all six trials, whilst application of azoxystrobin consistently reduced black dot severity. There were significant interactions between factors. The results clearly show how black dot disease severity can be reduced through an integrated approach to disease management.  相似文献   

11.
Wheat blast caused by Magnaporthe oryzae Triticum causes significant losses on wheat during outbreak years in several South American countries. Despite reports of wheat blast leaf lesions on some wheat cultivars, the importance of inoculum originating from leaves in severely affected commercial fields is disputed. It is generally considered that leaf lesions and/or sporulation on leaves do not usually appear before the occurrence of spike blast in wheat. The purpose of this study was to (i) determine the occurrence of wheat blast on basal leaves, (ii) estimate the number of conidia produced on these leaves, and (iii) determine the impact of current fungicide application practices on inoculum produced from sporulating lesions on basal wheat leaves. Inoculations at the three‐leaf stage showed that certain cultivar and isolate combinations caused more disease on old wheat leaves than young expanding leaves. Under optimum conditions, M. oryzae had the potential to produce tens to hundreds of thousands of conidia on small amounts of wheat basal leaves. A mean of 1 669 000 conidia were produced on 1 g dry basal leaves of a highly susceptible cultivar under optimum conditions for sporulation. Conidia production on leaves coincided with spike emergence under both greenhouse and field conditions. When field studies were conducted under natural epidemic conditions, foliar fungicide applications reduced the amount of M. oryzae conidia on basal leaves by 62–77% compared to non‐sprayed controls. An earlier application of foliar fungicides might reduce inoculum if conidia from basal leaves contribute to wheat spike blast development.  相似文献   

12.
Pineapple heart rot disease, caused by Phytophthora nicotianae (syn. P. parasitica), is responsible for significant annual reductions in crop yield due to plant mortality. In Ecuador, new infections arise during the rainy season and increase production costs due to the need for biocontrol and fungicide applications. Studies of P. nicotianae population structure suggest that certain genetic groups are associated with host genera; however, it is not clear how many host‐specific lineages of the pathogen exist or how they are related. The objectives of this study were to determine the level of genetic variation in the P. nicotianae population causing heart rot disease of pineapple in Ecuador and compare the genotypes found on pineapple to those previously reported from citrus, tobacco and ornamentals. Thirty P. nicotianae isolates collected from infected pineapple leaves from four farms were genotyped using nine simple sequence repeat loci. In addition, the DNA sequences of mitochondrial loci cox2 + spacer and trnG‐rns were analysed. Together, these loci supported a single clonal lineage with two multilocus genotypes differing in a single allele and low mitochondrial diversity. This lineage was distinct but closely related to isolates collected from vegetables and ornamentals in Italy. The results support the hypothesis of host specialization of P. nicotianae in intensive cropping systems and contribute to the understanding of population structure of this important pathogen.  相似文献   

13.
A 2‐year comprehensive field survey was conducted across major tomato‐growing areas of Iran. Two hundred and thirty‐four tomato fields and six tomato‐producing greenhouses were surveyed for the potential presence of bacterial spot disease. Five hundred and ninety‐six tomato samples with and without symptoms were analysed. While Xanthomonas spp. were found in association with tomato plants both with and without symptoms from five surveyed counties, the bacterial spot disease was observed only in plants from three of them. Only strains isolated from plants with symptoms induced disease symptoms on tomato, while those isolated from symptomless plants caused symptoms only on cabbage and common bean. None of the isolates caused disease symptoms on pepper and eggplant. Phylogenetic analysis showed that X. perforans is the causal agent of tomato bacterial spot in Iran, although X. campestris and X. axonopodis were also associated with symptomless tomato plants. All X. perforans isolates in this study were sensitive to streptomycin, copper sulphate and copper oxychloride at concentrations of 50 mg L?1, 200 mg L?1 and 0.8 g L?1, respectively. Unlike the type strain of X. perforans, isolates in this study did not produce bacteriocin against other Xanthomonas spp., nor were they detected using the usual species‐specific primer pair Bs‐XpF/Bs‐XpR. This suggests an atypical nature of X. perforans strains in Iran, which leads to the hypothesis that X. perforans strains in Iran may have a separate origin to those causing disease epidemics elsewhere. The aggregated dispersal pattern of the diseased tomato fields signifies the seedborne introduction of the pathogen into the country.  相似文献   

14.
Greeneria uvicola causes bitter rot on Vitis vinifera (bunch grapes) and Muscadinia rotundifolia (muscadine grapes) in warm moist temperate and subtropical regions. This study investigated the phylogenetic relationship of G. uvicola representatives from Australia (67 isolates), the USA (31 isolates), India (1 isolate) and Costa Rica (1 isolate) and compared their pathogenicity and fungicide sensitivity. Differences in cultural and conidial morphology were observed between the isolates from Australia and the USA. Phylogenetic relationships were determined based on three gene regions: the ribosomal DNA (rDNA) internal transcribed spacer 1 (ITS1–5?8S–ITS2), 28S large subunit (LSU) nuclear rDNA and β‐tubulin‐2. Greeneria uvicola isolates were clearly differentiated into four groups: isolates from Australia and India; USA isolates from V. vinifera; USA isolates from M. rotundifolia; and the isolate from Costa Rica. All isolates were pathogenic on V. vinifera (cv. Chardonnay) berries although those originating from M. rotundifolia were not as aggressive as isolates from V. vinifera, irrespective of geographical origin. Sensitivity to pyraclostrobin and salicylhydroxamic acid (SHAM) was studied. Despite differences in fungicide applications, hyphal growth inhibition was not significantly different for geographical location, cultivar, tissue, year of collection or different spray regimes. For the Australian and USA isolates, fungal growth inhibition was significantly greater for pyraclostrobin than for SHAM, and was significantly greater for the combined treatment than for each of the fungicides applied singly. The aetiological and epidemiological knowledge of bitter rot collected through this study will aid better prediction and management strategies of this pathogen.  相似文献   

15.
Sclerotinia stem rot (SSR) of oilseed rape (OSR, Brassica napus), caused by Sclerotinia sclerotiorum, is a serious problem in the UK and worldwide. As fungicide‐based control approaches are not always reliable, identifying host resistance is a desirable and sustainable approach to disease management. This research initially examined the aggressiveness of 18 Sclerotinia isolates (17 S. sclerotiorum, one S. subarctica) on cultivated representatives of B. rapa, B. oleracea and B. napus using a young plant test. Significant differences were observed between isolates and susceptibility of the brassica crop types, with B. rapa being the most susceptible. Sclerotinia sclerotiorum isolates from crop hosts were more aggressive than those from wild buttercup (Ranunculus acris). Sclerotinia sclerotiorum isolates P7 (pea) and DG4 (buttercup), identified as ‘aggressive’ and ‘weakly aggressive’, respectively, were used to screen 96 B. napus lines for SSR resistance in a young plant test. A subset of 20 lines was further evaluated using the same test and also in a stem inoculation test on flowering plants. A high level of SSR resistance was observed for five lines and, although there was some variability between tests, one winter OSR (line 3, Czech Republic) and one rape kale (line 83, UK) demonstrated consistent resistance. Additionally, one swede (line 69, Norway) showed an outstanding level of resistance in the stem test. Resistant lines also had fewer sclerotia forming in stems. New pre‐breeding material for the production of SSR resistant OSR cultivars relevant to conditions in the UK and Europe has therefore been identified.  相似文献   

16.
Ascochyta blight of pea is caused by four related fungi, Ascochyta pisi, Phoma koolunga, Ascochyta pinodes and Ascochyta pinodella. The latter two taxa appear to be much more common and economically significant worldwide but the relative impact of each fungus on ascochyta blight epidemics is not well understood. To study the spatiotemporal distribution of A. pinodes and A. pinodella infecting pea in France, 368 isolates were sampled monthly, from February to May, at three locations (Rennes, Boigneville and Dijon) and molecular markers were used to genotype isolates. The aggressiveness of isolates from the fourth sampling date was estimated using a detached leaf assay on the winter cultivar Enduro. Disease was low during the sampling period as climatic conditions were generally not conducive to disease development (cold temperature, low rainfall). Population genetic analysis showed that 99% of the observed variation could be attributed to variation within populations compared to only 1% among populations. Both species were observed in each location, although A. pinodella was observed at a lower frequency (6–32%). Moreover, results showed that both species could develop on different nodes of the plant. Significant differences in aggressiveness were observed between species and among isolates within species with A. pinodes isolates being significantly more aggressive on average than A.  pinodella isolates. These results emphasize the necessity to study the components of disease complexes in order to understand the impact of pathogen species interactions on disease and yield reduction as well as the dynamics of disease epidemics during the cropping season.  相似文献   

17.
Y. Tian  J. Sun  H. Li  G. Wang  Y. Ma  D. Liu  J. Quan  W. Shan 《Plant pathology》2015,64(1):200-206
Late blight caused by Phytophthora infestans is the most serious disease of potato worldwide. To understand the P. infestans population structure in northern Shaanxi, an emerging potato production region in China, 125 single‐lesion isolates were randomly collected from farmers' fields in 2009 and characterized phenotypically and genotypically. A mating type assay showed that 94 isolates were A1 mating type. Virulence determination of selected isolates on a set of differential potato lines containing R1 to R11, respectively, showed the presence of two pathotypes, of which the pathotype lacking avirulence genes Avr3, Avr4 and Avr10 was dominant. Isolates lacking all avirulence factors Avr1 to Avr11 were detected but at lower frequency (13·6%). Analysis for mtDNA haplotype showed all 61 examined isolates were IIa. A total of seven multilocus genotypes were distinguished among 125 isolates, as determined with seven polymorphic microsatellite markers. The genotype SG‐1 was dominant in the population with a frequency of 75·2% and was present throughout the region. Analysis of the phenotypic and genotypic structures of P. infestans populations indicated strict clonal reproduction of the pathogen and suggested that sexual reproduction probably does not occur. Potential implications for disease management are discussed.  相似文献   

18.
Exserohilum turcicum is the causal agent of northern leaf blight, a devastating foliar disease of maize and sorghum. Specificity of E. turcicum to either maize or sorghum has been observed previously, but molecular evidence supporting host specialization is lacking. The aim of this study was to compare the genetic structure of E. turcicum isolates collected from adjacent maize and sorghum fields in Delmas and Greytown in South Africa. In addition, the mode of reproduction of this pathogen was investigated. Isolates from maize (N = 62) and sorghum (N = 64) were screened with 12 microsatellite markers as well as a multiplex mating type PCR assay. No shared haplotypes were observed between isolates from different hosts, although shared haplotypes were detected between isolates from maize from Delmas and Greytown. Population structure and principal coordinate analyses revealed genetic differentiation between E. turcicum isolates from maize and sorghum. Analysis of molecular variance indicated higher among‐population variation when comparing populations from different hosts, than comparing populations from different locations. Lack of shared haplotypes, high proportion of private alleles, greater among‐population variance between hosts than locations and significant pairwise population differentiation indicates genetic separation between isolates from maize and sorghum. The high haplotypic diversity in combination with unequal mating type ratios and significant linkage equilibrium indicates that both sexual and asexual reproduction contributes to the population genetic structure of E. turcicum in South Africa.  相似文献   

19.
Cowger C  Mundt CC 《Phytopathology》2002,92(6):624-630
ABSTRACT The selective effect of quantitative host resistance on pathogen aggressiveness is poorly understood. Because two previous experiments with a small number of bread wheat cultivars and isolates of Mycosphaerella graminicola had indicated that more susceptible hosts selected for more aggressive isolates, we conducted a larger experiment to test that hypothesis. In each of 2 years, six cultivars differing in their levels of partial resistance were planted in field plots, and isolates were collected from each cultivar early and late in the growing season. The isolates were inoculated as populations bulked by cultivar of origin, field replicate, and collection date on seedlings of the same six cultivars in the greenhouse. The selective impact of a cultivar on aggressiveness was measured as the difference in aggressiveness between early and late isolates from that cultivar. Regression of those differences on disease severity in the field yielded significance values of 0.0531 and 0.0037 for the 2 years, with moderately resistant cultivars selecting for more aggressive isolates. In a related experiment, the protectant fungicide chlorothalonil was applied to plots of two susceptible cultivars to retard epidemic development. When tested in the greenhouse, isolates of M. graminicola from those plots were significantly more aggressive than isolates from the same cultivars unprotected by fungicide.  相似文献   

20.
Plug seedlings, widely used in cabbage cultivation in Japan, are often infected by seed-borne pathogens, especially the serious pathogen Alternaria brassicicola. Because information on seed infestation is scant in Japan, we investigated fungal infestation in commercial batches of cabbage seeds produced between 1984 and 2001. A total of 123 lots were divided into six groups by production period (1984–1989, 1994–1998, and 2001) and by use or nonuse of fungicide. One hundred seeds from each lot were incubated separately on agar at 25°C to isolate the predominant fungus. Alternaria brassicicola was isolated most frequently, 0%–94% of the seeds depending on seed lot or 6%–21% of the seeds grouped by production period and fungicide treatment. Thus, the pathogen was isolated even from seeds refrigerated for 17 years. Alternaria brassicicola accounted for 57%–95% of all isolated fungi by the group and was higher on older or fungicide-treated seeds. Seeds that were not treated with fungicide in lots grouped by production districts in western Japan were infested with A. brassicicola at a rate of over 12%, higher than that in the eastern region (<4%). Infestation was higher in the warmer areas of Japan. Eighty-five isolates, other than A. brassicicola, produced spots on cabbage cotyledons, although they were not isolated as frequently: less than 5% of seeds by group separated by production period and fungicide treatment. Most of these isolates were Alternaria alternata. This is the first report on the frequency of fungal infestation of commercial cabbage seeds in Japan.  相似文献   

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