隐地疫霉的鉴定和处理

疫情调查时发现辖区花卉生产基地的非洲菊大量萎蔫死亡，经分离培养，致病性测定，病原鉴定为隐地疫霉，是我国分布未广的潜在的检疫性有害生物。试验表明瑞毒霉－锰锌具有良好的控制效果。     

Oospores in cultures of Phytophthora infestans resulting from selfing induced by the presence of P. drechsleri isolated from blighted potato foliage

A Phytophthora species isolated from blighted potato foliage was identified as P. drechsleri , mating type A2. The isolate was found to be weakly pathogenic on a range of hosts. Pairings in vitro of P. drechsleri with British isolates of P. infestans mating type A1 when separated by a polycarbonate membrane resulted in selfed oospores of both species. The possibility that A1 P. infestans is induced to self in the field and the genetic consequences of such selfing are discussed.     

不同地区辣椒疫霉菌遗传多样性的RAPD分析

 通过利用12个十碱基随机引物对来自我国7个不同地理区域的56个辣椒疫霉菌株进行RAPD分析,探索了我国主要辣椒种植区间的辣椒疫霉菌的遗传分化关系。结果表明:1)受试56个菌株共产生70条谱带,其中多态性为56条,占80%,说明我国主要辣椒种植区的辣椒疫霉菌具有较丰富的遗传多样性;2)根据引物扩增的DNA指纹图谱,运用UPGMA分析法,以遗传相似系数0.6为阈值,将供试56个菌株划分为8个基因型(I、II、III、IV、V、VI、VII、VIII),发现除少数来自相近地理海拔的绝大多数菌株被划分为同一个基因型外,其它不同地理区域的菌株基因型的划分与地理来源无直接的关系。在此基础上,结合我国不同地理区域辣椒疫霉病发生情况,提出我国辣椒疫霉菌基因型的划分除少数与地理区域有关外,其它绝大多数地区的辣椒疫霉菌基因型的划分与地理来源无直接的相关性。     

Phytophthora infestans Populations from Tomato and Potato in North Carolina Differ in Genetic Diversity and Structure

ABSTRACT Phytophthora infestans causes a destructive disease on tomato and potato. In North Carolina (NC) potatoes are mostly grown in the east, whereas tomatoes are grown in the mountainous areas in the western part of the state. Five genotypes of P. infestans were identified from 93 and 157 isolates collected from tomato and potato over a 5 year period between 1993 and 1998. All isolates collected from potato in eastern NC were the US-8 genotype, whereas only a single isolate was the US-1 genotype. Tuber blight was found on immature daughter tubers in a single field in 1997, however infection on mature tubers was not observed. Within potato fields, a range of sensitivity to metalaxyl was observed among isolates but all were either intermediate or highly resistant to the fungicide. In contrast, isolates from tomatoes included previously reported US-7 and US-8 genotypes and two new genotypes called US-18 and US-19 (A2 mating type, allozyme genotype Gpi 100/100 and Pep 92/100). These genotypes had unique restriction fragment length polymorphism banding patterns, were sensitive to metalaxyl, and have not been reported elsewhere. All genotypes, with the exception of the US-1, were the Ia mitochondrial haplotype. Thus, isolates of P. infestans from tomato were more genetically diverse over time in NC than those from potato and include two new genotypes that are sensitive to metalaxyl.     

Population dynamics of metalaxyl-sensitive and metalaxyl-resistant isolates of Phytophthora infestans in untreated crops of potato

Each of six pairs of metalaxyl-sensitive (MS) and metalaxyl-resistant (MR) field isolates of Phytophthora infestans was inoculated as a mixture of 90% MS sporangia with 10% MR sporangia onto fungicide-free potato plants (cv. Alpha) in six walk-in plastic tunnels in each of 2 years. In both experiments, late blight killed the crops in 26-31 days. In all tunnels, the frequency of MR sporangia increased during the logarithmic phase of the epidemic to 70-85% of the population. Later, however, the frequency of M R sporangia decreased to 7-38% in six tunnels but continued to increase to 94-100% in the other six. The increased frequency of MR during the logarithmic phase was attributed to the shorter latent period and larger lesion size of MR compared to MS isolates and to the unlimited availability of uninfected host tissue. The later decrease in the frequency of MR in six tunnels was attributed to the lower sporulation capacity and the shorter infectious period of MR compared to MS isolates, and to the limitation of uninfected host tissue. The data showed that the population dynamics of P. infestans was dependent not only on fitness components of isolates, but also on the availability of uninfected host tissue.     

Isoenzyme polymorphism and segregation in isolates of Phytophthora infestans from Japan

Isoenzyme variation of 198 isolates of Phytophthora infestans collected from many locations in Japan during 1987–90, and of four pre-1987 isolates, was examined using starch gel electrophoresis. A previously unreported allele at malic isoenzyme locus/ME (90) was observed. An association between mating types and isoenzyme genotypes at three isoenzyme loci, glucosephosphate isomerase (GPI-1), peptidase (PEP-1) and ME, was found. At PEP-1, the A2 isolates from Japan had a previously unreported genotype (96/96). Normal segregation at the malic isoenzyme locus occurred in a cross of Japanese and Mexican parents. The results provide evidence of a change in the population genetic structure of P. infestans in Japan.     

Characteristics and pathogenicity of six Phytophthora isolates from pot plants

From several greenhouse plants showing foot and root rot symptomsPhytophthora isolates were gathered. Isolates fromPeperomia, Saintpaulia andSinningia were identified asP. nicotianae van Breda de Haan var.nicotianae and an isolate fromBegonia asP. cryptogea Pethybr. & Laff. Cardinal temperatures for the various isolates were determined. The specific and non-specific pathogenicity of the isolates was studied by inoculating the different crops with the different isolates, including aP. cryptogea isolate fromGerbera and aP. nicotianae var.nicotianae isolate from carnation. TheP. nicotianae var.nicotianae isolates appeared to be morphologically identical. Some of the isolates were similar in host range, but others exhibited differences in host specificity at 20°C as well as 25, 30 or 35°C. The same applies for the twoP. cryptogea isolates.     

Phylogenetic network analysis of South and North American Corynespora cassiicola isolates from tomato,cucumber, and novel hosts

European Journal of Plant Pathology - Corynespora cassiicola isolates display morphological, pathogenic, and ecological diversity, inducing target spot-like diseases in more than 500 hosts...     

Inter- and intraspecific morphometric variation and characterization of Phytophthora isolates from cocoa

Difficulties in the accurate identification of the Phytophthora species responsible for black pod disease of cocoa continue to hamper effective disease control. A re-evaluation of morphological characters ( Brasier & Griffin, 1979 ) and a detailed morphometric analysis of 161 Phytophthora isolates largely associated with black pod disease of cocoa from 17 countries worldwide have shown considerable inter- and intraspecific variation. Stable and more reliable parameters for the identification of the species responsible for the disease have been determined. Colony characteristics such as pattern and growth rate on V8 agar are reasonably characteristic for the cocoa Phytophthora species, and can be used to make preliminary identification to species level. Significant sporangial character variation was found within isolates of species from the same and different sources, highlighting the difficulties in making accurate identification on the basis of raw morphological data. Pedicel length was found to be the most consistent species-linked sporangial characteristic. Cluster plots of length/breadth ratios of sporangia versus reciprocals of sporangial pedicel length clearly separated all isolates into distinct species groups ( P. capsici , P. citrophthora , P. palmivora and P. megakarya ) and can be used reliably to identify accurately those pathogens involved in black pod disease outbreaks.     

French isolates of Phytophthora infestans from potato and tomato differ in phenotype and genotype

Prior to 1996, the A2 mating type of Phytophthora infestans was not detected on potato in France, but was found at one site on tomato in 1995. This finding lead to the question of the extent of differences and relationships existing between the populations of P. infestans present on each host. A collection of 76 isolates collected in France, mainly in 1996, from potato and tomato was characterised for mating type, allozyme genotype at the Gpi and Pep loci, and mitochondrial DNA haplotype; 74 of these isolates were also characterised for multilocus RFLP fingerprint, and 62 for virulence. All isolates except four showed allozyme genotypes (Gpi 90/100 or 100/100, Pep 83/100 or 100/100) and mtDNA haplotypes (Ia or IIa) characteristic of the populations introduced into Europe in the late 1970s. The four exceptions were isolates collected from tomato in Southern France in 1988-1991, which showed some characteristics of the former European populations (Gpi 86/100, Pep 92/100, mtDNA Ib). Both mating types were present among the collections from both hosts, but isolates with the A2 mating type were found on potato only in one garden crop, adjacent to tomato. Nine different RG57 fingerprints were observed, with a greater diversity among tomato isolates. Furthermore, tomato and potato collections differed markedly in the frequencies of genotypes present. Finally, tomato isolates generally had a lower virulence complexity than potato isolates. These data suggest that P. infestans populations on tomato and potato are largely separated, despite the occurrence of limited gene flow.     

Phylogenetic relationships and pathogenicity of Colletotrichum acutatum isolates from grape in subtropical Australia

The identity of Colletotrichum acutatum as the causal pathogen of grape ripe-rot, which causes yield loss and a bitter taint that lowers wine quality in Australian subtropical wine-grape regions, was confirmed using species-specific primers. Cultural, morphological and molecular methods (RAPD-PCR and sequencing of parts of the 5·8S-ITS regions and the β-tubulin-2 gene) were used to determine the phylogenetic relationships of Australian C. acutatum isolates from wine grapes and other horticultural crops. A combination of RAPD-PCR and β-tubulin-2 gene data showed that all wine-grape ripe-rot isolates from northern regions of New South Wales (NSW) and Queensland belong to a proposed new C. acutatum group (A9), together with isolates from Australian strawberry, mango, blueberry and olive. The 5·8S-ITS sequences for these grape pathogens were identical to published sequences for an isolate from Cyclamen (the Netherlands) and differed by 1 bp from isolates from Capsicum (Taiwan) and orange (Costa Rica). The grape ripe-rot isolates from the Shoalhaven Valley (southern NSW) were clustered within two other C. acutatum groups: A2 and A5. In vitro infection studies showed that Australian C. acutatum isolates from almond, blueberry, chilli, grape, mango, olive, strawberry and tomato were able to infect grape and could also infect blueberry and strawberry, indicating a lack of host specificity. This lack of host specificity, the genetic similarity with non-grape isolates, and the fact that many of the non-grape hosts were isolated from wine-growing regions, suggest the potential for cross-infection between grape and other horticultural crops.     

Phylogenetic analysis of partial sequences from Fig mosaic virus isolates in Turkey

Fig mosaic virus (FMV), which was described recently, is the only characterized causal agent of fig mosaic disease (FMD). It has six RNA segments and belongs to the Bunyaviridae family. In order to determine the genetic diversity of Turkish FMV isolates, the most common fig cultivars showing FMD symptoms were collected from different fig-growing provinces of Turkey. Nucleoprotein (Np) and Glycoprotein (Gp) gene-specific primers of FMV were used for RT-PCR analysis. According to RT-PCR results, 71 of 90 samples from 20 different cultivars and unknown fig seedlings were found to be infected by FMV. Among them, 41 isolates were sequenced and subjected to phylogenetic analyses based on the partial Gp and Np sequences at the amino acid level by the neighbor-joining method. The isolates showed more than 80% identity with reference FMV isolates (Acc. nos. FM991954.1 and FM864225.2). Based on phylogenetic analysis, the sequences clustered into two main groups for Np and Gp regions. Significant relationships between FMV isolates based on geographic origin and cultivars were not observed.     

Mefenoxam sensitivity and fitness analysis of Phytophthora nicotianae isolates from nurseries in Virginia, USA

Mefenoxam is one of the most commonly used fungicides for managing diseases caused by Phytophthora spp. on ornamentals. The objectives of this study were to determine whether Phytophthora nicotianae, a destructive pathogen of numerous herbaceous annual and perennial plant species in nurseries, has developed resistance to mefenoxam, and to evaluate the fitness of mefenoxam‐resistant isolates. Ninety‐five isolates of P. nicotianae were screened for sensitivity to mefenoxam on 20% clarified V8 agar at 100 a.i. µg mL^?1. Twenty‐five isolates were highly resistant to this compound with EC₅₀ values ranging from 235·2 to 466·3 µg mL^?1 and four were intermediately resistant with EC₅₀ values ranging from 1·6 to 2·9 µg mL^?1. Sixty‐six isolates were sensitive with EC₅₀ values less than 0·04 µg mL^?1. Nine resistant and seven sensitive isolates were tested for mefenoxam sensitivity on Pelargonium × hortorum cv. White Orbit. Mefenoxam provided good protection of pelargonium seedlings from colonization by sensitive isolates, but not by any resistant isolates. Four resistant and four sensitive isolates were compared for fitness components and their relative competitive ability on Lupinus Russell Hybrids in the absence of mefenoxam. Resistant isolates outcompeted sensitive ones within 3 to 6 sporulation cycles on lupin seedlings, regardless of their initial proportions in mixed zoospore inoculum. Resistant isolates exhibited greater infection rate and higher sporulation ability than sensitive ones when they were applied separately onto lupins. These results suggest that fungicide resistance may pose a serious challenge to the continued effectiveness of mefenoxam as a control option for nursery growers.     

Characterization of isolates of Phytophthora infestans collected in northwestern France from 1988 to 1992

Isolates of the potato late-blight pathogen Phytophthora infestans , collected in several French regions from 1988 to 1992, were characterized in order to determine the structure and pathogenicity of French populations and to compare them with other European samples. All 254 French isolates tested were of the Al mating type, as were two Sicilian, five Portuguese and one Spanish isolate. Metalaxyl sensitivity of 157 isolates was investigated. The frequency of resistance to this chemical decreased in western France from 1989 to 1992. Two glucose phosphate isomerase phenotypes (90/100 and 90/90) were detected among the 46 isolates tested; the former largerly predominated (75–80%) in the samples investigated. Both phenotypes corresponded to the population recently introduced into Europe. A third genotype (86/100), typical of the former European population, was found in one isolate from Picardy, originating from an artificially infected field trial. Five isolates from Portugal and Italy were of the 100/100 phenotype. Race patterns among 26 isolates from western France were very similar, and could not be explained by local selection. The unusual composition of the Brittany population, consisting of 'new' genotypes but all belonging to the Al mating type, is possibly related to the metapopulation type of structure of P. infestans in Europe.     

Anastomosis group and pathogenicity of isolates of Rhizoctonia solani from potato crops in South Australia

Isolates of Rhizoctonia collected from the stems, roots, tuber sclerotia and soil of potato crops in Virginia and Lenswood, South Australia, were identified to anastomosis groups (AG). Of the 301 multinucleate isolates of Rhizoctonia solani tested, 90% were AG-3, 7% were AG-4 and 2% were AG-5; 12 isolates were binucleate Rhizoctonia spp. This is the first report of isolates of AG-4 and AG-5 causing disease in potato crops in South Australia. All AG-3, AG-4 and AG-5 isolates tested caused rhizoctonia disease symptoms on the potato cultivar Coliban in pathogenicity trials conducted under glasshotise conditions. Both AG-3 and AG-5 isolates caused black scurf and stem cankers, although symptoms of black scurf were less severe with AG-5. AG-4 isolates produced the most severe stem and stolon cankers of all isolates tested. The pathogenicity of tuber-borne inoculum was confirmed by growing plants from sclerotia-infested tubers. AG-8 isolates from diseased barley and wheat produced severe root cankers and caused loss of feeder roots on inoculated potato plants. Results suggest that rhizoctonia disease in potato fields in South Australia is caused by a combination of different anastomosis groups and this has important implications for crop rotations.     

Susceptibility of Iberian trees to Phytophthora ramorum and P. cinnamomi

The capacity of Phytophthora ramorum to colonize the inner bark of 18 native and two exotic tree species from the Iberian Peninsula was tested. Living logs were wound-inoculated in a growth chamber with three isolates belonging to the EU1 and two to the NA1 clonal lineages of P. ramorum . Most of the Quercus species ranked as highly susceptible in experiments carried out in summer, with mean lesion areas over 100 cm² in Q. pubescens , Q. pyrenaica , Q. faginea and Q. suber and as large as 273 cm² in Q. canariensis , ca . 40 days after inoculation. Quercus ilex ranked as moderately susceptible to P. ramorum , forming lesions up to 133 cm² (average 17·2 cm²). Pinus halepensis and P. pinea were highly susceptible, exhibiting long, narrow lesions; but three other pine species, P. pinaster , P. nigra and P. sylvestris , were resistant to slightly susceptible. No significant difference in aggressiveness was found between the isolates of P. ramorum . In addition, there was evidence of genetic variation in susceptibility within host populations, and of significant seasonal variation in host susceptibility in some Quercus species. The results suggest a high risk of some Iberian oaks to P. ramorum , especially in forest ecosystems in southwestern Spain, where relict populations of Q. canariensis grow amongst susceptible understory species such as Rhododendron ponticum and Viburnum tinus . One isolate of P. cinnamomi used as positive control in all the inoculations was also highly aggressive to Iberian oaks and Eucalyptus dalrympleana .