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1.
ABSTRACT Colletotrichum gloeosporioides causes a serious crown rot of strawberry and some isolates from native plants are pathogenic to strawberry. C. gloeosporioides from lesions on wild grape and oak were sampled at two sites adjacent to commercial strawberry fields in Florida and two distant sites. Random amplified polymorphic DNA (RAPD) marker data and restriction enzyme digests of amplified rDNA were used to determine whether isolates were from the same C. gloeosporioides subgroup that infects strawberry. There were 17 to 24 native host isolates from each site that clustered with a group of strawberry crown isolates based on RAPD markers. Among strawberry isolates, there were two rDNA genotypes identified by restriction enzyme analysis. Both genotypes were present among native host isolates sampled from all four sites. There was some evidence that the different rDNA genotypes differentiated two closely related subpopulations, although the proportion of pathogenic isolates from native hosts among the two different genotypes was not different. The incidence of isolates pathogenic to strawberry was greater at sites close to strawberry fields relative to sites distant from strawberry fields for isolates with a BstUI(-)/MspI(+) rDNA genotype (44 versus 13%), a BstUI(+)/MspI(-) genotype (57 versus 16%), or when both genotypes were analyzed together (46 versus 15%). Based on these results, it appears that the C. gloeosporioides subgroup that causes crown rot on strawberry is widely distributed in Florida and that selection for pathogenicity on strawberry occurs in the area where this host is grown in abundance.  相似文献   

2.
ABSTRACT Recent findings from Michigan suggest that recombination may play a role in the survival and evolution of sensitivity to the fungicide mefenoxam in populations of Phytophthora capsici on cucurbit hosts. In 1998, 63 mefenoxam insensitive isolates were recovered from a squash field in which mefenoxam had been applied. Additional isolates were recovered from untreated squash fields planted at this location in 1999 (200 isolates) and the spring of 2000 (34 isolates). Isolates from 1998 and 1999 were characterized using fluorescent amplified fragment length polymorphism (AFLP) markers and all isolates were screened for compatibility type and mefenoxam sensitivity. In 1998 and 1999, 92 and 71% of the isolates, respectively, had unique multilocus AFLP genotypes with no identical isolates recovered between years. Seventy-two identical AFLP markers were clearly resolved in both the 1998 and 1999 sample sets, and fixation indices for the 37 polymorphic AFLP loci indicate little differentiation between years. There was no decrease in the frequency of resistant isolates during the 2 years without mefenoxam selection. We conclude that oospores play a key role in overwintering and that the frequency of mefenoxam insensitivity may not decrease in an agriculturally significant time period (2 years) once mefenoxam selection pressure is removed.  相似文献   

3.
Pratylenchus curvicauda, which was first described in metropolitan Perth in 1991, was recently identified in grain-growing areas in Western Australia. The biology of this root-lesion nematode, and especially its pest status, is unknown. We investigated its life cycle and interaction with host plants, because such information is essential for its management. The life cycle took 45 days to complete in a wheat cultivar maintained at 23°C. Over 10 weeks, the nematode multiplied in 26 of 61 genotypes; these host plants were all cereals and included widely grown cultivars of wheat and barley. Eighteen other cereal genotypes and 13 cultivars including canola, chickpea, ryegrass, lupin, soybean, and tomato, sustained the nematodes to different degrees without multiplication. Four cover crops were not suitable hosts. The patterns of attraction of the nematodes and penetration into roots of the host and tolerant plants were similar. The nonhosts attracted fewer nematodes, none of which penetrated the roots. Browning of infected roots was atypical—it occurred late in some roots, 55 days after inoculation, and in the presence of a fungus. The nematodes were confined to, and fed from, cortical cells. The ultrastructure of infected wheat and barley cells showed typical signs of damage caused by Pratylenchus spp. and included cell disorganization and lack of membrane integrity, disintegration of cytoplasm, hypertrophy of some nuclei, and deposition of tannin-like granules. This detailed characterization of P. curvicauda–host interaction indicates the nematode is likely to be a pest of major crops, and attention should be given to its management.  相似文献   

4.
ABSTRACT Spot blotch, caused by the fungal pathogen Cochliobolus sativus, is an important disease of barley in many production areas of the world. To assess genetic diversity in this pathogen, a worldwide collection of C. sativus isolates was evaluated for virulence on barley and DNA polymorphism. Three pathotypes (0, 1, and 2) were identified among the 22 isolates tested in this study and the 36 isolates characterized previously on three barley differentials (ND5883, Bowman, and NDB112) that differ in their resistance to C. sativus. Pathotype 2, which exhibits high virulence on cv. Bowman, was only found in North Dakota, whereas the other two pathotypes occurred in many other regions of the world. Genetic diversity of the 58 C. sativus isolates, together with isolates of three related pathogenic Cochliobolus spp. (C. heterostrophus, C. carbonum, and C. victoriae) was analyzed using amplified fragment length polymorphism (AFLP) markers. A total of 577 polymorphic AFLP markers were recorded among the 70 isolates of the four Cochliobolus spp. using eight primer combinations. Cluster analysis revealed distinct groups corresponding to the four different species, except in one case where race 0 of C. carbonum was placed in an outgroup that may belong to a different species. In C. sativus, 95 polymorphic AFLP markers were detected with the eight primer pairs used, and each isolate exhibited a unique AFLP pattern. Allelic diversity in the pathotype 2 group was lower (0.10) than in the pathotype 0 (0.23) and pathotype 1 (0.15) groups, indicating that pathotype 2 may have arisen more recently. Cluster analysis did not reveal a close correlation between pathotypes and AFLP groups, although two AFLP markers unique to pathotype 2 isolates were identified. This low correlation suggests that genetic exchange may have occurred through parasexual recombination in the fungal population. Some isolates collected from different regions of the world were clustered into the same AFLP group, suggesting that migration of the fungal pathogen around these regions has occurred.  相似文献   

5.
甜菜孢囊线虫Heterodera schachtii是严重危害甜菜生产的主要病原物,每年造成严重的经济损失,该线虫是我国对外重要的检疫性有害生物。本研究通过对十字花科、茄科、葫芦科、锦葵科、豆科、苋科和禾本科等16种作物29个品种进行人工接种,对其主要的寄主范围和生活史进行了测定。结果表明,甜菜孢囊线虫2龄幼虫能够侵染除小麦和玉米以外的其他14种作物25个品种,在苋科的甜菜和菠菜、茄科的番茄及十字花科等16个品种的根系能够完成生活史,形成白雌虫和孢囊。生活史调查发现,甜菜孢囊线虫接种到甜菜和油菜15 d和12 d后即可发育形成白雌虫,30 d后形成孢囊;而接种到西瓜根系后,不能正常发育,一直保持2龄幼虫虫态,无法完成生活史。上述结果表明甜菜孢囊线虫能够在甜菜、菠菜、番茄和十字花科作物上寄生,但是在不同寄主上的生活史存在一定的差异,其结果将为非寄主轮作防控甜菜孢囊线虫提供理论基础。  相似文献   

6.
Meloidogyne ethiopica is an important nematode pathogen causing serious economic damage to grapevine in Chile. In Brazil, M. ethiopica has been detected with low frequency in kiwifruit and other crops. The objectives of this study were to evaluate the intraspecific genetic variability of M. ethiopica isolates from Brazil and Chile using AFLP and RAPD markers and to develop a species‐specific SCAR‐PCR assay for its diagnosis. Fourteen isolates were obtained from different geographic regions or host plants. Three isolates of an undescribed Meloidogyne species and one isolate of M. ethiopica from Kenya were included in the analysis. The results showed a low level of diversity among the M. ethiopica isolates, regardless of their geographical distribution or host plant origin. The three isolates of Meloidogyne sp. showed a high homogeneity and clustered separately from M. ethiopica (100% bootstrap). RAPD screenings of M. ethiopica allowed the identification of a differential DNA fragment that was converted into a SCAR marker. Using genomic DNA from pooled nematodes as a template, PCR amplification with primers designed from this species‐specific SCAR produced a fragment of 350 bp in all 14 isolates of M. ethiopica tested, in contrast with other species tested. This primer pair also allowed successful amplification of DNA from single nematodes, either juveniles or females and when used in multiplex PCR reactions containing mixtures of other root‐knot nematode species, thus showing the sensitivity of the assay. Therefore, the method developed here has potential for application in routine diagnostic procedures.  相似文献   

7.
Disease observations and amplified fragment length polymorphism (AFLP) markers were used to study recent developments in the Puccinia striiformis f.sp. tritici population in Denmark. The fungus appeared spontaneously at 10 locations in Denmark in 1997 after it was not observed under natural conditions in 1996. The pattern of disease development and prevailing winds suggested that the fungus reappeared by airborne spores from the south or west. In 1998, disease incidence was more evenly distributed throughout the country. Forty-eight single lesion isolates were collected from most crops where the disease was observed in these years; all except one from 1997 belonged to two pathotypes that were not previously detected in the country, and both possessed the newly discovered Yr17 virulence. The isolates were characterized with AFLP markers together with 28 isolates representing eight of 13 pathotypes observed prior to 1996. Initial screening of 240 Pst I/ Mse I AFLP primer combinations on four isolates showed that a primer combination, on average, revealed 0·4 polymorphisms between any isolate pair. A selection of 21 primer combinations resulted in 28 AFLP markers, which revealed 16 AFLP phenotypes among all 76 isolates. The two Yr17- virulent pathotypes consisted of three AFLP phenotypes, which were observed in both 1997 and 1998; the two most frequent AFLP phenotypes occurred at most sampling locations and often within the same crop. AFLP diversity was larger among samples collected prior to 1996, and also in this period most AFLP phenotypes were observed at different sampling locations. These results are consistent with the features of an entirely asexually reproducing pathogen dispersed by aerial spores across large areas.  相似文献   

8.
Host Range Specificity in Verticillium dahliae   总被引：1，自引：0，他引：1  
Bhat RG  Subbarao KV 《Phytopathology》1999,89(12):1218-1225
ABSTRACT Verticillium dahliae isolates from artichoke, bell pepper, cabbage, cauliflower, chili pepper, cotton, eggplant, lettuce, mint, potato, strawberry, tomato, and watermelon and V. albo-atrum from alfalfa were evaluated for their pathogenicity on all 14 hosts. One-month-old seedlings were inoculated with a spore suspension of about 10(7) conidia per ml using a root-dip technique and incubated in the greenhouse. Disease incidence and severity, plant height, and root and shoot dry weights were recorded 6 weeks after inoculation. Bell pepper, cabbage, cauliflower, cotton, eggplant, and mint isolates exhibited host specificity and differential pathogenicity on other hosts, whereas isolates from artichoke, lettuce, potato, strawberry, tomato, and watermelon did not. Bell pepper was resistant to all Verticillium isolates except isolates from bell pepper and eggplant. Thus, host specificity exists in some isolates of V. dahliae. The same isolates were characterized for vegetative compatibility groups (VCGs) through complementation of nitrate nonutilizing (nit) mutants. Cabbage and cauliflower isolates did not produce nit mutants. The isolate from cotton belonged to VCG 1; isolates from bell pepper, eggplant, potato, and tomato, to VCG 4; and the remaining isolates, to VCG 2. These isolates were also analyzed using the random amplified polymorphic DNA (RAPD) method. Forty random primers were screened, and eighteen of them amplified DNA from Verticillium. Based on RAPD banding patterns, cabbage and cauliflower isolates formed a unique group, distinct from other V. dahliae and V. albo-atrum groups. Minor genetic variations were observed among V. dahliae isolates from other hosts, regardless of whether they were host specific or not. There was no correlation among pathogenicity, VCGs, and RAPD banding patterns. Even though the isolates belonged to different VCGs, they shared similar RAPD profiles. These results suggest that management of Verticillium wilt in some crops through crop rotation is a distinct possibility.  相似文献   

9.
Abstract

Brassicaceae plants have the potential as part of an integrated approach to replace fumigant nematicides, providing the biofumigation response following their incorporation is not offset by reproduction of plant-parasitic nematodes on their roots. Forty-three Brassicaceae cultivars were screened in a pot trial for their ability to reduce reproduction of three root-knot nematode isolates from north Queensland, Australia: M. arenaria (NQ1), M. javanica (NQ2) and M. arenaria race 2 (NQ5/7). No cultivar was found to consistently reduce nematode reproduction relative to forage sorghum, the current industry standard, although a commercial fodder radish (Raphanus sativus) and a white mustard (Sinapis alba) line were consistently as resistant to the formation of galls as forage sorghum. A second pot trial screened five commercially available Brassicaceae cultivars, selected for their biofumigation potential, for resistance to two nematode species, M. javanica (NQ2) and M. arenaria (NQ5/7). The fodder radish cv. Weedcheck, was found to be as resistant as forage sorghum to nematode reproduction. A multivariate cluster analysis using the resistance measurements, gall index, nematode number per g of root and multiplication for two nematode species (NQ2 and NQ5/7) confirmed the similarity in resistance between the radish cultivar and forage sorghum. A field trial confirmed the resistance of the fodder radish cv. Weedcheck, with a similar reduction in the number of Meloidogyne spp. juveniles recovered from the roots 8 weeks after planting. The use of fodder radish cultivars as biofumigation crops to manage root-knot nematodes in tropical vegetable production systems deserves further investigation.  相似文献   

10.
Virulent and non-virulent pathotypes of Leptosphaeria maculans were differentiated on the basis of cultural characteristics and virulence to cabbage plants. Surveys of isolates obtained from oilseed rape crops grown in England in 1982 and 1983 showed that virulent pathotypes predominated in some areas whereas in others they were infrequent or absent. Overall 41% of isolates from this crop were of the virulent type. Virulent types usually occurred most frequently in areas with a long history or a high density of oilseed rape. In vegetable and forage brassica seed crops in Essex virulent isolates formed a small proportion of the population, except in one swede crop from which 95% of isolates were virulent. Host specificity was not detected in cross-infection experiments using isolates from different hosts and localities.  相似文献   

11.
In Europe, sugar beet is often produced in a 3‐year rotation with cereals, leaving stubble fields fallow from cereal harvest until primary tillage in autumn in the year prior to sugar beet production. The weed flora on such fields could include host plants of Heterodera schachtii that is one of the most important pests of sugar beet. Crop sequences with non‐hosts and cover cropping with resistant cruciferous hosts during this period have been crucial for its management. Availability of resistant and tolerant sugar beet cultivars could entice growers to forego cover cropping, exacerbating weed problems during the fallow period. The objective of this study was to determine the reproductive potential of H. schachtii on weeds that develop during this period. Under glasshouse conditions, reproduction on 39 plant species was compared with that on oilseed radish and sugar beet of differing nematode host status. In 2 years in field microplots, 18 previously tested species were grown in H. schachtii‐infested soil during the typical fallow period at 60 plants m?2, and nine of these species were also grown at 180 plants m?2. There were variable results between years after 8 weeks of growth, but most weeds allowed lower reproduction (<10%) than the susceptible sugar beet; only Stellaria media at 180 plants m?2 and Thlaspi arvense at both plant densities increased nematodes. Such weed densities may seldom occur under commercial conditions; thus, weed management for nematological considerations during the stubble period may have limited importance.  相似文献   

12.
ABSTRACT To investigate host specialization in Macrophomina phaseolina, the fungus was isolated from soybean, corn, sorghum, and cotton root tissue and soil from fields cropped continuously to these species for 15 years in St. Joseph, LA. Chlorate phenotype of each isolate was determined after growing on a minimal medium containing 120 mM potassium chlorate. Consistent differences in chlorate sensitivity were detected among isolates from different hosts and from soil versus root. To further explore genetic differentiation among fungal isolates from each host, these isolates were examined by restriction fragment length polymorphism and random amplified polymorphic DNA (RAPD) analysis. No variations were observed among isolates in restriction patterns of DNA fragments amplified by polymerase chain reaction covering the internal transcribed spacer region, 5.8S rRNA and part of 25S rRNA, suggesting that M. phaseolina constitutes a single species. Ten random primers were used to amplify the total DNA of 45 isolates, and banding patterns resulting from RAPD analysis were compared with the neighbor-joining method. Isolates from a given host were genetically similar to each other but distinctly different from those from other hosts. Chlorate-sensitive isolates were distinct from chlorate-resistant isolates within a given host. In greenhouse tests, soybean, sorghum, corn, and cotton were grown separately in soil infested with individual isolates of M. phaseolina that were chosen based on their host of origin and chlorate phenotype. Root colonization and plant weight were measured after harvesting. More colonization of corn roots occurred when corn was grown in soil containing corn isolates compared with isolates from other hosts. However, there was no host specialization in isolates from soybean, sorghum, or cotton. More root colonization in soybean occurred with chlorate-sensitive than with chlorate-resistant isolates.  相似文献   

13.
Genotypic variation among 32 single-zoospore isolates (SZI) of Phytophthora infestans , derived asexually from two hyphal-tip parental isolates (PI-105 and PI-1) of the US-8 genotype, was assessed with 80 random amplified polymorphic DNA (RAPD) primers and 18 amplified fragment length polymorphic DNA (AFLP) primer pairs. In previous investigations, the SZIs from parental isolate PI-105 showed high levels of virulence variability and were differentiated into 14 races, whereas the SZIs from PI-1 showed identical virulence to the parent. The purpose of this investigation was to determine if phenotypic variation observed among SZIs of P. infestans could be detected at the DNA level in these isolates. Polymorphism was detected with 51 RAPD primers and with all 18 AFLP primer pairs in PI-105 SZIs. In SZIs from PI-1, polymorphism was also detected with 25 RAPD primers and 17 AFLP primer pairs. Cluster analysis using the unweighted pair-group method with arithmetic averages (UPGMA) separated the SZIs from parent PI-105 into six virulence groups, 11 RAPD groups and three AFLP groups. Cluster analysis of PI-1 SZIs, which all belong to the same virulence group, differentiated them into four RAPD groups and six AFLP groups. No close correlation among RAPD, AFLP and virulence groups could be established within the two progenies of SZIs. Results of this study suggest that there is a considerable level of inherent genetic variability among SZIs derived asexually from the same parental isolate. The possible mechanisms and implications of this genetic variation are discussed.  相似文献   

14.
The allelopathic effects of a water extract from Hemistepta lyrata were tested on the seeds of selected crops in Petri dishes. The results showed that the extract strongly inhibited the germination and seedling growth of wheat ( Triticum aestivum ), rape ( Brassica campestris ), and radish ( Raphanus sativus ), but only slightly inhibited those of sorghum ( Sorghum vulgare ) and cucumber ( Cucumis sativus ). The extract stimulated the growth of roots and hypocotyls at lower concentrations, while it inhibited their growth at higher concentrations. The malondialdehyde (MDA) content of cucumber and radish increased after treatment with the extract. These results indicated that the MDA concentration in plants is one important aspect of the allelopathic effects of H. lyrata .  相似文献   

15.
ABSTRACT Soil suppressiveness to Heterodera schachtii was demonstrated in a field at the research station of the University of California, Riverside. In two field trials planted to Swiss chard (Beta vulgaris), introduced H. schachtii multiplied 2.7 and 1.7 times more in preplant metam sodium-fumigated plots than in nontreated plots in 1994 and 1995, respectively. In greenhouse experiments, preplant treatments with metam sodium, methyl bromide, methyl iodide, formaldehyde, and aerated steam reduced suppressiveness of soil against H. schachtii to undetectable levels. H. schachtii multiplied significantly less in nontreated soil than in treated soil on Swiss chard. At harvest, the number of infective second-stage juveniles in suppressive soil was close to the lowest detection level, whereas high numbers were encountered in soils initially treated. In a crop rotation trial with host crops of H. schachtii, introduced H. schachtii populations were monitored for five cropping periods over 30 months in initially fumigated versus nontreated suppressive field plots. In fumigated plots, H. schachtii population levels increased in the first and second cropping periods and then declined in the third cropping period. In the fourth and fifth cropping periods, the nematode reproduction factor in the initially fumigated plots was not significantly different from that in suppressive plots.  相似文献   

16.
ABSTRACT Colletotrichum crown rot of strawberry in Florida is caused primarily by Colletotrichum gloeosporioides. To determine potential inoculum sources, isolates of Colletotrichum spp. from strawberry and various noncultivated plants growing in the areas adjacent to strawberry fields were collected from different sites. Species-specific internal transcribed spacer primers for C. gloeosporioides and C. acutatum were used to identify isolates to species. Random amplified polymorphic DNA (RAPD) markers were used to determine genetic relationships among isolates recovered from noncultivated hosts and diseased strawberry plants. Selected isolates also were tested for pathogenicity on strawberry plants in the greenhouse. In all, 39 C. gloeosporioides and 3 C. acutatum isolates were recovered from diseased strawberry crowns, and 52 C. gloeosporioides and 1 C. acutatum isolate were recovered from noncultivated hosts. In crown inoculation tests, 18 of the 52 C. gloeosporioides isolates recovered from noncultivated hosts were pathogenic to strawberry. Phylogenetic analysis using RAPD marker data divided isolates of C. gloeosporioides from noncultivated hosts into two separate clusters. One cluster contained 50 of the 52 isolates and a second cluster contained 2 isolates that were homothallic in culture. Isolates from strawberry were interspersed within the cluster containing the 50 isolates that were recovered from noncultivated hosts. The results are not inconsistent with the hypothesis that C. gloeosporioides isolates obtained from strawberry and noncultivated hosts adjacent to strawberry fields are from the same population and that noncultivated hosts can serve as potential inoculum sources for Colletotrichum crown rot of strawberry.  相似文献   

17.
 运用致病力和DNA多态性检测中国东北地区的35个大豆灰斑病菌分离物的遗传变异、根据菌株在9个品种(系)上的致病力反应可将其分为7个组。利用13个随机引物扩增供试菌株共计产生105个RAPD标记,其中78.1%具有多态性。通过聚类分析计算了各菌株间的遗传距离,并产生树状图,发现同一地区内及不同地区间的病菌表现遗传变异、致病性和DNA多态性间具有一定相关性。  相似文献   

18.
Plasmodiophora brassicae is an obligate biotroph that causes clubroot, one of the most damaging diseases of crucifers. Differential cultivars and random amplified polymorphic DNA markers were used to assess the extent of genetic diversity among nine single-gall populations of P. brassicae and 37 single-spore isolates (SSI) derived from four of those field samples. Isolates were classified into eight pathotypes, and each isolate was associated with a unique molecular genotype. Virulence and DNA polymorphisms were detected within and between field isolates, and among SSIs from different pathotypes, hosts and geographical origins. The relatively high level of genetic diversity among field isolates was similar to that among SSIs derived from a single-club field isolate. Molecular and pathogenicity-based classifications were not clearly correlated, but isolates belonging to pathotype P1 were clustered. Two RAPD markers were specific to pathotype P1. The finding that genetic differences can occur in P. brassicae field isolates will be an important consideration in resistance genetic studies and in choosing breeding strategies to develop durable clubroot resistance.  相似文献   

19.
黄瓜枯萎病菌遗传多样性的AFLP分析   总被引：4，自引：0，他引：4  
黄瓜枯萎病是由半知菌亚门尖孢镰刀菌黄瓜专化型(Fusarium oxysporumf.sp.cucumainum Owen)侵染引起的一种土传病害,是影响黄瓜生产的最主要病害之一[1].近年来随着分子生物学技术的迅速发展,国内外学者对于病原真菌的遗传多样性做了大量的研究,Wang等[2]对影响黄瓜枯萎病菌AFLP技术体系的多种因素作了探讨,得到了1种适合于黄瓜枯萎病菌AFLP分析的优化体系;Duan等[3]应用RAPD、ISSR和AFLP标记揭示出了西瓜枯萎病菌株在分子水平上的遗传多样性.  相似文献   

20.
The objectives of this work were to evaluate the genetic variability of Meloidogyne enterolobii by molecular markers, and develop species‐specific molecular markers for application in detection. Sixteen M. enterolobii isolates from different geographical regions (Brazil and other countries) and hosts were used in this study. The identification and purification of the populations were carried out based on isoenzyme phenotype. The DNA amplification of the intergenic region (IGS) of the rDNA and of the region between the cytochrome oxidase subunit II (COII) and 16S rRNA genes (mtDNA) produced specific fragments of the expected size for this nematode, i.e. 780 and 705 bp, respectively. Intraspecific variability among the isolates was evaluated with three different neutral molecular markers: AFLP, ISSR and RAPD. The results showed a low level of diversity among the isolates tested, indicating that M. enterolobii is a genetically homogeneous root‐knot nematode species. The RAPD method allowed the identification of a species‐specific RAPD fragment for M. enterolobii. This fragment was cloned and sequenced, and from the sequence obtained, a set of primers was designed and tested. The amplification of a 520‐bp‐long fragment occurred only for the 16 isolates of M. enterolobii and not for the 10 other Meloidogyne species tested. In addition, positive detection was achieved in a single individual female, egg‐mass and second stage juvenile of this nematode. This SCAR species‐specific marker for M. enterolobii represents a new molecular tool to be used in the detection of this nematode from field samples and as a routine diagnostic test for quarantine devices .  相似文献   

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