共查询到20条相似文献,搜索用时 31 毫秒
1.
Á. Mesterházy T. Bartók G. Kászonyi M. Varga B. Tóth J. Varga 《European journal of plant pathology / European Foundation for Plant Pathology》2005,112(3):267-281
Different sets of wheat genotypes were tested under field conditions by spraying inocula of isolates of seven Fusarium spp. and Microdochium nivale (formerly F. nivale) in the period 1998–2002. The severity of Fusarium head blight (FHB), Fusarium-damaged kernels (FDK), the yield reduction and the deoxynivalenol (DON) contamination were also measured to describe the nature of the resistance. The degrees of FHB severity of genotypes to F. graminearum, F. culmorum, F. avenaceum, F. sporotrichioides, F. poae, F.␣verticillioides, F. sambucinum and M. nivale were very similar, indicating that the resistance to F.␣graminearum was similar to that for other Fusarium spp. listed. This is an important message to breeders as the resistance relates not only to any particular isolate of F. graminearum, but similarly to isolates of other Fusarium spp. This holds true for all the parameters measured. The DON contamination refers only to DON-producers F. graminearum and F. culmorum. Highly significant correlations were found between FHB, FDK, yield loss and DON contamination. Resistance components such as resistance to kernel infection, resistance to DON and tolerance were identified in the more susceptible genotypes. As compared with western European genotypes which produced up to 700 mg kg−1 DON, the Hungarian genotypes produced only 100 mg kg−1 at a similar FDK level. This research demonstrates the importance of measuring both FDK and DON in the breeding and selection of resistant germplasm and cultivars. 相似文献
2.
Julie M. Steed Andreas Baierl Bruce D. L. Fitt 《European journal of plant pathology / European Foundation for Plant Pathology》2007,118(4):359-373
In winter oilseed rape experiments at Rothamsted in 2000/01 to 2002/03 growing seasons, the severity of phoma stem canker
epidemics in summer depended on the timing of phoma leaf spot epidemics in the previous autumn, and hence on the timing of
Leptosphaeria maculans ascospore release. The first major release of L. maculans ascospores was earlier in 2000 (26 September) and 2001 (18 September) than in 2002 (21 October). Consequently, the autumn
phoma leaf spot epidemic was also earlier in 2000 and 2001 than in 2002. The resulting stem canker epidemics were severe by
harvest (July) in 2001 and 2002 but not in 2003. No correlation was found between the severity or duration of phoma leaf spotting
(lesion days or lesion °C-days) and the subsequent severity of phoma stem canker epidemics. Rates of leaf production and loss
were similar in the three growing seasons. Out of ca. 25 leaves produced on plants during each season, leaf numbers 10–14 generally remained on plants for the longest. Treatment
with flusilazole + carbendazim in autumn decreased the severity of phoma leaf spotting for several weeks after treatment,
decreased the severity of stem canker the following summer and increased yield significantly in 2001 and 2002 but not in 2003.
The most effective timings for flusilazole + carbendazim application were when leaves 7–11 were present on most plants and
at least 10% of plants were affected by phoma leaf spot. Two half-dose applications of fungicide reduced phoma stem canker
and increased yield more than a single full dose application when phoma leaf spot epidemics were early (<800 °C-days after
sowing). 相似文献
3.
Helena P. Trenado Isabel M. Fortes Diamantina Louro Jesús Navas-Castillo 《European journal of plant pathology / European Foundation for Plant Pathology》2007,118(2):193-196
Tomato chlorosis virus causes yellow leaf disorder epidemics in many countries worldwide. Plants of Physalis ixocarpa showing abnormal interveinal yellowing and plants of Physalis peruviana showing mild yellowing collected in the vicinity of tomato crops in Portugal were found naturally infected with ToCV. Physalis ixocarpa and P. peruviana were tested for susceptibility to ToCV by inoculation with Bemisia tabaci, Q biotype. Results confirmed that ToCV is readily transmissible to both species. The infection was expressed in P. ixocarpa by conspicuous interveinal yellow areas on leaves that developed into red or brown necrotic flecks, while P. peruviana test plants remained asymptomatic. Infected plants of both P. ixocarpa and P. peruviana served as ToCV sources for tomato infection via B. tabaci transmission. This is the first report of P. ixocarpa and P. peruviana as natural hosts of ToCV. 相似文献
4.
Olga Afanasenko Nina Mironenko Olga Filatova Doris Kopahnke Ilona Krämer Frank Ordon 《European journal of plant pathology / European Foundation for Plant Pathology》2007,117(3):267-280
The genetics of host-pathogen interactions in the Hordeum vulgare – P. teres f. teres pathosystem was studied in twelve resistant barley accessions, i.e. CI 9825, CI 9819, Diamond, CI 4922, CI 5401, Harbin,
c-8755, c-21849, c-8721 c-23874, c-19979, c-15811. F2 analyses of crosses with susceptible genotypes employing various isolates (from Europe, USA, Canada, and Australia) revealed
that resistance is mostly isolate-specific and controlled by one or two genes. Segregation in ascospore progeny from two crosses
between isolates of different origin revealed that avirulence in P. teres is also determined by one or two genes. An epistatic effect of suppressor genes on avirulence genes is proposed for the genetics
of virulence to Diamond, Harbin, CI 5401 and c-8721 in the fungal crosses D (181-6 × A80) and F (H-22 × 92-178/9). Segregation
in F2 of crosses of three new sources of resistance (c-23874, c-19979, c-15811) to the susceptible cv. Pirkka was studied in laboratory
and greenhouse tests by using seven P. teres isolates, i.e. 181-6, d8-3, d8-4, d9-1, d9-4, F4 and F74. In addition, virulence to these barley accessions of ascospore
progeny from crosses of the same isolates was studied. Based on these studies it was concluded that depending on the isolate
used, resistance of c-23874 is determined at least by two genes and in c-19979 and c-15811 by three genes. The results of
this parallel analyses of genetics of resistance and genetics of virulence allows the postulation of a gene–for–gene interaction
in the P. teres – H. vulgare pathosystem. 相似文献
5.
Tetsuo Tamada 《Journal of General Plant Pathology》2007,73(1):76-80
Four lines (designated MR0, MR1, MR2, and M8) from 13 accessions of Beta vulgaris subsp. maritima were selected on the basis of phenotypes produced after foliar rub-inoculation with Beet necrotic yellow vein virus (BNYVV). The susceptible phenotype developed bright yellow local lesions, whereas the resistant phenotype had symptoms ranging
from no visible lesions to necrotic lesions at the inoculation site. MR1 and MR2 lines had a resistant phenotype depending
on the isolate and the MR0 line was susceptible to all isolates of BNYVV tested. The M8 line was highly susceptible; the virus
spread systemically and caused severe stunting. These plant lines will be useful for distinguishing BNYVV isolates having
different pathogenicities, especially those controlled by RNA3 and/or RNA5. 相似文献
6.
Masato Kawabe Kazunori Katsube Takanobu Yoshida Tsutomu Arie Kenichi Tsuchiya 《Journal of General Plant Pathology》2007,73(5):353-359
Twenty-eight isolates of Fusarium oxysporum f. sp. spinaciae (FOS; the causal agent of spinach wilt) collected from Japan were assessed for mating type and subjected to phylogenetic analysis.
Mating type analysis revealed all isolates to be MAT1-2, suggesting that there is no sexual recombination within the population.
Phylogenetic analyses based on nucleotide sequences of the ribosomal DNA intergenic spacer (IGS) and the mating type locus
(MAT1) suggested that FOS is polyphyletic. The cluster analysis based on IGS showed four phylogenetic groups (S1–S4) among the isolates. Two distinct
lineages, S1 and S3, included FOS isolates both of the vegetative compatibility group (VCG) types, 0330 and 0331, demonstrating that VCG differentiation in
FOS may not necessarily reflect the phylogenetic relationships based on IGS and MAT1-2-1. 相似文献
7.
Shin-ichi Fuji Nanae Mochizuki Masashi Fujinaga Makoto Ikeda Kouichi Shinoda Seiji Uematsu Hiromitsu Furuya Hideki Naito Fumiyoshi Fukumoto 《Journal of General Plant Pathology》2007,73(3):216-221
Alstroemeria plants were surveyed for viruses in Japan from 2002 to 2004. Seventy-two Alstroemeria plants were collected from Aichi, Nagano, and Hokkaido prefectures and 54.2% were infected with some species of virus. The
predominant virus was Alstroemeria mosaic virus, followed by Tomato spotted wilt virus, Youcai mosaic virus (YoMV), Cucumber mosaic virus (CMV), Alstroemeria virus X and Broad bean wilt virus-2 (BBWV-2). On the basis of nucleotide sequence of the coat protein genes, all four CMV isolates belong to subgroup IA. CMV
isolates induced mosaic and/or necrosis on Alstroemeria. YoMV and BBWV-2 were newly identified by traits such as host range, particle morphology, and nucleotide sequence as viruses
infecting Alstroemeria. A BBWV-2 isolate also induced mosaic symptoms on Alstroemeria seedlings. 相似文献
8.
Takeshi Toda Toshihiro Hayakawa Joseph Mwafaida Mghalu Shigeharu Yaguchi Mitsuro Hyakumachi 《Journal of General Plant Pathology》2007,73(6):379-387
Isolates of an unidentified Rhizoctonia sp. (UR isolates) were obtained from creeping bentgrass and Kentucky bluegrass with reddish brown sheath and foliar rots.
Because the UR isolates anastomosed with isolates of three varieties of Waitea circinata (var. oryzae, var. zeae, and var. circinata), colony morphology, hyphal growth rate at different temperatures, pathogenicity, sequence analysis of the internal transcribed
spacers (ITS) region of ribosomal RNA genes (rDNA) were compared. The colony color of mature UR isolates was distinct from
isolates of the other three varieties of W. circinata. In pathogenicity tests on creeping bentgrass, the severity of the disease caused by UR isolates was significantly higher
than that caused by the three varieties of W. circinata. Sequence similarities of the rDNA-ITS region between UR isolates and between isolates within each variety were high (97–100%),
but they were lower among isolates from UR and the varieties of W. circinata (88–94%). In a phylogenetic tree based on the rDNA-ITS sequences, UR isolates formed a cluster separate from each of the
clusters formed by the three varieties of W. circinata. These results indicate that the UR isolates clearly differ from the three varieties of W. circinata. We therefore propose that the UR isolates be classified as new Rhizoctonia sp. that are closely related to W.
circinata and that the disease on creeping bentgrass should be called Waitea reddish-brown patch disease (Sekikasshoku-hagusare-byo
in Japanese). 相似文献
9.
Antonín Dreiseitl Junmei Wang 《European journal of plant pathology / European Foundation for Plant Pathology》2007,117(4):357-368
Four hundred and sixty-one isolates of Blumeria
graminis f.sp. hordei were obtained from eight populations occurring on cultivated barley (Hordeum
vulgare) at four geographically distant locations in China during 2003 and 2004. Their virulence frequency was determined on 30 differential
lines. No isolate was virulent on differential lines possessing the resistance genes Mla1, Mla3, Mla6, Mla7, Mla9, Mla12, Mla13, Mlat, Mlg, Mla10, Mla22, Mla23, Mlp1, Ml(N81) and Mlmw. Virulences to the first nine resistance genes are prevalent in Europe and constitute the main part of genetic distance between
Chinese and European populations. Conversely, no isolate was avirulent on the differential lines possessing the genes Mla8 and Ml(Ch). The frequencies of isolates overcoming the genes Mla2, Mla11, Mlk1 and Mlk2 were .4–9.3%, and frequencies of isolates overcoming the genes Mlh, MlLa, Ml(Bw), Mlra, Ml(Ru2), mlw, MlGa, MlWo and Mlnn ranged from 18.2% to 98.7%. Based on reactions of differential lines possessing the genes Mlk1, Mlh, MlLa, Ml(Bw), Mlra and Ml(Ru2), pathotypes were identified and diversity parameters calculated. Eleven of 22 detected pathotypes were found in both years
and comprised 94.6% of isolates. Generally, the populations from different locations in 1 year were more closely related than
populations collected from the same locations in different years. Complete effectiveness of the resistance genes, for which
no corresponding virulences were found, will allow Chinese breeders to access many modern European barley cultivars that are
fully resistant to powdery mildew in China, including those possessing the non-host resistance gene mlo. 相似文献
10.
Hideki Watanabe Yoshihiro Taguchi Mitsuro Hyakumachi Koji Kageyama 《Journal of General Plant Pathology》2007,73(2):81-88
Pythium and Phytophthora species were isolated from kalanchoe plants with root and stem rots. Phytophthora isolates were identified as Phytophthora nicotianae on the basis of morphological characteristics and restriction fragment length polymorphism (RFLP) analysis of the rDNA-internal
transcribed spacer regions. Similarly, the Pythium isolates were identified as Pythium myriotylum and Pythium helicoides. In pathogenicity tests, isolates of the three species caused root and stem rots. Disease severity caused by the Pythium spp. and Ph. nicotianae was the greatest at 35°–40°C and 30°–40°C, respectively. Ph. nicotianae induced stem rot at two different relative humidities (60% and >95%) at 30°C. P. myriotylum and P. helicoides caused root and stem rots at high humidity (>95%), but only root rot at low humidity (60%). 相似文献
11.
Florian Chain Gérard Riault Maxime Trottet Emmanuel Jacquot 《European journal of plant pathology / European Foundation for Plant Pathology》2007,117(1):35-43
Serial passage experiments (SPE) of a Barley yellow dwarf virus-PAV (BYDV-PAV) isolate were performed on Zhong ZH and TC14 wheat lines to evaluate the durability of their resistance to BYDV. At different passage numbers (from the 2nd to the 114th), biological properties of the produced isolates were recorded either by monitoring infection percentages and virus titers of the first 3 weeks of viral infection or by measuring their impact on yield components. Statistical analyses using the area under pathogen progress curves and the area under concentration progress curves demonstrated that these two resistant lines induce, after only a few passages, a selection of variant(s) with significantly modified infection abilities. Isolates resulting from SPE performed on these lines induced important decreases of yield components. These results indicate that the use of Zhong ZH and TC14 lines in BYDV-resistant breeding programmes should be approached with caution. 相似文献
12.
Liriomyza cicerina (Rondani, 1875) (Diptera: Agromyzidae) is an important pest on chickpea (Cicer arietinum L.) in some regions of Turkey. The objective of this study was to determine whether the populations ofL. cicerina on different varieties of chickpea plants during the 2004 and 2005 production seasons affected yield in Sanliurfa province.
The trials were carried out using eight different varieties of chickpea with three replicates. During each season, larval
densities on leaves were assessed weekly. TheL. cicerina larval population was lowest on four varieties for both seasons. There were very minor differences in yield among the eight
varieties in the production seasons. There was no correlation found between larval density and yield loss.
http://www.phytoparasitica.org posting Jan. 14, 2007. 相似文献
13.
Kiyotaka Gotoh Seishi Akino Masayasu Kato Norio Kondo Shigeo Naito 《Journal of General Plant Pathology》2007,73(5):349-352
Twelve isolates of Japanese Phytophthora infestans, which differed from the major genotypes US-1, JP-1, JP-2, and JP-3, were analyzed for RG57 fingerprints, mtDNA haplotypes,
two allozyme genotypes, and mating types. Genotypes JP-1.1, JP-2.1, JP-2.2, JP-3.1, and JP-4 were newly defined. JP-1.1 and
JP-2.1 were isolated discontinuously from potato fields in several years, and JP-1.1 was found in Hokkaido and Kagoshima.
These results show that some minor genotypes can overwinter and disperse from their original site. 相似文献
14.
Chuan-qing Zhang Jin-wen Zhu Fang-lin Wei Shao-ying Liu Guo-nian Zhu 《Phytoparasitica》2007,35(3):300-313
Two hundred isolates ofBotrytis cinerea were collected from greenhouse vegetables between 2003 and 2006 to determine their baseline sensitivity to triadimefone,
penconazole, tebuconazole and fenhexamid. Mean values of 50% effective concentrations (EC50) of inhibiting growth were 4.853±5.102, 0.41±0.215, 0.19±0.099 and 0.36±0.891 mgl
−1, respectively (mean±SD). Individuals ofB. cinerea in the population differed by a factor (EC50 of the least sensitive isolate/EC50 of the most sensitive isolate) of 6625, 20, 603 and 1800, respectively. Naturally fenhexamid-resistant isolates were detected
with an unexpected high frequency of 10% although the pathogen population had never been exposed to this fungicide. The resistance
level (mean EC50 of resistant isolates / mean EC50 of sensitive isolates) was 19.5. These naturally resistant isolates also were resistantin vivo, and there was no significant difference in growth rate, conidial production or pathogenicity ability between naturally resistant
and wild sensitive isolates. These results indicated that there was a potential risk of practical resistance if fenhexamid
was applied alone. Negative cross-resistance was observed between fenhexamid and tebuconazole in 90% of the naturally resistant
isolates. Moreover, an obvious synergism of the antifungal activity of fenhexamid by tebuconazole was demonstrated in some
of the naturally fenhexamid-resistant isolates.
http://www.phytoparasitica.org posting May 9, 2007. 相似文献
15.
S.V. Tsygankova A.N. Ignatov E.S. Boulygina B.B. Kuznetsov E.V. Korotkov 《European journal of plant pathology / European Foundation for Plant Pathology》2004,110(8):845-853
Novel primers for rep-PCR were developed with the original software and based on `ancient diverged periodical sequences'. Rep-PCR with these primers was applied to study genetic relationships among 51 Xanthomonas campestris strains. The strains were collected from different countries including Russia, Japan, UK, Germany and Hungary. Reference strains of three X. campestrispathovars and five other Xanthomonas species were included. Based on qualitative differences in amplification profiles, the strains were divided into four major groups. Two subgroups recognised within X. campestrispopulation were similar to RFLP haplotypes. The third subgroup included strains of two other pathovariants and Japanese isolates of X. campestris pv. campestriswhile the fourth group comprised the other species of Xanthomonas. The analysis of the diversity within X. campestris resulted in the conclusion that isolates belong to distinct clonal populations (subgroups). The differences between the subgroups of X. campestris were only slightly smaller than between species of Xanthomonas. A PCR fragment about 600 bp amplified by primer KRPN2 was found in nearly all tested strains of X. campestris.SCAR primers designed for this marker produced a single specific band for strains of X. campestris, but not for other Xanthomonas, Pseudomonas and Erwiniastrains tested. Application of the new primer set for rep-PCR offers a rapid, simple and reproducible method for identification of bacterial strains. The X. campestris-specific SCAR primers may be used in diagnostics of this important plant pathogen. 相似文献
16.
P.V. Martínez-culebras P. Abad-campos J. García-jiménez 《European journal of plant pathology / European Foundation for Plant Pathology》2004,110(8):801-809
Acremonium
cucurbitacearum is a soil-borne pathogen that causes collapse of muskmelon and watermelon plants. Cluster analysis based on RAPD patterns, obtained from use of 25 primers, divided isolates of A. cucurbitacearum from Spain and USA into two major groups. Most isolates from the USA fell into group 1, however, genetic similarity was not highly correlated with geographical origins or with previously established VCG groups. Analysis of 5.8S-ITS sequences showed very little sequence variation among isolates of A. cucurbitacearum, most had identical 5.8S-ITS sequence. Nodulisporium melonis, previously reported to cause a similar disease in Japan, had a 5.8S-ITS sequence that was identical to that of isolate A-419 proposed as the type strain of A
cremonium
cucurbitacearum suggesting that the two fungal pathogens should be considered a single species. Phylogenetic analysis, based on the 5.8S-ITS region, indicated that A
cremonium
cucurbitacearum is a monophyletic taxon more closely related to Plectosphaerella cucumerina than to other species of the genus Acremonium. Based on the 5.8S-ITS nucleotide sequence, a polymerase chain reaction was designed and used for specific detection of A. cucurbitacearum in diseased plants. 相似文献
17.
Phialophora gregata f. sp. adzukicola, a causal agent of brown stem rot in adzuki beans, produces phytotoxic compounds: gregatins A, B, C, D, and E. Gregatins
A, C, and D cause wilting and vascular browning in adzuki beans, which resemble the disease symptoms. Thus, gregatins are
considered to be involved in pathogenicity. However, molecular analyses have not been conducted, and little is known about
other pathogenic factors. We sought to isolate nonpathogenic and gregatin-deficient mutants through Agrobacterium tumefaciens-mediated transformation (ATMT) for cloning of pathogenicity-related genes. The co-cultivation of P. gregata and A. tumefaciens for 48 h at 20°C with 200 μM acetosyringone resulted in approximately 80 transformants per 106 conidia. The presence of acetosyringone in the A. tumefaciens pre-cultivation period led to an increase in T-DNA copy number per genome. Of 420 and 110 transformants tested for their
pathogenicity and productivity of gregatins, one nonpathogenic and three gregatin-deficient mutants were obtained, respectively.
The nonpathogenic mutant produced gregatins, whereas the gregatin-deficient mutants had pathogenicity comparable to the wild-type
strain. This is the first report of ATMT of P. gregata. Further analysis of these mutants will help reveal the nature of the pathogenicity of this fungus including the role of
gregatin in pathogenesis. 相似文献
18.
Mara Quaglia Antonio Zazzerini 《European journal of plant pathology / European Foundation for Plant Pathology》2007,118(4):393-400
Diaporthe helianthi the causal agent of sunflower (Helianthus annuus) stem canker, causes significant reductions in yield and oil content in most sunflower-growing areas. With the aim of enhancing
host resistance, we selected in vitro sunflower calli against culture filtrates of two pathogen isolates (7/96 and 101/96).
This technique may be an effective and rapid tool to discriminate the most virulent D. helianthi isolate and to screen for host resistance in the early stage of a breeding programme. Further investigation on the mechanisms
involved in defence pathways showed no induction of salicylic acid and pathogenesis-related proteins in calli, indicating
that the host resistance is not associated with Systemic Acquired Resistance but probably other biochemical mechanisms. 相似文献
19.
E. F. Boys S. E. Roques A. M. Ashby N. Evans A. O. Latunde-Dada J. E. Thomas J. S. West B. D. L. Fitt 《European journal of plant pathology / European Foundation for Plant Pathology》2007,118(4):307-321
Light leaf spot (Pyrenopeziza brassicae) is an important disease on winter oilseed rape crops (Brassica napus) in northern Europe. In regions where economically damaging epidemics occur, resistance to P. brassicae in commercial cultivars is generally insufficient to control the disease without the use of fungicides. Two major genes for
resistance have been identified in seedling experiments, which may operate by decreasing colonisation of B. napus leaf tissues and P. brassicae sporulation. Much of the resistance present in current commercial cultivars is thought to be minor gene-mediated and, in
crops, disease escape and tolerance also operate. The subtle strategy of the pathogen means that early colonisation of host
tissues is asymptomatic, so a range of techniques and molecular tools is required to investigate mechanisms of resistance.
Whilst resistance of new cultivars needs to be assessed in field experiments where they are exposed to populations of P. brassicae under natural conditions, such experiments provide little insight into components of resistance. Genetic components are best
assessed in controlled environment experiments with single spore (genetically fixed) P. brassicae isolates. Data for cultivars used in the UK Recommended List trials over several seasons demonstrate how the efficacy of
cultivar resistance can be reduced when they are deployed on a widespread scale. There is a need to improve understanding
of the components of resistance to P. brassicae to guide the development of breeding and deployment strategies for sustainable management of resistance to P. brassicae in Europe. 相似文献
20.
Norio KONDO Yuki KOBAYASHI Futoshi SAKUMA Shohei FUJITA Kippei MURATA 《Journal of General Plant Pathology》2002,68(4):284-291
The distribution of two races (1 and 2) of Phialophora gregata f. sp. adzukicola, the causal agent of brown stem rot of adzuki bean, was examined using a total of 483 isolates obtained from 39 fields in
19 locations on Hokkaido, Japan between 1997 and 1999. Race 1 was predominant (416 isolates or 86.1%) in the commercial fields
tested. Race 2 was found in 25 fields (64.1%), including two fields of cultivar Kita-no-otome (resistant to race 1, but susceptible
to race 2), indicating that race 2 was widely distributed in most of the production areas in Hokkaido. Using amplified fragment
length polymorphisms (AFLP), a total of 67 polymorphic AFLP markers was recorded among 72 representative isolates (37 and
35 isolates of races 1 and 2, respectively), and 57 distinct haplotypes were detected. Cluster analysis revealed no close
correlation between races and AFLP groups. Thus, no difference was observed between values of gene diversity in each race
(0.253 and 0.284 in races 1 and 2, respectively), and the coefficient of gene differentiation was very low (G
ST
=0.015). Gene differentiation between both races by analysis of molecular variance was not significantly different from zero
(Φ=−0.001; p=0.403). However, the results of gene differentiation among regional populations (G
ST
=0.290, Φ=0.292; p<0.001) are not necessarily consistent with the result that isolates from the same district were generally not tightly clustered.
Received 15 April 2002/ Accepted in revised form 6 September 2002 相似文献