Interactions Between Meloidogyne artiellia, the Cereal and Legume Root-Knot Nematode, and Fusarium oxysporum f. sp. ciceris Race 5 in Chickpea

ABSTRACT In the Mediterranean Basin, Fusarium oxysporum f. sp. ciceris and the root-knot nematode Meloidogyne artiellia coinfect chickpea. The influence of root infection (after inoculation with 20 nematode eggs and second-stage juveniles per gram of soil) by two M. artiellia populations, from Italy and Syria, on the reaction of chickpea lines and cultivars with partial resistance to Fusarium wilt (CA 252.10.1.OM, CA 255.2.5.0, CPS 1, and PV 61) and with complete resistance to F. oxysporum f. sp. ciceris race 5 (CA 334.20.4, CA 336.14.3.0, ICC 14216 K, and UC 27) was investigated under controlled conditions. In genotypes with partial resistance, infection by M. artiellia significantly increased the severity of Fusarium wilt, irrespective of the fungal inoculum density (3,000 or 30,000 chlamydospores per gram of soil), except in cultivar CPS 1 at the lower fungal inoculum density. In genotypes with complete resistance to Fusarium wilt, infection by M. artiellia overcame the resistance to F. oxysporum f. sp. ciceris race 5 in CA 334.20.4 and CA 336.14.3.0 but not in ICC 14216 K, irrespective of the fungal inoculum density, and overcame the resistance in UC 27 only at the higher inoculum density. Infection by the nematode significantly increased the number of propagules of F. oxysporum f. sp. ciceris race 5 in root tissues of genotypes with complete resistance to Fusarium wilt, compared with roots that were not inoculated with the nematode, irrespective of the fungal inoculum density, except in ICC 14216 K, in which this effect occurred only at the higher inoculum density. Reproduction of an M. artiellia population from Syria in the absence of F. oxysporum f. sp. ciceris race 5 was significantly higher than that of a population from Italy in all tested chick-pea genotypes except ICC 14216 K. However, there was no significant difference between the reproduction rates of the two nematode populations in plants infected with F. oxysporum f. sp. ciceris race 5, irrespective of the fungal inoculum density and the reaction of the genotypes to the fungus.     

In planta and soil quantification of Fusarium oxysporum f. sp. ciceris and evaluation of Fusarium wilt resistance in chickpea with a newly developed quantitative polymerase chain reaction assay

Fusarium wilt of chickpea caused by Fusarium oxysporum f. sp. ciceris can be managed by risk assessment and use of resistant cultivars. A reliable method for the detection and quantification of F. oxysporum f. sp. ciceris in soil and chickpea tissues would contribute much to implementation of those disease management strategies. In this study, we developed a real-time quantitative polymerase chain reaction (q-PCR) protocol that allows quantifying F. oxysporum f. sp. ciceris DNA down to 1 pg in soil, as well as in the plant root and stem. Use of the q-PCR protocol allowed quantifying as low as 45 colony forming units of F. oxysporum f. sp. ciceris per gram of dry soil from a field plot infested with several races of the pathogen. Moreover, the q-PCR protocol clearly differentiated susceptible from resistant chickpea reactions to the pathogen at 15 days after sowing in artificially infested soil, as well as the degree of virulence between two F. oxysporum f. sp. ciceris races. Also, the protocol detected early asymptomatic root infections and distinguished significant differences in the level of resistance of 12 chickpea cultivars that grew in that same field plot infested with several races of the pathogen. Use of this protocol for fast, reliable, and cost-effective quantification of F. oxysporum f. sp. ciceris in asymptomatic chickpea tissues at early stages of the infection process can be of great value for chickpea breeders and for epidemiological studies in growth chambers, greenhouses and field-scale plots.     

Interactions of Pratylenchus thornei and Fusarium oxysporum f. sp. ciceris on Chickpea

ABSTRACT Fusarium oxysporum f. sp. ciceris and the root-lesion nematode Pratylenchus thornei coinfect chickpeas in southern Spain. The influence of root infection by P. thornei on the reaction of Fusarium wilt-susceptible (CPS 1 and PV 61) and wilt-resistant (UC 27) chickpea cultivars to F. oxysporum f. sp. ciceris race 5 was investigated under controlled and field conditions. Severity of Fusarium wilt was not modified by coinfection of chickpeas by P. thornei and F. oxysporum f. sp. ciceris, in simultaneous or sequential inoculations with the pathogens. Root infection with five nematodes per cm(3) of soil and 5,000 chlamydospores per g of soil of the fungus resulted in significantly higher numbers of propagules of F. oxysporum f. sp. ciceris with the wilt-susceptible cultivar CPS 1, but not with the wilt-resistant one. However, infection with 10 nematodes per cm(3) of soil significantly increased root infection by F. oxysporum f. sp. ciceris in both cultivars, irrespective of fungal inoculum densities (250 to 2,000 chlamydospores per g of soil). Plant growth was significantly reduced by P. thornei infection on wilt-susceptible and wilt-resistant chickpeas in controlled and field conditions, except when shorter periods of incubation (45 days after inoculation) were used under controlled conditions. Severity of root necrosis was greater in wilt-susceptible and wilt-resistant cultivars when nematodes were present in the root, irrespective of length of incubation time (45 to 90 days), densities of nematodes (5 and 10 nematodes per cm(3) of soil), fungal inocula, and experimental conditions. Nematode reproduction on the wilt-susceptible cultivars, but not on the wilt-resistant one, was significantly increased by F. oxysporum f. sp. ciceris infections under controlled and field conditions.     

Development of a Specific Polymerase Chain Reaction-Based Assay for the Identification of Fusarium oxysporum f. sp. ciceris and Its Pathogenic Races 0, 1A, 5, and 6

ABSTRACT Specific primers and polymerase chain reaction (PCR) assays that identify Fusarium oxysporum f. sp. ciceris and each of the F. oxysporum f. sp. ciceris pathogenic races 0, 1A, 5, and 6 were developed. F. oxysporum f. sp. ciceris- and race-specific random amplified polymorphic DNA (RAPD) markers identified in a previous study were cloned and sequenced, and sequence characterized amplified region (SCAR) primers for specific PCR were developed. Each cloned RAPD marker was characterized by Southern hybridization analysis of Eco RI-digested genomic DNA of a subset of F. oxysporum f. sp. ciceris and nonpathogenic F. oxysporum isolates. All except two cloned RAPD markers consisted of DNA sequences that were found highly repetitive in the genome of all F. oxysporum f. sp. ciceris races. F. oxysporum f. sp. ciceris isolates representing eight reported races from a wide geographic range, nonpathogenic F. oxysporum isolates, isolates of F. oxysporum f. spp. lycopersici, melonis, niveum, phaseoli, and pisi, and isolates of 47 different Fusarium spp. were tested using the SCAR markers developed. The specific primer pairs amplified a single 1,503-bp product from all F. oxysporum f. sp. ciceris isolates; and single 900- and 1,000-bp products were selectively amplified from race 0 and race 6 isolates, respectively. The specificity of these amplifications was confirmed by hybridization analysis of the PCR products. A race 5-specific identification assay was developed using a touchdown-PCR procedure. A joint use of race 0- and race 6-specific SCAR primers in a single-PCR reaction together with a PCR assay using the race 6-specific primer pair correctly identified race 1A isolates for which no RAPD marker had been found previously. All the PCR assays described herein detected up to 0.1 ng of fungal genomic DNA. The specific SCAR primers and PCR assays developed in this study clearly identify and differentiate isolates of F. oxysporum f. sp. ciceris and of each of its pathogenic races 0, 1A, 5, and 6.     

Quantitative Modeling of the Effects of Temperature and Inoculum Density of Fusarium oxysporum f. sp. ciceris Races 0 and 5 on Development of Fusarium Wilt in Chickpea Cultivars

ABSTRACT Races 0 (Foc-0) and 5 (Foc-5) of Fusarium oxysporum f. sp. ciceris differ in virulence and induce yellowing or wilting syndrome, respectively, in chickpea. We modeled the combined effects of soil temperature and inoculum density of Foc-0 and Foc-5 on disease developed in chickpea cvs. P-2245 and PV-61 differing in susceptibility to those races, using quantitative nonlinear models. Disease development over time in the temperature range of 10 to 30 degrees C and inoculum densities between 6 and 8,000 chlamydospores g(1) of soil was described by the Weibull function. Four response variables (the reciprocal incubation period, the final disease intensity, the standardized area under the disease progress curve, and the intrinsic rate of disease development) characterized the disease development. Response surface models that expressed the combined effect of inoculum density and temperature were developed by substituting the intrinsic rate of disease development in the Weibull or exponential functions with a beta function describing the relationship of response variables to temperature. The models estimated 22 to 26 degrees C as the most favorable soil temperature for infection of cvs. P-2245 and PV-61 by Foc-5, and 24 to 28 degrees C for infection of cv. P-2245 by Foc-0. At 10 degrees C, no disease developed except in cv. P-2245 inoculated with Foc-5. At optimum soil temperature, maximum disease intensity developed with Foc-5 and Foc-0 at 6 and 50 chlamydospores g(1) of soil respectively, in cv. P-2245, and with Foc-5 at 1,000 chlamydospores g(1) of soil in cv. PV-61. The models were used to construct risk threshold charts that can be used to estimate the potential risk of Fusarium wilt epidemics in a geographical area based on soil temperature, the race and inoculum density in soil, and the level of susceptibility of the chickpea cultivar.     

Yield loss in chickpeas in relation to development of fusarium wilt epidemics

ABSTRACT Development of 108 epidemics of Fusarium wilt of chickpea caused by Fusarium oxysporum f. sp. ciceris were studied on cvs. P-2245 and PV-61 in field microplots artificially infested with races 0 and 5 of F. oxysporum f. sp. ciceris in 1986 to 1989. Disease progression data were fitted to the Richards model using nonlinear regression. The shape parameter was influenced primarily by date of sowing and, to a lesser extent, by chick-pea cultivars and races of F. oxysporum f. sp. ciceris. Fusarium wilt reduced chickpea yield by decreasing both seed yield and seed weight. These effects were related to sowing date, chickpea cultivar, and virulence of the prevalent F. oxysporum f. sp. ciceris race. Regression models were developed to relate chickpea yield to Fusarium wilt disease intensity with the following independent variables: time to initial symptoms (t(is)), time to inflection point (t(ip)) of the disease intensity index (DII) progress curve, final DII (DII(final)), standardized area under DII progress curve (SAUDPC), and the Richards weighted mean absolute rate of disease progression (rho). Irrespective of the chickpea cultivar x pathogen race combination, the absolute and relative seed yields decreased primarily by delayed sowing. The relative seed yield increased with the delay in t(is) and t(ip) and decreased with increasing DII(final), SAUDPC, and rho. A response surface as developed in which seed yield loss decreased in a linear relationship with the delay in t(is) and increased exponentially with the increase of rho.     

Integrated management of fusarium wilt of chickpea with sowing date, host resistance, and biological control

ABSTRACT A 3-year experiment was conducted in field microplots infested with Fusarium oxysporum f. sp. ciceris race 5 at Córdoba, Spain, in order to assess efficacy of an integrated management strategy for Fusarium wilt of chickpea that combined the choice of sowing date, use of partially resistant chickpea genotypes, and seed and soil treatments with biocontrol agents Bacillus megaterium RGAF 51, B. subtilis GB03, nonpathogenic F. oxysporum Fo 90105, and Pseudomonas fluorescens RG 26. Advancing the sowing date from early spring to winter significantly delayed disease onset, reduced the final disease intensity (amount of disease in a microplot that combines disease incidence and severity, expressed as a percentage of the maximum possible amount of disease in that microplot), and increased chickpea seed yield. A significant linear relationship was found between disease development over time and weather variables at the experimental site, with epidemics developing earlier and faster as mean temperature increased and accumulated rainfall decreased. Under conditions highly conducive for Fusarium wilt development, the degree of disease control depended primarily on choice of sowing date, and to a lesser extent on level of resistance of chickpea genotypes to F. oxysporum f. sp. ciceris race 5, and the biocontrol treatments. The main effects of sowing date, partially resistant genotypes, and biocontrol agents were a reduction in the rate of epidemic development over time, a reduction of disease intensity, and an increase in chickpea seedling emergence, respectively. Chickpea seed yield was influenced by all three factors in the study. The increase in chickpea seed yield was the most consistent effect of the biocontrol agents. However, that effect was primarily influenced by sowing date, which also determined disease development. Effectiveness of biocontrol treatments in disease management was lowest in January sowings, which were least favorable for Fusarium wilt. Sowing in February, which was moderately favorable for wilt development, resulted in the greatest increase in seed yield by the biocontrol agents. In March sowings, which were most conducive for the disease, the biocontrol agents delayed disease onset and increased seedling emergence. B. subtilis GB03 and P. fluorescens RG 26, applied either alone or each in combination with nonpathogenic F. oxysporum Fo 90105, were the most effective treatments at suppressing Fusarium wilt, or delaying disease onset and increasing seed yield, respectively. The importance of integrating existing control practices, partially effective by themselves, with other control measures to achieve appropriate management of Fusarium wilt and increase of seed yield in chickpea in Mediterranean-type environments is demonstrated by the results of this study.     

Sporulation of Fusarium oxysporum f. sp. lycopersici on Stem Surfaces of Tomato Plants and Aerial Dissemination of Inoculum

ABSTRACT Plants exhibiting symptoms of wilt and xylem discoloration typical of Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici were observed in greenhouses of cherry tomatoes at various sites in Israel. However, the lower stems of some of these plants were covered with a pink layer of macroconidia of F. oxysporum. This sign resembles the sporulating layer on stems of tomato plants infected with F. oxysporum f. sp. radicis-lycopersici, which causes the crown and root rot disease. Monoconidial isolates of F. oxysporum from diseased plants were assigned to vegetative compatibility group 0030 of F. oxysporum f. sp. lycopersici and identified as belonging to race 1 of F. oxysporum f. sp. lycopersici. The possibility of coinfection with F. oxysporum f. sp. lycopersici and F. oxysporum f. sp. radicis-lycopersici was excluded by testing several macroconidia from each plant. Airborne propagules of F. oxysporum f. sp. lycopersici were trapped on selective medium in greenhouses in which plants with a sporulating layer had been growing. Sporulation on stems was reproduced by inoculating tomato plants with races 1 and 2 of F. oxysporum f. sp. lycopersici. This phenomenon has not been reported previously with F. oxysporum f. sp. lycopersici and might be connected to specific environmental conditions, e.g., high humidity. The sporulation of F. oxysporum f. sp. lycopersici on plant stems and the resultant aerial dissemination of macroconidia may have serious epidemiological consequences. Sanitation of the greenhouse structure, as part of a holistic disease management approach, is necessary to ensure effective disease control.     

Genetic diversity in Fusarium oxysporum f.sp. dianthi and Fusarium redolens f.sp. dianthi

Pathogenic isolates were selected representing all known vegetative compatibility groups (VCGs) and races of Fusarium oxysporum sensu lato from Dianthus spp. On basis of differences in the internal transcribed spacer region of the ribosomal DNA, six VCGs were classified as F. oxysporum f.sp. dianthi and four as F. redolens f.sp. dianthi. All VCGs of F. oxysporum f.sp. dianthi were characterized by unique restriction fragment length polymorphisms (RFLPs), unique overall esterase profiles, and unique virulence spectra, supporting a clonal lineage concept. Two VCGs of F. oxysporum f.sp. dianthi nevertheless comprised more than one race, but races within the same VCG shared the same distinct overall virulence spectrum. VCGs belonging to F. redolens f.sp. dianthi also had unique RFLPs and unique virulence spectra, but had grossly identical esterase profiles. Three new races (9, 10 and 11) are described for F. oxysporum f.sp. dianthi, and four for F. redolens f.sp. dianthi. Two races previously considered lost were recovered; race 7 was identified as a member of VCG 0021 of F. oxysporum f.sp. dianthi while race 3 was identified as a distinct VCG and race of F. redolens f.sp. dianthi. A summary of races and VCGs in F. oxysporum f.sp. dianthi and F. redolens f.sp. dianthi is presented.     

Plant defence reactions against fusarium wilt in chickpea induced by incompatible race 0 of Fusarium oxysporum f.sp. ciceris and nonhost isolates of F. oxysporum

Germinated seeds of 'kabuli' chickpea cv. ICCV 4 were inoculated with a conidial suspension of the incompatible race 0 of Fusarium oxysporum f.sp. ciceris (Foc) or of nonhost F. oxysporum resistance 'inducers', and 3 days later were challenged by root dip with a conidial suspension of highly virulent Foc race 5. Prior inoculation with inducers delayed the onset of symptoms and/or significantly reduced the final amount of fusarium wilt caused by race 5. However, the extent of disease suppression varied with the nature of the inducing agent; the nonhost isolates of F. oxysporum were more effective at disease suppression than the incompatible Foc race 0. Inoculation with the inducers gave rise to synthesis of maackiain and medicarpin phytoalexins in inoculated seedlings; these did not accumulate in plant tissues but were released into the inoculum suspension. Inoculation with inducers also resulted in accumulation of chitinase, β-1,3-glucanase and peroxidase activities in plant roots. These defence-related responses were induced more consistently and intensely by nonhost isolates of F. oxysporum than by incompatible Foc race 0. The phytoalexins and, to a lesser extent, the antifungal hydrolases, were also induced after challenge inoculation with Foc race 5. However, in this case the defence responses were induced in both preinduced and noninduced plants infected by the pathogen. It is concluded that the suppression of fusarium wilt in this study possibly involved an inhibitory effect on the pathogen of preinduced plant defences, rather than an increase in the expression of defence mechanisms of preinduced plants following a subsequent challenge inoculation.     

Gene genealogies support Fusarium oxysporum f. sp. ciceris as a monophyletic group

Fusarium oxysporum f. sp. ciceris (Foc), the causal agent of fusarium wilt of chickpea, consists of two pathotypes (yellowing and wilting) and eight races (races 0, 1B/C, 1A and 2–6) of diverse geographical distribution. Six Foc isolates, one each of races 0, 1B/C, 1A, 4, 5 and 6, representing the two pathotypes and the geographical range of the pathogen, showed identical sequences in introns of the genes for translation elongation factor 1α ( EF1 α), β-tubulin, histone 3, actin and calmodulin. Eleven additional Foc isolates representative of all races, pathotypes and geographical range, and three isolates of F. oxysporum (Fo) nonpathogenic to chickpea were further analysed for sequence variation in the EF1 α gene. All isolates pathogenic to chickpeas shared an identical EF1 α gene sequence, which differed from that shared by the three Fo isolates nonpathogenic to chickpea. EF1 α gene sequences from the 17 Foc isolates and the three Fo isolates were compared with 24 EF1 α gene sequences in GenBank from isolates of 11 formae speciales of F. oxysporum by parsimony analysis. Foc isolates formed a grouping distinct from other formae speciales and nonpathogenic isolates. These results indicate that F. oxysporum f. sp. ciceris is monophyletic.     

Influence of Temperature and Inoculum Density of Fusarium oxysporum f. sp. ciceris on Suppression of Fusarium Wilt of Chickpea by Rhizosphere Bacteria

The effects of temperature and inoculum density of Fusarium oxysporum f. sp. ciceris race 5 on suppression of Fusarium wilt in chickpea (Cicer arietinum) cv. PV 61 by seed and soil treatments with rhizobacteria isolated from the chickpea rhizosphere were studied in a model system. Disease development over a range of temperatures (20, 25, and 30 degrees C) and inoculum densities (25 to 1,000 chlamydospores per gram of soil) was described by the Gompertz model. The Gompertz relative rate of disease progress and final amount of disease increased exponentially and monomolecularly, respectively, with increasing inoculum densities. Disease development was greater at 25 degrees C compared with 20 and 30 degrees C. At 20 and 30 degrees C, disease development was greater at 250 to 1,000 chlamydospores per gram of soil compared with 25 to 100 chlamydospores per gram of soil. At 25 degrees C, increasing inoculum densities of the pathogen did not influence disease. Nineteen Bacillus, Paenibacillus, Pseudomonas, and Stenotrophomonas spp. out of 23 bacterial isolates tested inhibited F. oxysporum f. sp. ciceris in vitro. Pseudomonas fluorescens RGAF 19 and RG 26, which did not inhibit the pathogen, showed the greatest Fusarium wilt suppression. Disease was suppressed only at 20 or 30 degrees C and at inoculum densities below 250 chlamydospores per gram of soil. Bacterial treatments increased the time to initial symptoms, reduced the Gompertz relative rate of disease progress, and reduced the overall amount of disease developed.     

Physiological Specialization of Fusarium oxysporum f. sp. lactucae, a Causal Organism of Fusarium Root Rot of Crisp Head Lettuce in Japan

In 1995, Fusarium root rot of crisp head lettuce, caused by Fusarium oxysporum f. sp. lactucae, was simultaneously found in the Shiojiri and Kawakami areas of Nagano Prefecture, Japan. The Shiojiri and Kawakami isolates differed in pathogenicity to lettuce cultivars. Because of this distinct physiological specialization, these Shiojiri and Kawakami isolates should be designated as race 1 and race 2, respectively, using lines VP1010 (highly resistant to race 1), VP1013 (highly resistant to race 2) and variety Patriot (highly susceptible to both races) as differential varieties. This is the first report of races of Fusarium oxysporum f. sp. lactucae, Received 21 September 2000/ Accepted in revised form 21 March 2001     

Detection of Fusarium oxysporum f. sp. dianthi in Carnation Tissue by PCR Amplification of Transposon Insertions

ABSTRACT Strains of the carnation wilt pathogen, Fusarium oxysporum f. sp. dianthi, can be distinguished by DNA fingerprint patterns, using the fungal transposable elements Fot1 and impala as probes for Southern hybridization. The DNA fingerprints correspond to three groups of F. oxysporum f. sp. dianthi strains: the first group includes isolates of races 1 and 8; the second group includes isolates of races 2, 5 and 6; and the third group includes isolates of race 4. Genomic DNAs flanking race-associated insertion sites of Fot1 (from races 1, 2, and 8) or impala (from race 4) were amplified by the inverse polymerase chain reaction (PCR) technique. These regions were cloned and sequenced, and three sets of primers overlapping the 3' or 5' end of the transposon and its genomic insertion were designed. Using fungal genomic DNA as template in PCR experiments, primer pairs generated amplification products of 295, 564 and 1,315 bp, corresponding to races 1 and 8; races 2, 5, and 6; and race 4, respectively. When multiplex PCR was performed with genomic DNA belonging to races 1 and 8, 2, or 4, single amplimers were generated, allowing clear race determination of the isolate tested. PCR was successfully performed on DNA extracted from susceptible carnation cv. Indios infected with isolates representative of races 1, 2, 4, and 8.     

Influence of temperature on plant–rhizobacteria interactions related to biocontrol potential for suppression of fusarium wilt of chickpea

Seed and soil treatment with Pseudomonas fluorescens RGAF 19, P. fluorescens RG 26, Bacillus megaterium RGAF 51 and Paenibacillus macerans RGAF 101 can suppress fusarium wilt of chickpea ( Cicer arietinum ), but the extent of disease suppression by these rhizobacteria is modulated by soil temperature. In this work, the effect of temperature on plant–rhizobacteria interactions was assessed in relation to biocontrol potential for suppression of fusarium wilt of chickpea. Seed and soil treatment with those rhizobacteria delayed seedling emergence compared with nontreated controls, and either increased or had no deleterious effect on chickpea growth. Pseudomonas fluorescens isolates significantly increased chickpea shoot dry weight at 20°C and root dry weight at 25 and 30°C. All bacterial isolates colonized the chickpea rhizosphere and internal stem tissues at 20, 25 and 30°C, and there was a positive linear trend between bacterial population size in the rhizosphere and temperature increase. The maximum inhibition of mycelial growth and conidial germination of Fusarium oxysporum f. sp. ciceris race 5 in vitro occurred at a temperature range optimal for bacterial growth and production of inhibitory metabolites. These results demonstrate the need to understand the effects of environmental factors on the biological activities of introduced rhizobacteria of significant importance for plant disease suppression.     

A New Root-Knot Nematode, Meloidogyne baetica n. sp. (Nematoda: Heteroderidae), Parasitizing Wild Olive in Southern Spain

ABSTRACT High infection rates of wild olive (Olea europaea sp. sylvestris) feeder roots and soil infestation by a new root-knot nematode were found in sandy soil at Vejer de la Frontera (Cádiz), southern Spain. Morphometric traits and analyses of the nematode esterase electrophoretic pattern as well as of the internal transcribed spacer 1 (ITS1)-5.8S gene and D2-D3 fragment of the 28S gene of rDNA showed that specimens differed clearly from known root-knot nematodes. Studies of host-parasite relationships showed a typical susceptible reaction in naturally infected wild olive plants and in olive planting stocks (cvs. Arbequina and Picual) artificially inoculated with the nematode. However, the nematode did not reproduce in artificially inoculated chickpea, pea, and tomato. Because of the ability of this new nematode to infect wild and cultivated olives only, we suggest the common name, "Mediterranean olive root-knot nematode." The species is herein described and illustrated, and named as Meloidogyne baetica n. sp. The new root-knot nematode can be distinguished from other Meloidogyne spp. by (i) the perineal pattern, which is almost similar to that of M. artiellia, characterized by distinct inner striae forming two distinct longitudinal bands, extending throughout the perineum to just below the vulva; (ii) female excretory pore anterior to the level of stylet knobs, excretory pore distance from anterior end/length of stylet ratio extremely small (0.5 to 0.8); and (iii) second-stage juveniles with elongate-conoid tail. Phylogenetic trees derived from maximum parsimony analyses showed that M. baetica is closely related to M. artiellia, the cereal and legume root-knot nematode.     

The occurrence of a new genetic variant of Fusarium oxysporum f.sp. pisi

During a survey of root diseases of pea in Denmark, a new genetic variant of Fusarium oxysporum f.sp. pisi was isolated from vining peas in two widely separated geographical regions. In terms of pathogenicity on a set of differential pea lines, the Danish isolated closely resembled a race 6 isolate from the United States, DNA extracts of the isolates, restricted with the endonuclease Hind III, then probed with a homologous repetitive genomic fragment from the plasmid pDG106 by the Southern hybridization technique, gave a unique'fingerprint'pattern distinctly different from the American race 6 and all other known races. When probed with pDG312, containing a homologous ribosomal repeat unit, the pattern obtained for the Danish isolates was indistinguishable from races 1, 5 and 6 but distinctly different from 2A and 2B. The Danish isolates represent a separate vegetative compatibility group because they are compatible with each other but incompatible with the other known races. In pigmentation the new variant resembled races 1, 5 and 6 for the first 8-12 days, after which it began to secrete a dark purple pigment resembling that of race 2A and 2B. Until an additional line in the host differentials can separate the new genetic variant it should be considered a subgroup of F. oxysporum f. sp. pisi race 6.     

Vascular colonization patterns in susceptible and resistant tomato cultivars inoculated with Fusarium oxysporum f.sp. lycopersici races 0 and 1

The vascular colonization pattern of Fusarium oxysporum f.sp. lycopersici races 0 and 1 in tomato was studied in five susceptible and five resistant cultivar–fungus combinations during a 26-day period after inoculation by root immersion. Propagules spread discontinuously along the stems in all five cultivars 1 day after inoculation, irrespective of cultivar resistance. Five days later the fungus was limited to the stem bases in all cultivars. Between the fifth and 12th days, stem colonization by the fungus stopped in all cultivar–race combinations. Thereafter, the situation remained stable in resistant combinations, with inoculum distributed discontinuously, and no disease symptoms were apparent. By contrast, in the susceptible combinations a gradual upward colonization of the stems was seen such that fungal distribution was no longer discontinuous and disease symptoms appeared. These results suggest that a fungal 'incubation' period in the base of the vascular system is required before a secondary invasion of tissues occurs in susceptible genotypes. The slope of the regression line fitted between the height reached by the fungus up the stem ( y ) and the time after inoculation ( x ) provides a measure of the horizontal (polygenic) resistance in tomato cultivars     

农杆菌介导的西瓜枯萎病菌遗传转化

为获得带GFP标记的西瓜枯萎病菌转化株,用于后期观察病原菌侵染过程,采用农杆菌介导的方法,对西瓜枯萎病菌1号生理小种进行了遗传转化。结果表明:共培养时间为36h,枯萎病菌孢子和农杆菌AGL1比例为1∶1时该菌株的遗传转化效率最高,可以达到117.33个转化子/107个孢子。转化株的孢子、菌丝体及萌发的孢子均能发出稳定而强的绿色荧光。转化株的致病力检测显示其致病力与转化前的野生菌株致病力无明显差异。结果表明本研究获得的带GFP标记的西瓜枯萎病菌转化株可用于观察病菌在西瓜根系的侵染过程。     

Differences in Feeding Sites Induced by Root-Knot Nematodes, Meloidogyne spp., in Chickpea

ABSTRACT Root-knot nematodes (Meloidogyne spp.) are sedentary, obligate endoparasites in plants, where they induce specialized feeding sites. The feeding sites act as strong metabolic sinks to which photosynthates are mobilized. The histopathological modifications in the nematode-induced feeding sites of artificially inoculated chickpea cv. UC 27 were qualitatively and quantitatively compared using five isolates of M. artiellia and one isolate each of M. arenaria, M. incognita, and M. javanica. All Meloidogyne isolates infected chickpea plants, but root gall thickening was significantly less for M. artiellia isolates than for the other Meloidogyne species. Nevertheless, neither the number of giant cells in the feeding site (averaging four to six) nor the area of individual giant cells was influenced by nematode species or isolate. However, the number of nuclei per giant cell was significantly smaller, and the maximum diameters of nuclei and nucleoli were significantly greater, in giant cells induced by M. artiellia isolates than in those induced by M. arenaria, M. incognita, or M. javanica. In a second experiment, M. artiellia-induced giant cells in faba bean and rapeseed also contained a small number of large nuclei.