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1.
Although the causal agent of black root rot of Cucurbitaceae in Japan has been proposed as Phomopsis sclerotioides, the species identification of the pathogen has remained inconclusive because of a lack of spore formation. We confirmed that a Japanese isolate of Phomopsis sp. obtained from a diseased pumpkin root produced pycnidia containing α spores in sterilized bean pods. In phylogenetic analyses of rDNA-ITS regions, nine Japanese Phomopsis sp. isolates from melon, watermelon grafted onto bottle gourd, and pumpkin diagnosed with black root rot, formed a single clade with P. sclerotioides standard isolates. We identified the causal agent of the black root rot of melon, pumpkin, bottle gourd, and watermelon in Japan as P. sclerotioides and propose the Japanese name “Phomopsis-negusare-byo” for the disease. Patterns of random amplified polymorphic DNA (RAPD) of these Japanese isolates were also similar to those of P. sclerotioides, thus supporting the species identification. However, mycelial incompatibilities were found for many combinations among these P. sclerotioides isolates, suggesting some genotypic variations of this fungus in Japan at a level that the RAPD analyses cannot discriminate. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession numbers AB201430 to AB201444  相似文献   

2.
Plant–fungal specificity between cucurbitaceous crops and Diaporthe sclerotioides, the causal agent of black root rot, was studied using cucumbers (Cucumis sativa), melons (Cucumis melo), pumpkins (Cucurbita maxima), watermelons (Citrullus lanatus) and bottlegourd (Lagenaria siceraria var. gourda). Twelve D. sclerotioides isolates from these cucurbit species were cross‐inoculated. The virulence of the isolates was evaluated as the area under the disease progress curve (AUDPC). All cucurbit species were susceptible to each isolate, but AUDPCs were significantly different among the hosts, with the order of greatest to least being melon, cucumber, watermelon, bottlegourd and finally, pumpkin. The infectiveness of isolates was assessed as the quantity of D. sclerotioides DNA detected in the hypocotyls of seedlings 2 weeks after inoculation using a real‐time PCR protocol. The fungal DNA quantities varied among the species in the same order as the AUDPCs. Whilst there were statistically significant correlations between the virulence and infectiveness of D. sclerotioides isolates in cucumbers, melons and bottlegourds, their coefficients of determination were not high (r2 < 0·6). Orthogonal contrasts indicated no specificity in either the fungal virulence or infectiveness between D. sclerotioides isolates and the cucurbit hosts from which these isolates originated. Thus, although the degree of host susceptibility to D. sclerotioides varies among cucurbit species, the absence of specificity to the host species in either virulence or infectiveness suggests the pathogen may spread via various cucurbit crops, irrespective of their original host species.  相似文献   

3.
Ochradenus baccatus is a widely distributed shrub in desert regions of the Middle East and North Africa. This plant's nematicidal activity against the root‐knot nematode Meloidogyne javanica was evaluated because it has been found to contain exceptionally high levels of glucosinolates. In in vitro assays with aqueous extracts of the plant, 100% of second‐stage juveniles were immobilized after exposure to 4% root‐core extract for 48 h; 8% root‐core extract suppressed their hatching by 87%, whereas stem, flower and root bark showed lower activity. Incorporation of root core or bark into the soil, as fresh or dry powder at 1 and 0·5% (w/w), respectively, reduced the number of nematodes recovered from the soil by 95–100%, whereas the flower and stem were much less effective. Results from further pot experiments indicated that only the root bark consistently contains nematicidal compounds which are effective in soil, whereas the nematicidal activity of the root core in soil was inconsistent. The presence of non‐volatile lipophilic and lipophobic nematicidal compounds in the root bark was suggested by extraction with different polar solvents, but these compounds do not seem to be isothiocyanates – glucosinolate‐hydrolysed compounds with nematicidal activity. Very poor host status of Ochradenus baccatus to M. javanica, M. incognita and M. hapla, but with root‐penetration rates of juveniles similar to those in tomato roots, suggest that this plant may be used as a cover plant or trap plant to reduce nematode populations in the soil.  相似文献   

4.
The host suitability of commercial Vitis rootstocks commonly used in Spain (161‐49C, 41B, 1103P, 110R, 140Ru and SO4) to root‐knot nematodes (Meloidogyne arenaria, M. incognita, M. javanica) and Xiphinema index, and damage caused by nematode infection were determined under controlled conditions. The three root‐knot nematodes reproduced with a rate higher than one in all rootstocks, indicating that they are suitable hosts for these nematodes. Growth of rootstocks infected with the root‐knot nematodes was less vigorous than that of nematode‐uninfected controls in the majority of the rootstocks studied. Root infection resulted in moderate to severe root galling in all rootstocks. The shoot and main stem diameters appeared to be the most sensitive variables of damage caused by infection by Meloidogyne spp., with reduction rates from 36% and 53% in 161‐49C to 57% and 66% in 140Ru, respectively. The shoot height was not significantly affected by the root‐knot nematodes and the root fresh weight generally increased as a consequence of intensive galling. The nematode X. index caused significant root damage with a reproduction factor higher than one in all rootstocks. However, reproduction factor was significantly influenced by the rootstock and significantly decreased by about 12‐fold (5·7 to 18·1‐fold) with the increase in inoculum density from 100 to 1000 nematodes per plant. The root dry weight was reduced by X. index infections, and was the plant growth variable most affected by the nematode infection in all rootstocks at both inoculum densities. Meloidogyne arenaria, M. incognita, M. javanica and X. index, prevalent in many world vineyards, are all shown to have a damaging effect on the six tested rootstocks.  相似文献   

5.
BACKGROUND: Fluensulfone, a new nematicide of the fluoroalkenyl group, has proved to be very effective in controlling root‐knot nematodes, Meloidogyne spp., by soil application. The systemic activity of this compound against M. incognita on peppers via soil drenching and foliar spray was evaluated. RESULTS: Root application of fluensulfone via soil drenching showed slight and no nematode control activity when applied 4 and 10 days, respectively, after inoculation. A single foliar spray of peppers with a fluensulfone solution at 3.0 g L?1 prior to inoculation reduced the galling index by 80% and the number of nematode eggs by 73–82% of controls. The reduction in these parameters by fluensulfone was much higher than that obtained with oxamyl or fenamiphos at the same concentration. This activity was also observed when the plants were sprayed 21 days before inoculation. A series of experiments suggested that foliar spray with fluensulfone prior to inoculation reduces nematode invasion. However, foliar spray after inoculation did not inhibit nematode development inside roots. CONCLUSION: Fluensulfone showed relatively high nematode control activity when sprayed on the foliage before inoculation. Fluensulfone may be used as a foliar application, in addition to soil application, for root‐knot nematode control. Copyright © 2011 Society of Chemical Industry  相似文献   

6.
Bacterial soft rot is a globally significant plant disease that causes major losses in the production of many popular crops, such as potato. Little is known about the dispersal and ecology of soft‐rot enterobacteria, and few animals have been identified as vectors for these pathogens. This study investigates whether soil‐living and bacterial‐feeding nematodes could act as vectors for the dispersal of soft‐rot enterobacteria to plants. Soft‐rot enterobacteria associated with nematodes were quantified and visualized through bacterial enumeration, GFP‐tagging, and confocal and electron scanning microscopy. Soft‐rot enterobacteria were able to withstand nematode grazing, colonize the gut of Caenorhabditis elegans and subsequently disperse to plant material while remaining virulent. Two nematode species were also isolated from a rotten potato sample obtained from a potato storage facility in Finland. Furthermore, one of these isolates (Pristionchus sp. FIN‐1) was shown to be able to disperse soft‐rot enterobacteria to plant material. The interaction of nematodes and soft‐rot enterobacteria seems to be more mutualistic rather than pathogenic, but more research is needed to explain how soft‐rot enterobacteria remain viable inside nematodes.  相似文献   

7.
The suitability of watermelon cultivars and cucurbit rootstocks as hosts to Meloidogyne incognita and M. javanica was determined in pot and field experiments. Meloidogyne incognita showed higher reproduction than did M. javanica on watermelon and cucurbit rootstocks. The watermelon cultivars did not differ in host status when challenged with these two species and supported lower nematode reproduction than the cucurbit rootstocks. Rootstocks Lagenaria siceraria cv. Pelops and Cucurbita pepo AK15 supported lower reproduction than did the squash hybrid rootstocks (C. maxima × C. moschata). Egg production increased (P < 0·05) with a rising initial inoculum level (Pi) in the non‐grafted Sugar Baby but the reproduction factor Rf (eggs per plant/Pi) was similar at two Pi levels. The total egg production in the plants grafted onto squash hybrids RS841 and Titan was greater (P < 0·05) at the higher Pi, but the Rf values were lower. The development of field‐grown non‐grafted watermelon plants was significantly stunted in plots where nematodes were detected at planting. However, no differences were observed in plots with grafted plants. In plots with nematodes, non‐grafted and Titan‐grafted plants had similar yields that were higher than that of RS841‐grafted plants. In the commercial plastic houses with grafted watermelon, the average Rf value was 42‐fold, confirming the high susceptibility of squash hybrids as rootstocks for grafted watermelon. The Titan–Sugar Baby combination was tolerant to M. javanica.  相似文献   

8.
Accessions of Gossypium spp., some of them never previously tested, were evaluated for resistance to a local isolate of Meloidogyne incognita race 3 in greenhouse experiments. Nematode infection was characterized based on the galling and egg mass indexes and the reproduction factors (RF). Root‐knot nematode reproduction among the newly tested accessions varied from highly susceptible (AS0188, AS0189) to moderately resistant (MT123 no. 3), and some accessions showed highly reduced nematode reproduction (CIR1343, CIR1348, Fai Mui). Histological observations of two resistant accessions (G. barbadense CIR1348 and G. hirsutum TX‐25, respectively) showed that resistance occurs through a two‐stage mechanism in the first accession and through a single‐stage mechanism in the second. Parasitism is blocked early after second‐stage juvenile (J2) penetration or during its initial tissue migration (CIR1348) and the development of later‐stage juveniles into female adults is suppressed at a later stage (TX‐25 and CIR1348). Fluorescence and bright light microscopy showed that root cells surrounding nematodes exhibit a hypersensitivity‐like reaction, with the accumulation of presumably phenolic compounds and the presence of necrotic cells that limit the development of nematodes and the formation of giant cells. Underdeveloped giant cells with degenerated cytoplasmic content were found in small numbers in CIR1348 and in large numbers in TX‐25, along with deformed nematodes. The full characterization of the defence mechanisms of novel sources of resistance to the root‐knot nematode in cotton constitutes a first step towards their use in crop improvement.  相似文献   

9.
Abstract

In a survey of plant parasitic nematodes associated with or affecting rice throughout Nigeria, some important nematode pests, especially the white tip disease nematode, Aphelenchoides besseyi and the rice root nematodes Hirschmanniella spinicaudata and H. oryzae were identified from seed, soil and root samples from swamp rice fields respectively. The sugarcane cyst nematode, Heterodera sacchari occurred in swamp rice fields only around the major sugarcane estates in Nigeria. The root‐knot Meloidogyne incognita and the root lesion nematode, Pratylenchus brachyurus were also encountered in upland (rainfed) rice fields. The white tip disease nematode, A. besseyi occurred at low levels in soils and rice seeds throughout the country. High population levels of H. spinicaudata and H. oryzae were encountered especially in areas where monoculture of rice is practised. General chlorosis, poor tillering and significantly reduced yield have been observed due to H. spinicaudata. Rice plants attacked by H. sacchari also showed intense chlorosis, delayed and reduced tillering and reduced grain yield. The roots of attacked plants were twiggy, very necrotic and blackened. The root‐knot M. incognita and the root lesion nematodes P. brachyurus have both been observed to reduce rice yields. Rice cultivars screened for reactions to the nematodes showed varying degrees of susceptibilities. Some varieties were however resistant to the root‐knot nematode, M. incognita.  相似文献   

10.
A molecular‐based assay was employed to analyse and accurately identify various root‐knot nematodes (Meloidogyne spp.) parasitizing potatoes (Solanum tuberosum) in South Africa. Using the intergenic region (IGS) and the 28S D2–D3 expansion segments within the ribosomal DNA (rDNA), together with the region between the cytochrome oxidase subunit II (COII) and the 16S rRNA gene of the mtDNA, 78 composite potato tubers collected from seven major potato growing provinces were analysed and all Meloidogyne species present were identified. During this study, M. incognita, M. arenaria, M. javanica, M. hapla, M. chitwoodi and M. enterolobii were identified. The three tropical species M. javanica, M. incognita and M. arenaria were identified as the most prevalent species, occurring in almost every region sampled. Meloidogyne hapla and M. enterolobii occurred in Mpumalanga and KwaZulu‐Natal, respectively, while M. chitwoodi was isolated from two growers located within the Free State. Results presented here form part of the first comprehensive surveillance study of root‐knot nematodes to be carried out on potatoes in South Africa using a molecular‐based approach. The three genes were able to distinguish various Meloidogyne populations from one another, providing a reliable and robust method for future use in diagnostics within the potato industry for these phytoparasites.  相似文献   

11.
Several studies were carried out to determine (i) thermal requirements for development, egg production and emergence of juveniles, and completion of the life cycle of Meloidogyne incognita and Meloidogyne javanica on cucumber, (ii) the maximum multiplication rate and the equilibrium density of root‐knot nematodes on cucumber and yield losses in pot and plastic greenhouse experiments, and (iii) the relationships between relative leaf chlorophyll content (RLCC) and relative cucumber dry top weight biomass (RDTWB) in relation to increasing nematode densities at planting (Pi) in pot experiments. Thermal requirements of M. incognita and M. javanica on cucumber did not differ, irrespective of the biological stage. In the pot experiments, M. javanica completed one generation. The maximum multiplication rate (a) was 833, and the equilibrium density (E) varied according to the effective inoculum densities. The relationship between RDTWB and Pi fitted the Seinhorst damage function model. The RLCC value at 40 or 50 days post‐inoculation also fitted the damage model and was related to RDTWB. In greenhouse experiments, conducted from 2009 to 2012, M. incognita completed three generations. The values for a and E were 1147 and 625 second stage juveniles (J2) per 250 cm3 soil, respectively. The tolerance limit was below zero, and the minimum relative yield ranged from 0·12 to 0·34.  相似文献   

12.
为筛选对南方根结线虫具有致死效果的生防细菌,从山东省10个县市蔬菜主产区番茄根际土壤中分离可培养细菌,采用离体杀线虫试验测定分离菌株对南方根结线虫Meloidogyne incognita的致死活性,结合生理生化特征及分子生物学方法对高效杀线虫菌株进行分类鉴定,同时对其杀线虫特性进行表征,并通过盆栽试验进一步验证其生防潜力。结果显示,从山东省蔬菜主产区番茄根际土中分离到1株高效杀线虫菌株AMCC 100218,结合生理生化试验与16S rRNA序列分析,鉴定此菌株为和田鞘氨醇杆菌Sphingobacterium hotanense;该菌株对南方根结线虫2龄幼虫的致死效果可达88.87%,其杀线虫活性物质具有较好的热稳定性和储存稳定性,且耐碱不耐酸;盆栽试验结果表明,该菌能够显著减少土壤中的虫口密度,降低番茄发病率。表明和田鞘氨醇杆菌AMCC 100218菌株是1株具有防治根结线虫病潜力的生防细菌。  相似文献   

13.
X. Wang  B. Xue  J. Dai  X. Qin  L. Liu  Y. Chi  J. T. Jones  H. Li 《Plant pathology》2018,67(6):1436-1448
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14.
The prevalence and diversity of plant parasitic nematodes in Northern Ireland cereal and grassland was determined from 191 agricultural fields. A total of 18 nematode genera were detected, including economically important pests, Meloidogyne spp., Heterodera spp. and Pratylenchus spp., each of which were above economic damage thresholds in a significant proportion of the sites (92.4%, 70% and 28.6%, respectively). The detection of the root knot nematode, Meloidogyne minor (6% prevalence), was significant given its recent emergence across the turf grass sector and the prospect of M. minor becoming a common agricultural pest. Analyses of nematode prevalence and abundance highlighted significant associations with grass and cereals, soil types, soil grade (proxy for soil quality) and rainfall levels. Specifically, nematode populations varied between the two major soils (brown earths and gleys), while significant trends for increased nematode diversity and greater prevalence of both Meloidogyne and Pratylenchus with increasing rainfall were also observed. Multivariate analyses were performed to determine interactive effects and the relative importance of the factors affecting nematode populations. Notably, rainfall, in combination with either crop type or soil grade, had a significant effect on nematode abundance and diversity. The findings suggest significant changes in nematode populations have occurred over the last several decades and the possibility that these are linked to changing climate and cropping practices are discussed, as well as future concerns for plant parasitic nematode management.  相似文献   

15.
We developed polymerase chain reaction (PCR) assays to detect and quantify Phomopsis sclerotioides, the causal agent of black root rot of cucurbits. We used internal transcribed spacers 1 and 2 of the ribosomal DNA (rDNA) from representative isolates to search for target sequences. Primer pairs were selected after testing against 40 fungal isolates including 13 Ph. sclerotioides isolates, 9 Phomopsis isolates other than Ph. sclerotioides, and 18 soilborne fungi that were either pathogenic or nonpathogenic to cucurbits. Conventional PCR assays with the primer pair of CPs-1 (forward) and CPs-2 (reverse) produced target DNA amplicons from all Ph. sclerotioides isolates but none of the other isolates tested. From soil and root samples collected from fields naturally infested with black root rot of cucumber and melon, the CPs-1/CPs-2 primer pair successfully amplified target DNA fragments in conventional PCR assays. Moreover, we applied the CPs-1/CPs-2 primer pair in a real-time PCR assay with SYBR Green I, and PCR-amplified products were successfully quantified by reference to a standard curve generated by adding known amounts of target DNA. Target Ph. sclerotioides DNA fragments were similarly detected in artificially inoculated roots of cucumber, melon, pumpkin, and watermelon, but quantities of Ph. sclerotioides DNA in their hypocotyls of the hosts varied as follows: melon ≥ cucumber ≥ watermelon > pumpkin. These results suggest that Ph. sclerotioides infection is not species-specific but the rate of infection may differ among host species.  相似文献   

16.
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   

17.
Root‐knot nematodes (RKNs), Meloidogyne spp., are a major disease problem in solanaceous crops worldwide, including pepper (Capsicum spp.). Genetic control provides an economically and environmentally sustainable protection alternative to soil fumigants. In pepper, resistance to the main RKN species (M. incognita, M. javanica and M. arenaria) is conferred by the major genes (R genes) Me1, Me3 and N. However, RKNs are able to develop virulence, thus endangering the efficiency of R genes. Quantitative resistance (QR) against Meloidogyne spp. is expected to provide an alternative to R genes, or to be combined with R genes, to increase the resistance efficiency and durability in pepper. In order to explore the ability of QR to protect pepper against RKNs, five pepper inbred lines, differing in their QR level, were tested directly, or after combination with the Me1 and Me3 genes, for their resistance to a panel of M. arenaria, M. javanica and M. incognita isolates. The M. arenaria and M. javanica isolates showed low pathogenicity to pepper, unlike the M. incognita isolates. The QR, controlled by the pepper genetic background, displayed a high resistance level with a broad spectrum of action, protecting pepper against Me3‐virulent as well as avirulent M. incognita isolates. The QR was also expressed when combined with the Me1 and Me3 genes, but presented additive genetic effects so that heterozygous F1 hybrids proved less resistant than homozygous inbred lines. The discovery of this QR is expected to provide promising applications for preserving the efficiency and durability of nematode resistance.  相似文献   

18.
The reproductive behaviour of the root‐knot nematode Meloidogyne arenaria race 1 was compared on two wild species of Arachis (A. duranensis and A. stenosperma) and cultivated peanut (A. hypogaea cv. IAC‐Tatu‐ST). The three species were considered moderately susceptible, resistant, and susceptible, respectively. Penetration and development of the root‐knot nematode in the resistant species was reduced in comparison with that occurring in susceptible plants. Several cell features, including dark blue cytoplasm and altered organelle structure were observed in the central cylinder of A. stenosperma, indicating a hypersensitive‐like response (HR) of infested host cells. Neither giant cells, nor nematodes developed beyond the second stage, were found on A. stenosperma. Arachis duranensis showed a delay in the development of nematodes in the roots compared to A. hypogaea. The two wild peanut species were chosen to be the contrasting parents of a segregating population for mapping and further investigation of resistance genes.  相似文献   

19.
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20.
Endophytic fungi, which stimulate a variety of defence reactions in host plants without causing visible disease symptoms, have been isolated from almost every plant. However, beneficial interactions between fungal endophytes and pathogens from the same habitat remain largely unknown. An inoculation of Atractylodes lancea plantlets with Gilmaniella sp. AL12 (AL12) prior to infection with Fusarium oxysporum prevented the necrotization of root tissues and plant growth retardation commonly associated with fusarium root rot. Quantification of F. oxysporum infections using real‐time PCR revealed a correlation between root rot symptoms and the relative amount of fungal DNA. Pretreatment with AL12 reduced the accumulation of reactive oxygen species stimulated by F. oxysporum. An in vitro analysis of their interactions under axenic culture conditions showed AL12 could inhibit F. oxysporum growth. Additionally, F. oxysporum infections were shown to decrease salicylic acid (SA) production compared with control plantlets. SA biosynthesis inhibitors, 2‐aminoindan‐2‐phosphonic acid and paclobutrazol, abolished the inhibition of F. oxysporum growth in A. lancea even after inoculation with AL12. The results indicated that the fungal endophyte protected A. lancea not only by direct antibiosis, but also by reversing the F. oxysporum‐mediated suppression of SA production.  相似文献   

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