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1.
A study was performed in order to assess the presence of Xylella fastidiosa in imported ornamental plants, among them Olea europaea, Coffea arabica and Nerium oleander. Positive results were only obtained from C. arabica, where 15 plant samples tested positive for X. fastidiosa by PCR, nine from Costa Rica and six from Honduras. Transmission electron microscopy observations indicated that rod‐shaped bacterial cells exhibiting the characteristics of X. fastidiosa cells were present in the xylem vessels of leaf petioles obtained from the infected C. arabica plants. Diversity of X. fastidiosa in C. arabica plants was assessed through a multilocus sequence typing (MLST) analysis of seven housekeeping genes (leuA, petC, lacF, cysG, holC, nuoL and gltT) and compared with X. fastidiosa infecting different host plants worldwide. Based on this MLST analysis, the prevalence of different sequence types (STs) of X. fastidiosa in the C. arabica ornamental plants was demonstrated and related to different X. fastidiosa subspecies, underlining the risk of introducing additional genetic diversity for X. fastidiosa to Europe. ST53, related to X. fastidiosa subsp. pauca, was frequently found in these C. arabica samples. A second ST related to X. fastidiosa subsp. pauca, ST73, has been assessed in coinfection with ST53 in one individual plant. Additionally, ST72 and ST76, related to X. fastidiosa subsp. fastidiosa, have been recorded. Next to these previously described STs, a novel ST, namely ST77 has been revealed, related to X. fastidiosa subsp. fastidiosa. Isolation of X. fastidiosa from leaf petioles and midribs of infected C. arabica plants was successfully performed only after the application of an additional ultrasonication step during the extraction procedure. Based on this approach, a number of X. fastidiosa isolates were obtained and further characterized.  相似文献   

2.
Xylella fastidiosa (Xf) is a gram-negative bacterial plant pathogen that can infect over 500 plant species. While it is endemic in America, X. fastidiosa subsp. pauca was reported for the first time in Europe in 2013 on olive trees in southern Italy. The availability of fast, sensitive, and reliable diagnostic tools is indispensable for managing current and future outbreaks of Xf. In this paper, we use the OXford Nanopore Technologies (ONT) MinION platform for detecting and identifying Xf at species, subspecies, and sequence type (ST) level. Two workflows were developed: the first one provided a “shotgun” strategy, that is, exploring the possibility of detecting Xf within DNA extracted from plant samples. This allowed detection of Xf by direct DNA sequencing and identifying the subspecies only in samples with high bacterial levels. Nanopore amplicon sequencing was pursued as a second workflow. This consists of PCR amplification of a set of seven multilocus sequence typing (MLST) fragments, officially adopted for identifying Xf at type strain level, followed by Nanopore-sequencing of the amplicons and an ad hoc pipeline to generate MLST consensus calls. This combined approach, which takes only a few hours, allowed the detection and identification of Xf at ST level in plant material with low bacterial infection.  相似文献   

3.
An innovative inoculation process, involving the drilling of a trunk hole in 3 year-old olive trees and injecting a dense conidial suspension of Verticillium dahliae, was developed to study differentiation in foliar symptom expression between olive cultivars tolerant or susceptible to the pathogen. It was demonstrated that V. dahliae conidia could be translocated and colonize the xylem at the same distance above and below the point of trunk injection in both cultivars. However, the pathogen could be subsequently isolated at statistically significant percentages in susceptible cv. Amphissis compared to the tolerant cv. Kalamon, indicating operation of resistance mechanisms in the vascular phase of the disease. Consequently symptom development in the susceptible cultivar was at least sixfold more intensive compared to the tolerant cultivar, 6–11 months after trunk inoculation. Perennial olive orchard experiments, aimed at selecting Verticillium-resistant root-stocks, were conducted by applying the novel method in 2–3 year-old root-stock suckers of Amphissis olive trees and in the tolerant cvs Lianolia of Corfu and Koroneiki. It was indicated that potentially resistant root-stocks could be obtained following the trunk drilling technique. Resistance differentiation between cvs Amphissis and Kalamon was further verified through root inoculation by various V. dahliae microsclerotial concentrations and demonstrated that the trunk drilling inoculation procedure is equally efficient in resistance evaluation of olives to Verticillium wilt. The trunk inoculation procedure could be useful in selecting and screening root-stocks for resistance to V. dahliae and other vascular pathogens and could elucidate resistance mechanisms in woody plants against vascular wilt diseases.  相似文献   

4.
Xylella fastidiosa is a phytopathogenic bacterium that causes disease in many different crops worldwide. In Brazil, X. fastidiosa subsp. pauca causes citrus variegated chlorosis (CVC), which is a disease responsible for economic losses in the citrus agribusiness. Variable host responses to bacterial colonization and disease development have been observed. This work studies the colonization processes of a pathogenic GFP‐labelled X. fastidiosa citrus strain in sweet orange (susceptible) and tangor (resistant) parents and two resulting hybrids that exhibited contrasting responses to CVC. Xylella fastidiosa showed increased populations and movement in the susceptible genotypes, but slower compared to other hosts such as grapevine. Scanning electron microscopy revealed that the predominant pitted stem morphology in citrus makes the bacterial movement difficult. In susceptible genotypes X. fastidiosa can move from the primary to the secondary xylem, whilst it is confined to the primary xylem in resistant plants. Associated with this is an induction of lignification that occurs earlier in the resistant genotypes when in the presence of the pathogen, and represents a genetic mechanism that leads to formation of a physical barrier, impairing bacterial colonization.  相似文献   

5.
Xylella fastidiosa is a plant pathogenic bacterium emerging in Europe. In France its emergence has been demonstrated through interceptions of contaminated coffee plants and, in 2015, by a survey of natural settings. The first French focus of contamination was detected in 2015 in Corsica; since then, almost 300 foci have been found and nearly 30 plant species have been declared contaminated, with Polygala myrtifolia remaining the principal host, suffering from severe leaf scorch. This study reports on the diversity of X. fastidiosa identified in France in 2015. Multilocus sequence analysis/typing revealed the presence of mainly X. fastidiosa subsp. multiplex sequence types (STs) ST6 and ST7. A focus of X. fastidiosa subsp. pauca ST53 was identified in mainland France; one sample contaminated by X. fastidiosa subsp. sandyi ST76, one novel recombinant, and coinfections of different isolates in individual samples were also identified, but could not be confirmed by successive samplings, indicating limited or transient contamination. Koch's postulates were fulfilled for two isolates of X. fastidiosa subsp. multiplex on P. myrtifolia, one being ST6 and the other ST7. Comparative genomics of the genome sequences of three French isolates (one ST6 and two ST7) with available sequences revealed that, unlike the American Dixon strain, the French ST6 and ST7 strains are devoid of a plasmid encoding a complete type IV secretion system. Other differences regarding phage sequences were highlighted. Altogether, the results suggest that the emergence of X. fastidiosa in France is linked to several introduction events of diverse strains from different subspecies.  相似文献   

6.
The quick decline syndrome of olive (OQDS) is a disease that appeared all of a sudden some years ago in a restricted area near the city of Gallipoli (Ionian coast of the Salento peninsula, southern-east Italy) and began spreading through the heavily olive-grown countryside of lower Salento. Xylella fastidiosa, a quarantine pathogen of American origin previously undetected in the European Union territory, except for two unconfirmed records from Kosovo and Turkey, proved to be consistently associated with symptomatic trees. X. fastidiosa is a Gram-negative bacterium that invades and multiplies in the xylem vessels of infected hosts, from which it is acquired by xylem-feeding insect vectors (belonging to Auchenorrhyncha, including cicadellids sharpshooter leafhoppers group, Cicadellidae, Cicadellinae), and aphrophorids (cercopids and spittlebugs, Cercopidae) and transferred to other plants. The Salentian strain of X. fastidiosa, denoted CoDiRO, was obtained in axenic culture. Its genome, a DNA molecule ca. 2.5 million base-pairs in size, was sequenced and identified as a genotype of X. fastidiosa subsp. pauca molecularly identical to an isolate of the same subspecies from Costa Rica. In nature, strain CoDiRO infects a number of woody and shrubby hosts but not grapevines and citrus and is mainly transmitted by Philaenus spumarius (meadow spittlebug), a froghopper quite common in the Salento area where it thrives primarily on olive. Since OQDS eradication and sanitation of infected olives are unfeasible, strategies have been envisaged for restraining the spread of the pathogen and its vector within the boundaries of the currently infected zone.  相似文献   

7.
Resistance of 23 important olive cultivars to Verticillium dahliae has been evaluated in four experiments under controlled conditions. Nine-month-old nursery olive plants were inoculated with a cotton non-defoliating (ND) (V4) or a cotton defoliating (D) (V117) isolate of V. dahliae. Resistance was evaluated by assessing symptom severity using a 0–4 rating scale and estimating the area under disease progress curves. The percentage of plants killed and of those which recovered from the disease were used as additional parameters for including a particular cultivar into a defined category. Most of the evaluated cultivars were susceptible, although at different levels, to both isolates of V. dahliae. All cultivars were more susceptible to the D pathotype than to the ND one. A group of 11 cultivars, including several important Spanish cultivars, were susceptible or extremely susceptible to both pathotypes of V. dahliae. A second group showed differences of resistance depending on the pathotype used. They were susceptible or extremely susceptible to the D pathotype but resistant or moderately susceptible to the ND one. Finally, 'Frantoio', 'Oblonga' and 'Empeltre' were moderately susceptible to the D isolate of V. dahliae and resistant to the ND one. The resistance of 'Empeltre' was evident by the plant ability to recover from infection with either isolates. 'Empeltre' is considered to be a valuable cultivar for inclusion in breeding programmes for resistance to Verticillium wilt.  相似文献   

8.
Pierce's disease (PD) of grapevine is caused by the bacterium Xylella fastidiosa. In this study, an integrated approach was applied to assess PD susceptibility among different Vitis vinifera cultivars that incorporated disease severity, bacterial pathogen abundance and loss of stem xylem hydraulic conductivity. It was hypothesized that levels of PD susceptibility in V. vinifera can be attributed in part to the host anatomical features that are shaped by its pedigree background. Two popular wine grape cultivars were initially selected from the occidentalis group, Merlot and Cabernet Sauvignon, and one from the orientalis group, Thompson Seedless. The more recently bred table grape cultivar Scarlet Royal, that has mixed pedigree parentage, was also included. PD susceptibility was compared to the known PD resistant b43-17 V. arizonica/candicans wild grape species from North America. The data indicated that Thompson Seedless was ranked as the most susceptible to PD because it significantly exhibited the most severe disease symptoms at 12 weeks post-inoculation and hosted the highest X. fastidiosa titre of the cultivars, and lost over 90% of its stem hydraulic conductivity. In contrast, the other three cultivars displayed less susceptibility to PD. The way in which the xylem anatomy could impact PD susceptibility in V. vinifera cultivars is discussed, together with how grape pedigrees and their cognate centre of domestication may have influenced xylem anatomical features. This work provides a reference framework to further test the hypothesis that V. vinifera cultivars with wide xylem vessels may be more prone to PD decline.  相似文献   

9.
Verticillium wilt of olive (VWO) is probably the most devastating fungal disease for olive trees worldwide, and currently the main cultivars are susceptible or moderately susceptible to this disease. The evaluation of resistant cultivars as rootstocks to control the disease has scarcely been explored, and mainly in short-term studies under controlled conditions, which usually do not correspond with field evaluations. The main objective of this study was to assess the responses to VWO of different scion × rootstock combinations of the olive cultivars Picual, Arbequina, Changlot Real, and Frantoio in a long-term field experiment with a soil highly infested with the defoliating pathotype of Verticillium dahliae. The results showed that grafting the susceptible cultivar Picual onto resistant rootstocks delayed the onset of the disease symptoms; however, after 4 years, it was observed that all combinations that contain Picual (a) were extensively colonized by V. dahliae; (b) developed severe symptoms of the disease; and (c) had plant mortality similar to Picual growing on its own roots. This result highlights the importance of long-term field experiments to evaluate VWO and shows that grafting susceptible olive cultivars onto resistant ones does not provide a durable control of VWO under high inoculum potential, as V. dahliae is able to progress through the resistant rootstock and then extensively colonize and kill the susceptible scion. However, the high inoculum potential observed in this study does not allow us to consider the evaluated resistant cultivars as completely ineffective under lower inoculum densities.  相似文献   

10.
Olive knot disease caused by Pseudomonas syringae subsp. savastanoi is widespread all over Greece where olive is grown and its severity varies from heavy in some areas and cultivars to very mild in others. Hypertrophied enlargements (galls or knots) more or less spherical in shape and up to 2.5 cm in diameter develop mostly on shoots, twigs, branches and trunks. Fruit infection, as roughly circular brown spots of 0.5-2.5 mm in diameter, is another form of disease which develops during wet summers. All olive cultivars are equally susceptible to the pathogen. However, the differences in disease distribution and severity observed between cultivars and areas are directly related to the degree of wounding from whatever cause (frost, hailstorm, harvesting injuries), especially when they are accompanied by rainy and wet weather or moist winds. Harvesting by beating the trees with sticks is an important epidemiological factor for disease incidence in Greece. Suggested control measures are summarized.  相似文献   

11.
Mango wilt, caused by Ceratocystis fimbriata, is one of the most important diseases affecting mango yields in Brazil. Information regarding the infection process of C. fimbriata in the stem tissues of mango from different cultivars and the basis of host resistance to the pathogen is rare in the literature. Thus, the objective of the study was to investigate how infection by two isolates of C. fimbriata can be affected by mango cultivar‐specific mechanisms of resistance. Disease progress on the inoculated stem tissues of the mango cultivars was evaluated and stem sections were obtained from the site of inoculation and prepared for histopathological observations using light microscopy. The factors mango cultivars and C. fimbriata isolates and their interaction were significant for all measures of disease development. Plants from the cultivars Espada, Haden and Palmer inoculated with isolates of C. fimbriata were more susceptible, whereas plants from the cultivars Tommy and Ubá were moderately resistant and resistant, respectively. Histopathologically, fungal isolates apparently massively colonized the stem tissues of plants from the susceptible cultivars Espada, Haden and Palmer, starting from the collenchyma and moving in the direction of the cortical parenchyma, xylem vessels and pith parenchyma. By contrast, on stem tissues of plants from the resistant cultivars Tommy Atkins and Ubá, most of the cells reacted to C. fimbriata infection by accumulating amorphous material. The results from the present study strongly indicated the importance of phenolic compounds for mango cultivar resistance against infection by Brazilian C. fimbriata isolates.  相似文献   

12.
Anatomical modifications of xylem and phloem tissues of grapevine (Vitis vinifera) stems of shoots infected by the flavescence dorée phytoplasma (FDp) were first observed and described in the 1960s, but never quantified in detail. In this paper, we describe and quantify the impact of FDp on grapevine stem tissues, and relate it to the level of expression of symptoms and to cultivar-specific FDp susceptibility. For this purpose, we measured and quantified the anatomical parameters of xylem and phloem tissues of a tolerant (Merlot) and a susceptible (Chardonnay) cultivar. For each cultivar, thin sections of eight shoots with symptoms from FDp-infected grapevines, eight symptomless shoots from the same FDp-infected grapevines, and eight symptomless shoots from symptomless grapevines (control) were compared. Results showed general inhibition of xylem growth and proliferation of phloem tissues (hyperplasia) with lack or irregular arrangement of the fibre-sclereids in the axial phloem of the stems from shoots with symptoms, irrespective of the cultivar. Xylem vessels of infected Merlot shoots were partly occluded by tyloses and a higher number of smaller vessels were produced than in control plants. Thus, the anatomical responses confirmed the detrimental effect of FDp on stems of infected grapevine shoots, including impaired stem development and lack of periderm formation. Statistically significant differences were found between the two cultivars with different levels of susceptibility to FDp infection.  相似文献   

13.
In the present study, we evaluated the susceptibility of different commercial olive cultivars to verticillium wilt. Two Verticillium dahliae isolates, obtained from olive and artichoke, were used in pathogenicity tests. Two-year-old rooted cuttings were inoculated using either the root-dip or the stem-wounding method. The results were similar with both inoculation methods. Cvs Carolea and Cipressino proved to be moderately susceptible whereas Cassanese, Nocellara del Belice, Nocellara Etnea, Tonda Iblea and Uovo di Piccione were very susceptible. The response of cv. Coratina varied from susceptibility to moderate susceptibility.  相似文献   

14.
Infection by Spongospora subterranea of roots of two potato (Solanum tuberosum) cultivars, either very resistant or very susceptible to powdery scab on their tubers, was studied in a glasshouse experiment. Plants grown in sand/nutrient solution culture were inoculated with S. subterranea sporosori 2 weeks after planting. Plant parameters, the intensity of zoosporangium infection in roots, numbers of Spongospora root galls and amounts of Spongospora DNA in roots, measured using quantitative PCR (qPCR), were assessed at sequential harvests. Inoculation with S. subterranea reduced water use (56 days after planting) by 26% in the tuber resistant cultivar compared with uninoculated plants, and by 60% in the susceptible cultivar. Inoculation did not affect growth of the resistant cultivar, nor shoot mass of the susceptible cultivar, but caused a 38% reduction in root mass of the susceptible cultivar. The intensities of zoosporangium development in both cultivars were similar. The susceptible cultivar had approximately four times more Spongospora root galls g?1 root mass than the resistant cultivar. Quantitative PCR detected S. subterranea DNA in roots 1 week after inoculation, and indicated a twofold greater amount of pathogen DNA in roots of the susceptible than the resistant cultivar. This study suggests that the S. subterranea zoosporangium stage in host roots is affected differently by host resistance factors than the sporosorus (root gall and tuber scab) stages. The study has also demonstrated the usefulness of qPCR for sensitive and consistent detection of S. subterranea across the duration of potato root infection.  相似文献   

15.
A. C. PAPPAS 《EPPO Bulletin》1993,23(3):405-409
Mycocentrospora cladosporioides has been recorded as present and widely distributed on olive fruits and leaves in Greece since 1972. The fungus frequently appears on the lower surface of the older leaves, growing like a dark olivaceous mould. The disease, known as cercosporiosis, sometimes causes severe defoliation. Green and mature olives are occasionally attacked. The severity of fruit infection seems to be related to mild humid weather in the 3 months prior to harvest. Diseased fruits show superficial slightly sunken irregular dry spots often covered by the characteristic fructifications of the fungus. Infection of artificially inoculated detached olives starts with the appearance of slow-growing brown lesions surrounding the lenticels. Cultivars producing large fruits for table use (e.g. Conservolia) are more susceptible. The fungus grows very slowly in culture and forms only a few conidia. Epidemiology and control have been little studied. Copper-based fungicides used for olive scab control are not always effective against cercosporiosis.  相似文献   

16.
Twenty tomato (Solanum lycopersicon) cultivars were screened for resistance against bacterial spot disease incited byXanthomonas axonopodis pv.vesicatoria under field conditions with and without pathogen infection. Screening was done by artificially inoculating aX. axonopodis pv.vesicatoria suspension to 4-week-old tomato seedlings and observing them for typical symptoms of the disease. Seedlings were categorized into highly resistant, resistant, susceptible and highly susceptible cultivars on the basis of disease incidence. Tomato cultivars were screened for defense-related enzymes, total phenols and lignin contents. The temporal patterns of all these enzymes were estimated with a moderately susceptible tomato cultivar. Native PAGE analysis of both peroxidase (POX) and polyphenol oxidase (PPO) was carried out for the time course of enzyme activities and also by selecting three different tomato cultivars, following infection with the pathogen. Based on the inducible amounts of these enzymes upon pathogen infection, the tomato cultivars were correlated with the disease incidence under field conditions. A significant (P≤0.05) correlation was observed between the degree of host resistance and the enzyme levels. In highly resistant tomato cultivars the enzyme levels, total phenols and lignin contents were increased in comparison with highly susceptible tomato cultivars. Isoform analysis of POX and PPO enzymes indicated a clear difference between resistant and susceptible tomato cultivars in the number of isoforms and also in the intensity of each isoform in the presence of pathogen infection. The possible regulation of defense-related enzymes in imparting host resistance is discussed. http://www.phytoparasitica.org posting March 11, 2008.  相似文献   

17.
Initial experiment on the reactions of five Japanese cultivars of cucumber toColletotrichum orbiculare infection in the greenhouse revealed that cv Suyo and Gibai were susceptible and moderately susceptible, respectively, while cv Shogoin fushinari and Sagami hanjiro were resistant to infection byC. orbiculare; cv Ochiai fushinari was moderately resistant. The ability of 16 plant growth promoting fungi (some isolates belonged to species ofPhoma and some non-sporulating isolates) isolated from zoysiagrass rhizospheres to induce systemic resistance in the above five cucumber cultivars was tested by growing plants in potting medium infested with barley grain inocula of PGPF in the greenhouse. The second true leaves of 21-day-old plants were challenge inoculated withC. orbiculare and disease assessed. Nine, out of 16 isolates, caused significant reduction of disease caused byC. orbiculare in at least two cultivars.Phoma isolates (GS8-1 and GS8-2) and non-sporulating isolates (GU21-2, GU23-3, and GU24-3) significantly reduced the disease in all the five cultivars. The disease suppression in cucumber was due to the induction of systemic resistance, since the inducer(s) and the pathogen were separated spatially and that the inducer did not colonize aerial portions. The resistance induced by certain isolates in a susceptible cultivar was less than that in a resistant cultivar. Disease suppression caused by isolate GU21-2 was similar to theC. orbiculare induced control in certain cultivars. The average rate of expansion of lesion diameter on leaves due toC. orbiculare was slower due to induction with the selected plant growth promoting fungi compared to the uninduced control plants. Roots of four cultivars were colonized by only three isolates, however, roots of one cultivar (Suyo) was colonized by five isolates suggesting the cultivar-specific root colonization ability.Abbreviations cv cultivar(s) - PGPF plant growth promoting fungal isolates - PGPR plant growth promoting rhizobacteria  相似文献   

18.
Verticillium wilt is the most serious olive disease in the Mediterranean countries and worldwide. The most effective control strategy is the use of resistant cultivars. However, limited information is available about the level and source of resistance in most of the olive cultivars and there are no published data using microsclerotia, the resting structures of Verticillium dahliae, as the infective inoculum. In the present study, we correlated symptomatology and the presence of the fungus along with the DNA relative amount (molecules μl−1) of a defoliating (D) and a non-defoliating (ND) V. dahliae strain in the susceptible cv. Amfissis and the tolerant cvs Kalamon and Koroneiki, as quantified by the Real-Time QPCR technology. The viability of the pathogen in the plant tissues was confirmed by isolating the fungus on PDA plates, while symptom assessment proved the correlation between the DNA relative amount of V. dahliae in plant tissues and cultivar susceptibility. It was further demonstrated that the D and ND strains were present at a significantly higher level in cv. Amfissis than in cvs Kalamon and Koroneiki. It was finally observed that the relative amount of the pathogen in roots was lower than in stems and shoots and declined in plant tissues over time. These data constitute a valuable contribution in evaluating resistance of olive cultivars or olive root-stocks to V. dahliae pathotypes.  相似文献   

19.
After the first confirmed outbreak of Xylella fastidiosa in the European Union (EU), associated with an olive disease denoted olive quick decline syndrome, mandatory surveys are now carried out in the member States and inspections increased at EU entry points such as ports. Such activities led to the interception of X. fastidiosa-infected coffee plants in consignments originating from Central America. Similarly, the geographic expansion of the olive decline epidemic area of the Apulia region (southern Italy) prompted investigations to identify new host plants. Here we report the interception of three novel bacterial sequence types in Italy, based on multi-locus sequence typing, that cluster with different X. fastidiosa subspecies, illustrating the risk of the introduction of additional pathogen genetic diversity into Europe. In the epidemic area of Apulia, new foci as well as host plant species positive with X. fastidiosa, including cherry, myrtleleaf and rosemary, were found to be all infected with the same sequence type of this bacterium (ST53, or CoDiRO strain). This work highlights the limited knowledge of X. fastidiosa phylogenetic and phenotypic diversity, the risk of novel X. fastidiosa introductions via contaminated plant material, and corroborates other studies indicating that the Apulia epidemic emerged from a single introduction of this pathogen into the region.  相似文献   

20.
Colletotrichum lagenarium is the casual agent of anthracnose disease of melons. Light and scanning electron microscopy were used to observe the infection process of C. lagenarium on the leaves of two melon cultivars differing in susceptibility. On both cultivars conidia began germinating 12 h after inoculation (hai), forming appressoria directly or at the tips of germ-tubes. By 48 hai appressoria had melanised and direct penetration of host tissue had begun. On the susceptible cultivar, infection vesicles formed within 72 hai and developed thick, knotted primary hyphae within epidermal cells. By 96 hai C. lagenarium produced highly branched secondary hyphae that invaded underlying mesophyll cells. After 96 hai, light brown lesions appeared on the leaves, coincident with cell necrosis and invasion by secondary hyphae. While appressoria formed more quickly on the resistant cultivar, fewer germinated to develop biotrophic primary or invasive necrotrophic secondary hyphae than on the susceptible cultivar. These results confirm that C. lagenarium is a hemibiotrophic pathogen, and that resistance in melons restricts colonisation by inhibiting the development of necrotrophic secondary hyphae.  相似文献   

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