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1.
Moniliophthora perniciosa is the causal agent of witches’ broom in Theobroma cacao (cacao). Three biotypes of M. perniciosa are recognized, differing in host specificity, with two causing symptoms on cacao or Solanaceae species (C‐ and S‐biotypes), and the third found growing endophytically on lianas (L‐biotype). The objectives of this study were to clarify the genetic relationship between the three biotypes, and to identify those regions in the Brazilian Amazon with the greatest genetic diversity for the C‐biotype. Phylogenetic reconstruction based on the rRNA ITS regions showed that the C‐ and S‐biotypes formed a well‐supported clade separated from the L‐biotype. Analysis of 131 isolates genotyped at 11 microsatellite loci found that S‐ and especially L‐biotypes showed a higher genetic diversity. A significant spatial genetic structure was detected for the C‐biotype populations in Amazonia for up to 137 km, suggesting ‘isolation by distance’ mode of dispersal. However, in regions containing extensive cacao plantings, C‐biotype populations were essentially ‘clonal’, as evidenced by high frequency of repeated multilocus genotypes. Among the Amazonian C‐biotype populations, Acre and West Amazon displayed the largest genotypic diversity and might be part of the centre of diversity of the fungus. The pathogen dispersal may have followed the direction of river flow downstream from Acre, Rondônia and West Amazon eastward to the rest of the Amazon valley, where cacao is not endemic. The Bahia population exhibited the lowest genotypic diversity, but high allele richness, suggesting multiple invasions, with origin assigned to Rondônia and West Amazon, possibly through isolates from the Lower Amazon population.  相似文献   

2.
The development of the basidiomycete Moniliophthora perniciosa in resistant and susceptible Theobroma cacao genotypes was analysed. The infection process leading to broom formation in shoot apexes was characterized by studying the kinetics of basidiospore germination, mode of penetration and colonization of the pathogen. Both resistant and susceptible cacao genotypes were inoculated with M. perniciosa and kept in the greenhouse for 90 days, explants were collected, treated for histological studies and meristematic tissues were observed by electron and light microscopy. Variation in the kinetics of germination between the cacao genotypes was detected 4 h after inoculation. The fungal penetration occurred through the star‐shaped trichome base, natural openings on the cuticular surface and stomata. Host responses between genotypes were found to be different. Compared with non‐infected plants, the swelling of all the stem tissues was evident at 60 days after inoculation. In the susceptible genotype, typical symptoms developed and fungal colonization was more intense than in resistant genotypes, which showed little or no fungal colonization. The investigations reported herein provide an important step in understanding the pattern of pre‐ and post‐penetration events of M. perniciosa in cacao genotypes with different levels of resistance to this disease.  相似文献   

3.
Crinipellis perniciosa causes a serious disease of cacao known as witches broom (WB). Heritable resistance to witches broom has been used in cacao improvement programs. SCA6 and SCA12 are highly resistant and are the most commonly used parents in the breeding schemes. However, SCA hybrids are not resistant to witches broom in all production areas. Presumably, different populations of C. perniciosa cause these variable responses. Amplified fragment length polymorphism (AFLP) markers were used to assess variation and population structure in this pathogen. We examined 40 isolates of C. perniciosa and one isolate of Melanotus subcuneiformis. Nine of 64 primer pairs produced consistent and informative DNA amplification, and were used to screen all isolates. Fifteen haplotypes (AFLP fingerprints) were detected with 186 polymorphic markers. Cluster analysis grouped isolates of the C biotype (pathogenic on cacao) from Bolivia, Brazil, Ecuador and Trinidad together in a major cluster that was distinct from isolates of the S biotype (pathogenic on solanaceous hosts) and M. subcuneiformis. Isolates of the C biotype were divided further into well supported, country-specific groups. Segregation of AFLP alleles was not observed among basidiospore isolates from the same basidiome, broom, tree or field, supporting previous reports that the fungus did not outcross. The results corroborated prior conclusions that C. perniciosa was probably introduced into the Bahia state of Brazil from the Amazon basin. Representative isolates from the genetically distinct groups that were revealed will be used to examine pathogenic specialization in C. perniciosa and differential responses that have been reported in SCA6-derived germplasm.  相似文献   

4.
Moniliophthora perniciosa, causal agent of witches’ broom disease in cacao plantations in South America and the Caribbean Islands, has co‐evolved with its host cacao, but the pathogen has also emerged in many solanaceous hosts in Brazil, including economically important food crops and wild species. This study was carried out to: (i) determine the existence of host subpopulations of M. perniciosa in Brazil; (ii) estimate gene and genotypic diversity of M. perniciosa host subpopulations infecting solanaceous hosts in southeastern Bahia and Minas Gerais states, Brazil; and (iii) estimate the amount and directionality of historical migration of M. perniciosa subpopulations. Up to 203 M. perniciosa isolates collected from solanaceous hosts with symptoms from Bahia and Minas Gerais states in Brazil and from Theobroma spp. (cacao) and Herrania spp. were characterized with 11 microsatellite markers. Factorial correspondence analyses, minimum‐spanning network and Bayesian clustering revealed genetic clusters associated with their host of origin. Significant subpopulation differentiation was evident (ΦST = 0.30, P ≤ 0.05) among M. perniciosa host subpopulations. Most of the multilocus microsatellite genotypes (MLMGs) were host‐specific, with few MLMGs shared among subpopulations. Pairwise comparisons among M. perniciosa host subpopulations were significant, except between jurubeba (Solanum paniculatum) and cultivated solanaceous subpopulations. The combined analyses rejected the null hypothesis that M. perniciosa in Brazil is a single genetic population not structured by host. These findings support a scenario of introduction and subsequent adaptation to solanaceous hosts that should be taken into consideration to improve mitigation and management of M. perniciosa.  相似文献   

5.
Xie W  Wang S  Wu Q  Feng Y  Pan H  Jiao X  Zhou L  Yang X  Fu W  Teng H  Xu B  Zhang Y 《Pest management science》2011,67(1):87-93
BACKGROUND: The polyphagous B‐biotype Bemisia tabaci (Gennadius) has developed a high resistance to commonly used insecticides in China. To illustrate the induced changes by host plant, bioassay and biochemical research on five different host populations were investigated. RESULTS: Except for bifenthrin, all tested insecticides showed lower toxicity to the B. tabaci poinsettia population compared with other host populations. Moreover, four insecticides, the exceptions being abamectin and fipronil, showed highest toxicity towards the tomato population. The LC50 values of the poinsettia population, particularly towards acetamiprid, were 14.8‐, 10.3‐ and 7.29‐fold higher than those of tomato, cucumber and cabbage respectively. The CarE activities of B. tabaci cabbage and cucumber populations were all significantly higher than those of poinsettia, cotton and tomato populations. The ratio of the cabbage population was 1.97‐, 1.79‐ and 1.30‐fold higher than that of poinsettia, cotton and tomato respectively. The frequency profiles for this activity also have obvious differences. The GST and P450 activities of the cucumber population were the lowest in the five host populations. CONCLUSION: Long‐term induction of host plants for B‐biotype B. tabaci could influence their susceptibilities to several insecticides. Rational selection and usage of insecticides for particular hosts will be helpful for resistance management and control of this species. Copyright © 2010 Society of Chemical Industry  相似文献   

6.
In 2005, severe leaf curling and yellowing were observed on tomato plants on Ishigaki Island. Because the symptoms were consistent with infection by a begomovirus, we used a polymerase chain reaction (PCR) with specific primers for begomovirus DNA-A and DNA satellite component (DNA-β) and detected products of the expected sizes from symptomatic tomato plant samples. DNA sequence analyses of the PCR products revealed that the symptomatic tomato plants were associated with Ageratum yellow vein virus (AYVV) infection. We confirmed AYVV transmission from the naturally infected weed host, Ageratum conyzoides, to healthy tomato plants by the insect vector Bemisia tabaci B biotype. This report is the first of AYVV occurrence in Japan.  相似文献   

7.
The troubled history of the two major diseases of the chocolate tree (Theobroma cacao) in South America, witches' broom and frosty pod, is reviewed, concentrating on critical aspects of the aetiology as well as the phylogeny of the causal agents. Both diseases are caused by sister species within the genus Moniliophthora, belonging to the Marasmiaceae family of mushrooms. The witches' broom pathogen, Moniliophthora perniciosa, evolved on the Amazonian side of the Andes and induces brooms not only in cacao and its relatives in the genera Theobroma and Herrania (Malvaceae), but also in species in the plant families Bignoniaceae, Malpighiaceae and Solanaceae, on which the mushrooms (basidiomata) are produced. Moniliophthora roreri, the type species of the genus, evolved as a pod pathogen on endemic Theobroma species on the western side of the northern Andean Cordillera. Because Moniliophthora was described originally as the asexual form of an unknown basidiomycete, the generic diagnosis is amended here to accommodate species with agaricoid basidiomata. In addition, the new variety M. roreri var. gileri is designated for the morphotype occurring on Theobroma gileri, in northwest Ecuador. Cytology studies indicate that the supposed conidia of M. roreri are, in fact, sexual spores (meiospores) and it is posited that the fruiting structure represents a much‐modified mushroom. Finally, based on preliminary data from pathogenicity testing, it is hypothesized that the true causal agent of both diseases is an as yet unidentified infectious agent vectored into the host by the fungus.  相似文献   

8.
Ralstonia solanacearum is a phytopathogenic bacterium that colonizes the xylem vessels of host plants leading to a lethal wilt disease. Although several studies have investigated the virulence of R. solanacearum on adult host plants, infection studies of this pathogen on the seedling stages of hosts are less common. In a preliminary observation, inoculation of R. solanacearum F1C1 on 6‐ to 7‐day‐old tomato seedlings by a simple leaf‐clip strategy resulted in a lethal pathogenic condition in seedlings that eventually killed these seedlings within a week post‐inoculation. This prompted testing of the effect of this inoculation technique in seedlings from different cultivars of tomato and similar results were obtained. Colonization and spread of the bacteria throughout the infected seedlings was demonstrated using gus‐tagged R. solanacearum F1C1. The same method of inoculating tomato seedlings was used with R. solanacearum GMI1000 and independent mutants of R. solanacearum GMI1000, deficient in the virulence genes hrpB, hrpG, phcA and gspD. Wildtype R. solanacearum GMI1000 was found to be virulent on tomato seedlings, whereas the mutants were found to be non‐virulent. This leaf‐clip technique, for inoculation of tomato seedlings, has the potential to be a valuable approach, saving time, space, labour and costs.  相似文献   

9.
ABSTRACT Ceratocystis cacaofunesta (formerly C. fimbriata) causes a lethal wilt disease of cacao (Theobroma cacao) in the Caribbean and Central and South America. Recent studies employing phylogenetics, intersterility, and host range separate the cacao pathogen from other strains of the C. fimbriata complex. Ceratocystis wilt has been managed through genetic resistance, but the disease is an emerging problem in Bahia, Brazil, where it was recently introduced. Genetic studies indicate that populations of the fungus in Costa Rica, Colombia, and Bahia may have been introduced on cacao cuttings; whereas populations in Rond?nia, Brazil, and western Ecuador appear to be native. The fungal genotype present in Bahia is similar to those found in Rond?nia and may have been introduced on propagative material with witches' broom resistance.  相似文献   

10.
This study determined the tuf gene sequence of the phytoplasma specific to paulownia witches’‐broom from Nanyang, China (hereby designated PaWB‐Ny). The PaWB‐Ny tuf gene was 1185 nucleotides in length and confirmed that the phytoplasma belongs to subgroup 16SrI‐D of aster yellows. Three characteristic GTP‐binding protein motifs were identified based on the peptide deduced from the tuf gene sequence. Results suggested that the elongation factor EF‐Tu was localized in the cytoplasm and lacked hydrophobic transmembrane domains. Antibodies against PaWB‐Ny EF‐Tu were prepared by rabbit immunization with glutathione‐S‐transferase (GST)‐tagged EF‐Tu fusion protein expressed in Escherichia coli. EF‐Tu exhibited a molecular weight of ～43 kDa and was detected in PaWB‐infected paulownia plants by western blot analysis. Indirect enzyme‐linked immunosorbent assays (ELISA) and dot blotting analyses were performed with freezing and thawing treatments during antigen preparation. Dilution of extracts to an appropriate scale significantly reduced non‐specific reactions. The resultant PaWB EF‐Tu antibody reacted with antigens from plants infected with periwinkle virescence and chinaberry tree witches’‐broom phytoplasmas, but not those infected with jujube witches’‐broom or bishopwood witches’‐broom phytoplasma. The EF‐Tu was characteristically localized within the phytoplasmal cytoplasm of infected plant phloem tissues.  相似文献   

11.
This paper presents the results from a survey that was carried out to determine the host plants of tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in five States in Sudan. This survey was carried out in greenhouses and open‐field vegetable production areas between the years 2011 and 2014 using pheromone traps. The survey showed that the main host plant of T. absoluta is tomato (Lycopersicon esculentum), but it also attacks potato (Solanum tuberosum), eggplant (S. melongena) Jimson weed (Datura stramonium) and S. dubium in the family Solanaceae, and broad bean (Vicia faba) and alfalfa plant (Medicago sativa) in the family Fabaceae. This paper is the first record of the following plans being hosts for T. absoluta: Watermelon (Citrullus lanatus) in the family Cucurbitaceae, Physic nut (Jatropha curcas) in the family Euphorbiaceae, spiny amaranth (Amaranthus spinosus) in the family Amaranthaceae, Ramtouk (Xanthium brasilicum) in the family Asteraceae and S. dubium. The study showed that the leafminer male numbers and the symptoms were significantly increased in S. melongena and S. dubium after severe damage and complete loss of the main host, the tomato crop and these two species may be the preferred alternative host plants.  相似文献   

12.
The soilborne pathogen Verticillium dahliae invades its host via the root, and spreads systemically throughout the plant. Although a functional root system of appropriate size is essential for water and nutrient uptake, to date, effects of pathogens on root morphology have not been frequently investigated. Therefore, this study aims to improve knowledge of how V. dahliae infection impairs root morphological characteristics of tomato, considering plant growth and physiological responses, particularly those involved in defence in roots and leaves over a growing period of up to 28 days post‐inoculation. Verticillium dahliae infection suppressed the growth of both shoot and root. Diseased plants developed a smaller leaf area, and exhibited a reduction in the rate of photosynthesis and stomatal conductance. An early response to pathogen invasion in the host root was the up‐regulation of several defence‐related genes, such as proteinase inhibitor II (Pin2), β‐1,3‐glucanase A (GluA) and two pathogenesis‐related genes (PR‐1a, PR‐1b). However, this response did not prevent colonization of the roots by the pathogen. Although a high variability in pathogen density was found within the root system, a significant increase of both the specific root length and surface area was observed in response to pathogen invasion; these traits correlated with water use efficiency. Morphological changes of the root may represent an adaptive response evolved to sustain the supply of both water and nutrients in the presence of the pathogen.  相似文献   

13.
Hoagland's solution (HS), a defined nutrient supplement for plants, has been previously reported to stimulate zoospore release from resting spores of the potato pathogen Spongospora subterranea f. sp. subterranea. This study obtained direct empirical evidence for an increase in zoospore release with HS treatment, and identified Fe‐EDTA as the stimulant component of HS. Stimulation of resting spores by HS and Fe‐EDTA resulted in greater and earlier zoospore release compared to a distilled water control, and in the presence of a susceptible tomato host plant resulted in enhanced root infection. Given the labile nature of S. subterranea zoospores, it was postulated that stimulation of premature release of zoospores from the dormant resting spores in absence of susceptible hosts could reduce soil inoculum levels. In two glasshouse trials in the absence of host plants, both Fe‐EDTA and HS soil treatments reduced S. subterranea soil inoculum levels, providing proof of concept for the ‘germinate to exterminate’ approach to inoculum management.  相似文献   

14.
An accession of Camelina microcarpa suspected to be resistant to sulfonylurea herbicides was identified in Oregon in 1998 field experiments. Greenhouse research confirmed that the putative resistant biotype was resistant to chlorsulfuron and metsulfuron on a whole plant level. Compared with the resistant (R) biotype, the susceptible (S) biotype was 1000 and 10 000‐fold more sensitive to metsulfuron and chlorsulfuron respectively. The R biotype was also resistant to other sulfonylurea, sulfonylaminocarbonyl‐triazolinone, imidazolinone and triazolopyrimidine herbicides. An in vivo enzyme assay indicated that acetolactate synthase (ALS) from the R plants required 111 times more chlorsulfuron to inhibit activity by 50% compared with the amount required to have a similar effect on ALS from S plants. Analysis of the nucleotide and amino acid sequences demonstrated that a single‐point mutation from G to T in the als1 gene conferred the change from the amino acid tryptophan to leucine at position 572 in the resistant biotype. This research confirmed that ALS inhibitor resistance in an Oregon accession of C. microcarpa is based on an altered target site conferred by a single‐point mutation.  相似文献   

15.
The response of Cuscuta campestris Yuncker, a non‐specific above‐ground holoparasite, to amino acid biosynthesis inhibitor (AABI) herbicides, was compared with other resistant and sensitive plants in dose–response assays carried out in Petri dishes. Cuscuta campestris was found to be much more resistant to all AABI herbicides tested. The I50 value of C. campestris growth inhibition by glyphosate was eightfold higher than that of transgenic, glyphosate‐resistant cotton (RR‐cotton). The I50 value for C. campestris shoot growth inhibition by sulfometuron was above 500 μM, whereas that of sorghum roots was only 0.004 μM. Cuscuta campestris exposed to glyphosate gradually accumulated shikimate, confirming herbicide penetration into the parasite and interaction with an active form of the target enzyme of the herbicide, 5‐enolpyruvylshikimate‐3‐phosphate synthase. More than half of the C. campestris plants associated with transgenic, glyphosate‐resistant sugarbeet (RR‐sugarbeet) treated with glyphosate or with transgenic, sulfometuron‐resistant tomato (SuR‐tomato) treated with sulfometuron recovered and resumed regular growth 20–30 days after treatment. New healthy stems developed, followed by normal flowering and seed setting. The results of the current study demonstrate the unique capacity of C. campestris to tolerate high rates of AABI. The mechanism of this phenomenon is yet to be elucidated.  相似文献   

16.
A stolbur‐type phytoplasma is the putative pathogen of grapevine yellows disease that causes economic damage to vineyards in most growing areas around the world. The pathogen is known to be transmitted to vines by two planthoppers, Hyalesthes obsoletus and Reptalus panzer; the latter is found in Europe but has not yet been observed in Israel. The establishment of a vector–pathogen–plant relationship requires that the pathogen and the vector meet on a shared host plant. This does not happen in the ecosystem examined here, where two different principal host plants for the obligate pathogen and its vector exist: the pathogen is established on vines, while its vector, H. obsoletus, develops on Vitex agnus‐castus. The present study verified that: (i) the vector cannot complete its life cycle on vines; (ii) V. agnus‐castus does not grow in the immediate vicinity of vines, and does not harbour the pathogen; and (iii) the pathogen is not vertically transmitted from mother to offspring. Moreover, in a thorough search of plants in vine growing areas, no other plants were found that host both the vector and the pathogen. However, it was found that the planthopper can acquire the phytoplasma from infected vines. Nonetheless, this does not prove the ability of the planthopper to further transmit the pathogen to vines and does not explain the presence of the vector on the non‐preferred vines. Thus, the enigma of the pathogen–vector–host triangle in this system remains unresolved.  相似文献   

17.
The immunodominant membrane protein Imp of several phytoplasmas within the ‘Candidatus Phytoplasma aurantifolia’ (16Sr‐II) group was investigated. Eighteen isolates from Iran (11), East Asia (5), Africa (1) and Australia (1) clustered into three phylogenetic subgroups (A, B and C) based on the 16S rDNA and imp genes, regardless of geographic origin. The imp gene sequences were variable, with more non‐synonymous than synonymous mutations (68 vs 20, respectively), even though many of the non‐synonymous ones (75%) produced conservative amino acid replacements. Eight codon sites on the extracellular region of the protein were under positive selection, with most of them (75%) coding for non‐conservative amino acid substitutions. Full‐length (21 kDa) and truncated (16 kDa) Imp proteins of two economically important Iranian phytoplasmas [lime witches’ broom (LWB) and alfalfa witches’ broom (AlWB‐F)] were expressed as His‐tagged recombinant proteins in Escherichia coli. An antiserum raised against full‐length recombinant LWB Imp reacted in western blots with membrane proteins extracted from LWB‐infected periwinkle and lime, indicating that Imp (19 kDa) is expressed in infected plants and is a membrane‐associated protein. The same polyclonal antibody also detected native Imp in proteins from periwinkles infected by phytoplasmas closely related to LWB (subgroup C) only, confirming phylogenetic clustering based on 16S rDNA and imp genes. Imp proteins of LWB and AlWB‐F isolates were also recognized by an antiserum raised against an enriched preparation of AlWB‐F phytoplasma cells, demonstrating the antigenic properties of this protein.  相似文献   

18.
Thirty-nine isolates of Phytophthora infestans were collected from the wild host Solanum ochranthum in the highland tropics of Ecuador and characterized with a set of phenotypic and molecular markers (mating type, metalaxyl sensitivity, the allozyme loci Gpi, and Pep, mitochondrial DNA haplotype, RFLP, and SSR), as well as for pathogenicity on various hosts. Three groups of isolates (A, B, and C) were identified based on their multilocus genotypes and variable abilities to cause disease on different hosts. Group A had a combination of alleles for the Gpi (86/100), Pep (96/100) and mtDNA (Ia) loci, as well as an RFLP fingerprint, that have not been reported for P. infestans in Ecuador, or elsewhere. Group B shares many marker characteristics with the US-1 lineage described in Ecuador on tomato, pear melon (S. muricatum), and S. caripense, but has SSR alleles not present in typical US-1 isolates. Group C for all markers tested is identical to the EC-1 lineage described on cultivated and wild potatoes in Ecuador. All isolates from S. ochranthum were able to re-infect their host of origin in the detached leaf assay; however, we did not draw clear conclusions as to the relative aggressiveness of the three groups on this host. Isolates of group A were the most specialized and were generally non-pathogenic or weakly pathogenic on all hosts other than S. ochranthum. Groups B and C infected tuber-bearing hosts, including the cultivated potato but were generally non-pathogenic on other non-tuber bearing hosts. Solanum ochranthum was infected by isolates coming from tuber-bearing Solanum hosts (i.e., the EC-1 lineage of P. infestans) and some US-1 isolates from non-tuber bearing hosts. Thus, in nature this species might be a potential reservoir of inoculum of different pathogen populations able to infect the cultivated hosts potato, tomato and pear melon (S.␣muricatum). Unlike potato and tomato in Ecuador, each of which is primarily attacked by a highly specialized pathogen population, S. ochranthum appears to harbour at least three pathogen groups of␣different genetic make-up. The unresolved issue of potential host specificity in isolates found on S.␣ochranthum could complicate efforts to use this species in tomato improvement.  相似文献   

19.
Tomato chlorosis virus (ToCV) is an emerging crinivirus in Brazil that causes an economically important disease in tomato (Solanum lycopersicum) and other solanaceous species. ToCV is transmitted predominantly by the whitefly Bemisia tabaci Middle East‐Asia Minor 1 (MEAM1, formerly biotype B), in a semipersistent manner. As all cultivated tomato varieties and hybrids are susceptible to this crinivirus, the main alternatives for the control of the disease are the use of healthy seedlings for transplanting and the chemical control of the insect vector. The objective of this work was to evaluate the responses of tomato genotypes to infection with this crinivirus and their tolerance to the disease in order to support the development of other alternatives for disease control. Resistance to infection was evaluated by ToCV inoculation with viruliferous B. tabaciMEAM1 followed by virus detection by RT‐PCR and RT‐qPCR. To measure tolerance to the disease, plant development and fruit yield of ToCV‐infected and healthy plants were compared. Among 56 genotypes, only the lineage IAC‐CN‐RT (S. lycopersicum ‘Angela Gigante’ × S. peruvianum ‘LA 444‐1’) was highly resistant to infection with ToCV. Tolerance to the disease over two trials with different genotypes showed variable results. The effect of ToCV on plant development varied from 2.9% to 71.9% reduction, while yield loss varied from 0.2% to 51.8%. The highly ToCV‐resistant lineage IAC‐CN‐RT, which is also resistant to a Spanish isolate of ToCV, might be useful for tomato breeding programmes.  相似文献   

20.
As a major component of the cell wall, lignin has been suggested to play an important role in the plant defence response to various pathogens. However, how lignin is involved in plant pathogen interaction is still unclear. Here, a series of transgenic tobacco lines were cultivated with a range of differences in lignin content and composition. Evaluation of pathogen resistance in these plants indicated that lower total lignin content aggravated the severity of tobacco black shank and bacterial wilt diseases, while increased sinapyl lignin (S) alleviated the disease symptoms. The regression analysis indicated both lignin content and S lignin were positively correlated with disease resistance. These two factors had additive effects, exhibiting stronger correlation with disease resistance when they were combined. Neither guaiacyl lignin (G) nor S/G ratio showed close correlation with disease resistance. The expression of pathogenesis‐related protein genes PR2 and PR3 was induced after pathogen inoculation. However, the up‐regulation of PR2 and PR3 was not associated with a disease resistance‐induced increase in lignin content. These data collectively suggest that both total lignin content and S lignin are main factors that contribute to the basic defence response in tobacco.  相似文献   

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