Exogenous systemin has a contrasting effect on disease resistance in mycorrhizal tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis>) plants infected with necrotrophic or hemibiotrophic pathogens

A study was performed to determine the effect of the systemin polypeptide on the bio-protective effect of arbuscular mycorrhizal fungi (AMF) in tomato plants infected with Alternaria solani, Phytophthora infestans or P. parasitica. Before infection, tomato plants were colonized with two different AMF, Glomus fasciculatum or G. clarum. In addition, a group of inoculated plants was treated with systemin, just after emergence. The exogenous application of systemin marginally suppressed the resistance against A. solani leaf blight observed in G. fasciculatum mycorrhizal plants but significantly enhanced it in plants colonized with G. clarum. Systemin induced resistance to P. parasitica in leaves of G. fasciculatum mycorrhizal plants, in which AMF colonization alone was shown to have no protective effect. Conversely, none of the treatments led to resistance to root or stem rots caused by P. infestans or P. parasitica. The above effects did not correlate with changes in the activity levels of β-1,3-glucanase (BG), chitinase (CHI), peroxidase (PRX), and phenylalanine ammonium lyase (PAL) in leaves of infected plants. However, they corroborated previous reports showing that colonization by AMF can lead to a systemic resistance response against A. solani. Systemic resistance to A. solani was similarly observed in non-mycorrhizal systemin-treated plants, which, in contrast, showed increased susceptibility to P. infestans and P. parasitica. The results indicated that the pattern of systemic disease resistance conferred by mycorrhizal colonization was dependent on the AMF employed and could be altered by the exogenous application of systemin, by means of a still undefined mechanism.     

Observations on blight (Phytophthora infestans) and resistant potatoes at Toluca, Mexico

A late blight epidemic studied at Toluca, Mexico, in 1962 may have started from stems infected at soil level by soil-borne Phytophthora infestans. Its severity was demonstrated by the large differences in the rate foliage was destroyed and in yield of tubers between fungicide-sprayed and unsprayed susceptible and resistant cultivars. The foliage resistances of some Mexican and European cultivars were compared using conventional blight keys and recording the destruction of marked leaves. Cultivars reacted in four ways: (1) Up-to-Date and Alpha leaves were infected and killed soon after plants emerged; (2) Bertita, Conchita and Florita abscissed many infected lower-canopy leaves, and many infections on upper leaves aborted; (3) Elenita leaves had a few lesions in which the fungus grew slowly but remained alive; (4) Greta showed no infection until the potato plants met between rows but then infections developed rapidly and the foliage soon died. Mexican cultivars, except for Elenita, had few blighted tubers; susceptible European cultivars were killed before many tubers formed. Most spores were released during the morning, as in Europe, and leaf infection seemed associated with days with rain when much of the night remained humid. Cool nights lengthened incubation and generation times.     

Genetic mapping from field tests of qualitative and quantitative resistance to Phytophthora infestans in a population derived from Solanum tuberosum and Solanum berthaultii

Under controlled field conditions, a Solanum backcross population segregated for resistance to Phytophthora infestans. The population (`BCT') had been derived previously by crossing the Solanum tuberosum dihaploid USW2230 × Solanum berthaultii PI473331 to obtain the hybrid M200-30, and then backcrossing the hybrid to the S. tuberosum dihaploid HH1-9. Resistance was assessed from analyses of epidemics in small plots of each individual genotype, and data were recorded as area under the disease progress curve (AUDPC). The parents of the original cross (USW2230 and a selection from PI473331) were not included in the test, but the hybrid was incompatible and HH1-9 was compatible with the tester strain of P. infestans (US-8 lineage). Somewhat more than half of the progeny also were incompatible with the tester strain, indicating the presence of an R gene. This gene segregated from the S. berthaultii parent and mapped 4.8 cm from the RFLP marker TG63 on chromosome 10. We deduce that the R gene is not R-1, R-2, R-3, R-6, or R-7 and is probably not R-4, R-5, or R-10. Among the remaining, compatible progeny, there was a wide range of quantitative resistance. All were more resistant than the susceptible cultivar Superior, and most individuals were much more resistant than the moderately resistant cultivar Kennebec. AUDPC values among the sub-population of compatible genotypes ranged from about 400 to 1500 units the first year and from 400 to 1760 units the second year. At least five quantitative trait loci (QTLs) were detected in this sub-population in both 1997 and 1998, including one detected through segregation of alleles from both the hybrid parent and the recurrent S. tuberosum parent. A model of main and epistatic effects explained 56% and 66% of the variation observed for quantitative resistance to late blight in 1997 and 1998, respectively. Several of the QTLs for late blight resistance were located in regions of the genome to which QTLs for late maturity have previously been mapped.     

Progeny tests of barley,wheat, and potato regenerated from cell cultures after in vitro selection for disease resistance

Summary Because plant cells cultured in vitro express genetic variability and since they can be regenerated into functional plants, procedures have been designed to use this system for the production of plants with new important agronomic characteristics, particularly for disease resistance. For barley, wheat, and potato somaclones have been found that were less susceptible to a toxin of Helminthosporium, fusaric acid, Fusarium coeruleum, F. sulphureum, or Phytophthora infestans, when screened in the first in-vitro-derived generation. Here the progeny of such somaclones is evaluated after natural and artificial infection, using greenhouse-grown or field material. The progenies of the same somaclones did not express detectable differences, which indicated that no heterozygous mutations occurred. Most lines and clones differed in their level of susceptibility to the pathogen compared to the level of the starting material, but these data were in no instance significant. It is discussed here whether this lack of significance is due to a lack of genetic differences or whether the test procedures are in adequate for detecting and securing the slight, probably quantitative, alterations.     

<Emphasis Type="Italic">CaMi</Emphasis>, a root-knot nematode resistance gene from hot pepper (<Emphasis Type="Italic">Capsium annuum</Emphasis> L.) confers nematode resistance in tomato

Several root-knot nematode (Meloidogyne spp.) resistance genes have been discovered in different pepper (Capsium annuum L.) lines; however, none of them has yet been cloned. In this study, a candidate root-knot nematode resistance gene (designated as CaMi) was isolated from the resistant pepper line PR 205 by degenerate PCR amplification combined with the RACE technique. Expression profiling analysis revealed that this gene was highly expressed in roots, leaves, and flowers and expressed at a lower level in stems and was not detectable in fruits. To verify the function of CaMi, a sense vector containing the genomic DNA spanning the full coding region of CaMi was constructed and transferred into root-knot nematode susceptible tomato plants. Sixteen transgenic plants carrying one to five copies of T-DNA inserts were generated from two nematode susceptible tomato cultivars. RT-PCR analysis revealed that the expression levels of CaMi gene varied in different transgenic plants. Nematode assays showed that the resistance to root-knot nematodes was significantly improved in some transgenic lines compared to untransformed susceptible plants, and that the resistance was inheritable. Ultrastructure analysis showed that nematodes led to the formation of galls or root knots in the susceptible lines while in the resistant transgenic plants, the CaMi gene triggered a hypersensitive response (HR) as well as many necrotic cells around nematodes. Rugang Chen and Hanxia Li are contributed equally to this work.     

High-resolution Mapping and Analysis of the Resistance Locus <Emphasis Type="Italic">Rpi-abpt</Emphasis> Against <Emphasis Type="Italic">Phytophthora infestans</Emphasis> in Potato

Introduction of more durable resistance against Phytophthora infestans causing late blight into the cultivated potato is of importance for sustainable agriculture. We identified a new monogenically inherited resistance locus that is localized on chromosome 4. The resistance is derived from an ABPT clone, which is originally a complex quadruple hybrid in which Solanum acaule, S. bulbocastanum, S. phureja and S. tuberosum were involved. Resistance data of the original resistant accessions of the wild species and analysis of mobility of AFLP markers linked to the resistance locus suggest that the resistance locus is originating from S. bulbocastanum. A population of 1383 genotypes was screened with two AFLP markers flanking the Rpi-abpt locus and 98 recombinants were identified. An accurate high-resolution map was constructed and the Rpi-abpt locus was localized in a 0.5 cM interval. One AFLP marker was found to co-segregate with the Rpi-abpt locus. Its DNA sequence was highly similar with sequences found on a tomato BAC containing several resistance gene analogues on chromosome 4 and its translated protein sequence appeared to be homologous to several disease resistance related proteins. The results indicated that the Rpi-abpt gene is a member of an R gene cluster.     

Reaction of Certain Solanaceous and Asteraceous Plant Species to Inoculation with Phytophthora infestans in Cameroon

Experiments were conducted to detect potential hosts of Phytophthora infestans, causal agent of potato late blight among weeds occurring in Cameroon. Isolates of P. infestans isolated from garden huckleberry (Solanum scabrum), potato (S. tuberosum) and tomato (S. lycopersicon) were inoculated on detached leaves of 12 solanaceous and 14 asteraceous species collected from the potato agroecosystem in the western highlands of Cameroon. Isolates of P. infestans from huckleberry and potato infected the same host plants as well as gboma eggplant (S. macrocarpon) and two asteraceous weeds; Billy goatweed (Ageratum conyzoides) and Dichrocephala (Dichrocephala integrifolia). Inoculum from potato caused late blight symptoms on haemorrhage plant (Aspilia africana); while inoculum from tomato resulted in late blight on worowo (Solanecio biafrae). This is the first report of late blight infection on S. macrocarpon, A. conyzoides, Sol. biafrae and Asp. africana in Cameroon. The research results indicate that some asteraceous and solanaceous weeds may be alternative hosts of P. infestans in the potato agroecosystem.     

Production and characterization of somatic hybrids between <Emphasis Type="Italic">Solanum tuberosum</Emphasis> L. and <Emphasis Type="Italic">S. pinnatisectum</Emphasis> Dun.

Interspecific somatic hybrids between the dihaploid Solanum tuberosum and the wild species S. pinnatisectum Dun. were produced via protoplast fusion. Protoplast isolation, electrofusion, culture of post-fusion products and regeneration of calli/shoots were undertaken following optimized protocols. Regenerants were characterized for hybridity, ploidy and resistance to Phytophthora infestans (Mont.) de Bery, causal fungal pathogen of late blight disease. From a total of 126 regenerated macrocalli, 12 somatic hybrids were confirmed by possessing species-specific diagnostic bands of their corresponding parents as revealed by RAPD, SSRs and cytoplasmic-DNA analyses. Tetraploid status of the 12 hybrids was determined using flow cytometry analysis. Intermediate phenotypes for leaf, flower, and tuber characteristics and high male fertility were observed in field-grown hybrid plants. Hybrids were highly resistant to foliage late blight based on field assessment for two seasons. In contrast, moderate level of resistance to foliage blight was observed in hybrids based on the detached leaf assay under laboratory conditions. Overall, somatic hybrids with moderate levels of resistance to foliage blight were identified, and these will be useful for in situ hybridization in potato breeding efforts.     

QTL analysis of late blight resistance in a diploid potato family of Solanum phureja × S. stenotomum

Field resistance to Phytophthora infestans (Mont.) de Bary, the causal agent of late blight in potatoes, has been characterized in a potato segregating family of 230 full-sib progenies derived from a cross between two hybrid Solanum phureja × S. stenotomum clones. The distribution of area under the disease progress curve values, measured in different years and locations, was consistent with the inheritance of multigenic resistance. Relatively high levels of resistance and transgressive segregations were also observed within this family. A genetic linkage map of this population was constructed with the intent of mapping quantitative trait loci (QTLs) associated with this late blight field resistance. A total of 132 clones from this family were genotyped based on 162 restriction fragment length polymorphism (RFLP) markers. The genome coverage by the map (855.2 cM) is estimated to be at least 70% and includes 112 segregating RFLP markers and two phenotypic markers, with an average distance of 7.7 cM between two markers. Two methods were employed to determine trait–marker association, the non-parametric Kruskal–Wallis test and interval mapping analysis. Three major QTLs were detected on linkage group III, V, and XI, explaining 23, 17, and 10%, respectively, of the total phenotypic variation. The present study revealed the presence of potentially new genetic loci in this diploid potato family contributing to general resistance against late blight. The identification of these QTLs represents the first step toward their introgression into cultivated tetraploid potato cultivars through marker-assisted selection.     

Expression of the Phytophthora infestans ipiB and ipi0 genes in planta and in vitro

The ipiB and ipiO genes of the potato late blight fungus Phytophthora infestans (Mont.) de Bary were isolated from a genomic library in a screen for genes induced in planta. Expression of these genes was studied during pathogenesis on various host tissues and different host plants, some of which show specific resistance against P. infestans infection. During pathogenesis on leaves and tubers of the fully susceptible potato cultivar (cv.) Ajax and on leaves of the fully susceptible tomato cv. Moneymaker, the P. infestans ipiB and ipiO genes show a transient expression pattern with highest mRNA levels in the early stages of infection. During the interaction with leaves of the partially resistant potato cv. Pimpernel, the expression is also transient but accumulation and disappearance of the mRNAs is delayed. Also in P. infestans inoculated onto a race-specific resistant potato cultivar and onto the nonhost Solanum nigrum, ipiB and ipiO mRNA is detectable during the initial stages of infection. Apparently, the expression of the ipiB and the ipiO genes is activated in compatible, incompatible and nonhost interactions. In encysted zoospores, ipiB and ipiO mRNA accumulation was not detectable, but during cyst germination and appressorium formation on an artificial surface the genes are highly expressed. Expression studies in mycelium grown in vitro revealed that during nutrient starvation the expression of the ipiB and ipiO genes is induced. For ipiO gene expression, carbon deprivation appeared to be sufficient. The ipiO gene promoters contain a sequence motif that functions as a glucose repression element in yeast and this motif might be involved in the regulation of ipiO gene expression.     

Use of asymmetric somatic hybridization for transfer of the bacterial blight resistance trait from Oryza meyeriana L. to O. sativa L. ssp. japonica

Bacterial blight is one of the major diseases affecting rice productivity. To improve the resistance of cultivated rice to bacterial blight, we introduced a bacterial blight resistance trait from Oryza meyeriana, a wild rice species, into an elite japonica rice cultivar (Dalixiang) using asymmetric somatic hybridization. One hundred and thirty-two independent lines were regenerated. The hybrid plants possessed several morphological features of the donor species, O. meyeriana. Random amplified polymorphic DNA analysis revealed that hybrid plants exhibited banding patterns derived from their parental genotypes. For the majority of the hybrids, resistance to bacterial blight pathogens was intermediate to that observed for O. meyeriana and O. sativa (cv. Dalixiang). Four of the hybrid lines exhibited a high bacterial blight resistance, but it was less than that observed for O. meyeriana. These results demonstrate that O. meyeriana can be used as a good genetic source for improving bacterial blight resistance in commercial rice cultivars through asymmetric somatic hybridization.Abbreviations 2,4-D: 2,4-Dichlorophenoxyacetic acid - IOA: Iodoacetamide - NAA: -Naphthaleneacetic acid - PEG: Polyethylene glycol Communicated by P. Lakshmanan     

Phenotypic markers of Phytophthora infestans

Abstract

Phytophthora infestans is one of the most destructive pathogens of potato and causal agents of notorious disease late blight. Different chemicals are used to control the pathogen of late blight but the most commonly used is metalaxyl; its extensive use of has caused decreased sensitivity in the P. infestans population. The metalaxyl sensitivity of the Pakistani population of P. infestans is investigated in the present study. For this purpose, 178 isolates of P. infestans were obtained from the lesions of diseased potato leaves and stems, and samples were collected from the different potato-growing areas of Pakistan, where late blight is a problem. Sensitivity of the isolates of P. infestans was investigated by metalaxyl sensitivity test and with the help of test isolates were divided into three categories, i.e. sensitive, intermediate and resistant, based on their Co-efficient of mycelial growth inhibition (CMGI) values. During the study, highest percentage (50.17%) of resistant isolates was observed in the population of Punjab (zone 2), whereas the lower percentage (33.33%) was observed in the population of Swat valley (zone 6b). In the present study, it was discovered that P. infestans late blight-causing fungus has adopted more resistance against metalaxyl because of its wide use.     

致病疫霉效应蛋白Pi16275的功能研究

[目的]分析致病疫霉效应蛋白Pi16275的超量表达对病原菌致病性的影响,明确Pi16275的亚细胞定位,筛选Pi16275在植物中的互作靶标蛋白及靶标蛋白在抵御病原菌侵染过程中的作用,初步揭示Pi16275在病原菌侵染植物过程中的作用机制.[方法]利用农杆菌介导的烟草瞬时表达系统在烟草叶片表皮细胞中瞬时表达Pi162...     

Effects of arbuscular mycorrhiza (AM) on health ofLinum usitatissimum L. infected by fungal pathogens

Effects of arbuscular mycorrhizal (AM) symbiosis on health ofLinum usitatissimum infected by fungal pathogens were investigated exemplarily. Physiological and biochemical analyses were done to explain the mechanisms underlying the AM effects. AM plants showed increased resistance against the wilt pathogen (Fusarium oxysporum f. sp.lini), the level of this effects depended on the plant cultivars which all showed the same level of root colonization by arbuscular mycorrhizal fungi (AMF). In contrary to that, AM plants were highly susceptible against the shoot pathogenOidium lini, but they suffered less than non-AM plants in terms of shoot fresh weight, CO₂ assimilation and content of sucrose in shoot apex. This indicates that AM not only activates resistance mechanisms but also can induce tolerance against pathogens. The concentration of phytohormones such as auxin- and gibberellin-like substances were increased in shoots of AM plants. In roots the ethylene production was increased, too. Furthermore the content and composition of free sterols were highly altered in leaves of AM plants. Root infection by AMF caused an increased respiratory activity and a reduced degree of DNA methylation, but both modifications only occurred in infected root parts indicating an increasing gene activity. The presented results suggest that nearly all parts of a plant are influenced by AM but not in the same manner. In the case of mildewed linseed the effect of AM on plant health was impressing, it indicates that AM has an ability to induce tolerance.     

Multiple factors control the level of resistance induced in tomato by Fusarium oxysporum f. sp. cucumerinum

Fourteen wild type and three UV-irradiated isolates of Fusarium oxysporum f. sp. cucumerinum (Foc) were evaluated as to the level of resistance they could induce in tomato to late blight caused by Phytophthora infestans. Tomato plants were induced by applying a suspension of Foc microconidia directly to the surface of the potting media without disturbing the tomato roots. Upper leaves of tomato plants were inoculated with P. infestans, and a reduction in lesion expansion was used as an index of induced resistance. All fourteen wild type isolates of Foc significantly reduced expansion of late blight lesions. One of the wild type isolates produced a significantly weaker resistance response than the other isolates. None of the UV-irradiated isolates induced significant resistance. The same Foc isolates were compared as to their virulence and their pigment production in culture, and considerable variation among them was revealed for both characteristics. Positive correlations existed both between the level of induced resistance and virulence, and between the level of induced resistance and pigmentation. The gradual increment in the level of induced resistance and the exceptions to the correlations between induced resistance and the two characteristics investigated suggest that multiple factors contribute to the induction of resistance by Foc.     

Redirection of the phenylpropanoid pathway to feruloyl malate in <Emphasis Type="Italic">Arabidopsis</Emphasis> mutants deficient for cinnamoyl-CoA reductase 1

Cinnamoyl-CoA reductase 1 (CCR1, gene At1g15950) is the main CCR isoform implied in the constitutive lignification of Arabidopsis thaliana. In this work, we have identified and characterized two new knockout mutants for CCR1. Both have a dwarf phenotype and a delayed senescence. At complete maturity, their inflorescence stems display a 25–35% decreased lignin level, some alterations in lignin structure with a higher frequency of resistant interunit bonds and a higher content in cell wall-bound ferulic esters. Ferulic acid-coniferyl alcohol ether dimers were found for the first time in dicot cell walls and in similar levels in wild-type and mutant plants. The expression of CCR2, a CCR gene usually involved in plant defense, was increased in the mutants and could account for the biosynthesis of lignins in the CCR1-knockout plants. Mutant plantlets have three to four-times less sinapoyl malate (SM) than controls and accumulate some feruloyl malate. The same compositional changes occurred in the rosette leaves of greenhouse-grown plants. By contrast and relative to the control, their stems accumulated unusually high levels of both SM and feruloyl malate as well as more kaempferol glycosides. These findings suggest that, in their hypolignified stems, the mutant plants would avoid the feruloyl-CoA accumulation by its redirection to cell wall-bound ferulate esters, to feruloyl malate and to SM. The formation of feruloyl malate to an extent far exceeding the levels reported so far indicates that ferulic acid is a potential substrate for the enzymes involved in SM biosynthesis and emphasizes the remarkable plasticity of Arabidopsis phenylpropanoid metabolism.