Blight Fungus Phytophthora Infestans Research Articles

Correspondence of Charles Darwin on James Torbitt's project to breed blight-resistant potatoes

The most prolific of Darwin's correspondents from Ireland was James Torbitt, an enterprising grocer and wine merchant of 58 North Street, Belfast. Between February 1876 and March 1882, 141 letters were exchanged on the feasibility and ways of supporting one of Torbitt's commercial projects, the large-scale production and distribution of true potato seeds (Solan um tuberosum) to produce plants resistant to the late blight fungus Phytophthora infestans, the cause of repeated potato crop failures and thus the Irish famines in the nineteenth century. Ninety-three of these letters were exchanged between Torbitt and Darwin, and 48 between Darwin and third parties, seeking or offering help and advice on the project. Torbitt's project required selecting the small proportion of plants in an infested field that survived the infection, and using those as parents to produce seeds. This was a direct application of Darwin's principle of selection. Darwin cautiously lobbied high-ranking civil servants in London to obtain government funding for the project, and also provided his own personal financial support to Torbit.

Race nonspecific resistance for potato late blight

The late blight fungus ( Phytophthora infestans) rots susceptible species of potato plants. None of the major varieties of potato ( Solanum tuberosum) grown in the USA is resistant to US-8, the most prevalent genotype of the fungus. Now, Junqi Song, James Bradeen and colleagues have cloned the RB gene from the wild diploid potato species, Solanum bulbocastanum, using a map-based approach in combination with long-range PCR. Transgenic plants containing the gene, normally fully susceptible, displayed broad-spectrum late blight resistance.

Sprinkling Irrigation Enhances Production of Oospores of Phytophthora Infestans in Field-Grown Crops of Potato

ABSTRACT Two field experiments were conducted to study the effect of overhead sprinkling irrigation on oospore formation by the late blight fungus Phytophthora infestans in potato. Total rain (natural + sprinkling) accumulated in treatments of experiment 1 (winter 1997 to 1998) were 765, 287, and 219 mm and treatments of experiment 2 (winter 1999 to 2000) were 641, 193, and 129 mm. Sporangia from 11 isolates of P. infestans were combined in eight pairs, seven of A1 and A2 and one of A2 and A2 mating type, and were sprayed on field-grown potato crops (42 plants per plot at 7 m(2) each) and examined for their ability to form oospores in the host tissues. In experiment 1, oospores were recorded in a total of 132 of 1,680 leaflets (7.9%), 24 of 105 stems, and 2 of 90 tubers. In experiment 2, oospores were recorded in 40 of 519 leaflets (7.7%), but not in any of the 90 stems or the 45 tubers examined. Both the proportion of leaflets containing oospores and the number of oospores per leaflet increased with time after inoculation and were dependent on the rain regime, the position of leaves on the plant, and the isolate pair combination. In both field trials, increasing the rainfall significantly enhanced oospore production in leaves. Leaf samples collected from the soil surface had significantly more oospores than those collected from the midcanopy. Two pairs in experiment 1 were more fertile than the others, whereas the pair used in experiment 2 was the least fertile. The total number of oospores per leaflet usually ranged from 10 to 100 in experiment 1, but only from 2 to 10 in experiment 2. Maximal oospore counts in the field were 200 and 50 in experiments 1 and 2, respectively, but ranged from approximately 2,000 to 12,000 oospores per leaflet in detached leaves in the laboratory. We concluded that P. infestans can produce oospores in the foliage of field-grown potato crops, especially when kept wet by regular overhead sprinkling irrigation, but production was far below that in the laboratory.

The fungicidal diamine (E)‐( N , N , N ′, N ′‐tetraethyl)‐1,4‐diaminobut‐2‐ene increases spermine concentration in the late blight fungus Phytophthora infestans

Mycelial growth, polyamine concentrations and the activities of enzymes of polyamine biosynthesis and catabolism were examined in the late blight fungus Phytophthora infestans, grown in the presence of the putrescine analogue (E)‐(N,N,N′,N′‐tetraethyl)‐1,4‐diaminobut‐2‐ene (E‐TED). Growth of P. infestans was significantly reduced by 5 mmol l−1 E‐TED but concentrations of 1 mmol l−1 or less had no effect. All concentrations of E‐TED significantly increased the spermine concentrations in fungal tissue but these increases were not accompanied by any significant alterations in enzyme activities. An examination of the uptake of 14C‐spermine into cells grown in the presence of E‐TED indicated that spermine could be subject to replacement by E‐TED at intracellular binding sites. E‐TED‐treated cells were shown to excrete spermine at significantly higher levels than untreated cells. Permeabilization of cells with n‐butanol removed this difference. Possible causes for this difference are discussed.

Inhibition of lysine biosynthesis in Phytophthora infestans

Four inhibitors of the lysine biosynthetic enzyme dihydrodipicolinate synthase (DHDPS) were examined for their effects on the late blight fungus Phytophthora infestans . One of these compounds, dipicolinic acid, reduced mycelial growth of P. infestans by 61% and completely controlled blight infection of leaf discs when used at 1 mM. The other inhibitors, chelidamic acid, chelidonic acid and dimethyl cis -piperidine-2,6-dicarboxylate, were less effective against P. infestans in vitro and in vivo . The effects of dipicolinic acid and chelidonic acid on mycelial growth were partly overcome by the addition of lysine to the growth medium. Both of these compounds reduced DHDPS activity and lysine concentrations in P. infestans , although they had no effect on activities of aspartate kinase and diaminopimelic acid decarboxylase. Both dipicolinic acid and chelidonic acid reduced in vitro activity of DHDPS from P. infestans .

Primary structure and expression of acidic (class II) chitinase in potato.

Infection of potato (Solanum tuberosum) leaves by the late blight fungus Phytophthora infestans or treatment with fungal elicitor leads to a strong increase in chitinase activity. We isolated cDNAs encoding acidic (class II) chitinases (ChtA) from potato leaves and determined their structures and expression patterns in healthy and stressed plants. From the total number of cDNAs and the complexity of genomic DNA blots we conclude that acidic chitinase in potato is encoded by a gene family which is considerably smaller than that encoding basic (class I) chitinase (ChtB). The deduced amino acid sequences show 78 to 96% identity to class II chitinases from related plant species tomato, tobacco) whereas the identity to basic chitinases of potato is in the range of 60%. RNA blot analysis revealed that both acidic and basic chitinases were strongly induced by infection or elicitor treatment and that the induction occurred both locally at the site of infection and systemically in upper uninfected leaves. In contrast, a differential response to other types of stress was observed. Acidic chitinase mRNA was strongly induced by salicylic acid, whereas basic chitinase mRNA was induced by ethylene or wounding. In healthy, untreated plants, acidic chitinase mRNA accumulated also in an organ-, cell-type- and development-specific manner as revealed by RNA blot analysis and in situ RNA hybridization. Relatively high transcript levels were observed in old leaves and young internodes as well as in vascular tissue and cells constituting the stomatal complex in leaves and petioles. Lower, but appreciable mRNA levels were also detectable in roots and various flower organs, particularly in sepals and stamens. The possible implications of these findings in pathogen defense, development and growth processes are discussed.

Pathogen‐Defence Gene prp1–1 from Potato Encodes an Auxin‐Responsive Glutathione S‐Transferase

Genetic studies have previously implicated the prp1 gene family in the defence of potato against infection with the late blight fungus Phytophthora infestans. Here, we show that the concentrations of PRP1 mRNA as well as protein rapidly increase in potato leaves after fungal infection and stay at high levels during an extended period of the infection cycle. After separation of subcellular components by differential centrifugation, PRP1 protein was identified in the cytosolic fraction. Expression studies with chimeric promoter/beta-glucuronidase gene constructs in transgenic potato plants provided evidence that transcription of the prp1-1 gene, representing one member of the prp1 gene family, is at least partly responsible for the accumulation of PRP1 mRNA and protein upon fungal infection. After expression of the prp1-1-coding sequence in Escherichia coli, the corresponding 26-kDa protein exhibited glutathione S-transferase activity with Km values of 9.8 mM and 0.11 mM for the artificial standard substrate 1-chloro-2,4-dinitrobenzene and glutathione, respectively. Photoaffinity labeling of the protein with tritiated 5-azido-indole-3-acetic acid suggested that the phytohormone indole-3-acetic acid or a structurally related compound serve as a regulator or substrate of the prp1-1 encoded glutathione S-transferase. This assumption was further supported by the inhibitory effect of the phytohormone on the enzyme activity in vitro. The implications of these findings for a potential involvement of indole-3-acetic acid in the control of defence reactions are discussed.

Lipid-derived signals that discriminate wound- and pathogen-responsive isoprenoid pathways in plants: methyl jasmonate and the fungal elicitor arachidonic acid induce different 3-hydroxy-3-methylglutaryl-coenzyme A reductase genes and antimicrobial isoprenoids in Solanum tuberosum L.

Induction of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR; EC 1.1.1.34) is essential for the synthesis of steroid derivatives and sesquiterpenoid phytoalexins in solanaceous plants following mechanical injury or pathogen infection. Gene-specific probes corresponding to different HMGR genes (hmg1 and hmg2) were used to study HMGR expression in potato tissue following treatment with methyl jasmonate, a lipoxygenase product of linolenic acid, or arachidonic acid, an elicitor present in the lipids of the potato late blight fungus Phytophthora infestans. Treatment of potato discs (2.2 cm in diameter) with low concentrations (0.45-45 nmol per disc surface) of methyl jasmonate nearly doubled the wound-induced accumulation of hmg1 transcripts and steroid-glycoalkaloid (SGA) accumulation, reduced the abundance of hmg2 transcripts, and did not induce phytoalexins. High concentrations of methyl jasmonate (2-4.5 mol per disc surface) suppressed hmg1 mRNA and SGA accumulation but did not affect hmg2 mRNA abundance or induce phytoalexins. In contrast, arachidonate treatment strongly suppressed hmg1 and strongly induced hmg2 mRNA in a concentration-dependent manner. There was a corresponding suppression of SGA accumulation and an induction of sesquiterpene phytoalexin accumulation by this elicitor. Lipoxygenase inhibitors reduced the wound-induced accumulation of hmg1 transcripts and suppressed SGA levels, effects that were overcome by exogenous methyl jasmonate (45 nmol per disc surface). The results (i) suggest that methyl jasmonate can function as a signal for hmg1 expression and SGA induction following wounding and (ii) indicate that the arachidonate- and jasmonate-response pathways are distinct in relation to HMGR gene expression and isoprenoid product accumulation. The results also are consistent with placement of the HMGR activities encoded by hmg1 and hmg2 within discrete steroid and sesquiterpenoid biosynthetic channels.

Primary structure and expression of mRNAs encoding basic chitinase and 1,3-?-glucanase in potato

Infection of potato leaves (Solanum tuberosum L. cv. Datura) by the late blight fungus Phytophthora infestans, or treatment with fungal elicitor leads to a strong increase in chitinase and 1,3-beta-glucanase activities. Both enzymes have been implicated in the plant's defence against potential pathogens. In an effort to characterize the corresponding genes, we isolated complementary DNAs encoding the basic forms (class I) of both chitinase and 1,3-beta-glucanase, which are the most abundant isoforms in infected leaves. Sequence analysis revealed that at least four genes each are expressed in elicitor-treated leaves. The structural features of the potato chitinases include a hydrophobic signal peptide at the N-terminus, a hevein domain which is characteristic of class I chitinases, a proline- and glycine-rich linker region which varies among all potato chitinases, a catalytic domain, and a C-terminal extension. The potato 1,3-beta-glucanases also contain a N-terminal hydrophobic signal peptide and a C-terminal extension, the latter comprising a potential glycosylation site. RNA blot hybridization experiments showed that basic chitinase and 1,3-beta-glucanase are strongly and coordinately induced in leaves in response to infection, elicitor treatment, ethylene treatment, or wounding. In addition to their activation by stress, both types of genes are regulated by endogenous factors in a developmental and organ-specific manner. Appreciable amounts of chitinase and 1,3-beta-glucanase mRNAs were found in old leaves, stems, and roots, as well as in sepals of healthy, untreated plants, whereas tubers, root tips, and all other flower organs (petals, stamen, carpels) contained very low levels of both mRNAs. In young leaves and stems, chitinase and 1,3-beta-glucanase were differentially expressed. While chitinase mRNA was abundant in these parts of the plant, 1,3-beta-glucanase mRNA was absent. DNA blot analysis indicated that in potato, chitinase and 1,3-beta-glucanase are encoded by gene families of considerable complexity.

Isolation of putative pathogenicity genes of the potato late blight fungus Phytophthora infestans by differential hybridization of a genomic library

Plant pathogens produce pathogenicity factors which enable them to parasitize and colonize their host. A strategy for identifying pathogenicity factors involves the isolation and characterization of genes encoding these factors. Potential pathogenicity genes are genes whose expression is induced during pathogenesis. In order to isolate such genes of the late blight Fungus Phytophthora infestans , a genomic library of P. infestans DNA was differentially hybridized using labelled first strand cDNA probes synthesized on mRNA isolated from P. infestans infected potato leaves and on mRNA isolated from the fungus grown on a basic medium in culture. In total, nine distinct in planta induced ( ipi) genes were selected. Expression studies revealed that the mRNA levels of seven of these genes, ipiA, ipi C, ipiD, ipiJ1, ipiJ2, ipiN and ipi Q increased 5-10 fold during colonization. The two other genes, ipi B and ipiO, showed a transient expression pattern with the highest mRNA levels in the early stages of infection.

Promoter sequences of a potato pathogenesis-related gene mediate transcriptional activation selectively upon fungal infection

Transcription of at least one member of the potato prp1 gene family, prp1-1, is activated at early stages of potato infection with the late blight fungus Phytophthora infestans. In this paper we present evidence that mRNA encoded by prp1-1 does not accumulate in response to abiotic environmental cues which stimulate transcription of other defence-related genes. Regulatory elements were identified in the 5' terminal region of prp1-1 by assaying the expression pattern of chimeric promoter/beta-glucuronidase gene constructs in transgenic potato. A 273 bp fragment comprising the promoter sequence between positions -402 and -130 was sufficient for rapid and strictly localized transcriptional activation at infection sites during the development of late blight disease. Like the native promoter, this truncated promoter did not mediate transcriptional activation in response to other abiotic stimuli. The use of the identified regulatory region to generate conditional mutations selectively at infection sites is discussed.

Evolutionary Biology of Phytophthora: I. Genetic System, Sexuality and the Generation of Variation

The Oomycete genus Phytophthora encompasses over fifty morphological species. Most are plant pathogens, responsible for some of the world's most destructive diseases of crops and native vegetation. Examples include the European potato famine of the mid19th century caused by the potato blight fungus Phytophthora infestans, the recent dieback of entire eucalypt forest ecosystems in Australia due to Phytophthora cinnamomi root rot, and the continuing heavy loss of cocoa to "black pod" disease in the tropics, caused mainly by P. palmivora and P. megakarya ( 101 ). Some Phytophthoras, including P. injestans, are relatively host specific, but others have very wide host ranges. Thus, P. cinnamomi is listed as parasitizing over 900 different plants (277). Economically and historically, therefore, the genus has exerted a

Systemic resistance of potato plants against Phytophthora infestans induced by unsaturated fatty acids

Five unsaturated fatty acids were tested for their ability to induce systemic resistance in potato plants (cv. Bintje) to the late blight fungus Phytophthora infestans . Arachidonic acid and eicosapentaenoic acid applied to leaves 1–3 of potato plants at a dose of about 1 mg per plant induced 94% to 97% protection in leaves 4 to 11, respectively. Linoleic acid, linolenic acid and oleic acid provided 82%, 39% and 42% protection, respectively. Protection was evident as a reduction in lesion number and lesion diameter. It was maximal in plants challenged 5 days after induction and lasted for at least 12 days. A prior infection of lower leaves with P. infestans also induced up to 88% protection in the upper leaves. The mechanism involved in the induction of systemic resistance of potato plants by fatty acids is not understood.

Nucleotide sequence of a pathogenesis-related gene of potato

Environmental stresses cause rapid and specific changes in plant metabolism. Among the various metabolic activities stimulated in potato during the defense response are that of enzymes required for phytoalexin synthesis [2], chitinases and 1,3-fl-glucanases [7], as well as phenylalanine ammonia-lyase and 4-coumarate CoA-ligase [3, 5]. Treatment of potato tuber disks with arachidonic or eicosapentaenoic acid elicits the accumulation of several mRNAs [8]. cDNA clones corresponding to two of these mRNAs (pSTH-2 and pSTH-21) were isolated and characterized [9]. They were found to accumulate in tubers upon wounding and elicitor treatments. pSTH-2 related mRNAs also accumulate in stems upon wounding and in potato and tomato leaves treated with a mycelial homogenate from the late blight fungus Phytophthora infestans [9]. Proteins encoded by these cDNAs (pSTH-2 and pSTH-21) were found to be highly similar to pea pathogenesis-related (PR) protein pi49 and pI 176 [4], to parsley PR protein PRI-1 and PR1-3 [ 10], and to Betvl, the major pollen allergen from white birch [ 1]. The two potato cDNA clones were used to screen a genomic library made in the vector 2 EMBL 3. One hybridizing clone was characterized and shown to contain a gene corresponding to pSTH-21. Its nucleotide sequence is presented in Fig. 1. The gene is made of two exons that are 100~o identical to the pSTH-21 cDNA clone, including the 5' and 3' untranslated regions [9]. The intervening sequence is 347 bp long and interrupts the coding region at amino acid 57. As in the case for many plant genes, no AAUAAA consensus polyadenylation signal sequence can be found in the vicinity of the poly(A) addition site [6]. Multiple transcription start sites have been identified by reverse transcription of polyadenylated RNA from elicitortreated tuber disks, using as a primer a synthetic oligonucleotide complementary to nucleotides 957 to 971. The fact that STH-21 is part of a multigene family [8, 9] could explain this result. Sequences homologous to TATA and CAAT boxes are located at position 22 (TATAAATA) and 117 (CAAAT), respectively, from the most upstream transcription start site. Identical sequences are also located 27 and 67/102bp upstream of the transcription start site of the parsley PRI-1 gene [10].

Direct observation of the structure of mycelial cell walls from the potato blight fungus Phytophthora infestans by solid-state13C NMR

Mycelial cell walls from the potato blight fungus (Phytophthora infestans) (Mont.) de Bary were examined in the solid state by 13C nuclear magnetic resonance spectroscopy with cross‐polarization and magic‐angle spinning. The spectrum was free from interference by spinning sidebands. The main component of the cell walls had the spectral properties of a β‐(1,3′)‐glucan. Protein appeared to be present also. The presence of β‐(1,6′)‐linked glucose residues, cellulose or chitin was not ruled out, but there was no evidence for these as major components of the cell walls.

Purification and Characterization of Extracellular Pectinesterases from Phytophthora infestans

Constitutively produced extracellular pectinesterases from culture filtrates of the potato late blight fungus Phytophthora infestans were purified and characterized. One enzyme (PE II) was purified to homogeneity. Sodium dodecyl sulfate electrophoresis of the second enzyme (PE I) revealed two protein bands; there are indications that both proteins are pectinesterases, which were not separable by a number of different techniques. Thus, P. infestans might produce three pectinesterases in vitro. Enzyme activities were optimal in the neutral pH range and were largely dependent on the presence of NaCl or CaCl(2) in the reaction medium. The molecular weight of the PE I-complex was between 45 and 48 kilodaltons, and the one of PE II was between 35 and 40 kilodaltons. Further investigations will help us to clarify the role of these enzymes during pathogenesis.

Structure‐activity relationships in triorganotin biocides: The influence of the anionic radical

AbstractBioassay data are reported for seven triorganotin compounds (R3SnX), in which R=phenyl, cyclohexyl, or 2‐methyl‐2‐phenylpropyl, and × is the anionic form of the organic chelating ligands quinolin‐8‐ol, quinoline‐8‐thiol, 1,3‐diphenylpropane‐1,3‐dione, or 3‐hydroxyflavone, when tested against an organophosphorus‐resistant species of the two‐spotted spider mite (Tetranychus urticae), the potato blight fungus (Phytophthora infestans), and the vine downy mildew fungus (Plasmopara viticola). The relationship between the activity and the co‐ordination number of the tin atom is discussed, and it is shown that the anionic group × can, in some instances significantly affect the biological properties.

Transformations of steroids and the steroidal alkaloid, solanine, by Phytophthora infestans

The following steroids and steroidal alkaloids have been incubated with the blight fungus Phytophthora infestans: androst-4-ene-3,17-dione, cholesterol, cholesteryl acetate, cholesteryl myristate, cholesteryl palmitate,cholesteryl stearate, dehydroisoandrosterone, 6α-hydroxy-androst-4-ene-3,17-dione, 6β-hydroxyandrost-4-ene-3,17-dione, 11α-hydroxyprogesterone, pregnenolone, progesterone, sitosterol, sitosteryl acetate, solanidine, solanine, stigmasterol, stigmasteryl acetate and testosterone. No hydroxylation was observed, but the fungus is able to oxidize alcohol functions at C-3β, C-6α, C-11β and C-17β to carbonyl. In addition, hydrolysis of acetate to hydroxyl at C-3β, and of solanine to solanidine, was observed. The relationship between metabolism and the nature of substitution at C-17β is discussed.

Inheritance of Resistance to Blight (Phytophthora infestans) in Potatoes: Strain C and its Relationships

SynopsisThe common strain A of the blight fungus (Phytophthora infestans) and two new strains, B and C, have been employed in testing potato varieties and seedling progenies, bred from the wild species S. demissum, for resistance to the disease. The reactions of seedlings to infection with strain C are compared with those of strains A and B. The C strain is shown to be more virulent than A, since it attacks some A resistant as well as all A susceptible plants. Likewise the B strain is more virulent than A. The difference between the pathogenicity of strains B and C, however, is not one of degree of virulence; one plant may be B resistant-C susceptible, while another may be B susceptible-C resistant. This difference is essentially of a qualitative nature. Resistance to these strains, which is manifested by the hypersensitive condition of the plant's cells, is produced in the presence of three major independent genes, Re, Rb and Rbc, which confer resistance to strains A and C, A and B, and A, B and C respectively. Segregations in each case are similar in type, and are characterised by an excess of recessive individuals.

XX.—Inheritance of Resistance to Blight (Phytophthora infestans) in Potatoes: Comparison of A and B Strains

Previous reports (Black, 1943, 1945) on the resistance of potatoes to the blight fungus (Phytophthora infestans) have shown the existence of at least two major genetic factors (Ra and Rb) in the host, and the occurrence of not less than two strains (A and B) of the pathogen.From the studies then reported, it was concluded that the two genes had been brought into the potato from different phyletic sources and that one, Ra, when in the dominant state, conferred resistance to strain A, while similarly Rb conferred resistance to strain B.