Analysis of gene sequences for the nucleocapsid protein from <Emphasis Type="Italic">Tomato spotted wilt virus</Emphasis> for promoting RNA-mediated cross-protection using the <Emphasis Type="Italic">Potato virus X</Emphasis> vector system

Virus interactions between Tomato spotted wilt virus (TSWV) and Potato virus X (PVX) containing the nucleocapsid protein (N) gene sequences were examined to evaluate the capacity of the N gene sequences from TSWV to promote RNA-mediated cross-protection. Plants simultaneously inoculated with TSWV and PVX containing the 3 96bp of the N gene were highly resistant to TSWV infection, whereas no such resistance was observed in plants inoculated with TSWV and PVX containing the 5 96bp. These results suggest that the 3 portion of the N gene has a higher capacity for promoting RNA-mediated cross-protection of TSWV.     

Molecular evidence that a lily-infecting strain of Tulip breaking virus from Japan is a strain of Lily mottle virus

The sequence of the 3-terminal 2074 nucleotides (nts), excluding the 3-poly (A) tail, of RNA of a potyvirus isolated from lily (Lilium Asiatic hybrid cv. Enchantment) in Japan, currently tentatively designated as Tulip breaking virus-li (TBV-li), was determined. The sequence started within a single open reading frame (ORF) that encoded the carboxyl terminus of the large nuclear inclusion protein (NIb) and the complete 275-amino-acid coat protein (CP), followed by a 3-untranslated region (3-UTR) of 204 nts. The CP of TBV-li shared 91% amino acid (aa) sequence identity with that of TBV lily strain Dutch isolate (TBV-lily). The nt sequences of their 3-UTR were 94% identical. However both viruses shared only 60–65% sequence identities with TBV tulip strain Niigata isolate in the corresponding regions. The results suggest that TBV-li is closely related to TBV-lily, and that these two TBV lily strains should be classified into a species different from TBV tulip strains. We therefore support a proposal to rename TBV-lily Lily mottle virus (LMoV), and suggest that TBV-li is another strain of LMoV (LMoV-J).     

Changes in susceptibility of bean leaves (Phaseolus vulgaris) to Sclerotinia sclerotiorum and Botrytis cinerea by pre-inoculative ozone exposures

The effects of ozone on the susceptibility of leaves ofPhaseolus vulgaris toSclerotinia sclerotiorum andBotrytis cinerea have been investigated. Seedlings of one ozone-sensitive (Pros) and five relatively ozone-insensitive cultivars (Gamin, Precores, Groffy, Narda, Berna) were exposed to different ozone concentrations (0, 120, 180 and 270 g m^–3) for 8 h. One day after the exposures, primary leaves were detached and immediately inoculated with spores of either pathogen suspended in water or in a 62.5 mM KH₂PO₄ (Pi) solution. Visible ozone injury differed between the cultivars and increased with increasing ozone concentration. On the leaves of non-exposed plants, spores of the pathogens suspended in water caused very few lesions, whereas fungal pathogenicity was stimulated by addition of Pi to the inoculum. Ozone-injured leaves of all cultivars exhibited lesions after inoculation of the leaves with the pathogens suspended in water, and the number of lesions was positively correlated with the level of ozone injury for either pathogen and cultivar. The increase in susceptibility of bean leaves in response to increasing ozone concentrations was greater forB. cinerea than forS. sclerotiorum when spores were suspended in water, but was similar when the spores were suspended in Pi.In general, the number of lesions following inoculation with spores in Pi increased with increasing ozone concentration. However, the number of lesions in the ozone-insensitive Groffy was reduced by an exposure to 120 g m^–3 but increased with higher concentrations. This pattern of susceptibility response to the pathogens was not found in the other ozone-insensitive cultivars and, thus, did not appear to be related to the inherent ozone-insensitivity in bean.     

Some coat protein constituents from strawberry latent ringspot virus expressed in transgenic tobacco protect plants against systematic invasion following root inoculation by nematode vectors

The coding sequences in RNA2 for the coat proteins (CP) of strawberry latent ringspot virus (SLRSV) were modified and amplified using polymerase chain amplification reactions (PCR) to facilitate their expression inAgrobacterium tumefaciens-transformedNicotiana tabacum Xanthi-nc. The coding sequences for the smaller capsid protein (S, 29kDa) and that for the theoretical precursor of L and S (P, 73kDa) had ATG initiation codon sequences added at the 5-proximal Ser/Gly (S/G) cleavage site in the unmodified sequence. The sequence coding for the larger of the two proteins of mature SLRSV capsids (L, 44kDa) had an ATG codon added at its 5 S/G site and a TAG stop codon sequence added at the 3-proximal S/G site. The P, L and S proteins were expressedin planta to a maximum concentration of 0.01 % of total extractable proteins but did not assemble into virus-like particles. When challenged by mechanical inoculation with virus particles or viral RNA, and compared with control plants, tobacco plants (primary transgenic clones or S1 and S2, kanamycin-resistant seedlings) expressing the virus capsid subunits separately, or their precursor, decreased the accumulation of SLRSV particles in inoculated leaves and fewer plants became invaded systemically. In experiments in which the roots of seedlings were exposed to SLRSV-carrying vector nematodes (Xiphinema diversicaudatum), SLRSV was detected in the roots of non-transformed control tobacco plants (6/20) and in transgenic tobacco expressing the L protein (7/40), but not in any of 25 tobacco plants expressing the S protein or in 35 expressing the P protein. This is the second example of CP-mediated resistance to virus inoculation by nematode vectors.     

Resistance of rose rootstocks to crown gall (Agrobacterium tumefaciens)

Various types of rose rootstocks were tested for their resistance to crown gall. The rootstock Iowa State University (ISU) 60–5 was the most resistant, followed by Brooks 48, Clarke 1957 and Welch. Rosa multiflora, R. noisettiana (Manetti) and Basye No. 3 were very susceptible. The inoculations were made with four isolates ofAgrobacterium tumefaciens (Smith et Townsend) Conn, respectively from aDahlia sp.,Rosa spp. andPrunus persica. It was found that the isolate fromDahlia was a different race to the isolates fromRosa andPrunus spp.Samenvatting Bij onderstammen van rozen, kunstmatig geïnoculeerd metAgrobacterium tumefaciens (Smith et Townsend) Conn., werden verschillen in resistentie tegen wortelknobbel gevonden. Het meest resistent was Iowa State University (ISU) 60–5, gevolgd door Brooks 48, Clarke 1957 en Welch, Zeer vatbaar warenRosa multiflora, R. noisettiana (Manetti) en Basye No. 3. De vier isolaten vanA. tumefaciens, gebruikt voor de inoculaties, waren respectievelijk afkomstig van eenDahlia sp.,Rosa spp. enPrunus persica. Het isolaat vanDahlia en de isolaten vanRosa enPrunus spp. behoorden tot twee verschillende fysiologische rassen. De vorming van tumoren was in sommige gevallen afhankelijk van de methode van inoculatie; inoculaties bij de stambasis waren meer succesvol dan in het midden van de stam.     

A greenhouse test for screening sugar-beet (Beta vulgaris) for resistance to beet necrotic yellow vein virus (BNYVV)

Small differences in activity between batches of purified beet necrotic yellow vein virus (BNYVV) were observed in ELISA. A four-parameter modelled dose-response curve of purified BNYVV was used for the conversion of ELISA values to virus concentrations. Seedlings of the susceptible cultivar Regina and the partially resistant cultivars Nymphe and Rima were tested for resistance to BNYVV in a mixture of sand and infested soil. Plants were grown in a green-house with low nutrient supply and at temperatures below the optimum of both the vectorPolymyxa betae and BNYVV. Root systems were small and consisted mainly of lateral roots. Significant differences in average virus concentrations were found between cultivars, both when using the complete root systems and when using either the top or the bottom part of the root systems. Average virus concentrations in Regina were always significantly higher than in Rima and higher than in Nymphe on all occasions except one (P<0.05). Differences between Nymphe and Rima were less evident. Variation between plants was greatest within Rima. The test described in this paper can be used for the discrimination of different cultivars and for the identification of individual plants with resistance to BNYVV.     

Diapause in the nematodeGlobodera pallida

Over a period of 12 months new and old cysts ofGlobodera pallida were hatched in potato root diffusate according to a novel nematode-response hatching protocol. In this protocol, cysts were set to hatch at the beginning of autumn and then left to indicate when their hatching ability was exhausted (when less than 100 juveniles/replicate/week emerged) before another batch of cysts was set to hatch. At any time of the year for the 12 months this experiment was conducted there were cysts hatching. After 12 months of hatching, eight hatching curves were obtained. Based on the hatching curves of the new and old cysts, diapause was shown to be present in new cysts in autumn, winter and early spring. However, diapause was absent in late spring and summer.Infectivity assays to distinguish between juveniles obtained in the periods when cysts were in diapause and when cysts had overcome their diapause failed to show any significant difference in their infectivity. There was no significant difference in the number of eggs in new and old cysts. Based on this observation, it was suggested that high emergence in old cysts may not be a result of few eggs in the cyst but rather due to absence of diapause. Also the presence of large numbers of eggs in old cysts even after being stored for 12 months outdoors in the soil does not support the theories of spontaneous hatching, micro-organism induced hatching or persistence of hatching factors in the soil.     

A carlavirus-specific PCR primer and partial nucleotide sequence provides further evidence for the recognition of cowpea mild mottle virus as a whitefly-transmitted carlavirus

Cowpea mild mottle virus (CMMV) has physicochemical properties typical of carlaviruses, but has remained unclassified due to a number of unusual properties, including no serological cross-reaction with 18 carlaviruses; production of brush-like inclusion bodiesin vivo; and the ability to be transmitted by whiteflies (Bermisia tabaci). In this paper we report the use of a carlavirus specific PCR primer to identify CMMV as a member of the carlavirus group. This is confirmed by nucleotide sequence (958 nucleotides) from the 3 terminal region of CMMV RNA which contains a partial open reading frame (ORF) having high similarity with the coat proteins of other carlaviruses. The sequence also contains an 11.7K ORF at the 3 terminus, containing a zinc-finger motif which is unique to carlaviruses.     

Histology of roots of resistant and susceptible carnation cultivars from soil infested with fusarium oxysporum f.sp. dianthi

Fusarium wilt-resistant Novada and wilt-susceptible Early Sam carnations were planted in soil infested withFusarium oxysporum f.sp.dianthi, and their roots studied after five and ten weeks. Both in Novada and Early Sam, the extravascular tissue of undamaged young root parts were scarsely colonized. In roots of Novada, infected xylem vessels were usually occluded with gums and surrounded by phellem tissue. In mature parts of roots, the phellem surrounding occluded vessels often merged with the external phellem surrounding the vascular cylinder, after which the occluded vessels were shed from the roots. The phellem at the root surface appeared to be a strong barrier to fungal invasion. In roots of Early Sam carnations, as well as in a few roots of Novada carnations, the defence responses did not result in compartmentation of the fungus, and colonization and degradation of the vascular tissues followed. Diseased roots finally healthy. Shoots of Early Sam carnations, and eventually a few shoots of Novada carnations, were colonized and developed wilt symptoms.Samenvatting Resistente Novada en vatbare Early Sam anjers werden geplant in grond besmet metFusarium oxysporum f.sp.dianthi. Na vijf en tien weken werden de wortels van de planten bestudeerd. De extravasculaire delen van onbeschadigde jonge wortelgedeelten waren in beide cultivars nauwelijks gekoloniseerd. In de wortels van Novada waren geïnfecteerde houtvaten meestal verstopt door gommen en omgeven door kurkweefsel. In oudere wortelgedeelten sloot het kurkweefsel rond verstopte vaten vaak aan op het kurkweefsel aan de buitenkant van het vaatweefsel, waarna de aangetaste vaten werden uitgestoten uit de wortel. Het kurkweefsel aan het worteloppervlak leek een belangrijke barrière te vormen tegen het binnendringen van de schimmel. In de wortels van Early Sam en in enkele wortels van Novada mislukte het afweerproces, en werd het vaatweefsel door de schimmel gekoloniseerd en vervolgens afgebroken. Aangetaste wortels werden na afloop van tijd hol. De bovengrondse delen van de meeste Novada anjers werden niet gekoloniseerd en bleven gezond. De bovengrondse delen van de Early Sam anjers, en op den duur die van enkele Novada anjers, werden gekoloniseerd en verwelkten.     

Some new races ofPuccinia striiformis

In the Netherlands in 1961 three new field races were found ofPuccinia striiformis, the causal fungus of yellow rust on wheat. Two of these, viz. the Falco race and the Opal race, together with the already known Etoile de Choisy race, constitute the so-called Nord-group of races, which is now clearly distinguished from the so-called Rubis-group. Most dangerous and interesting is the third of the new races. This so-called Cleo race proved to be the first to break both resistance to the Nord-group and resistance to the Rubis-group. On wheat seedlings in the greenhouse all three new races behaved like green-house race W(ageningen) 8=B(raunschweig) 55.Samenvatting Er zijn van de schimmelPuccinia striiformis Westend., de veroorzaker van de gele roest van tarwe, in Nederland in 1961 drie nieuwe veldfysio's gevonden. Dit zijn het Falco-fysio, het Opal-fysio en het Cleo-fysio. De eerste twee bleken met het reeds bekende Etoile de Choisy-fysio een groep te vormen, de z.g. Nord-groep, die zich duidelijk onderscheidt van de reeds beter bekende Rubis-groep van fysio's. Eerstgenoemde groep kenmerkt zich o.a. door de aantasting van het tarweras Nord, de laatstgenoemde door de aantasting van Rubis (zie tabel 1). Het belangrijkst en het gevaarlijkst is het Cleo-fysio. Dit bleek voor zover bekend het eerste en enige fysio te zijn dat zowel de resistentie tegen de Rubis-groep als die tegen de Nord-groep doorbreekt. Het heeft zodoende een zeer breed aantastingsspectrum. Van de tarwerassen die voorkomen in de 39ste Nederlandse Rassenlijst voor Landbouwgewassen (1964) zijn de volgende negen rassen vatbaar voor het Cleo-fysio met een aantastingsgraad van 6 tot 9 (Internationale Schaal): Cleo, Cappelle Desprez, Heine's VII, Hector, Stella, Sambo, Mado, Wodan en Jufy I. Bovendien bleek het Cleo-fysio in vergelijking met de andere veldfysio's goed te overwinteren en in 1964 reeds op vele plaatsen in Nederland aanwezig te zijn. Het Cleo-fysio maakt het des te noodzakelijker bij de selectie op resistentie tegen gele roest te werken op een brede genetische basis. Bij toetsing op tarwekiemplanten in de kas gedroegen de drie nieuwe fysio's zich alle als het kasfysio W(ageningen) 8 =B(raunschweig) 55 (zie tabel 2).     

Biochemical properties of the pathogenesis-related proteins from tobacco

This review describes the discovery and identification of the pathogenesis-related proteins (PRs) from tobacco. In crude leaf extracts the PRs are distinguished from the proteins in uninfected plants by their solubility at pH 3, resistance to a range of proteases, and mobility in polyacrylamide gels upon electrophoresis (PAGE) in non-denaturing conditions. PAGE has been used as a qualitative and semi-quantitative assay for PRs, and their migration in gels made from different acrylamide concentrations has been used to identify charge and size isomers and electrophoretically identical PRs in different tobacco cultivars. The subunit composition and molecular weight (mol. wt) of the four PRs identified first in Xanthi-nc were determined by SDS-PAGE; staining the gels has shown that these same four proteins in Samsun NN did not contain carbohydrate, lipid or nucleic acid, nor were they isozymic forms of twenty five enzymes known to increase in activity following infection with TMV. Evidence suggests that most of the PRs in Xanthi-nc and Samsun NN are extracellular.The purification of several PRs from Xanthi-nc, Samsun NN and other tobaccos is described, as well as their mol. wt, subunit and amino acid composition. PRs 1a, b and c consist of a single polypeptide and have similar mol. wt and amino acid compositions. Antisera prepared against purified Xanthi-nc b₁ protein have been used to determine serological relationships between PRs and form the basis of a very sensitive quantitative assay using ELISA. The regulation of synthesis of some PRs has been shown to involve translational control.     

The isolation of a further new race of Erysiphe graminis DC. f.sp. hordei Marchal and the genetical basis of the resistance of ‘Lyallpur 3645’

Besides the race Amsel-C₂, a new race of barley mildew (Erysiphe graminis DC. f.sp.hordei Marchal) has been isolated from a still resistant variety L 94. This race has provisionally been denoted Lyallpur 3645-C₁₇. It is able to overcome the resistance of Lyallpur 3645.It appears most likely that the barley variety Lyallpur 3645 has two closely linked genes for resistance, one for hypersensitivity and the other for an intermediate type of reaction. The first is present in the variety Amsel and both in Heine 4808.The reactions indicate that race Lyallpur 3645-C₁₇ has only one gene for virulence in addition to the ones present in race Amsel-C₂.A survey is given of the seedling reaction of some 60 previously very or moderately resistant varieties, after infection with the two new races.Samenvatting Twee fysio's van gerstemeeldauw,Erysiphe graminis DC. f.sp.hordei Marchal zijn gevonden, waarvan één niet eerder is beschreven. Dit laatste fysio wordt voorlopig aangeduid als Lyallpur 3645-C₁₇, het andere is het zgn. Amsel-C₂-fysio.Met behulp van beide fysio's is duidelijk geworden dat de lijn Lyallpur-3645 twee nauw gekoppelde resistentiegenen bezit; een gen voor een overgevoeligheidsreactie en een ander gen voor een intermediaire reactie.In het ras Amsel is alleen het overgevoeligheidsgen aanwezig, in Heine 4808, evenals Amsel afkomstig van kruisingen met Lyallpur 3645, zijn beide genen aanwezig.Het fysio Lyallpur-3645-C₁₇ lijkt daarom één gen voor virulentie meer te hebben dan Amsel-C₂.Tenslotte is een overzicht gegeven van de kiemplantreactie na infectie met beide fysio's van ongeveer 60 gerstrassen die eerder zeer goed of matig resistent waren.     

Saponaria vaccaria ‘Pink Beauty’, a new test plant for carnation mottle virus

Saponaria vaccaria Pink Beauty was found to be a test plant for carnation mottle virus. Its value was compared with that ofChenopodium amaranticolor for indexing for the virus, and this bioassay was compared with a serological diagnosis. Serological double-diffusion tests gave the quickest reactions, but proved to be the least sensitive; addition of 1M urea did not increase sensitivity. Local lesions resulting from infectivity tests on detached leaves ofC. amaranticolor in a climate room could be counted after 1 week and these tests were about equally sensitive as those on leaves on intact plants of this species in the glasshouse, which were read after about 10 days. Infectivity tests onSaponaria vaccaria Pink Beauty resulted in systemic symptoms 10 to 14 days after inoculation; this method appeared to be the most sensitive.Samenvatting Na de ontdekking, datSaponaria vaccaria Pink Beauty gevoelig is voor het vlekkerigheidsvirus van anjer, werd de waarde van de toetsplantenmethoden met deze en andere indicatorplanten onderling vergeleken en met de gebruikelijke serologische toets voor dit virus. De serologische dubbel-diffusiemethode leverde het snelst resultaten op, maar was het minst gevoelig. Ook toevoeging van 1M ureum aan het medium vergrootte deze gevoeligheid niet. Inoculatie van losse bladeren vanChenopodium amaranticolor in een klimaatkamer leverde lokale lesies op, welke na een week konden worden geteld. Deze methode was vrijwel even betrouwbaar als toetsing op bladeren aan intacte planten van dezelfde soort in de kas, welke reacties na 10 dagen afgelezen konden worden. De traagste, maar gevoeligste methode was de infectietoets metS. vaccaria Pink Beauty die ook waarde heeft voor het aantonen van enkele virussen, waarvoorC. amaranticolor niet vatbaar is.Stationed at the Experiment Station for Floriculture in the Netherlands, Aalsmeer, the Netherlands.This work was carried out during a stay of the student Miss van Olphen at the Experiment Station at Aalsmeer, the Netherlands.     

Effects of fusaric acid on cells from tomato cultivars resistant or susceptible toFusarium oxysporum f. sp.Lycopersici

Cell suspension cultures were set up from two tomato cultivars, one resistant, (Rio grande) and one susceptible (63.5) toFusarium oxysporum f. sp.lycopersici. Growth rates of the two cell cultures were comparable. Toxicity of fusaric acid, expressed as the fresh weight loss, was analyzed: It was significant in both cases after 10 h, but toxicity was twice as high for 63.5 suspension cells. In the same way, electrolyte leakage caused by fusaric acid was three times more important for 63.5 suspension cells. Moreover, fusaric acid treatment resulted in an acidification of the extracellular medium for 63.5 suspension cells (0.4 pH unit), whereas an alkalization was observed for Rio grande suspension cells (0.2 pH unit). Preliminary experiments suggest that fusaric acid was partially metabolized by Rio grande suspension cells, however, no detoxified forms of fusaric acid were detected either in cells or in culture filtrates. For these two tomato cultivars, the differences in sensitivity to fusaric acid of cultivated cells correspond to the differences in plant susceptibility toFusarium oxysporum f. sp.lycopersici.Abbreviations BAP 6-benzylaminopurine - conductivity - 2,4-D 2,4-dichlorophenoxyacetic acid - EtOAc ethyl acetate - FA fusaric acid - resistivity     

A biochemical mechanism for the gene-for-gene resistance of tomato to Cladosporium fulvum

Model experiments were carried out with the tomato varieties Moneymaker (no resistance genes), Leaf Mould Resister No. 1 (resistance gene Cf 1), Vetomold (resistance gene Cf 2) and V 473 (resistance genes Cf 1 and Cf 2) and various physiological races ofCladosporium fulvum. Leaking of³²P from labelled leaf disks, was obtained on infiltration with high molecular weight excretion products from incompatible races ofC. fulvum but not with those from compatible races. These products were obtained by Sephadex G-25 gel filtration of culture filtrates.The observations are in line with our hypothesis that the gene-for-gene relation existing between tomato andC. fulvum is based on interaction of specific fungal excretion products with specific receptors in the host which may be located in the cell membrane. The presence of these fungal compounds is supposed to be controlled by four avirulence genes (A₁, A₂, A₃ and A₄) and that of the receptors by the four resistance genes (Cf 1, Cf 2, Cf 3 and Cf 4). Results obtained from experiments with tomatoes Cf 1, Cf 2 and Cf 1 Cf 2 suggest that leakage followed by the hypersensitivity reaction occurs whenC. fulvum races possessing a specific avirulence allele penetrate into a host carrying the corresponding resistance allele.It is not yet clear why growth ofC. fulvum is stopped when leakage of the host tissue resulting in the hypersensitive reaction takes place. No compound toxic toC. fulvum is present or is formed in homogenates of tomato leaves.Samenvatting Modelproeven werden uitgevoerd met de tomatenvariëteiten Moneymaker (geen resistentiegenen), Leaf Mould Resister No. 1 (resistentiegen Cf 1), Vetomold (resistentiegen Cf 2), V 473 (resistentiegen Cf 1 en Cf 2) en verschillende fysiologischen rassen vanCladosporium fulvum. Bladponsjes van radioactief gemerkte bladeren (gemerkt met³²P) werden geïnfiltreerd en geïncubeerd met cultuurfiltraatfracties (fractionering over Sephadex G-25) vanC.fluvum. Waargenomen werd dat ponsjes, behandeld met cultuurfiltraat van een niet compatibeleC.fulvum, een grotere uitlek van radioactief gemerkt materiaal te zien gaven dan in de, gevallen waarin een compatibele schimmel werd gebruikt.Deze waarnemingen stemden overeen met onze hypothese dat de gen-om-gen relatie die bestaat tussen tomaten enC.fulvum, gebaseerd, is op een interactie van specifieke schimmelprodukten met specifieke receptoren in de plantencellen, mogelijk in de membranen. De produktie van de specifieke stoffen door de schimmel zou worden bepaald door vier avirulentiegenen (A₁, A₂, A₃ en A₄), en de aanwezigheid van de specifieke receptoren in de plantencel door de vier resistentiegenen Cf 1, Cf 2, Cf 3 en Cf 4.De waarnemingen, verkregen uit de proeven met de tomaten Cf 1, Cf 2 en Cf 1 Cf 2, doen vermoeden dat de uitlek een gevolg is van een overgevoeligheidsreactie die optreedt, indien een fysio vanC.fulvum, dat een specifiek avirulentie allel bezit, een gastheer binnendringt die beschikt over een bijpassend resistentie allel.Het is tot nu toe niet duidelijk waarom de groei vanC.fulvum stopt indien, uitlek op gaat treden als gevolg van de overgevoeligheidsreactie. In homogenaten van tomatenbladeren werd geen stof gevonden die de groei vanC.fulvum remt.     

Scytalidium Wilt of Citrus

In July 1998, a sudden wilt of Star Ruby grapefruit (Citrus paradisi Macf.) occurred in Israel in a region with a warm Mediterranean climate. The wilt of the middle and upper canopy of main limbs was accompanied by gum oozing from the affected branches. The bark of these branches attained a dark colour and the epidermis sloughed off easily revealing a mass of black powder, resulting from copious sporulation of dark conidia. Both the bark and the xylem were intensively colonized with mycelium. The fungus was identified as Scytalidium lignicola Pesante, based on the characteristic mixture of some colourless and dark conidia, produced in branched chains by conversion of the vegetative hyphae. Artificial inoculations induced typical disease symptoms and the fungus was reisolated, thus confirming Koch's postulates. Similar symptoms appeared in Star Ruby interim segments which had been cut and top grafted with various citrus cultivars. This is the first detailed report of pathogenicity of S. lignicola to citrus trees. It is postulated that the disease developed after predisposition of Star Ruby grapefruit trees by comprehensive pruning followed by extremely hot conditions.     

Variation of chrysanthemum virus B

In an attempt to unravel the complexity of chrysanthemum virus B eight isolates were grafted onto the chrysanthemum indicator cultivars Fanfare, Good News, Mistletoe, and Pink Marble. Six symptomatologically different entities could be distinguished. However, withantisera prepared against two of the isolates, no serological differences were detected. It is concluded that chrysanthemum virus B consists of many strains and that the number of strains that can be distinguished depends on the number of indicator cultivars used. The Good News, Yellow Doty, Nightingale, Improved Bronze Daisy and September Morn, mosaic viruses described by Brierley and Smith (1958) as well as the vein mottle, dwarf mottle and necrotic mottle viruses named by Hollings and Stone (1967) should be considered as strains of chrysanthemum virus B.Samenvatting In een poging de complexiteit van het chrysantevirus B te ontrafelen werden acht isolaten geënt op de chrysante-indicatorrassen Fanfare, Good News, Mistletoe en Pink Marble. Zes symptomatologisch verschillende eenheden konden worden onderscheiden (Tabel 1; Fig. 1,2 en 3), die echter serologisch niet verschilden. De conclusie wordt getrokken dat van het virus vele stammen voorkomen en dat het anntal te onderscheiden stammen afhangt van het aantal indicatorrassen dat men gebruikt. Ook de vijf mozaïekvirussen van Brierley en Smith (1958) en de leden van het leaf mottling complex van Hollings en Stone (1967) dienen als stammen van het chrysantevirus B te worden beschouwd.Stationed at the Research Station for Floriculture, Aalsmeer.     

Virulence variation and DNA polymorphism in Sphaerotheca fuliginea, causal agent of powdery mildew of cucurbits

Strains of Sphaerotheca fuliginea, one of the causal agents of powdery mildew of cucurbits, were examined for differences in virulence, mating type and DNA polymorphism. The 28 strains were chosen to be diverse according to host and geographic origin. Characterization of virulence phenotypes was based on the expression of symptoms on 4 species of cucurbits and 6 cultivars of melon. Two pathotypes, capable of attacking either cucumber cv. Marketer and melon cv. IranH and squash cv. Diamant or cucumber cv. Marketer and melon cv. IranH were observed. Tests on melon cultivars revealed 3 races. In tests of sexual compatibility with reference strains, heterothallism was observed for all isolates. Frequency of the two mating types differed significantly in the population. DNA polymorphism was determined both by restriction fragment length polymorphism (RFLP) of the ribosomal internal transcribed spacers (ITS) and 5.8S DNA amplified by the polymerase chain reaction and by random amplified polymorphic DNA (RAPD). For any one of the 11 restriction enzymes tested all strains presented an identical pattern of ITS RFLP. RAPD analysis, using 22 primers which provided reproducible patterns, revealed a relatively low degree of polymorphism. Furthermore, cluster analysis based on RAPD data (152 markers) did not separate groups within the species S. fuliginea. No association could be found between virulence, mating type, geographical and host origin and RAPD patterns. The lack of association between phenotypic and molecular markers and the close fit to linkage equilibrium for the characters examined suggest that recombination may play a role in populations of S. fuliginea.     

Race-specific aspects of polygenic resistance of barley to leaf rust,Puccinia hordei

Partial resistance of barley to leaf rust,Puccinia hordei, is characterized by a reduced rate of epidemic development in spite of a susceptible infection type. Barley cultivars vary greatly for partial resistance and its components. In a test for interaction between host cultivars and pathogen isolates most variation was of a horizontal nature. However, in the combination between Julia and the rust isolate 18, a differential interaction (vertical effect) occured; Julia had lost a small part of its partial resistance. The same interaction was found for latent period (LP), the most important component of partial resistance. Julia showed a shortened LP for isolate 18. Genetic analyses revealed, that Julia carries a polygene for longer LP not present in the other cultivars. The effect of this polygene appears to be broken by isolate 18 indicative for a gene-for-isolate relation, and even for a gene-forgene relation.Samenvatting Partiële resistantie van gerst voor dwergroest,Puccinia hordei, is gekenmerkt door een vertraagde epidemie-opbouw ondanks een vatbaar infectietype. Gerstrassen variëren sterk in partiële resistentie en haar componenten. In een toets ter bestudering van de interactie tussen waardplant en pathogeenisolaat bleek de meeste variatie horizontaal van aard te zijn. In de combinatie van Julia met isolaat 18 werd echter een differentiële interactie waargenomen; Julia had een klein deel van zijn partiële resistentie verloren. Dezelfde interactie werd waargenomen voor de belangrijkste component van partiële resistentie, de latentieperiode (LP); Julia had een iets verkorte LP voor isolaat 18. Genetische analyses toonden aan, dat Julia een polygen voor langere LP bevat; dit gen is niet aanwezig in de andere bestudeerde rassen. Er wordt verondersteld dat het effect van dit polygen door isolaat 18 is doorbroken. Dit wijst op een gen-om-isolaat en zelfs op een gen-om-gen-relatie.     

The β-tubulin Gene is a Useful Target for PCR-based Detection of an Albino Ophiostoma piliferum Used in Biological Control of Sapstain

The potential of Cartapip, an albino Ophiostoma piliferum, as a biocontrol agent against sapstain in logs has been tested in Germany. To detect the albino strain in field-tested wood, the usefulness of the -tubulin gene as a target region for developing PCR-based assays was evaluated with 102 strains of O. piliferum and 31 strains of other wood-inhabiting species. A partial -tubulin gene sequence of O. piliferum strains from different geographic origins was amplified by PCR and analyzed by restriction enzyme digestions and DNA sequencing. Variation in size and nucleotide sequences was found in intron regions indicating that intraspecific variation is present in the -tubulin gene. Consequently, -tubulin gene-derived PCR methods using PCR–RFLP patterns generated by HinfI and SpeI and sequence-specific primers Cat1 and Cat2, were developed and their specificity for Cartapip was accessed with field-tested logs and lumber. The -tubulin gene-based PCR methods were found to be valuable tools for rapid and reliable identification of Cartapip in field-tested logs and lumber in Germany. Specificity tests against other wood-inhabiting species and wild type O. piliferum strains from diverse nations showed that the Cat1 and Cat2 primers have potential to be used in other European countries, New Zealand, Alberta and British Columbia.