Pathogenic variation in poplar rust <Emphasis Type="Italic">Melampsora larici-populina</Emphasis> from England

Using a leaf disc method, 19 isolates of the poplar rust, Melampsora larici-populina , and one isolate of M.populnea from England were inoculated on to 25 poplar clones belonging to Populus nigra and P.trichocarpa, and hybrids between P. deltoides and P. nigra, P. deltoidesand P. trichocarpa, P.tacamahaca and P.trichocarpa, and P. alba and P. tremula. Disease was scored based on the pustule area and inoculum density. In terms of whether sporulating uredinia formed, the 19 isolates showed seven different patterns to the tested poplar clones. The majority of the rust isolates infected P. nigra P3090 and Vereecken, P.nigra×P. deltoides Casale and Tasman, P. tacamahaca×trichocarpa 36 and Balsam Spire, and P.trichocarpa Blom. Populus trichocarpa×P. deltoides 69039/4 was infected by only three isolates collected from southern England. No visible symptoms appeared on P. alba ×P. tremulaTower and P.trichcarpa×P. deltoides×P. deltoides76028/5 in inoculations with M. larici-populina isolates. Populus alba×P.tremula Tower was infected only by M. populnea. When M. larici-populina isolates were tested using AFLP, no differences were found either between isolates from different geographical regions or between those having narrow spectrum of virulence and those showing wide spectrum of virulence on the tested clones. The results suggest that the UK rust populations possess virulences which were found in races E1, E2, E3 and E4 in continental Europe and that rust having virulence patterns similar to race E4 has occurred in UK poplar plantations since 1996.     

Induced Resistance to Cyst and Root-knot Nematodes in Cereals by DL-β-amino-n-butyric Acid

Foliar sprays and soil drenches with DL--amino-n-butyric acid (BABA) reduced the number of Heterodera avenae and H. latipons cysts on wheat and barley. Foliar sprays of wheat with 8000mgl^–1 BABA reduced the number of H. avenae cysts by 90%, whereas 2000mgl^–1 BABA was enough to reduce the number of H. latipons cysts by 79%. Multiple spray treatments with 2000mgl^–1 BABA at 10-day intervals reduced the number of H. avenae cysts on wheat and barley. A soil drench of wheat with 125mgl^–1 BABA reduced the number of H. latipons cysts by 93% and H. avenae cysts by 43%. Second-stage juveniles of these nematodes penetrated and formed syncytia in wheat roots soil-drenched with BABA. More adult males of H. avenae were produced in BABA (<250mg1^–1)-treated wheat roots (~76%) than in untreated roots (27%). Soil drenches with higher concentrations of BABA inhibited development of adult males and females. Several chemical elicitors of induced resistance were tested for their ability to reduce the number of H. avenae cysts on wheat. Only BABA was found to be an effective resistance inducer. The number of egg masses of an unidentified Meloidogyne sp. root-knot nematode, which infects only monocots, was also reduced by 95% by a soil drench of wheat with 500mgl^–1 BABA. Development of this nematode inside the BABA-treated roots was also inhibited.     

Comparison of immunofluorescence microscopy and dilution-plating for the detection of Xanthomonas campestris pv. campestris in crucifer seeds

The correlation between immunofluorescence microscopy (IF) and dilution-plating on nutrient starch cycloheximide agar (NSCA) or NSCA with the addition of nitrofurantoin and vancomycin (NSCAA) was studied for the detection ofXanthomonas campestris pv.campestris (Xcc) in crucifer seeds. When checking 50 l of the seed extract in IF, IF and dilution-plating gave corresponding results (both positive or negative) for 45.4–56.4% of the samples tested. No differences were observed in this respect between tests using a polyclonal antiserum (PCA 94) and replicate tests using monoclonal antibodies (MCA 20H6). When 20 l of the seed extract was checked in IF, 67.3–71.3% of the samples tested were both positive or negative with dilutionplating and IF. IF negative and dilution-plating positive samples were found for 0.0–7.3% of all samples tested. The percentage of IF positive and dilution-plating negative samples ranged from 26.7–29.2 (20 l seed extract checked) to 41.8–47.3% (50 l seed extract checked). Generally, the probability of isolating Xcc increased with increasing numbers of fluorescent cells found in IF. Above 10 000 cells per ml the probability of isolating Xcc ranged from 57.1–81.8%. Increasing the extraction time from 5 min to 2.5 h shaking showed no significant increase of the number of samples found positive in IF and dilution-plating. However, when using both 5 min and 2.5 h shaking as compared to 5 min shaking only, more samples can be found positive in IF (1.0–14.5%) and dilution-plating (3.0–18.5%). Examining 1 l instead of 50 l of the sample smear, would increase the correspondence between IF and dilution-plating results up to minimally 69.1% (MCA 20H6). However, the risk of false-negative results in IF as compared to dilution-plating would also increase.     

Effect of chemotherapeutically active amino acids on pathogenicity and growth of a wild type strain and a nutritional mutant of Cladosporium cucumerinum Ell. et Arth.

The pathogenicity of a wild type strain and a nutritional mutant ofCladosporium cucumerinum was not changed after prolonged culturing on media containing D-serine, L-threo--phenylserine or DL--aminobutyric acid. Growth of the wild type strain was inhibited by D-serine, whereas the mutant was found able to utilize this compound. Both strains were able to grow in a medium containing L-threo--phenylserine as sole source of nitrogen. These results support the hypothesis that the increase in resistance to both strains of cucumber seedlings treated with the compounds just-mentioned is not due to a direct inhibition of the development of the pathogen.Samenvatting De pathogeniteit van een wild type stam en een mutant vanCladosporium cucumerinum werd niet beïnvloed door kweken op media, die D-serine, L-threo--phenylserine of Dl--aminoboterzuur bevatten. De groei van de wild type stam werd door D-serine geremd, terwijl de mutant deze verbinding als stikstofbron kon gebruiken. Beide stammen waren in staat te groeien in een medium dat alleen L-threo--phenylserine als stikstofbron bevatte. Deze resultaten steunen de hypothese dat de toename in resistentie van komkommerkiemplanten tegen beide stammen, veroorzaakt door behandeling met de genoemde verbindingen, niet het gevolg is van een directe remming van de ontwikkeling van het pathogeen.     

Conjugation of δ-endotoxin from Bacillus thuringiensis with abamectin of Streptomyces avermitilis as a new type of biocide, GCSC-BtA, for control of agricultural insect pests

Conjugation of -endotoxin from Bacillus thuringiensis with abamectin, a toxin of Streptomyces avermitilis, was carried out to form a new type of biocide, GCSC-BtA based on Germany-China Scientific Cooperation research, for the control of agricultural insect pests. The strategy for biochemical linkage was designed by conjugating an amino group in B.t. protoxin with a carboxyl group in carboxylated abamectin under the treatment of conjugator EDC [1-Ethyl-3-(3-dimethylaminopropyl carbodiimide Hydrochloride)]. The formation of B.t. protoxin was processed by solubilizing B.t. crystal in 25mM dithiothreitol (DTT) at 37°C for 2h. The carboxylated abamectin was formed by carboxylating the NaH-activated abamectin with 10mg/ml butyric anhydride at 111°C in a water-circumfluent condensation device for 2h. The conjugating reaction, consisting of 5mg/ml B.t. protoxin, 10mg/ml carboxylated abamectin and 19.17mg/ml EDC, was successfully conducted at room temperature for 24h. Significant differences were found between pure abamectin, carboxylated abamectin and the conjugated BtA by means of UV-photo absorptions recorded at wavelengths 354, 438, 518, 600nm (P<0.01). LT₅₀ of the conjugated GCSC-BtA to the 3^rd instar larvae of Plutella xylostella (L.) (Lep., Plutellidae) was 35.27 g a.i./ml, about 62% and 76% of that caused by the B.t. protoxin and the caxboxylated abamectin, respectively. The conjugated GCSC-BtA caused 87.14% mortalities in larvae of P. xylostella, 93.75% in adult Myzus persicae (Sulzer) (Hom., Aphididae) and 89.33% in adult Phyllotreta vittata Fabricius (Col., Chrysomelidae) as compared to 48.33% by the B.t. crystal only in P. xylostella. The symptoms caused by conjugated GCSC-BtA in the 3^rd instar of P. xylostella were black color in the head part and white-yellow in the abdomen of dead larvae, which differed from the black color or the white-yellow all along the body caused by either the B.t. crystal or the abamectin, respectively. It was concluded that the conjugated GCSC-BtA biocide had a broader host spectrum and a faster killing speed than either the B.t. crystal or abamectin alone for the control of agricultural pests.     

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.     

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     

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.     

Identity of red currant spoon leaf virus

Summary Red currant spoon leaf virus, isolated from red currant in The Netherlands, is a strain of raspberry ringspot virus; it shares most of its antigenic groups with the type strain from Scottish raspberry but causes distinctive symptoms inPetunia hybrida. It differs from tomato ringspot virus, obtained byHildebrand (1942) from red currant in the United States.Klesser's (1951) red currant ringspot virus is probably the same as red currant spoon leaf virus.Samenvatting Het hier beschreven onderzoek heeft uitgewezen, dat het in Nederland uit rode bes geïsoleerde lepelbladvirus (van der Meer, 1960) een stam van het ringspot-virus van framboos is. Hoewel het lepelbladvirus de meeste antigenen gemeen heeft met de type-stam van het framboze-ringspot-virus, die uit een Schotse frambozeplant werd verkregen (tabel 1), kunnen beide worden onderscheiden op grond van de symptomen die zij opPetunia hybrida teweegbrengen. Het lepelbladvirus verschilt van het ringspot-virus van tomaat, dat in de Verenigde Staten doorHildebrand (1942) uit rode bes werd geïsoleerd. Het doorKlesser (1951) bestudeerde ringspot-virus van rode bes is waarschijnlijk hetzelfde als het lepelbladvirus.     

Electron microscopic observations on haustoria isolated from cucumber leaves infected with powdery mildew

The fine structure of haustoria isolated from cucumber leaves infected with powdery mildew (Sphaerotheca fuliginea) was studied. Electron microscopy showed a haustorial body of 5–7 which contains many mitochondria and is surrounded by an electron lucent sheath of up to 4 in thickness. The sheath is limited by a heavily invaginated membrane of about 0.03 . The central body is connected with the sheath membrane by fingerlike convoluting protrusions.Samenvatting Er werd elektronenmicroscopisch onderzoek verricht aan haustoriën, geïsoleerd uit komkommerbladen geïnfecteerd met echte meeldauw (Sphaerotheca fuliginea).De haustoriën bevatten een centraal lichaam van 5 to 7 met veel mitochondriën dat omgeven is door een schede van maximaal 4 die de elektronenbundel gemakkelijk doorlaat. De schede wordt begrensd door een geïnvagineerde membraan van ongeveer 0,03 .Het centrale lichaam is via kronkelend verlopende uitstulpingen verbonden met de schedemembraan.The study has been carried out at the Laboratory of Phytopathology, State Agricultural University, Wageningen, in connection with the activities of T.N.O. Research Unit for Internal Therapy of Plants.     

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.     

Morphological studies on attachment of spores of <Emphasis Type="Italic">Magnaporthe grisea</Emphasis> to the leaf surface of rice

Rice leaves were inoculated with spores of Magnaporthe grisea, and the number of fluorescence-labeled spores that attached to the leaf surface were counted before and after leaves were dipped and then stirred in water. Just 5% of the spores were retained on the leaf surface 1h after inoculation; the percentage retained then increased rapidly between 1.25 and 1.50h, and most had attached by 2h. Scanning electron microscopy revealed that most conidia were lying on a few wart-like protuberances 2–4µm high. Spores became attached when the germ tubes were long enough to reach the leaf surface, at least 3µm, by mucilaginous substances at the tip. Retained spores swayed when water was added under the cover glass from one side, indicating that the attachment was confined to the tips of germ tubes. Spores are attached to the rough leaf surface by mucilaginous substances – not at the tip of spore as reported on smooth artificial substrates but at the tip of the germ tubes.     

Differences in pathogenesis observed among susceptible interactions of carnation with four races of Fusarium oxysporum f.sp. dianthi

Susceptible interactions of Early Sam carnations with races 1,2,4, and 8 ofFusarium oxysporum f. sp.dianthi differed in pathogenesis, both after stem and after root inoculation. Race 1 induced pallescence and withering of leaves. Affected vascular tissue had a uniform pallid to pale brown colour; though heavily colonized, it was not or virtually not degraded. Defence reactions developed only slowly. Race 2 induced yellowing, of the midribs in particular, and withering of leaves. Affected vascular tissue was white with dark brown margins. Colonized tissue was degraded to leave vascular cavities. At lower heights of colonization, many defence reactions developed, which sometimes resulted in localization of the pathogen. Race 4 induced a similar pathogenesis as race 2, except for less intensive defence reactions. Race 8 induced midrib lesions on, and pallescence, withering and necrosis of leaves. Affected vascular tissue had a uniform light brown colour. Degradation of colonized vascular tissues was rare; instead, many defence reactions were observed, even at high heights in the plants.Races 1, 2 and 4 ofF. oxysporum f. sp.dianthi did not induce disease symptoms in Novada carnations, known to be highly resistant to race 2. Stem-inoculated plants localized the infection close to the inoculation site; stems of root-inoculated plants remained unaffected. The localization response also occurred in Early Sam and Novada carnations stem-inoculated withF. oxysporum f. sp.lycopersici.Samenvatting Tussen interacties van Early Sam-anjers met fysio's 1, 2, 4 en 8 vanF. oxysporum f. sp.dianthi werden verschillen in ziekteontwikkeling gevonden na wortel-zowel als stengelinoculatie. Fysio 1 gaf verbleking en verdroging van de bladeren. Aangetast vaatweefsel was gelijkmatig vaal of lichtbruin van kleur, en werd hevig gekoloniseerd, maar vrijwel niet afgebroken. Afweerreacties kwamen slechts traag op gang. Fysio 2 gaf vergeling, in het bijzonder van de hoofdnerven, en verdroging van de bladeren. Aangetast vaatweefsel was wit met donkerbruine randen. Gekoloniseerd weefsel werd afgebroken, hetgeen leidde tot de vorming van holten in het vaatweefsel. In de lagere gekoloniseerde delen traden veel afweerreacties op, hetgeen soms lokalisatie van het pathogeen tot gevolg had. Fysio 4 gaf eenzelfde ziekteontwikkeling als fysio 2, maar minder afweerreacties. Fysio 8 gaf lesies bij de hoofdnerven, en verbleking, verdroging en necrose van bladeren. Aangetast vaatweefsel was gelijkmatig lichtbruin van kleur. Afbraak van gekoloniseerd vaatweefsel werd zelden waargenomen; veel afweerreacties vergezelden de kolonisatie tot hoog in de stengel.Inoculatie van Novada anjers met fysio's 1,2 en 4 vanF. oxysporum f. sp.dianthi had geen ziektesymptomen tot gevolg. Via de stengel geïnoculeerde planten lokaliseerden de infectie ter hoogte van het inoculatiepunt; de stengels van via de wortels geïnoculeerde planten waren onaangetast. De lokalisatiereactie trad ook op in Early Sam en Novada anjers na inoculatie via de stengel metf. oxysporum f. sp.lycopersici.     

Infection of Tomicus piniperda (Col., Scolytidae) with Canningia tomici sp. n. (Microsporidia, Unikaryonidae)

Canningia tomici sp. n. (Microsporidia, Unikaryonidae) infects the midgut epithelium, the gut muscules, Malpighian tubules, connective tissues, adipose tissues and the gonads of the pine shoot beetle, Tomicus piniperda (L.) (Coleoptera, Scolytidae). The infection is present in populations of Tomicus piniperda in Europe and in the United States. Uninucleate oval single spores occur in two sizes: 2.8±0.4× 1.4±0.4m and 3.8±0.3×2.0±0.2m. The polar filament of this microsporidium is fixed subapically in a flat anchoring disc. The thick posterior lamellae of the binary polaroplast are asymmetric due to the lateral fixation of the polar filament.     

Biological control of cucumber powdery mildew by Tilletiopsis minor

Samenvatting Onder optimale omstandigheden konT. minor de ontwikkeling van komkommermeeldauw (Sphaerotheca fuliginea) tegengaan.Spuiten met 2×10⁷ sporen ml^–17 dagen na inoculatie met komkommermeeldauw gaf een reductie van meeldauwontwikkeling van ongeveer 90%. Wanneer een tweede bespuiting met dezelfde concentratie sporen 3 dagen na de eerste werd toegepast bleven de planten vrij van meeldauw tot ze werden opgeruimd 3 weken later.Bij een R.L. lager dan 70% en een temperatuur boven 30 °C had geen van de behandelingen succes. T. minor bleek ongevoelig voor dimethirimol (Milcurb) bij een concentratie van 125 g ml^–1, terwijl er gemakkelijk een mutant kon worden verkregen, die resistent was tegen 100 g fenarimol ml^–1, bij gelijk blijvende groeikracht en pathogeniteit ten opzichte van komkommermeeldauw, waardoorT. minor ingepast kan worden in een schema voor geïntegreerde bestrijding.     

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.     

Analysis of molecular diversity in <Emphasis Type="Italic">Crinipellis perniciosa</Emphasis> with AFLP markers

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.     

Interactive Effects of Host, Pathogen and Mineral Nutrition on Grey Leaf Spot Epidemics in Uganda

Grey leaf spot incited by Cercospora zeae-maydis is a new devastating foliar disease of maize in East Africa. For effective control, elucidation of the most critical elements of the grey leaf spot disease pyramid is important. This study investigated the role of mineral nutrition, pathogen variability and host resistance in the epidemic. Trials were conducted under field and controlled environments. The 28 isolates used in the controlled environment varied significantly (P 0.05) in parasitic fitness measured indirectly as disease efficiency, but no infection pattern could be attributed to known C. zeae-maydis pathotypes. Data from field trials showed that host resistance and mineral nutrition significantly (P 0.05) affected disease efficiency, with highest disease development occurring in nitrogen-augmented plots. Exclusive phosphorus application had no clear effect on grey leaf spot epidemics but combined application with nitrogen significantly (P 0.05) reduced the predisposition effects of nitrogen to the disease. Overall, treated plots had less disease than unfertilised plots. Fertiliser application had no effect on sporulation capacity, while cultivars significantly affected it. Geographic differences in amount of disease were observed, suggesting environment influences on grey leaf spot incidence. The results suggest that the current grey leaf spot epidemics in East Africa are due to favourable cultivars, poor mineral nutrition and environmental interactions.     

Toxigenic Fusarium Species of Liseola Section in Pre-harvest Maize Ear Rot, and Associated Mycotoxins in Slovakia

The occurrence of Fusarium species of Liseola section and related toxins was investigated for two years (1996 and 1998) on maize ear rot samples collected in the most important areas for maize growing in Slovakia. The species most frequently isolated was F. verticillioides, followed by F. proliferatum in 1996 and F. subglutinans in 1998. Most of the strains belonged to mating populations A, D, and E of the teleomorph Gibberella fujikuroi. Fusarium graminearum was also frequently recovered in both the years of investigations. Toxin analysis of maize ears showed that most of the samples (21 out of 22) were contaminated with at least one toxin. In particular, the concentration of fumonisin B₁, and fumonisin ₂ was up to 26.9 and 5.1gg^-1, respectively in 1996, and up to 12.1 and 6.3gg^-1, respectively in 1998. Beauvericin was detected only in one sample in 1996. Seven samples in 1996 were contaminated by fusaproliferin up to 8.2gg^-1, but just traces of the toxin were found in one sample in 1998. All 29 strains of F. verticillioides, two of three strains of F. proliferatum and none of eight F. subglutinans strains isolated from samples produced fumonisin B₁ in culture on whole maize kernels (0.1–5646 and 940–1200ugg^-1, respectively). Two strains of F. subglutinans and two of F. proliferatum produced beauvericin (up to 65 and 70gg^-1, respectively). Ten strains of F. verticillioides produced beauvericin: 9 strains produced a low amount (up to 3gg^-1), while only one of them produced a high level of toxin (375gg^-1). Fusaproliferin was produced by two F. proliferatum strains (220 and 370gg^-1), by seven F. subglutinans (20–1335gg^-1) and by three F. verticillioides (10–35gg^-1). This is the first report on fusaproliferin production by F. verticillioides, although at low level.     

Resistance to carbendazim in Pseudocercosporella herpotrichoides from Dutch wheat fields

Culm base samples were collected in August 1984, from winter wheat fields in Groningen, Flevoland and near Wageningen in Gelderland. In contrast to fields in the latter two areas, fields in Groningen were characterized by intensive wheat cultivation and yearly applications of benzimidazole fungicides for eyespot control. Seventy-seven isolates ofPseudocercosporella herpotrichoides were recovered. Forty-three percent of recovered isolates were carbendazim-resistant, all of which originated from fields in Groningen. Resistant isolates were detected among both rye- and wheat-types of the pathogen. Rye-type isolates were identified asP. herpotrichoides var.acuformis and those of the wheat-type asP. herpotrichoides var.herpotrichoides.Samenvatting Monsters van de halmbasis van tarwestro werden in augustus 1984 verzameld van percelen met wintertarwe in Groningen, Flevoland en bij Wageningen in Gelderland. In tegenstelling tot de percelen in de twee laatstgenoemde gebieden, waren de percelen in Groningen gekenmerkt door intensieve tarweteelt en door jaarlijkse bespuitingen met benzimidazool fungiciden tegen de oogvlekkenziekte. In totaal werden 77 isolaten vanPseudocercosporella herpotrichoides verkregen. Drieënveertig procent van de isolaten was resistant tegen carbendazim en alle resistente isolaten waren afkomstig van percelen in Groningen. Resistente isolaten werden zowel bij het rogge- als bij het tarwetype van het pathogeen aangetroffen. Isolaten van het roggetype werden geidentificeerd alsP. herpotrichoides var.acuformis en die van het tarwetype alsP. herpotrichoides var.herpotrichoides.