Virus elimination by meristem-tip culture from a range of Alstroemeria cultivars

A technique for virus elimination by meristem culture was developed for a range ofAlstroemeria cultivars. Meristems were excised from the rhizome tips and placed on a medium with indole-3-butyric acid, the required concentration of which was cultivar dependent: Six to eight weeks after dissection a shoot had formed which was transferred to a medium without growth regulators. On filter paper bridges, in a liquid medium, root formation was better than on a solid medium. In many cases a new rhizome developed. If not, the plantlet eventually died. Transfer into soil was more successful with the plantlets rooted in liquid medium than with those rooted in solid medium. Virus elimination was cultivar dependent, but in most cultivars plants resulting negatively in serological tests could be obtained. After repeated testing and selection for horticultural properties these plants may be used to start high quality mother plots.Samenvatting Een techniek werd ontwikkeld om door middel van meristeemcultuur virus te elimineren uit een aantalAlstroemeria cultivars. De meristemen werden uit de toppen van de rhizomen geprepareerd en op een voedingsbodem met IBA als auxine geplaatst. De IBA-concentratie nodig voor scheutvorming was afhankelijk van de cultivar. Na een periode van zes tot acht weken had het meristeem zich ontwikkeld tot een scheutje, dat vervolgens werd overgebracht op een voedingsbodem zonder groeistoffen. In ongeveer twee maanden vormden zich dan wortels. Deze wortelvorming was beter op een vloeibare voedingsbodem met papieren bruggetjes dan op een vaste voedingsbodem van agar. In veel, maar niet in alle gevallen, vormde zich ook een nieuw rhizoom. Indien geen rhizoom werd gevormd stierf de plant. Gewortelde plantjes groeiden beter in grond indien de beworteling op papieren bruggetjes had plaatsgevonden. Het succes van het elimineren van hetAlstroemeria-mozaïek virus hing af van de cultivar. Na herhaalde toetsing kunnen de negatief reagerende planten worden gebruikt voor de opbouw van een partij gezonde moederplanten. Op deze manier kan de kwaliteit van het uitgangsmateriaal vanAlstroemeria worden verbeterd.     

Efficiency of eradication of four viruses from garlic (Allium sativum) by meristem-tip culture

Mechanical inoculation tests and ELISA with sap from garlic plants used for sanitation by meristem-tip culture revealed four viruses, viz. garlic common latent virus (GCLV) (carlavirus), the garlic strains of leek yellow stripe virus (LYSV-G), onion yellow dwarf virus (OYDV-G) (aphid-borne potyviruses), and onion mite-borne latent virus (OMbLV-G) (taxonomically unassigned virus). The same tests performed on explants grownin vitro showed elimination efficiencies of 100% for LYSV-G, 92% for OYDV-G, 62% for GCLV, and less then 54% for OMbLV-G.Meristem tips excised from garlic cloves and bulbils, 0.15–1.0 mm in size, were tested for regeneration and efficiency of virus elimination after transfer to Murashige and Skoog medium. Successful regeneration into plantlets was obtained with 71% of the meristems from cloves and 72% of those from bulbils, but virus elimination was easiest from cloves: 38% of all explants from cloves and 25% of those from bulbils were virus-free. The efficiency of elimination increased with increasing weight of the cloves, irrespective of the virus. Small tip size seemed to favour virus elimination, but sizes smaller than 0.4 mm led to increasing failure of regeneration.Micropropagation was most successful when cytokinins were omitted from the medium and the garlic shoot was split. Multiplication factors of 3–6 were obtained.     

Recent observations on leafy gall in Liliaceae and some other families

Corynebacterium fascians, which causes leafy gall, has been shown to be responsible for the unusual symptoms recently found in lilies. The symptoms are described and the different bacterial isolates compared by biochemical, serological and pathogenicity experiments. No evidence could be found for the existence of specialized strains even though considerable variation in virulence could be demonstrated. Although the role of variation in susceptibility of the different lily cultivars should not be underestimated, it would appear that high inoculum levels ofC. fascians in the soil may be largely responsible for these outbreaks.Also included in this study are the results of biochemical, serological and pathogenicity experiments ofC. fascians which has been isolated fromKalanchoe, Euphorbia, Brodiaea, Hebe andVerbascum.Samenvatting Reeds een aantal jaren was in lelies een woekering in stengelbollen bekend, die echter sporadisch voorkwam en economisch van weinig betekenis was. Tijdens de zomer van 1977 echter trad de ziekte op één enkel perceel zo ernstig op dat zeer aanzienlijke oogstderving het gevolg was. Behalve de stengelbol kan ook de hoofdbol misvormd zijn. Bovendien kunnen misvormde stengelbollen lange spruiten vormen, zgn. sabeltandvorming. Soms is het wortelstelsel gereduceerd; in de kas zijn verdikte stengels waargenomen. De ziekte staat nu bekend onder de naam woekerziekte.Door de PD te Wageningen en het LBO te Lisse werd de bacterieCorynebacterium fascians (Tilford) Dows. uit het zieke materiaal geïsoleerd. In gezamenlijk onderzoek werd nagegaan of de bacterie de veroorzaker is van bovengenoemde symptomen en of hier sprake is van een op lelie gespecialiseerde stam.Biochemische en serologische vergelijkingen tussen isolaten vanC. fascians uit lelie,Kalanchoe, Euphorbia, Brodiaeea, Hebe enVerbascum laten zien dat er zeer weinig verschillen bestaan. Alle isolaten reageren op een standaard antiserum met titers variërend tussen 1: 640–1: 5120.Een oriënterende inoculatieproef werd uitgevoerd op het LBO in 1977. Daarna werden op de PD 10 van de 25 isolaten uit lelie en 8 uit andere waardplanten getoetst op lelie, chrysant en lathyrus. Uit de inoculatieproeven blijkt, dat de bacterie de veroorzaker is van de waargenomen symptomen. Tussen de isolaten blijkt een groot verschil in pathogeniteit te bestaan (12–100% aantasting), zonder dat dit aan herkomst gebonden is. Het voorkomen van op lelie of andere waardplanten gespecialiseerde stammen is daarom niet aan te nemen.In hoeverre de hevige aantasting een gevolg is van een opbouw van de bacterie-populatie door een te nauwe vruchtwisseling en mechanische rooimethoden moet worden nagegaan.     

Virus transmission by aphids in potato crops

This paper reviews the contribution of vector activity and plant age to virus spread in potato crops. Determining which aphid species are vectors is particularly important for timing haulm destruction to minimize tuber infection by potato virus Y (PVY). Alate aphids of more than 30 species transmit PVY, and aphids such asRhopalosiphum padi, that migrate in large numbers before flights of the more efficient vector,Myzus persicae, appear to be important vectors. Differences in methodology, aphid biotypes and virus strains prevent direct comparisons between estimates of vector efficiencies obtained for aphids in different countries in north western Europe. M. persicae is also the most efficient vector of potato leafroll virus (PLRV), but some clones ofMacrosiphum euphorbiae transmit PLRV efficiently toNicotiana clevelandii and potato test plants. The removal of infected plants early in the season prevents the spread of PLRV in cool regions with limited vector activity. The proportion of aphids acquiring PLRV from infected potato plants decreases with plant age, and healthy potato plants are more resistant to infection later in the season. Severe symptoms of secondary leafroll developed on progeny plants of cv. Maris Piper derived from mother plants inoculated with PLRV in June or July of the previous year. Progeny plants derived from mother plants inoculated in August showed only mild symptoms, but the concentration of PLRV in these plants was as high as that in the plants with severe symptoms.     

Tumours of Begonia and some other ornamentals,induced by Corynebacterium fascians

In 1975 many tumours were observed in plants ofBegonia Schwabenland grown in Aalsmeer. Submersion of the roots ofNicotiana megalosiphon seedlings in a homogenate of tumorous tissue, induced tumours after two weeks. Short periods of submergence yielded results similar to those obtained after longer periods. Tumour homogenates lost their infectivity after ten min at 50°C. Aphids transmitted the infectious agent.Treatment with propylene oxide did not inhibit infectivity completely. Filtration through a 450 nm filter removed the infectious agent.Tobacco tumor virus or a viroid could not be isolated. Cultures ofCorynebacterium fascians, isolated from tumours ofN. megalosiphon were highly infectious and induced tumours in healthyN. megalosiphon andBegonia. Tumorous tissue homogenates ofPelargonium zonale, Dahlia sp.,Gladiolus sp., andLilium sp. also caused tumours inN. megalosiphon, from whichC. fascians was isolated. It was not possible to produce tumours inN. megalosiphon with homogenates from roses with symptoms of bud proliferation.Samenvatting In 1975 werden vele tumoren waargenomen inBegonia Schwabenland op Aalsmeerse bedrijven (Fig. 1). De infectiositeit van tumorweefsel kon goed en snel worden vastgesteld door de wortels van zaailingen vanNicotiana megalosiphon in een homogenaat van tumorweefsel te dompelen. Tumoren ontstonden na twee weken, de eindbeoordeling geschiedde na een maand (Fig. 2). Ook verschillende andereNicotiana spp.,Melilotus officinalis (Fig. 3) enPisum odoratum (Fig. 4) werden aangetast.Bij de infectiositeitstoets gaven zeer korte dompeltijden even goede resultaten als langere (Tabel 1). Infectieus sap verloor zijn infectievermogen na 10 min verhitting bij 50°C. Bladluizen brachten de smetstof over. Propyleenoxide verminderde de infectiositeit wel, doch onderdrukte deze niet totaal. Bij filtratie door een 450 nm filter bleef het infectieuse agens op het filter achter. Het tumor-inducerende agens was ook aanwezig in die delen van planten met tumoren welke gezond leken en het ging voor een gering deel over met zaad (Tabel 2).Uit tumoren konden wij geen tabakstumorvirus of een viroïde isoleren. Culturen vanCorynebacterium fascians, geïsoleerd uit tumoren vanN. megalosiphon bleken zeer infectieus en veroorzaakten tumoren inN. megalosiphon enBegonia. Homogenaten van tumorweefsel vanPelargonium zonale, dahlia (Fig. 5), gladiool (Fig. 6) enLilium Mid Century Hybrid Enchantment (Fig. 7) veroorzaakten ook tumoren opN. megalosiphon, waaruitC. fascians werd geïsoleerd. Met sap van kroeskopzieke rozen konden wijN. megalosiphon niet besmetten.     

Susceptibility of German spring barley cultivars to loose smut populations from different European origins

Forty-two registered spring barley cultivars from the German official list were tested under natural infection conditions for susceptibility to loose smut (Ustilago tritici f.sp. hordei) during two test cycles at two locations. Only cv. Steffi was found to be resistant to the local loose smut population. Cultivar Sigrid showed lowest susceptibility because of flowering inside the leaf sheath. Less than 1% infection at all sites showed up in cvs Auriga, Jacinta and Hendrix. Twenty-one cultivars had an infection rate of less than 2%. Cultivar Danuta displayed the highest susceptibility with an average of 12.6%. Another 23 spring barley accessions with expected loose smut resistance were inoculated artificially with loose smut populations obtained from 11 locations in Germany and neighbouring countries. Only Jet with the resistance Un3/6, CDC Freedom with Un8, CIho9973 with quantitative resistance, as well as Lino and GangTuoQuingKeHao1 remained disease-free. In addition to these, another eight accessions in this test group are recommended to become part of a differential tester set to distinguish origins of loose smut. Statistical analysis showed that for scoring of cultivars more importance has to be given to the number of locations for infestation than to the number of test locations to determine the degree of attack. In view of the existing inspection limits for production of certified seed in European countries, the currently registered German barley cultivars put organic seed producers and breeders at high risk in respect to loose smut infection, if the number of generations for multiplication under organic farming increases.     

Development and fecundity ofSitobion avenae on some wheat cultivars under laboratory conditions

Nymphal development time and fecundity ofSitobion avenae (F.) (Homoptera: Aphididae) were determined on nine widespread wheat varieties cultivated in Tekirdağ Region in Turkey. Tests were carried out in controlled environment chambers (25±1°C, 65±5% r.h.; 16:8, L:D). Development time (±S.E.) ranged from 5.75±0.25 to 7.20±0.20 days. Fecundity per female ofS. avenae was found to be the highest (12.87±1.50) on wheat cv. ‘Sana’. In this investigation cvs. ‘MV-17’, ‘Miryana’, ‘Pehlivan’ and ‘Saraybosna’ were particularly resistant againstS. avenae. http://www.phytoparasitica.org posting July 8, 2002.     

Differences in resistance in onion cultivars to pink root rot disease in Iran

Forty-five onion (Allium cepa) cultivars were evaluated for disease resistance to the fungal pathogen Pyrenochaeta terrestris (pink root disease). Forty-three Iranian cultivars and two commercially exotic resistant cultivars (Texas Early Grano and Yellow Sweet Spanish) were grown in a glasshouse for two successive years (2003 and 2004) in Isfahan, Iran. Susceptibility of the cultivars was determined using a scale of 0–3. Six cultivars had significantly lower susceptibility of pink root compared to the exotic ones. High susceptibility tended to be associated with high mean scores (2–3), and the highly resistant cultivars had the lowest scores (0–1). In addition, the 45 examined cultivars were ranked from 1 to 45 according to their markedly differing reactions to P. terrestris, which differed markedly. Of 32 cultivars that were less resistant, 30 with an intermediate status or tolerance (1–2) differed considerably in their rank order. No pink root symptoms were seen in the early stages, but on blotter paper or wheat-straw agar some roots turned pink with no pycnidia formation, whereas on potato dextrose agar medium (PDA) with a few fresh healthy and sterile onion roots on the surface, mycelia and pycnidia were recovered. Variance and cluster analysis showed similar results among the cultivars with various levels of resistance, tolerance and susceptibility as determined by scoring scales.     

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     

Virus transmission by host-specific strains ofOlpidium bornovanus andOlpidium brassicae

Zoospores of 12 isolatesO. bornovanus from geographically diverse sites and representing the three host specific cucurbit strains were tested as vectors for seven viruses using watermelon bait plants and the in vitro acquisition method. All isolates of the cucumber, melon, and squash strains transmitted melon necrotic spot carmovirus (MNSV) and cucumber necrosis tombusvirus (CNV) but none transmitted petunia asteroid mosaic tombusvirus (PAMV) or tobacco necrosis necrovirus (TNV). The isolates varied as vectors of three other carmoviruses: cucumber leaf spot virus (CLSV); cucumber soil borne virus (CSBV); and squash necrosis virus (SqNV). All cucumber isolates transmitted CLSV and SqNV but not CSBV. Some of the melon isolates transmitted CLSV and SqNV but none transmitted CSBV. Two squash isolates transmitted CSBV and SqNV but not CLSV. Two isolates ofO. brassicae transmitted only TNV and a third did not transmit any of the viruses. The species of bait plant sometimes affected transmission. The most efficient vector strains ofO. bornovanus, as determined by reducing zoospores and virus in the inoculum, were the cucumber strain for CLSV; the cucumber strain for CNV if cucumber was the bait plant or melon strain if watermelon was the bait plant; and the squash strain for SqNV. The plurivorous strain ofO. brassicae was the most efficient vector of TNV.Olpidium bornovanus is the first vector reported for CSBV and is confirmed as a vector of SqNV. It is proposed that all carmoviruses may have fungal vectors.Ligniera sp. did not transmit any of the viruses in one attempt.Abbreviations CLSV cucumber leaf spot virus - CNV cucumber necrosis virus - CSBV cucumber soil borne virus - MNSV melon necrotic spot virus - PAMV petunia asteroid mosaic virus - SqNV squash necrosis virus - TNV tobacco necrosis virus - TBSV tomato bushy stunt virus     

Yellows of lettuce and some other vegetable crops in the Netherlands caused by beet western yellows virus

A virus isolated from lettuce (Lactuca sativa), endive (Cichorium endivia), witloof chicory (C. intybus), and spinach (Spinacia oleracea), and from some weeds was shown to be beet western yellows virus (BWYV) by its host range, particle morphology and serology. It resembled previously described European isolates but differed from American strains in its inability to infectBeta vulgaris, Brassica pekinensis andRaphanus sativus. The most useful host for routine indexing wasCrambe abyssinica. Virus particles in purified preparations stained with uranyl acetate were isometric, ca. 27 nm in diameter. Purified virus reacted with antiserum to an American strain of BWYV in infectivity neutralization gel diffusion and serologically specific electron-microscopy tests.The field reaction to BWYV of cultivars of lettuce, otherLactuca species and someCichorium species was investigated and differences in symptom expression were observed. On the basis of observations during two seasons BWYV appeared to be widely distributed but seemed of minor economic importance to lettuce growing. It may be a potentially important pathogen of endive and chicory.Samenvatting Reeds gedurende enkele jaren trekt in Nederland een vergelingsziekte van sla (Fig. 1 en 2) de aandacht. In 1977 en 1978 werd de ziekte nader bestudeerd en ook waargenomen in andijvie, witlof (Fig. 3) en spinazie. Uit zieke planten van deze vier gewassen en uit de onkruiden herderstasje en kruiskruid, groeiend in de buurt van de zieke sla, kon doorMyzus persicae op persistente wijze een virus worden overgebracht. Het werd op grond van zijn waardplantenreeks (Tabel 1), deeltjesmorfologie (Fig. 4A) en serologie (Fig. 4B) herkend als het in de USA beschreven beet western yellows virus (BWYV).Het Nederlandse virus komt overeen met in andere landen gerapporteerde Europese isolaten van het virus, maar verschilt van Amerikaanse doordat het niet in staat is om biet, chinese kool en radijs te infecteren. Daarom is voor het virus door Bos en Ashby (1978) de Nederlandse naam slavergelingsvirus ingevoerd. De meest geschikte indicatorplant voor routinetoetsing isCramble abyssinica (Tabel 2). De reactie van herderstasje varieert al naar individu van nagenoeg letaal tot vrijwel symptoomloos (Fig. 5).In gedeeltelijk gezuiverde preparaten bleken de deeltjes bolvormig te zijn en ca. 27 nm in diameter (Fig. 4A). Zulke preparaten reageerden met antiserum tegen een Amerikaanse stam van het virus (BWYV) in toetsen die gebruik maken van infectieneutralisering, gel-diffusie en serologisch-speciefieke elektronenmikroskopie. Bij laatstgenoemde techniek werd een fraaie deeltjesklontering waargenomen (Fig. 4B), die ontbrak na incubatie van gezuiverd virus met een antiserum tegen het niet verwante kersebladrolvirus (Fig. 4C).Bij veldwaarneming in 1977 van 20 slarassen, waarbij tot 60% van de planten van één ras werden aangetast, bleken twee rassen niet of weinig vatbaar (Tabel 3). Bij inoculatie in de kas bleken ze echter volledig vatbaar. In 1978 werd een aantal soorten en rassen vanCichorium enLactuca blootgesteld aan natuurlijke en aan kunstmatige infectie. BehalveC. intybus Groenlof IVT waren allen vatbaar, ookL. sativa Gallega de Invierno,L. serriola enL. virosa.Het virus lijkt algemeen voor te komen. Meestal is de infectiegraad niet hoog. Vanwege de lange incubatieduur in sla is het virus in dat gewas bij de hier toegepaste teeltwijze waarschijnlijk van geringe betekenis. Het lijkt echter een potentieel belangrijk pathogeen voor andijvie en witlof.Guest research worker, Plant Diseases Division, DSIR, Private Bag, Christchurch, New Zealand, with financial assistance from the International Agricultural Centre, Wageningen, and Ministry of Education and Science, The Hague.     

Comparison ofPotato Virus Y andPlum Pox Virus transmission by two aphid species in relation to their probing behavior

Two different aphid species,Myzus persicae (Sulzer) andHyalopterus pruni (Geoffroy) (Homoptera: Aphididae), were used to analyze their ability to transmit two different potyviruses,Potato virus Y (PVY) andPlum pox virus (PPV), to pepper (Capsicum annuum) andNicotiana benthamiana plants, respectively. In parallel experiments,M. persicae consistently transmitted both viruses with high efficiency, whereasH. pruni always failed to transmit either virus. This is in contrast to previous reports describingH. pruni as a vector of these potyviruses. Different aphid probing behavior among individual aphids of each species was obtained in electrical penetration graph (EPG) experiments performed on pepper plants. This suggested thatH. pruni did not transmit these potyviruses due to behavioral differences during probing that impeded virus acquisition and/or inoculation. It was found thatM. persicae usually makes its first probe within the first 2 min, whereasH. pruni individuals remained for more than 10 min on the plant before starting to probe. Furthermore,M. persicae individuals displayed their first intracellular puncture during the first minute of probing whereasH. pruni needed ∼ 15 min to penetrate the cell plasmalemma with their stylets. In addition, intracellular stylet punctures occurred very frequently forM. persicae but was a rare event, never exceeding a single one, forH. pruni. The relevance of these findings for the epidemiological spread of potyviruses by different aphid species is discussed. http://www.phytoparasitica.org posting May 14, 2006.     

Molecular Identification of Oat Mosaic Virus as a Bymovirus

A partial sequence of Oat mosaic virus (OMV) has been obtained for four isolates of the virus from four European countries. This represents the first available sequence data for this important disease of winter-sown oats. The longest clone of 1699 nucleotides was obtained from infected English oats using a degenerate primer, designed to members of the Potyviridae family. Alignment of the predicted amino acid sequence with members of the Potyviridae showed closest identity with viruses of the Bymovirus genus. The predicted amino acid sequence has one open reading frame corresponding to part of the NIb and capsid protein, with a 3 untranslated region of 351 nucleotides, followed by a poly(A) tail. PCR primers were designed to the coat protein and NIb gene of members of the Bymovirus genus and used to obtain partial sequences of 1441 nucleotides at the 3 end of infected oats from both Wales and France. A specific primer set designed to the English isolate was used to generate a product of 701 nucleotides from OMV-infected oat leaves from Ireland. All four isolates are highly conserved at the amino acid level.The first two authors contributed equally to the work     

Evaluation of glyphosate-tolerant soybean cultivars for resistance to bacterial pustule

Xanthomonas axonopodis pv. glycines causes bacterial pustule of soybean, which is a common disease in many soybean-growing areas of the world and is controlled by a single recessive gene (rxp gene) commonly found in many conventional glyphosate-sensitive soybean cultivars. Since glyphosate-tolerant cultivars are commonly planted today, there has been no information about whether these new cultivars have bacterial pustule resistance. The goal of this study was to screen glyphosate-tolerant soybean cultivars for resistance to X. axonopodis pv. glycines. Three experiments were completed to evaluate resistance. In experiment 1, 525 commercial glyphosate-tolerant cultivars from 2001 were inoculated with X. axonopodis pv. glycines strain UIUC-1. Following inoculation, many of the cultivars were resistant (developed no detectable pustule symptoms) although 152 (~29%) developed bacterial pustule. In experiment 2, the aggressiveness of three strains (UIUC-1, UIUC-2, and ATCC 17915) of X. axonopodis pv. glycines were compared on three bacterial pustule-susceptible, glyphosate-tolerant cultivars. One strain (UIUC-1) was less aggressive than the other two (UIUC-2 and ATCC 17915) on all three cultivars examined. In experiment 3, 45 cultivars from 2005 (all different from 2001) were inoculated with X. axonopodis pv. glycines ATCC 17915. A range of disease severities developed with five cultivars (11%) having disease severity ratings as high as or higher than those on a susceptible check cultivar. Overall, these results suggested that resistance to bacterial pustule occurs in glyphosate-tolerant soybean cultivars, but not at 100% frequency, which means bacterial pustule outbreaks could occur when a susceptible cultivar is planted and conditions are conducive for bacterial pustule development.     

Use of some plant extracts to control Biomphalaria alexandrina snails with emphasis on some biological effects

The present work was carried out to evaluate, the molluscicidal activity of cold water, boiled water, methanol, ethanol, acetone and chloroform extracts of some plant species against Biomphalaria alexandrina snails. Preliminary screening tests on 10 plant species showed that the highest molluscicidal potency was recorded for Euphorbia splendens, Atriplex stylosa and Guayacum officinalis. Exposure of B. alexandrina snails to plant’s methanol extracts led to a significant reduction in their survival and growth rates. In addition, newly hatched snails were susceptible to plant’s methanol extracts than elder ones. LC₂₅ of methanol extract from these plants caused a considerable reduction in the infectivity of Schistosoma mansoni miracidia to the snails. It caused a reduction in number of cercariae per snail during the patent period and in the period of cercarial shedding. The results, also, revealed that the glucose concentration in treated snails was increased in haemolymph, while soft tissue glycogen decreased. The activities of glycogen phosphorylase, succinate dehydrogenase (SDH), glucose-6-phosphatase and acetylcholinesterase (AchE) in homogenate of snail’s tissues were reduced (P < 0.001) in response to treatment with plants methanol extract, while glucose-6-phosphate dehydrogenase (G-6-PD) activity increased (P < 0.001). It was concluded that the application of LC₂₅ of methanol extracts of E. splendens, A. stylosa and G. officinalis may be helpful in snail control as it interferes with the snails’ biology and physiology.     

Responses of cucumber cultivars to induction of systemic resistance against anthracnose by plant growth promoting fungi

Initial experiment on the reactions of five Japanese cultivars of cucumber toColletotrichum orbiculare infection in the greenhouse revealed that cv Suyo and Gibai were susceptible and moderately susceptible, respectively, while cv Shogoin fushinari and Sagami hanjiro were resistant to infection byC. orbiculare; cv Ochiai fushinari was moderately resistant. The ability of 16 plant growth promoting fungi (some isolates belonged to species ofPhoma and some non-sporulating isolates) isolated from zoysiagrass rhizospheres to induce systemic resistance in the above five cucumber cultivars was tested by growing plants in potting medium infested with barley grain inocula of PGPF in the greenhouse. The second true leaves of 21-day-old plants were challenge inoculated withC. orbiculare and disease assessed. Nine, out of 16 isolates, caused significant reduction of disease caused byC. orbiculare in at least two cultivars.Phoma isolates (GS8-1 and GS8-2) and non-sporulating isolates (GU21-2, GU23-3, and GU24-3) significantly reduced the disease in all the five cultivars. The disease suppression in cucumber was due to the induction of systemic resistance, since the inducer(s) and the pathogen were separated spatially and that the inducer did not colonize aerial portions. The resistance induced by certain isolates in a susceptible cultivar was less than that in a resistant cultivar. Disease suppression caused by isolate GU21-2 was similar to theC. orbiculare induced control in certain cultivars. The average rate of expansion of lesion diameter on leaves due toC. orbiculare was slower due to induction with the selected plant growth promoting fungi compared to the uninduced control plants. Roots of four cultivars were colonized by only three isolates, however, roots of one cultivar (Suyo) was colonized by five isolates suggesting the cultivar-specific root colonization ability.Abbreviations cv cultivar(s) - PGPF plant growth promoting fungal isolates - PGPR plant growth promoting rhizobacteria     

Differential interaction of Mycosphaerella brassicicola and brassica cultivars

Isolates ofMycosphaerella brassicicola, originating from various locations in Europe, differed in their virulence on a differential set of brassica cultivars, as measured by the number of lesions per leaf. Hypersensitivity and significant cultivar-isolate effects were observed, indicating a differential host-pathogen interaction. Although expression of resistance depends on plant development, the differential host-pathogen interaction was found in all plant stages tested. This is the first report on the existence of physiological specialization ofM. brassicicola.     

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.     

Characterization ofRhizoctonia solani isolates from potatoes in turkey and screening potato cultivars for resistance to AG-3 isolates

A total of 304Rhizoctonia solani isolates and 60 binucleateRhizoctonia-like fungi were recovered from stems and tubers of infected potato plants over a 2-yr period in northeast Turkey.R. solani isolates were identified to 11 anastomosis groups (AGs): AG-1 (0.66%), AG-2-1 (5.6%), AG-2-2 (0.99%), AG-3 (83.9%), AG-5 (4.6%), AG-6 (0.66%), AG-8 (1.32%), AG-9 (0.33%), AG-10 (1.32%), AG-12 (0.33%), and AG-13 (0.33%). In the greenhouse tests, most of the AG-3 isolates were significantly more virulent than isolates belonging to other AGs on potato cv. Batum. Isolates of other anastomosis groups differed in their virulence. Results indicated that AG-3 is an important pathogen on potatoes grown in the study area. Five of 22 commercial and local potato cultivars evaluated for their reaction toR. solani AG-3 isolates (TP-2) under greenhouse conditions were highly resistant; the remaining cultivars exhibited different levels of susceptibility to the pathogen isolate. http://www.phytoparasitica.org posting July 14, 2005.