bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors affecting infection cushion development by Rhizoctonia solani AG‐1 IA and IB on soybean leaves
Authors: KOUSIK C.S. , SNOW J. P. , BERGGREN G. T.
Published: April 2007

Infection cushions were formed by isolates of Rhizoctonia solani, anastomosis group 1 IA (AG‐1 IA, aerial blight) and AG‐1 IB (web blight) on leaves of all 10 soybean cultivars tested. Isolates of AG‐1 IA and IB did not form infection cushions on soybean leaf surface replicas of either resistant or susceptible cultivars. More infection cushions were formed by isolates of AG‐1 IA and IB on collodion membranes placed over leaves of susceptible cultivars compared with resistant cultivars. Isolates of AG‐1 IC. AG‐4 and AG‐5, also formed infection cushions on soybean leaves. However, the isolates of other anastomosis groups did not form infection cushions on soybean leaves. Differential induction of infection cushion formation by the leaves of various plant species was observed, AG‐1 IA formed infection cushions on more graminaceous hosts than AG‐1 IB, Our results suggest that a chemical stimulus is needed for infection cushion formation. Glucose and 3‐O‐methylglucose repressed disease severity caused by AG‐1 IA and IB isolates to the same extent. Disease severity and the number of infection cushions formed on leaves of ten soybean cultivars were correlated. Fewer infection cushions were formed on resistant cultivars than on susceptible cultivars.
Prevalence and pathogenicity of spinach root pathogens of the genera Aphanomyces, Phytophthora, Fusarium, Cylindrocarpon, and Rhizoctonia in Sweden
Authors: LARSSON M. , OLOFSSON J.
Published: April 2007

In a 4‐year disease survey in commercial spinach fields, pathogens were isolated from spinach root pieces placed on selective agar media. Aphanomyces cladogamus was the most abundant pathogen, followed by Phytophthora. cryptogea and Fusarium oxysporum. Rhizoctonia solani was found only occasionally. Other pathogens isolated were F. redolens, F. sambucinum and Cylindrocarpon destructans. P. cryptogea was the most severe pathogen, causing death of most plants, but A. cladogamus also caused severe root damage. Isolates of F. oxysporum ranged from highly pathogenic, i.e. P. oxysporum f.sp. spinaciae race 1. to moderately pathogenic and non‐pathogenic, Rhizoctonia solani isolates also varied widely in their pathogenicity. Only a small number of the F. redotens and F. sambucinum isolates were pathogenic and most C. destructans isolates were weakly pathogenic. Isolation frequencies were relatively stable from year to year, but P. cryptogea was isolated more frequently in autumn than in spring. No clear relationships were found between pathogen prevalence and disease severity index of surveyed field plants, between pathogen prevalence and plant developmental stage, or between prevalence of the different pathogens isolated.
Variation in host range, systemic infection and epidemiology of Leptosphaeria maculans
Authors: JOHNSON R. D. , LEWIS B. G.
Published: April 2007

The A and B groups (aggressive and non‐aggressive) of Leptosphaeria maculans were compared in studies of host range, infection phenotypes and epidemiology. Isolates of both groups infected a wide range of cruciferous hosts including Brassica napus, B. rapa, B. oleracea, B. juncea, B. carinata. B. nigra, Thlaspi arvense and Raphanus sativus. On cotyledons, B‐group isolates were generally more aggressive than A‐group isolates, causing local lesions and subsequent systemic invasion of the majority of test species. On susceptible stems, A‐group isolates caused cortical lesions; B‐group isolates, if they reached the stem, usually caused pith lesions with no external symptoms. In a susceptible line of B. napus, CrGC5, systemic infections of the leaf and petiole were similar with both groups, but the B‐group rarely entered the stem to form cortical lesions or cankers. At two different field locations, natural epidemics caused by the two groups on oilseed rape leaves were similar in overall pattern, B‐group lesions occurred slightly later but the incidence increased more rapidly and reached a maximum slightly earlier than that of the A group. The two groups differed markedly in stem infection patterns. Infection of the cortex near the base of the stem and the development of a typical stem canker was caused entirely by the A group. However the B group often caused considerable damage to the pith. Superficial chlorotic lesions on stems and inflorescences were mainly attributable to the B group. In view of the stem pith infection by the B group without external symptoms, its importance on oilseed rape may have been underestimated previously.
The response of oilseed rape (Brassica napus ssp. oleifera) accessions with different glucosinolate and erucic acid contents to four isolates of Peronospora parasitica (downy mildew) and the identification of new sources of resistance
Authors: NASHAAT N. I. , RAWLINSON C. J.
Published: April 2007

A total of 101 Brassica napus ssp. oleifera accessions with seed differing in glucosinolate and erucic acid contents were screened for resistance to four isolates of Peronospora parasitica at the cotyledon stage. Two groups of accessions with different resistance factors were identified. Lines that were homogeneous for resistance were selected from seedling populations of accessions that exhibited a heterogeneous reaction to some isolates. The resistance of one group differs from that of cv, Cresor, the only oilseed rape cultivar reported to have an isolate‐specific gene for resistance to P. parasitica. The isolate specificity of the second group was identical to that of cv, Cresor, A comparison of the response of host accessions which expressed moderate to full susceptibility at the cotyledon stage, with no clear differential response to any of the four P. parasitica isolates, indicated that those with high glucosinolate and high erucic acid contents (12 accessions) were slightly but significantly less susceptible than those with high glucosinolate and low erucic acid (19 accessions), or low glucosinolate and low erucic acid contents (28 accessions). The mean differences between accessions with low erucic acid but differing in glucosinolate content were inconsistent. The last result was further confirmed by investigating the expression of resistance to three isolates of P. parasitica at three different seedling growth stages among 11 accessions of oilseed rape with seeds low in erucic acid but differing in glucosinolate content.
The incidence of Pythium spp. and Aphanomyces cochlioides associated with the sugar‐beet growing soils of Britain
Authors: PAYNE P. A. , ASHER M. J. C. , KERSHAW C. D.
Published: April 2007

In a survey of fungi causing seedling diseases of sugar beet using a soil bioassay, Aphanomyces cochlioides and Pythium spp. were found to occur in 39% and 31%, respectively, of 341 sugar‐beet fields selected in a stratified random sample in England, The frequency of A. cochlioides‐infested soils varied widely in the different sugar‐beet growing areas of the country. Soil pH was the single factor most strongly associated with the distribution of the pathogen, but regression models applied to combinations of factors indicated that soil texture and the interval between sugar‐beet crops were also relevant to its frequency. It was detected less often in soils of high pH (≥ 75). heavy texture and where the interval between sugar‐beet crops exceeded 5 years. No significant associations were found between the proportion of soils with Pythium spp. and soil or cropping factors.
Infection of plum and nectarine flowers by Botrytis cinerea
Authors: FOURIE J. F. , HOLZ G.
Published: April 2007

The ability of Botrytis cinerea to infect plum and nectarine flowers was studied in moist chambers and in the orchard. Within 36 h of inoculation, the pathogen penetrated and colonized the stamens, styles and petals on shoots placed in moist chambers, causing blossom blight. Similar lesion development was observed following inoculation with dry and wet conidia, Hyphae were usually distorted in stylar tissue, but grew normally in petals and filaments. Growth of the fungus through filaments into the sepals or floral tubes, or through the transmitting tissue of the style into the ovary, was never observed. Symptoms of blossom blight were not observed on inoculated shoots in the orchard. The floral tube, bearing the sepals and stamens, dehisced within 14 days of fruit set and infected floral parts did not remain attached to young developing fruit. No relation was found between post‐harvest decay and flower infection. Losses following post‐harvest decay might have been caused by direct penetration of ripening fruit and not by flower infection. The importance of infected floral parts as a source of secondary inoculum on ripening fruit is discussed.
Seed treatment for the control of Sphaerotheca fuliginea in muskmelon seedlings
Authors: COHEN R. , SHTIENBERG D.
Published: April 2007

The effects of powdery mildew (caused by Sphaerotheca fuliginea)on muskmelon seedlings and the efficacy of seed treatment with systemic fungicides were examined under controlled environmental conditions. The fresh weight of seedlings infected with powdery mildew was substantially less than that of uninoculated seedlings 5 weeks after inoculation, and the inoculated seedlings shrivelled 1 week later. The fungicides fenarimol and triadimenol applied to the seeds did not affect germination and suppressed powdery mildew effectively when applied at a rate equivalent to 8 g fungicide product per kg seed. Under conditions moderately conducive to the pathogen, fenarimol markedly reduced disease severity and its effect when applied as a seed treatment was as effective as foliar treatment. When conditions were highly conducive to the pathogen, seed treatment with fenarimol was not effective. Development of powdery mildew and efficacy of the seed treatments were related to soil type: disease developed earlier and more intensely on seedlings grown in sandy soil than those in organic medium, and seed treatment had a more pronounced effect on seedlings grown in sandy soil. The results indicate that fungicidal treatment of muskmelon seeds may offer an adequate means of reducing powdery mildew infections on seedlings.
Production of a proteinaceous phytotoxin by Ascochyta rabiei grown in expressed chickpea sap
Authors: CHEN Y.‐M. , STRANGE R. N.
Published: April 2007

Production of the solanapyrone toxins by Ascochyta rabiei is nutrient dependent. When grown on a medium consisting entirely of expressed sap from the aerial parts of young chickpea plants (PSM). only low concentrations of the solanapyrones were produced (< 24 μM). However, toxicity of 4‐day‐old culture filtrates to isolated cells of chickpea leaflets was comparable with that obtained from 12‐day‐oId culture filtrates on Czapek Dox nutrients supplemented with chickpea seed extract or cations—media that are conducive to solanapyrone production. The additional toxic component which peaked at 4 days in culture was heat labile, losing about 50% of its activity on boiling for 10 min. Affinity for solid‐phase extraction media, precipitation with ammonium sulphate and acetone, ionization properties and UV absorption characteristics suggested that the toxin was a polypeptide. The toxin was purified by solid‐phase extraction, acetone precipitation and high performance liquid chromatography (HPLC) on a C2 column. Hydrolysis of the purified toxin yielded 14 amino acids, and calculation of the numbers of residues of each amino acid suggested a molecular mass of 7, 551 Da, A band corresponding to this molecular mass was present on SDS‐PAGE gels. However, both the native peptide and its hydrolysate contained a compound that reacted with p‐anisaldehyde suggesting the possibility of a glycosidic moiety.
Fungal foliar plant pathogen epidemics: modelling and qualitative analysis
Authors: KOSMAN E. , LEVY Y.
Published: April 2007

A new approach for modelling epidemics caused by fungal foliar plant pathogens is presented. The model is described by a system of differential equations, and is simple enough to allow a qualitative analytical study of the main epidemiological factors that determine the rate of disease progress during a single growing period. The model was analysed and compared with Vanderplank's basic equations of plant disease development and some of Jeger's models. Results of qualitative investigation of the model, and close similarity between simulated and observed dynamics of disease development, show that this new approach may be used to compare and analyse some foliar fungal disease epidemics in more detail than formerly.
Detection of the source of infection of apple trees by Cylindrocarpon heteronema using DNA polymorphisms
Authors: BROWN A. E. , MUTHUMEENAKSHI S. , SWINBURNE T. R. , LI R.
Published: April 2007

Restriction fragment length polymorphisms (RFLPs) of the ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) of isolates of Cylindrocarpon heteronema were analysed using rDNA from Saccharomyces carlsbergensis and mtDNA from C. heteronema as probes. These analyses revealed intraspecific heterogeneity; four rDNA and six mtDNA restriction pattern categories were observed among the isolates tested. The two main rDNA RFLP categories, both of which subdivided into two mtDNA categories, detected within the UK isolates could not be associated with the localities from which they were obtained, but the majority of isolates originating from trees produced in the same nursery, irrespective of where they were finally planted, belonged to the same category.
Influence of barley variety mixtures on severity of scald and net blotch and on yield *
Authors: MUNDT C. C. , HAYES P. M. , SCHÖN C. C.
Published: April 2007

Two susceptible barley cultivars and two moderately resistant advanced breeding lines were grown as pure stands and as the 11 possible equi‐proportional mixtures over three field seasons, in the presence of scald and net blotch. Plots were either inoculated with infested straw, or non‐inoculated and sprayed with fungicide. On average, the variety mixtures restricted leaf disease development by 12%. However, mixtures of either or both susceptible cultivar/s with the moderately resistant line 1861018 restricted disease severity by 20‐32%. Generally, the mixtures did not increase yield relative to the mean of the pure stands. However, in the year of highest disease severity, yield was increased by 7% owing to mixing in the inoculated plots. In addition, one mixture consistently increased yield (mean of 4%) and one mixture had consistently lower yields (mean of 6%)) over years and inoculation treatments. Thus, careful evaluation is required in this environment and with these genotypes in order to identify mixtures with positive effects on disease control and yield.
The infestation of tomato seed by Fusarium oxysporum f.sp. radicis‐lycopersici
Authors: MENZIES J. G. , JARVIS W. R.
Published: April 2007

The infestation of seed by Fusarium oxysporum f.sp. radicis‐lycopersici occurred at rates of 0‐1 to 0‐01 % in fruit on stem‐infected plants. Direct infection of fruit in the flower or young developing fruit stage resulted in a grayish‐brown lesion on the stylar end of the fruit or mummification. F. oxysporum f.sp. radicis‐lycopersici was isolated from all seeds in such fruit. Picked fruit inoculated on the stem scar also became infected but 96 h after inoculation of the fruit, the seed was not infested or infected. The contact of clean seed with hands that had previously handled F. oxysporum f.sp. radicis‐lycoperisid‐infesied sawdust resulted in a high level of seed infestation. The fungus survived on seed sent across Canada and stored for up to 12 weeks. Treatment with NaOCl or 0·1 N HCl did not completely disinfest infested seed.
Viability, germination and infection potential of oospores of Phytophthora infestans
Authors: PITTIS J. E. , SHATTOCK R. C.
Published: April 2007

Matings between five A1 and five A2 wild‐type isolates of Phytophthora infestans from potato and tomato crops in the United Kingdom produced oospores in vitro in all cases examined. Oospores from the majority of crosses germinated, albeit at a low level (max 13‐4%), after extraction from agar cultures by high‐speed blending and treatment with novoZym 234. Viability of oospores from 20 crosses was tested by three methods. Two methods involved stains, either tetrazolium bromide (MTT) or phloxine B, and the third measured plasmolysis in 2 M NaCl. Both staining methods indicated a high percentage viability but gave false‐positive results with heat‐killed oospores. The plasmolysis method gave a lower percentage viability but no false positives. Oospores produced in vitro and stored either in sterile H2O or in soil at temperatures between 0 and 20 C survived for between 5 and 7 months, the length of the experiments. Oospores buried in non‐sterile field soil survived for up to 8 months (January‐August). Inoculation of potato with zoospores of AI and A2 isolates produced oospores in stems but not in leaf tissue. In some, but not all cases, rapidly growing potato shoots (15‐mm long) were successfully infected with oospores produced in vitro.
Resistance to benomyl in Botrytis allii from shallots
Authors: GLADDERS P , CARTER M. A. , OWEN W. F
Published: April 2007

The first occurrence of resistance to benomyl in Botrytis allii in the UK is reported. Resistant isolates were detected on imported shallots for home garden use in 1990.
A garlic (Allium sativum) leaf blight caused byStemphylium vesicariumin Brazil
Authors: BOITEUX I. S , LIMA M. F. , SOBRINHO J. A. MENEZES , LOPES C. A
Published: April 2007

The causal agent of a fohar disease of garlic (Allium sutivum) was identified asStemphylium resicarium(Wallr) Simm Disease symptoms were reproduced on garlic leases 8 to 10 days after inoculation in a greenhouse (temperature range 22‐26 C) Onion and tomato, two previously reported hosts of S,testcarnon.were also artificially infected with the isolate from garlic. This is believed to be the first report ofS. testcarnomcausing a severe leaf blight of garlic in the New World area.
Outbreak of MAV‐type barley yellow dwarf virus on wheat in the Garhwal Hills in India
Authors: KHETARPAL R. K. , KUMAR J. , BEUVE M. , PARAKH D B. , NATH RAM
Published: April 2007

A serious outbreak of barley yellow dwarf luteovirus (BYDV, MAV‐type) on wheat in the Garhwal Hills, Central Himalayas, India is reported. This is the first conclusive evidence based on serology for the presence of MAV‐BYDV in India.
First record of Erysiphe cruciferarum on Lunaria biennis in Greece
Authors: VAKALOUNAKIS D. J.
Published: April 2007

This is first record of Erysiphe ownterarum on Lunaria biennis (syn L. annua) in Greece.
Screening for Sclerotinia resistance in Helianthus tuberosus L. (Jerusalem artichoke) varieties, lines and somaclones, in the field and in vitro
Authors: CASSELLS A. C. , WALSH M.
Published: April 2007

Yields in large‐scale ‘continuous’ cultivation of H. tuberosus (Jerusalem artichoke) can be greatly reduced by Sclerotinia sclerotiorum, which causes a basal stem and tuber rot. In 34 varieties/lines of H. tuberosus from European, Russian and Canadian breeding programmes, responses to the pathogen varied from field resistance to 34% stem rot, cultivars Nahodka and Columbia showing c. 25% stem rot after three seasons of cultivation on the same site. Attempts to develop an in‐vitro selection for S. sclerotiorum resistance based on culture of H. tuberosus nodes on media precolonized with Sclerotina were unsuccessful. There was a strong positive correlation between capacity of nodes to grow in vitro on calcium‐free medium and field resistance. Somaclones of'Nahodka’ selected on the latter basis showed no field infection when grown on land that was heavily contaminated with the pathogen, and they were resistant to artificial inoculation with the pathogen.
Persistence and fitness of carbendazim‐ and dicarboximide‐resistant isolates of Monilinia fructicola (Wint.) Honey in flowers, shoots and fruit of stone fruit
Authors: SANOAMUANG N. , GAUNT R. E.
Published: April 2007

Flowers on detached peach shoots and ripe fruit were inoculated under controlled conditions in order to estimate the competitive ability of Monilinia fructicola isolates sensitive and resistant to carbendazim and dicarboximide fungicides. Isolates varied considerably, but there was no consistent relationship between carbendazim resistance and competitive ability; there was, however, evidence of reduced competitive ability in the single dicarboximide‐resistant and the dual dicarboximide/high carbendazim‐resistant isolate examined. The ability to produce conidia on twig cankers inoculated in late spring 1989 was retained under field conditions by all sensitive and resistant isolates for at least 1 year. Dicarboximide‐resistant isolates produced fewer conidia than the carbendazim‐resistant and sensitive isolates on cankers. The production of conidia on mummified fruit inoculated in February 1990 decreased in the field during the winter and the following spring, but some conidia were produced by all isolates. Measures of pathogenicity, virulence and fitness for all isolates were similar to the original values after survival for 1 year. The evidence presented in this paper supports field observations that carbendazim‐resistant isolates are likely to persist permanently in the M. fructicola population, whereas dicarboximide‐resistant isolates are more likely to decline unless fungicide selection pressure is maintained.
Induced resistance in host mixtures and its effect on disease control in computer‐simulated epidemics
Authors: LANNOU C. , DE VALLAVIEILLE‐POPE C. , GOYEAU H.
Published: April 2007

The epidemic simulator EPIMUL was modified and used to study how induced resistance affected the development of epidemics in host mixtures. In the model, induced resistance resulted from the interaction of host tissue with avirulent spores and caused a reduction in the efficacy of virulent spores deposited afterwards. We denned three parameters to describe induced resistance: the level of protection, defined as the magnitude of reduction in the virulent spore efficacy for infecting host tissue; the host surface area protected by an interaction with one avirulent spore; and the duration of protection of the host tissue, in days. In our simulations, induced resistance slowed the epidemics and gave better disease control in the mixtures, even if protection lasted for only 2 days. The disease reduction in the mixture attributable to induced resistance was approximately proportional to the level of protection. The effect of induced resistance increased as the protected area increased. Epidemics were virtually unaffected by induced resistance restricted to the infection site, but the effect of induced resistance initially increased rapidly as larger areas were protected. There was little further gain as the protected area increased from 2·6% to 26%. The influence of induced resistance was reduced when the interactions between virulent and avirulent pathogens were reduced.
Essential oil production increased by using virus‐free patchouli plants derived from meristem‐tip culture
Authors: SUGIMURA Y. , PADAYHAG B. F. , CENIZA M. S. , KAMATA N. , EGUCHI S. , NATSUAKI T. , OKUDA S.
Published: April 2007

For the production of virus‐free patchouli (Pogostemon cablin), isolated meristem tips were cultured on a medium supplemented with 0·2 ppm 6‐benzylaminopurine. Multiple shoot proliferation was initiated during the culture. Complete plantlets were regenerated by transferring multiple shoots to a medium devoid of phytohormones. Plantlets thus produced were transplanted to soil with a high rate of survival and tested by enzyme‐linked immunosorbent assay (ELISA) to check elimination of patchouli mild mosaic virus. Following further propagation by stem cuttings, virus‐free plants were grown in the northern and southern parts of Mindanao Island, Philippines. Significant increases in biomass and essential oil yield were observed in virus‐free plants grown at both localities. Using gas chromatographic analyses, a full set of major sesquiterpenes was detected in the essential oils recovered from virus‐free patchouli plants. Reinfection of healthy clones with the virus took place within 4 months of cultivation in the field.
The inheritance of virulence of Phytophthora infestans to potato
Authors: AL‐KHERB S. M. , FININSA C. , SHATTOCK R. C. , SHAW D. S.
Published: April 2007

Of 31 matings between isolates of P. infestans from several countries, six yielded enough progeny for analysis of inheritance of the virulence phenotype. Virulence was determined in vitro after inoculation of detached leaflets of nine differential lines of potato, each carrying a different gene for resistance. Parents of three matings carried an isozyme marker (glucosephosphate isomerase) which allowed the hybridity of most progeny to be confirmed. Apparently non‐hybrid progeny from all three matings were probably selfs or apomicts; these were discarded. The inheritance of virulence in two sib‐cross and one backcross family was determined. Patterns of inheritance in F1 and F2 indicated the presence of a gene‐for‐gene interaction in which alleles of a single locus in the pathogen conditioned virulence or avirulence on each differential. Although the hypothesis that avirulence alleles were dominant and virulence alleles were recessive was supported by many of the data, unexpected segregations were obtained. Alternative hypotheses to explain the latter included low aggressiveness in a proportion of the progeny, a second locus inhibiting avirulence in one parent, a different locus in each parent determining avirulence/virulence on one R‐gene, and dominance of some alleles determining virulence. Avirulent field isolates appeared to be heterozygous (A vravr) rather than homozygous (Avr Avr) at avirulence loci. A somatic segregation from avirulence to virulence at three avirulence loci was postulated for one parental isolate. Evidence for linkage of these three loci suggested that the observed somatic segregation resulted from mitotic crossing‐over.
Effect of temperature on virulence of Rhizoctonia solani on soybean leaves and seedlings
Authors: KOUSIK C. S. , SNOW J. P. , BERGGREN G. T. , HARVILLE B. G.
Published: April 2007

Isolates representing 11 anastomosis groups (AGs) of Rhizoctonia solani from various geographic locations and host plants were tested for virulence on soybean leaves at 15, 20, 25, 30, and 35°C, and on soybean seedlings at 20, 25, and 30°C. Numbers of infection cushions formed on soybean leaves were determined using light microscopy. Isolates of AG‐1 IA, AG‐1 IB and AG‐5 were more virulent on soybean leaves at 20, 25, and 30°C than isolates of AG‐1 IC and AG‐4. Maximum numbers of infection cushions were formed on soybean leaves by AG‐1 (IA, IB, and IC), AG‐4, and AG‐5 at 25 and 30°C. The other AGs tested did not form infection cushions on soybean leaves although some caused minimal disease severity. Isolates of AG‐1 IA formed significantly more infection cushions and caused greater disease severity than AG‐1 IB and other isolates at 35°C. Maximum seedling infection, based on per cent area of hypocotyl region covered by lesions occurred at 25 C for AG‐1 (IA, IB, and IC) and AG‐4. Isolates of AG‐5 caused greater seedling infection at 20°C than at 25 and 30°C. The other AGs tested caused only minimal damage to the seedlings. Isolates of AG‐4 and AG‐5 are not known to cause Rhizoctonia foliar blights of soybean in Louisiana, but their potential to be destructive foliar pathogens is confirmed.
Inter‐isolate variation for virulence in Plasmopara halstedii (sunflower downy mildew) from Hungary
Authors: VIRANYI F. , GULYA T. J.
Published: April 2007

A total of 82 isolates of Plasmopara halstedii, collected from all production areas of Hungary between 1976 and 1993, were assessed for their virulence pattern on a standard set of sunflower differentials under glasshouse conditions. The isolates were classified into six pathogenic races each representing a particular virulence phenotype. From 1976 until 1988 all the isolates were found to be virulent only on sunflowers possessing no known resistance genes, thus classified as race 1. There was an apparent shift in the virulence of the P. halstedii population collected after 1988. Six races (1, 2, 3, 4, 8 and 9) were identified among the 45 samples collected between 1989 and 1993, with races 1 and 3 predominant, at a frequency of 35% each. While the increase in race virulence is undoubtedly due to selection imposed by resistant hybrids, the origin of the new races is unknown. Whether new races have arisen from the indigenous P. halstedii population, or whether they have been imported from abroad, can only be reliably determined by DNA techniques, such as fingerprinting.
Effect of the fungal pathogen Bipolaris sorokiniana toxin prehelminthosporol on barley root plasma membrane vesicles
Authors: OLBE M. , SOMMARIN M. , GUSTAFSSON M. , LUNDBORG T.
Published: April 2007

The effects of the phytotoxin prehelminthosporol from the fungal pathogen Bipolaris sorokiniana on the activities of the plasma membrane H+‐ATPase, Ca2+‐ ATPase, and 1, 3‐β‐glucan synthase in barley roots were investigated in vitro. Plasma membranes were isolated by aqueous polymer two‐phase partitioning. Proton pumping by the H+‐ATPase was drastically reduced in a dose‐dependent manner, with complete inhibition at 500 μM prehelminthosporol, while inhibition of ATP hydrolysis was less drastic, with a 35% inhibition at 500 μM toxin. Ca2+ uptake was also reduced, although to a lesser extent than proton pumping, with a maximal inhibition of 60% at 500 μM toxin. The 1, 3‐β‐glucan synthase activity was weakly stimulated at toxin concentrations below 100 μM, with higher concentrations being inhibitory. Taken together, our results indicate that prehelminthosporol exerts its effect in at least two ways. First, it appears to disrupt the membrane barrier and thus seriously interfere with establishment of the proton gradient that drives ion and nutrient uptake and affect the efflux of Ca2+ to maintain the low cytoplasmic concentration of Ca2+ essential for the function of Ca2+ as a messenger in signal transduction. Secondly, it appears to inhibit the enzyme activities. The 1, 3‐β‐glucan synthase is activated by Ca2+ and can operate in the presence of low concentrations of prehelminthosporol (which may induce Ca2+ leakage into the cytoplasm and hence activate the enzyme), to produce callose to seal leaky membranes.
Selection of bacterial antagonists for the biological control of Rhizoctonia solani in oilseed rape (Brassica napus)
Authors: FIDDAMAN P. J. , ROSSALL S.
Published: April 2007

Spore‐forming bacteria isolated from oilseed rape (OSR) roots were tested for biological control activity against Rhizoctonia solani damping‐off of OSR, using a simple slurry coat formulation. From a total of 239 strains which were tested, Bacillus subtilis 205 was selected as the most promising biocontrol agent (BCA). A known isolate of B. subtilis (NCIMB 12376), which had previously shown activity against R. solani in cotton, was used as a standard comparison throughout. In an in vivo screening, pre‐emergence damping‐off disease control by B. subtilis 205 was excellent, with plant stands being almost as high as non‐diseased controls. However, post‐emergence survival was less good, although the surviving plants exhibited significantly reduced hypocotyl rot. Growth‐room trials which assessed the effect of ambient temperature on the biological control efficacy of B. subtilis strains 12376 and 205 showed that isolate 205 was more effective at lower temperatures. Disease control by isolate 205 at 15°C/10°C (day/night) suggests that this bacterium could operate under autumn sowing field conditions. Further investigations also indicated that the addition of iron (III) to the BCA formulation may enhance disease control by both bacilli. The potential of bacterial BCAs for the control of seedling diseases is discussed.
The incidence of strains of barley yellow dwarf virus in perennial ryegrass crops in south‐west and central Scotland
Authors: DEMPSTER L. C. , HOLMES S. J. I.
Published: April 2007

The incidence of barley yellow dwarf virus (BYDV) in perennial ryegrass (Lolium perenne) crops in four areas of south‐west and central Scotland was investigated between March 1988 and February 1989. BYDV was detected in 93·8% of the grass swards using an indirect enzyme‐linked immunosorbent assay (ELISA). This enabled the seasonal periodicity of the BYDV strains to be monitored over 12 months for the first time in Scotland. The incidence of the RPV, PAV and MAV strains of BYDV declined between March and July 1988, before gradually rising in August. Incidence increased markedly in September, especially of the RPV and MAV strains, and then gradually decreased over the winter months, before stabilizing in February 1989. The incidence of the different strains in perennial ryegrass leys varied between geographical areas and between fields within areas. Most ryegrass samples contained a mixture of the three strains of BYDV. RPV was the most common strain in Ayrshire, while the incidence of PAV was highest in Wigtownshire and that of MAV was highest in Dumfriesshire and Stirlingshire. The incidence of BYDV increased with the age of the sward. The role of perennial ryegrass as a source of virus for the infection of cereals is discussed.
Characterization of chilli vein‐banding mottle virus isolated from pepper in Thailand
Authors: SIRIWONG P. , KITTIPAKORN K. , IKEGAMI M.
Published: April 2007

A virus with flexuous particles, previously designated chilli veinal mottle virus (CVMV)‐CM1, which causes dark green spot, green vein‐banding and leaf distortion on peppers in Thailand, was isolated and characterized. The host range of this virus was restricted to the Solanaceae. The mean particle length in crude sap was 765 nm and the mean particle width was 13 nm. The virus was purified from pepper or Nicotiana glutinosa by extraction in phosphate buffer, followed by chloroform clarification and precipitation with PEG. The partially purified virus was further purified by sucrose density gradient centrifugation. This protocol consistently yielded 8–19mg virus/kg infected leaves. The purified virus had a UV absorption spectrum typical of nucleoprotein, with a minimum at 246 nm, a maximum at 260 nm, and a slight shoulder at 290 nm. The A260/A280 ratio was in the range 1·20–1·28, and the Amax/Amin ratio was in the range 1·11–1·27; the buoyant density in CsCl was 1·328g/cm3 Virions contained a single‐stranded RNA of c. 10kb and a single major protein of molecular weight 34000. The virus induced cytoplasmic inclusions in infected cells, which were observed as pinwheels, scrolls and laminated aggregates. It was not serologically related to potato virus Y (PVY, PVY‐O, PVY‐T), pepper mottle virus (PepMoV), pepper veinal mottle virus (PVMV), tobacco etch virus (TEV), papaya ringspot virus (PRSV), or peanut stripe virus (PStV), but is related to chilli veinal mottle virus occurring in Malaysia. On the basis of particle morphology, physico‐chemical and biological properties and cytopathology, it is considered to be a potyvirus. As this virus was serologically distinct from well‐known potyviruses, it is thought to be a new pepper potyvirus found in Thailand. Since the virus induces a typical dark green spotting, patching and banding along the vein in established infected peppers, the new and more descriptive name ‘chilli vein‐banding mottle virus’(CVbMV) is proposed.
Parasitism of the root‐lesion nematode Pratylenchus thornei on chickpea
Authors: CASTILLO P. , JIMENEZ‐DIAZ R. M. , GOMEZ‐BARCINA A. , VOVLAS N.
Published: April 2007

Pratylenchus thornei‐chickpea interactions were investigated under controlled and fluctuating environmental conditions in the growth chamber, greenhouse and shadehouse. Under controlled conditions, P. thornei infected chickpea lines 12071/10054 and P2245 and cultivars Andoum 1, JG62 and UC27. Line P 2245 and cv. JG 62 were the most susceptible genotypes on the basis of root damage and nematode reproduction, but nematode infection did not significantly reduce root and shoot weights. Cultivars Andoum 1 and UC27 and line 12071/10054 showed the least root damage and nematode reproduction. Inoculation of cv. Andoum 1 with 2500, 5000 or 10000 nematodes per plant in pots did not affect shoot weight, regardless of the conditions of water stress of the plants. However, root weight was significantly reduced by nematode infection in plants grown under water stress and fluctuating temperature conditions in the greenhouse, but was not affected by any other treatment. The nematode reproduction index was not affected by soil water content under shadehouse conditions, but was greater on plants watered to soil water‐holding capacity than in water‐stressed plants under greenhouse conditions. For both environments, the nematode reproduction index decreased when inoculum density was greater than 5000 nematodes per plant.
A model system for rapid selection for resistance and investigation of resistance mechanisms in Fusarium wilt of oil palm
Authors: MEPSTED R. , FLOOD J. , PAUL T. , AIREDE C. , COOPER R. M.
Published: April 2007

Fusarium wilt (Fusarium oxysporum f.sp elaeidis) is the most serious disease of oil palm in Africa. Control measures are dependent upon breeding for resistance, but the lack of a rapid screen for resistance and lack of understanding of the underlying resistance mechanisms has constrained breeding programmes. A novel petiole infusion technique is reported that exploits the ability of the majority of petiole cells to express disease resistance or susceptibility. A clear correlation was found between disease resistance or susceptibility of six clones and external symptoms and fungal colonization in petioles. Antifungal compounds accumulated in resistant but not in susceptible clones in response to inoculation; there was also some evidence of preformed antifungal compounds in resistant clones. Further investigation of resistance mechanisms can be undertaken using this model system. The use of this novel technique, both as a potential rapid replacement for current nursery selection methods (time reduced from 8 months to 8 days) and as an assessment of resistance in individual field palms, is discussed.*
Genome characterization of a new strain of peanut chlorotic streak virus causing chlorotic vein banding disease of groundnut (Arachis hypogaea L.) in India
Authors: SATYANARAYANA T. , BROGLIO E.P. , SREENIVASULU P. , REDDY D.V.R. , NAYUDU M.V.
Published: April 2007

The double‐stranded DNA of the chlorotic vein banding isolate of peanut chlorotic streak virus (PCISV‐CVB), isolated from purified virus, resolved into circular and linear molecules similar to those of other caulimoviruses. A physical map of viral DNA was constructed, which showed the PCISV‐CVB DNA to be circular and composed of approximately 8·2 kbp. A number of restriction sites were found to be shared with a similar caulimovirus, PCISV, Nevertheless, several differences between physical maps of the two viruses suggest that PCISV‐CVB should be considered as a distinct strain of PCISV. Bam HI‐cleaved PCISV‐CVB DNA was cloned into pUC 118 and was infectious when cleaved from the cloning vector and inoculated onto Vigna unguiculata.
Suppressive effects of N‐triacontanol on symptoms of mulberry dwarf disease and on the causal phytoplasma
Authors: QUN DAI , ZHI‐HUAN SUN
Published: April 2007

N‐triacontanol (TRIA) was applied over a period of 1 year to dwarf mulberry plants (Morus alba) with symptoms caused by mulberry dwarf phytoplasma. The treated plants recovered, and symptoms of the disease did not reappear for at least 3 years. Over this period, light‐microscope UV fluorescence tests using berberine sulphate failed to detect phytoplasmas in the phloem of young shoots from the treated plants.
Cocoa production in Ecuador in relation to dry‐season escape from pod rot caused by Crinipellis perniciosa and Moniliophthora roreri
Authors: MADDISON A. C. , MACIAS G. , MOREIRA C. , ARIAS R. , NEIRA R.
Published: April 2007

Cropping and disease patterns were observed over a period of 4 years in individual cocoa trees at three contrasting sites near Quevedo, Ecuador, with the aim of evaluating the importance of dry season production and the consequent avoidance of pod disease caused by Crinipellis perniciosa and Moniliophthora roreri. Distinction of the diseases on necrotic pods was aided by splitting open pods after removal from the tree. The year was divided into wet season (April to September) and dry season (October to March) harvest periods. The 3‐month lag between the actual wet and dry seasons and these harvest periods allowed time for symptom development. Combined disease losses ranged from 19·0% to 62·1 % at the various sites. At all sites and in each year, more ripe healthy pods were harvested in the dry season harvest period than in the wet season harvest period. In general, pod losses caused by C, perniciosa were curtailed more sharply by the dry season than those caused by M. roreri, which at one site caused as much damage in the dry season as in the wet season. The proportion of the annual production falling in the dry season harvest period varied among sites and between years at a given site. A comparison of trees from two progenies growing side by side showed consistent differences in cropping patterns, and identified certain trees that were productive, yielded consistently in the dry season harvest period, and were little affected by M, roreri. Analysis of long‐term rainfall data for the Quevedo region indicated that years which lack a normal dry season do occur, but only once every 10 years on average. Further exploitation of disease escape through selection and breeding appears to be both feasible and appropriate.
Effects of low temperature on mycelial growth and spore germination of Botrytis allii in culture and on its pathogenicity to stored garlic bulbs
Authors: TIAN S. P. , BERTOLINI P
Published: April 2007

Botrytis allii was incubated at 20, 10,4, 2,0, – 2 and –4° to investigate effects of temperature on growth, sporulation and germination on potato dextrose agar (PDA), and to estimate incidence and severity of disease on garlic bulbs inoculated with the pathogen during storage. B. allii‐was capable of growing to a colony diameter of 17 mm after 20 weeks, sporulating and germinating on PDA at temperature as low as – 4°C. After 12 weeks at –4 and ‐2°C the mycelial growth was observed only on 45–54% of bulbs wound‐inoculated with conidial suspension, and infection was limited to 5 mm in diameter on the surface of inoculation sites without producing any symptoms of the disease. Temperature responses were similar for mycelial growth, conidial germination and infection, but mycelial growth and sporulation was slower and later on garlic bulbs than in culture. Wounds were readily colonized by B. allii. No disease was found on unwounded bulbs that were inoculated with conidial suspensions and with mycelial plugs at various temperatures. Only 16–95% of cloves became infected by contact with other cloves within the same bulb after 12 weeks of storage at temperatures of 4–20 C.
Anastomosis group and pathogenicity of isolates of Rhizoctonia solani from potato crops in South Australia
Authors: BALALI G. R. , NEATE S. M. , SCOTT E. S. , WHISSON D. L. , WICKS T. J.
Published: April 2007

Isolates of Rhizoctonia collected from the stems, roots, tuber sclerotia and soil of potato crops in Virginia and Lenswood, South Australia, were identified to anastomosis groups (AG). Of the 301 multinucleate isolates of Rhizoctonia solani tested, 90% were AG‐3, 7% were AG‐4 and 2% were AG‐5; 12 isolates were binucleate Rhizoctonia spp. This is the first report of isolates of AG‐4 and AG‐5 causing disease in potato crops in South Australia. All AG‐3, AG‐4 and AG‐5 isolates tested caused rhizoctonia disease symptoms on the potato cultivar Coliban in pathogenicity trials conducted under glasshotise conditions. Both AG‐3 and AG‐5 isolates caused black scurf and stem cankers, although symptoms of black scurf were less severe with AG‐5. AG‐4 isolates produced the most severe stem and stolon cankers of all isolates tested. The pathogenicity of tuber‐borne inoculum was confirmed by growing plants from sclerotia‐infested tubers. AG‐8 isolates from diseased barley and wheat produced severe root cankers and caused loss of feeder roots on inoculated potato plants. Results suggest that rhizoctonia disease in potato fields in South Australia is caused by a combination of different anastomosis groups and this has important implications for crop rotations.
Detection of Erwinia carotovora subsp. atroseptica and Erwinia chrysanthemi in potato tubers using polymerase chain reaction
Authors: SMID E. J. , JANSEN A. H. J. , GORRIS L. G. M.
Published: April 2007

Soft rot erwiniae are a group of notorious plant pathogens for which currently available detection methods are inadequate. Based on the polymerase chain reaction, specific and sensitive detection of Erwinia carotovora subsp. atroseptica and E. chrysanthemi in potato tubers has been achieved. The composition of the PCR primers used in two specific detection systems is based on identification of the consensus of sequences of metalloprotease‐coding genes present in soft rot erwiniae. Bacterial DNA was extracted from the potato tuber matrix by differential centrifugation in order to avoid interference of potato‐derived compounds with the performance of the PCR assay. The PCR assay jjerformed with the E. carotovora subsp. atroseptica specific primer set was found to be capable of distinguishing E. carotovora subsp. atroseptica from all other Erwinia species and the closely related subspecies E. carotovora subsp. carotovora. With the E. chrysanthemi specific primer set, agarose gel electrophoresis is required for unequivocal differentiation between E. chrysanthemi and other erwiniae. Combined with the efficient extraction procedure, the assay allowed specific detection of less than 103 culturable erwiniae per tuber. The specificity and sensitivity of the assay were not reduced in the presence of a 100‐fold excess of DNA from both related and unrelated bacteria. This PCR‐based method for detection of erwiniae in potato tubers provides a relatively fast and sensitive alternative to routinely applied serological methods.
Effects of crop rotation and removal of crop debris on the soil population of two isolates of Verticillium dahliae
Authors: MOL L. , SCHOLTE K. , VOS J.
Published: April 2007

Microsclerotia of Verticillium dahliae are produced in large numbers on senescing parts of host plants and remain viable in the soil for many years. Changes in the population density, i.e. density of microsclerotia, in the soil were measured in micro‐plots using two isolates of V. dahtiae, specific to either field bean or potato, several crop sequences comprising potato, field beans and barley, and either the removal of aerial debris of the crops or incorporation into soil.

Potato was more susceptible to the potato isolate and field bean more susceptible to the field bean isolate. Removal of debris of potato and field bean reduced numbers of microsclerotia in the soil in the subsequent years, but removal of barley straw had no effect. Initially non‐infested control micro‐plots became infested, probably by the growth of potato roots into the naturally infested subsoil. The rate of increase of the microsclerotial population in the non‐infested control micro‐plots was larger than in the initially infested treatments, because more colonized debris was produced. It is concluded that removal of aerial debris of host crops is important to reduce the soil population of V. dahtiae.