bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of physiological and serological profiles of Pseudomonas syringae pv. pisi for pea blight identification
Authors: GRONDEAU C. , SAUNIER M. , POUTIER F. , SAMSON R.
Published: April 2007

Phenotypic variability of the pea blight bacterium, Pseudomonas syringae pv. pisi, was studied on a large collection of strains isolated in France, as well as those obtained from foreign collections. Some other pseudomonads encountered on peas, particularly P.s. pv. syringae, were included in the study to evaluate differential tests for identification purposes. All the isolates that induced watersoaking on the pea cultivar Kelvedon Wonder after inoculation were considered to be P.s. pv. pisi. The other pseudomonads gave either no reaction or a hypersensitive reaction. When they corresponded to P. syringae according to the LOPAT test, they were referred to as P.s. pv. syringae.

P.s. pv. pisi did not show a single uniform phenotype. The variation of the different tests was estimated (fluorescence+ 93%; esculin‐86%; dl‐lactate‐85%; homoserine + 75%; INA + 97%). Three O‐sero‐groups contained P.s. pv. pisi strains: APT‐PIS (88.5%), HEL2 (11.4%) and RIB (0.1%). When the main criteria were combined, eight profiles were encountered within P.s. pv. pisi. This diversity was not linked to race structure or geographical origin of the strains. Profile PI was the most frequent (72.8%), and it was specific to the pathovar pisi. The strains belonging to the other profiles could be confused with some P.s. pv. syringae strains because of the serological heterogeneity of that pathovar. For instance, the pv. pisi strains belonging to profiles P2 and P4 resembled some of the P.s. pv. syringae found on peas and required pathogenicity tests on pea for their identification. The confusing pea isolates represented 12.8% of the total 4740 strains studied.
Disease‐yield relationship in barley. II. Contribution of stored stem reserves to grain filling
Authors: GAUNT R. E. , WRIGHT A. C.
Published: April 2007

The effect of disease in two cultivars of barley, sown at different times in two seasons, on the relative importance of stored carbohydrate reserves and current photosynthesis for grain filling was assessed. Three methods of measuring stem reserve contributions to grain filling are reviewed and compared. Disease reduced stem dry weight and the amount of stored carbohydrate in most situations. In contrast, the total amount of stored carbohydrates used for grain filling was often increased by disease. The magnitude of these effects varied with the method used for estimation, and was also different in the crops sown at different times and in different seasons. The estimates of stem reserve contributions to grain filling ranged up to a maximum of 50% in some cases. At least 10 t/ha of reserve material was retranslocated in the healthy 1984 crop studied using 14C pulse feeding, and up to 0.3 t/ha more was utilized in a diseased crop. The effect of disease on the storage and utilization of stem reserves depended on the time of epidemic development, its duration, and the yield potential of the crop. This suggests that crops could be characterized as those which are very sensitive to disease during grain filling, with low stem reserves or high yield potential, and those with lower sensitivity, with more stem reserves or lower yield potential. Such interacting factors could be incorporated in future plant and yield‐loss mechanistic models.
Characteristics of the transmission of Sumatra disease of cloves by tube‐building cercopoids, Hindola spp.
Authors: EDEN‐GREEN S. J. , BALFAS R. , SUTARJO T. , JAMALIUS
Published: April 2007

Repeated transmission tests showed that the tube‐building cercopoids Hindolafulva (in Sumatra) and H. striata (in Java) were natural vectors of Sumatra disease of cloves, caused by Pseudomonas syzygii. In tests on experimental transmission of P, syzygii, H, striata collected from a disease‐free area acquired bacteria within 4 h of access to infected plants and transmitted them within 4 h of access to healthy test plants. Transmission was persistent and commenced within 24 h of acquisition feeding, but there was evidence for a short latent period between acquisition and transmission of bacteria. After acquisition feeding, P. syzygii was isolated from 67% of insects that transmitted the disease and also from 3% of those that did not. Times to death of test plants following first exposure to both naturally and experimentally infective insects showed log‐normal distributions with similar slopes. Younger (1‐year) seedlings died slightly sooner (median response time = 200 days) than older (2‐ to 3‐year) test plants (median response time = 280 days). The bacterial content of test plants was positively correlated with time to death.
Occurrence of barley yellow dwarf virus in cereals and grasses of the low‐rainfall wheatbelt of South Australia
Authors: HENRY M. , FRANCKI R. I. B. , WALLWORK H.
Published: April 2007

South Australia is in the dry temperate zone where most cereal crops are grown in an area of low rainfall, with a crop‐free season from December to April. The incidence of barley yellow dwarf virus (BYDV) was assessed by ELISA from 1989 to 1991 in wheat crops and irrigated pastures of South Australia. The incidence of BYDV was low in most wheat crops of the low‐rainfall area in 1989 and 1990 (less than 1% of plants infected), but moderate levels of infection (1–10%) were observed in some early‐sown crops. BYDV infection was more widespread in the high‐rainfall area (south east of South Australia). A high incidence of BYDV was observed in the irrigated pastures of the three areas surveyed (4–86%). Of the five previously described strains, the Rhopalosiphum padi/Sitobion avenae strain (PAV) was the most common in wheat samples (> 90%). PAV and the R. padi‐specific strain (RPV) were found in pasture grasses, alone or in mixed infection. Virus incidence was greater in Festuca spp. (56%) and Lolium perenne (30%) than in other species (2‐–9%).
A new yellowing disease of cucurbits caused by a luteovirus, cucurbit aphid‐borne yellows virus
Authors: LECOQ H. , BOURDIN D. , WIPF‐SCHEIBEL C. , BON M. , LOT H. , LEMAIRE O. , HERRBACH E.
Published: April 2007

Since 1988, a yellowing disease of melon, cucumber and zucchini squash has been frequently observed in summer and autumn crops in France. Infected plants show yellowing and thickening of the older leaves; symptom intensity differs depending upon cultivar and season, and can be easily overlooked when plants are already infected by mosaic‐inducing viruses or other pathogens. The disease is associated with the presence of a virus with spherical particles c. 25 nm in diameter, which is readily transmitted in a persistent manner by the aphids Myzus persicae and Aphis gossypii, but not mechanically. Serological analysis, nucleic‐acid‐hybridization experiments and host‐range studies indicate that the virus is distantly related to, but distinct from, beet western yellows virus (BWYV). We propose to name this virus cucurbit aphid‐borne yellows virus (CABYV), and to consider it as a tentative new member of the luteovirus group. CABYV was found to reduce significantly the yields of melon and cucumber by decreasing the number of fruit per plant but not by altering the fruit shape or quality. Preliminary investigations of the epidemiology of CABYV indicate that the virus is common in weeds and in cultivated cucurbits. CABYV was frequently detected in various regions of France, suggesting that it is one of the most prevalent viruses infecting cucurbits in this country.
Studies on the control of zucchini yellow mosaic virus in courgettes by mild strain protection
Authors: WALKEY D. G. A. , LECOQ H. , COLLIER R. , DOBSON S.
Published: April 2007

Mild‐strain cross protection was used in field trials at Wellesbourne and in Jersey in attempts to protect courgette plants against severe strains of zucchini yellow mosaic virus. Test plants were sap inoculated with the mild strain and then challenged by an aphid‐transmitted severe strain after different periods. Approximately 14 days of incubation were required following mild‐strain inoculation to provide protection against subsequent infection by severe strains. No protection occurred if severe strains were introduced 2 days (48 h) after mild‐strain inoculation and protection was intermediate if the severe‐strain challenge occurred after 7–8 days. Some breakdown in protection occurred in the later stages of the trial at Wellesbourne, but not in Jersey. This loss of protection may be associated with high inoculum pressures.
A new disease of passion fruit in Mauritius: postharvest stem‐end rot caused by Phomopsis tersa
Authors: LUTCHMEAH R. S.
Published: April 2007

Symptoms of post‐harvest stem‐end rot of passion fruit caused by Phomopsis tersa are described for the first time. Under laboratory conditions, following artificial inoculation, first symptoms occurred 4–11 days after harvest, depending on the length of the peduncles of fruits when harvested and whether fruits were injured. It is concluded that the pathogen invades the fruit through the peduncle and damaged skin.
Detection of double‐stranded RNA and virus‐like particles in Australian isolates of Pythium irregulare
Authors: GILLINGS M. R. , TESORIERO L. A. , GUNN L. V.
Published: April 2007

Mycelial extracts of Pythium irregulare were processed using CF‐11 chromatography and analysed by gel electrophoresis for double‐stranded RNA (dsRNA) content. DsRNA molecules of between 1 and 6 kb were found in 33 of 39 isolates tested. The dsRNA profiles of individual isolates remained unchanged after repeated subculturing of hyphal tips, after storage under water for 2 years, or when single zoospores were used to generate subcultures. However, dsRNA profiles varied between isolates, and even within individual populations; in the one case eight different dsRNA types were recovered upon testing 17 isolates from a single wheatfield. Isometric virus‐like particles (VLPs) of approximately 45 nm were found in isolates containing dsRNA, while no such particles could be found in isolates in which dsRNA was not detected. Electrophoretic profiles of dsRNA extracted from partial purifications of VLPs were identical to those of dsRNA extracted from whole mycelium, suggesting that the dsRNA is at least partially encapsidated. Attempts to transmit dsRNA between isolates by hyphal anastomosis or by coinfection in wheat plants were unsuccessful, with only parental types being recovered. Analysis of 29 isolates representing 14 other Pythium species failed to detect dsRNA, even when co‐isolated with P. irregulare known to contain dsRNA
Studies on the mechanism of transmission of pollen‐associated tobacco streak ilarvirus virus by Thrips tabaci
Authors: SDOODEE R. , TEAKLE D. S.
Published: April 2007

Mixed instars of Thrips tabaci were allowed to feed on test seedlings of cucumber, the thrips were removed and wounds caused by thrips feeding dusted with tobacco streak virus (TSV) carried in tomato pollen. Transmission of TSV occurred in three out of the four experiments conducted. When Chenopodium amaranticolor test seedlings were dusted with infective tomato pollen, and thrips introduced for varying periods before being killed with insecticide, TSV transmission occurred after exposure to thrips for 1 h, 5 h, 1 day or 2 days, but not 5 min. Pollen‐washing experiments indicated that TSV was carried both internally and externally in pollen of tomato and several weed hosts. T. tabaci was able to transmit TSV from pollen of Nicotiana clevelandii and Nicandra physalodes, and TSV from tomato pollen was transmitted to several weed species. It is concluded that T. tabaci transmits TSV associated with tomato pollen by a mechanical mechanism whereby virus carried externally, or released from inside the pollen, infects feeding wounds.
The effect of hot‐water treatment on the levels of antifungal diene and quiescence of Colletotrichum gloeosporioides in avocado fruits
Authors: PLUMBLEY R. A. , PRUSKY D. , KOBILER I.
Published: April 2007

Quantitative changes in the antifungal compound 1‐acetoxy‐2‐hydroxy‐4‐Oxo‐heneicosa‐12, 15‐diene in harvested avocado fruits, and the development of symptoms caused by Colletotrichum gloeosporioides, were investigated following treatment with hot water at 55°C for 10 min. The concentration of the compound in the peel and flesh was 2000 and 2600 μg/g fresh weight, respectively, at the time of harvest, but decreased rapidly during the first 24 h. Levels of the diene had substantially recovered after 50 h. However antifungal diene levels in the peel of hot‐water‐treated fruit did not recover until 98 h. The levels in the flesh were unaffected by the treatment. Following inoculation, hot‐water‐treated fruits developed clear symptoms after 2 days, whereas untreated fruits showed only minor symptoms after 6 days. If inoculation was delayed by 24, 48 or 72 h after treatment, then symptoms on treated fruits did not develop until the sixth day as observed for untreated fruits. The correlation between the two systems suggests that quiescence is probably maintained by the level of antifungal diene present in the peel at the time of fungal penetration and the formation of a subcuticular hypha.
A new filamentous virus in shallot
Authors: VISHNICHENKO V. K. , KONAREVA T. N. , ZAVRIEV S. K.
Published: April 2007

Serological analysis (ELISA, immunoblotting, and immunoelectron microscopy) of the partially purified virus preparations obtained from shallot plants (selection sample no. 83) inoculated with the Mongolian isolate of onion yellow dwarf potyvirus (OYDV) revealed neither an OYDV coat protein antigen nor virions decorated by the corresponding antiserum. At the same time, these preparations contained many flexuous filamentous virus particles (FFVP) with a modal length of 780 nm. It is suggested that shallot no. 83 is resistant at least to the Mongolian isolate of OYDV, while the discovered FFVPs are the virions of some other viral agent. The nature and origin of a new virus are now under study in this laboratory
Fireweed (Epilobium angustifolium) as a possible inoculum reservoir for root‐rotting Armillaria species
Authors: KLEIN‐GEBBINCK H. W. , BLENIS P. V. , HIRATSUKA Y.
Published: April 2007

Two glasshouse experiments were conducted to determine the potential for Armillaria species to infect fireweed and subsequently use it as a food base for attacking lodgepole pine. Aspen segments colonized by A. mellea and A. ostoyae were used to inoculate fireweed roots. Both species caused infection, although the former was more pathogenic, attacking 28 of 42 inoculated fireweed roots as opposed to 8 of 60 in the case of the latter species. None of the nine pines inoculated with segments of fireweed roots colonized by A. ostoyae became infected, even though the isolates were pathogenic on pine when aspen segments were used as the food base. In contrast, 8 of 29 pine seedlings inoculated with fireweed colonized by A. mellea were killed, thus suggesting that fireweed could play some role in the epidemiology of this disease.
Comparative pathogenicity of Pythium species associated with poor seedling establishment of rice in Southern Australia
Authors: COTHER E. J. , GILBERT R. L.
Published: April 2007

Isolates of Pythium attributable to thirteen named species and to species group F (sensu van der Plaats‐Niterink) were isolated from roots of field‐grown rice seedlings showing poor root development and lack of vigour. P. arrhenomanes and group F were the most commonly isolated species. The roots of 15‐week‐old rice plants yielded only P. flevoense, P. vanterpoolii, P. rostratum and Pythium group G of which the latter two were not obtained from seedling roots.

In pot tests with representative Pythium isolates, P. arrhenomanes was most pathogenic to rice seedlings, causing pre‐ and post‐emergence death and average reductions in shoot and root growth in surviving seedlings of 48 and 70%, respectively. P. irregulare killed seedlings before but not after emergence, whilst the response of rice seedlings to P. myriotylum apparently depended on the length and timing of a cold shock treatment. P. pyrilobum did not reduce seedling number or shoot growth but reduced root growth. P. vanterpoolii and group F were not pathogenic in the tests. P. coloratum, P. echinulatum, P. flevoense, P. oedochilum, P. oligandrum, P. periilum, P. pyrilobum and P. rostratum were isolated infrequently and had no adverse effects on seedlings in pathogenicity tests, although P. myriotylum, P. oligandrum, and P. periilum were associated with significant increases in shoot growth. P. tracheiphilum was isolated from one site but its pathogenicity was not tested.

This is the first record of P. coloratum, P. echinulatum, P. flevoense, P. irregulare, P. oedochilum, P. oligandrum, P. periilum, P. pyrilobum and P. tracheiphilum from rice roots.
Production of the phytotoxins, solanapyrones A and C and cytochalasin D among nine isolates of Ascochyta rabiei
Authors: LATIF Z , STRANGE R. N. , BILTON J. , RIAZUDDIN S.
Published: April 2007

Nine isolates of Ascochyta rabiei from Pakistan were grown in still culture on Czapek Dox liquid medium supplemented with aqueous extracts of the seed of one of two cultivars, a desi (6153) or a kabuli (Cypressa). Toxicity of the culture filtrates from both media was assayed with cells isolated from the leaves of both cultivars and concentrations of the phytotoxins. solanapyrone A and solanapyrone C, in the filtrates were determined by high‐performance liquid chromatography (HPLC). For eight of the fungal isolates, toxicity and solanapyrone concentration were correlated, r varying from 0·383 to 0·859 according to medium and assay cultivar, but culture filtrates of another isolate, which was the most active by more than an order of magnitude, contained cytochalasin D but neither of the solanapyrones.
Blackening on yam in response to Colletotrichum gloeosporioides
Authors: WINCH J. E. , JACKSON G. V. H. , NEWHOOK F. J. , COLE J. S.
Published: April 2007

A blackening confined to the cuticle and/or outer epidermal cell walls of mature leaves of Dioscorea alata was found to be associated with the appressoria of the fungus Colletotrichum gloeosporioides on plants subjected to high levels of inoculum in the field and to dense spore suspensions in controlled tests. The blackening occurred with little evidence of fungal penetration into the host cells. Preliminary analyses of the nature of the blackening detected melanin‐like compounds and suggest the involvement of phenolic compounds and water‐soluble chemicals, possibly enzymes, in the blackening process.
The role of phytoalexins in resistance to fusarium wilt in pigeon pea(Cajanus cajan)
Authors: MARLEY P. S. , HILLOCKS R. J.
Published: April 2007

Mechanisms of resistance to fusarium wilt(Fusarium udum)were investigated in pigeon pea cultivars from Malawi. Wilt‐susceptible (Malawi local) and wilt resistant (ICP 9145) plants were stem‐inoculated with a spore suspension containing 2·106conidia/ml of the pathogen. Occlusion of a small proportion of infected vessels was observed, but the resistant reaction appeared to depend mainly on rapid phytoalexin synthesis. Four fungitoxic isoflavonoid phytoalexins—hydroxygenistein, genistein, cajanin and cajanol‐were isolated from plants 15 days after inoculation. Cajanol was identified as the main antifungal compound. The concentration of cajanol was 329·4 μg/g in the resistant cultivar as against 88·6 μg/g in the susceptible cultivar 15 days after inoculation. Crude extract from the resistant plants sampled at 24 h after inoculation contained 34·8 μg ml of cajanol. The LD50value of cajanol for spore germination was determined as 35μg/ml. The cajanol content of fungus‐infected ICP 9145 10 days after inoculation totally inhibited conidial germination ofF. udum.
Effects of antagonistic microorganisms on the post‐harvest development of Colletotrichum gloeosporioides on mango
Authors: KOOMEN I. , JEFFRIES P.
Published: April 2007

Potential microbial antagonists of Colletotrichum gloeosporioides were isolated from blossom, leaves and fruit of mango and screened using a series of assay techniques. In total 648 microorganisms, including bacteria, yeasts and filamentous fungi, were isolated and tested for their inhibition of growth of C. gloeosporioides on malt extract agar. In vitro, 121 organisms inhibited the fungus and were tested further for their ability to affect conidial germination. Of these isolates, 45 bacteria and yeasts inhibited germination. These were inoculated onto mangoes artificially infected with C. gloeosporioides and assessed for their potential to reduce the development of anthracnose lesions. Seven isolates were chosen for use in a trial in the Philippines using freshly harvested fruit. This final screening procedure yielded two potential candidates for further trials, isolate 204 (identified as Bacillus cereus) and isolate 558 (identified as Pseudomonas fluorescens). In post‐harvest trials under commercial conditions, isolates 204 and 558 were both tested in combination with different application methods including the addition of adhesive material, peptone, fruit wax or sucrose polyester. Application of isolate 204 did not reduce disease development, whereas application of 558 significantly reduced anthracnose development. No additional benefit was achieved by incorporating the bacteria in adhesive material, peptone, fruit wax or sucrose polyester.
An assessment of aesculin hydrolysis, vegetative compatibility and DNA polymorphism as criteria for characterizing pathogenic races within Fusarium oxysporum f.sp. vasinfectum
Authors: BRIDGE P D. , ISMAIL M. A. , RUTHERFORD M. A.
Published: April 2007

Fifteen strains, assigned to four pathogenic races of Fusarium oxysporum f.sp. vasinfectum on the basis of host range, were characterized by means of vegetative compatibility, restriction fragment length polymorphisms (RFLPs) and pigmentation on aesculin‐containing medium. Isolates were divided into two major vegetative compatibility groups (VCGs) comprising Races 1 and 2 (VI) and Race 3 (V2). The two VCGs were represented by a single RFLP pattern. An additional RFLP pattern was observed for a single Race 4 isolate. Isolates received as belonging to Races 2, 3 and 4 blackened aesculin agar, while designated and presumed Race 1 isolates gave a negative reaction.
New records of Cylindrocladium and Cylindrocladiella spp. in South Africa
Authors: CROUS P. W. , PHILLIPS A. J. L. , WINGFIELD M. J.
Published: April 2007

Three species of Cylindrocladium (Cm.) and three of Cylindrocladiella (Ca.) were collected from forestry plantations and nurseries in South Africa. These fungi include species previously recorded in South Africa. Cm. scoparium and Ca. parva, as well as new records for the country: Cm. clavatum. Cm. colhounii, Ca. camelliae and an undescribed Cylindrocladiella. Single‐conidium isolates of all six fungi tested were pathogenic to Eucalyptus grandis, Medicago truncatula, Arachis hypogaea, Glycine max and Pisum sativum. Only Cm. clavatum was pathogenic to Solanum tuberosum. Cm. species were more virulent than the Ca. species, with Cm. clavatum being the most virulent of all the fungi.
Partial purification of a virus associated with a Spanish isolate of citrus ringspot
Authors: NAVAS‐CASTILLO J. , MORENO P. , CAMBRA M. , DERRICK K.
Published: April 2007

A citrus ringspot isolate from Star Ruby grapefruit (RS‐SR) was mechanically transmitted to Chenopodium quinoa. RS‐SR was partially purified by differential centrifugation, fractionation in a sucrose gradient, and agarose gel electrophoresis of selected fractions. Infectivity of concentrated extracts on C. quinoa was lost in individual fractions of the gradient, but it was recovered by combining a top and a bottom component. Both components contained a 48‐kDa protein not found in similar preparations from healthy plants. After further purification the 48 kDa protein was detected at the top edge of the agarose gel. In the initial experiments a 38‐kDa protein was found in the same fractions that later contained the 48‐kDa protein. An antiserum obtained to the 38 kDa protein reacted in Western blots with both the 38‐ and the 48‐kDa proteins, whereas another antiserum raised to the Florida isolate CRSV‐4 (also containing a 48‐kDa protein) did not react with the 38‐kDa protein, indicating that the latter was probably a degradation product of the 48‐kDa protein. Filamentous flexous particles were observed by serologically specific electron microscopy in crude extracts from RS‐SR‐infected C. quinoa plants. These results indicate that RS‐SR is associated with a two‐component virus similar to those associated with several psorosis and ringspot isolates, and serologically related to CRSV‐4.
Pseudomonas syringae pv. avellanae pathovar nov., the bacterium causing canker disease on Corylus avellana
Authors: PSALLIDAS P. G.
Published: April 2007

The results of an extensive study of 170 morphological, physiological, biochemical, serological and pathological characters of 18 representative isolates from the filbert canker pathogen are presented. These indicate that the bacterium responsible for the disease of filberts (Corylus avellana) in Greece is properly characterized as a typical member of the species Pseudomonas syringae. It is placed in group Ia according to the LOPAT tests. The differences in some characters between Pseudomonas syringae pv. syringae and the filbert Pseudomonas, as well as its host specificity, justify its classification as a new pathovar of Pseudomonas syringae and the name of Pseudomonas syringae pv. avellanae pv.nov. is proposed for the bacterium causing the disease ‘bacterial canker’ of Corylus avellana.
The effect of humidity on the expression of partial resistance to powdery mildew in barley
Authors: NEWTON A. C.
Published: April 2007

Seedling leaves of four cultivars of barley, three of which express partial resistance, were inoculated with powdery mildew (Erysiphe graminis f.sp. hordei) and enclosed in an apparatus which enabled accurate control of humidity, air speed and temperature. Infection frequency was always greater at high humidity (>95%) than at low humidity (40–50%). Cultivar 7204 (Ethiopian) showed a greater reduction in infection frequency at both 12 and 16°C, and more reduction in biomass per colony at 16°C under low humidity than the other cultivars. The potential for exploiting such differences in barley breeding is discussed.
Influence of beet soil‐borne virus on mechanically inoculated sugar beet
Authors: KAUFMANN A. , KOENIG R. , ROHLOFF H.
Published: April 2007

Seven‐day‐old seedlings of three different sugar‐beet varieties (Carla, Rizor and Desirée) were inoculated mechanically with the Ahlum isolate of beet soil‐borne virus (BSBV) in crude sap from infected leaves of Chenopodium quinoa. Control plants were mock‐inoculated with sap from healthy C. quinoa. After potting up, the plants were arranged in a randomized block design on nine neighbouring benches in a glasshouse. Plants were sampled after 11 weeks, the fresh weight of the tap roots determined and the presence of virus checked by ELISA. Considerable variation in tap‐root growth was observed between benches. Overall, BSBV inoculation reduced tap‐root weight of Rizor and Carla by c. 20%. Problems arising in attempts to assess yield loss due to BSBV in naturally infected sugar beet are discussed.
Black leaf streak (Mycosphaerella fijiensis) in Uganda
Authors: TUSHEMEREIRWE W. K. , WALLER J. M.
Published: April 2007

The occurrence of black leaf streak caused by Mycosphaerella fijiensis is reported on a number of banana cultivars in Uganda, demonstrating the spread of the disease from West and Central to East Africa since the early 1980s.
Selection methods for determining resistance of carnation cultivars to Fusarium oxysporum f.sp. dianthi
Authors: BEN‐YEPHET Y. , REUVEN M. , MOR Y.
Published: April 2007

The level of resistance of carnation (Dianthus caryophyllus) cultivars to wilt caused by Fusarium oxysporum f.sp. dianthi was compared in root‐dip‐inoculated plants grown in pots (filled with tuff or sandy soil) in a greenhouse and plants grown in a field where the soil was artificially infested with the fungus. In the field, wilt symptoms appeared first in susceptible and subsequently in resistant cultivars; none was immune. Variations in the level of resistance were expressed either by different percentages of wilted plants (i.e. disease incidence) or by delayed disease progress as compared to a susceptible cultivar. The range of disease severity in the field, ranked on a scale from 0 to 4, was highly and significantly correlated with the percentage of diseased plants. The greenhouse test was unreliable as a predictor of the degree of resistance observed in the field. Similar wilt levels in the greenhouse and the field were found only in susceptible cultivars.
Screening for potential antagonists of Pseudocercosporella herpotrichoides, the causal agent of eyespot disease of cereals
Authors: CLARKSON J. P. , LUCAS J. A.
Published: April 2007

The eyespot fungus Pseudocercosporella herpotrichoides survives on straw colonized during infection of a previous cereal crop, which then serves as an inoculum source for subsequent infection cycles. Tests were devised to identify fungal antagonists capable of competing with the pathogen on straw, and suppressing inoculum production and host infection. The 228 fungal isolates from wheat seedlings, plants or straw were screened for activity, along with 13 fungi and a commercial strain of Streptomyces griseoviridis which had proven biocontrol activity against other fungal pathogens. Potential antagonists were selected on the basis of inhibition or overgrowth of P. herpotrichoides on several contrasting nutrient media. Co‐inoculation of straw with the pathogen and test antagonists reduced disease severity in pot trials using this straw as an inoculum source. When straw pre‐inoculated with the pathogen was used, fewer antagonists proved effective in suppressing eyespot disease. However, one isolate, a Trichoderma sp., gave positive results both in vitro and in infection trials using different inoculation procedures, and may therefore be an effective antagonist of P. herpotrichoides during the saprophytic survival phase of the pathogen life cycle.
Application of Pseudomonas fluorescens isolates to wheat as potential biological control agents against take‐all
Authors: CAPPER A. L. , HIGGINS K. P.
Published: April 2007

Two isolates of Pseudomonas fluorescens (2–79 and 13–79) from the USA were evaluated in the UK as biological control agents against Gaeumannomyces graminis var. tritici, the cause of take‐all in wheat. Biological control agents were applied as seed coatings in carboxymethyl cellulose (CMC) to seven wheat trials sown in 1987 and 1988 on fen peat and clay soils, and as peat‐based and microgranule formulations in one of these trials. In a trial of spring wheat on fen peat, all treatments with biological control agents reduced the percentage take‐all infection of crown roots and seminal roots, but the effects of only one isolate were statistically significant (P<0·05). Effects of biological control agents on infection rates in five other trials were not significant. In the trial in which application methods were compared, peat‐based inoculum initially appeared most effective but none of the treatments reduced take‐all significantly throughout the season. Application of biological control agents was associated with yield increases in several trials; these were not consistently associated with effects on take‐all. These results suggest that the isolates of P. fluorescens have potential to reduce take‐all and increase yields of wheat in the UK, but the beneficial effects are inconsistent. There is a need to develop isolates which reliably control severe take‐all in a variety of soil types.
Effect of bacterial blight (Pseudomonas syringae pv. pisi) on the growth and yield of single pea (Pisum sativum) plants under glasshouse conditions
Authors: ROBERTS S. J.
Published: April 2007

Single pea (Pisum sativum) plants cvs Kelvedon Wonder and Solara, growing in pots in a glasshouse, showed significant reductions in seed yield of 24, 47 or 71% following inoculation with pea bacterial blight (Pseudomonas syringae pv. pisi) during reproductive, vegetative or both reproductive and vegetative growth stages, respectively. These yield reductions were seen as reduced numbers of seeds per pod combined with changes in the numbers of pods per plant. Examination of the importance of different disease parameters on yield showed that mean disease on the whole plant was the most important. Equations describing the relationship between seed yield or the natural log of the total weight and mean disease were derived.
Distribution and frequency of occurrence of potato cyst nematode pathotypes in Northern Ireland
Authors: ZAHEER K. , FLEMING C.C. , TURNER S. J.
Published: April 2007

The distribution and frequency of occurrence of potato cyst nematodes, Globodera rostochiensis and G. pallida, were examined in Northern Ireland. Globodera rostochiensis (pathotype Rol) was the most abundant species, while Pal and Pa3 pathotype reactions could be discerned within G. pallida. Unlike other parts of the UK, species proportions appear not to have changed over the last 20 years, probably as a result of the legislative control currently practised combined with the limited use of Rol‐resistant cultivars within the country. Differences in the geographical distributions of the three pathotypes were observed, and these are discussed in relation to original potato cyst nematode introductions and subsequent agricultural practices.
Transgressive segregation for resistance to Pyrenophora teres in barley
Authors: CHERIF M. , HARRABI M.
Published: April 2007

Populations of F1, F2, F1× parent 1 (BC1), F1× parent 2 (BC2), and F3 resulting from two crosses between four susceptible varieties of barley used in national and international breeding programmes were tested at the seedling stage for their resistance to an isolate of Pyrenophora teres which is virulent to the parental varieties. Infection type, average lesion size, and number of lesions per unit leaf area were used to assess disease reaction. In the two crosses, F2 and especially F3 generations (produced by self pollination of selected resistant F2 plants) showed more resistance expressed by infection type and average lesion size than either parent. The frequency distributions of F2 and F3 generations derived from these crosses were continuous and showed transgressive segregation for resistance. The results indicated that the four cultivars used in this study possessed additive genes for resistance to P. teres. Thus useful resistance could be obtained following crossing of susceptible cultivars and selection in succeeding generations.
Diversity and variation in expression of resistance to Erysiphe fischeri in Senecio vulgaris
Authors: BEVAN J. R. , CRUTE I. R. , CLARKE D. D.
Published: April 2007

The reactions of 20 inbred lines of Senecio vulgaris (groundsel) to inoculation with up to 10 isolates of Erysiphe fischeri (powdery mildew) were investigated in a number of repeat experiments. There was considerable variation among isolate/plant line reaction phenotypes with examples of both isolate‐specific complete resistance and isolate‐specific partial resistance. Some plant lines possessed high levels of partial resistance to all isolates tested. Incubation temperature and plant age influenced the infection types of some isolate/plant line combinations. In this pathosystem, complete and partial resistance, together with age‐dependent and temperature‐dependent resistance, appear to have evolved to facilitate a defence strategy based on a complex mosaic of interacting factors.
An adapted selective medium for the quantitative isolation of Trichoderma species
Authors: ASKEW D. J. , LAING M. D.
Published: April 2007

Further modifications were made to a previously amended Trichoderma‐selective medium (TSM), by replacing fenaminosulf with propamocarb or metalaxyl. Both were effective in suppressing Oomycetes but propamocarb was superior. Quantitative isolation of Trichoderma species from soil was possible.
Inhibitory effects of essential oil components extracted from celery (Apium graveolens) on the growth of Septoria apiicola, causal agent of leaf spot disease
Authors: DONOVAN A. , ISAAC S. , COLLIN H. A.
Published: April 2007

Leaf spot disease of celery (Apium graveolens), caused by the fungus Septoria apiicola, is a major disease for which there is only limited host resistance. Some factors affecting the response of the fungus to essential oil components of host tissue were investigated using a susceptible blanching celery (var. Celebrity) and a more resistant green celery (var. Cutting) as hosts. After infection the time taken for pycnidia to appear on the surface was 16 days in Cutting and 13 days in Celebrity, but only limited leaf necrosis occurred in Cutting whereas the whole leaf rapidly became necrotic in Celebrity. Although the composition of the essential oil (limonene, β‐pinene, terpinene, caryophyllene, sesquiterpenes and phthallides) was comparable in both varieties, Cutting contained over four times the total concentration of oil found in Celebrity. Extracts of the essential oil from Cutting were found to be more inhibitory to the growth of Septoria in culture. Of the terpenes tested (limonene, β‐pinene, and caryophyllene), β‐pinene was most inhibitory to the growth of hyphae on solid and liquid media. The role of the essential oil as part of a constitutive defense mechanism in host resistance to Septoria is discussed.
Expression of the PR‐b1′ gene in roots of two Nicotiana species and their amphidiploid hybrid infected with virulent and avirulent races of Chalara elegans
Authors: TAHIRI‐ALAOUI A. , DUMAS‐GAUDOT E. , GIANINAZZI S. , ANTONIW J. F.
Published: April 2007

The expression levels of PR‐b1′ gene coding for PR‐b1′ protein (a PR‐1 group protein) were investigated in the roots of two Nicotiana species and their amphidiploid hybrid in response to infection by virulent (84–1) or avirulent (85–26) races of black root rot fungus Chalara elegans. Nicotiana glutinosa is susceptible to C. elegans, while Nicotiana debneyi and the amphidiploid hybrid N. glutinosa×N. debneyi are highly resistant. The results showed that irrespective of whether the plant is susceptible or resistant, and the fungal race virulent or avirulent, low infection rates induce low levels of PR‐b1′ mRNA, and high infection rates result in high production of PR‐b1′ mRNA. The amphidiploid hybrid, which expresses the protein PR‐b1′, constitutively, showed similar PR‐b1′ mRNA levels with both races of C. elegans. At maximal levels of accumulation, PR‐b1′ mRNA is quantitatively similar in the two Nicotiana species, and the amphidiploid hybrid, whatever the nature of the inoculum.
Influence of environmental conditions on dispersal of Botrytis cinerea conidia and on post‐harvest infection of gerbera flowers grown under glass
Authors: KERSSIES A.
Published: April 2007

Dispersal of Botrytis cinerea in a gerbera crop grown in two glasshouses 30 km apart was studied over a period of 18 months, in 1988 and 1989. Conidia were caught in spore traps consisting of agar in petri dishes exposed at different heights in the crop in each glasshouse. No seasonal patterns could be identified in the spore catches, assessed as colonies on the agar traps after incubation. The number of lesions caused by conidial infection of gerbera flowers following incubation, however, showed a distinct pattern. In spring and early summer few lesions were recorded whereas at other times of the year many lesions appeared. In linear regression analysis, variation in numbers of colonies (spore catches) could not be explained by environmental factors recorded during the experiments. Linear regression accounted for 77% and 81% of the variation in the number of lesions on flowers in the two glasshouses, in terms of relative humidity (postively correlated), global radiation outside the glasshouse (negatively correlated) and age of the crop (positively correlated). Despite differences in the systems by which the gerbera crop was produced and in the spore catches, the numbers of lesions on gerbera flowers in the two glasshouses were significantly correlated though not significantly different from each other.
A strain of Trichoderma viride pathogenic to germinating seedlings of cucumber, pepper and tomato
Authors: MENZIES J. G.
Published: April 2007

An isolate of Trichoderma viride from the surface of an apparently healthy tomato root was found to be pathogenic to seedlings of cucumber, pepper and tomato in laboratory and greenhouse experiments. In laboratory experiments, when seeds of each host species were inoculated with conidia of the pathogen, the subsequent growth of seedlings was decreased and they developed light‐brown water‐soaked lesions on their roots and crowns. The pathogen could be re‐isolated from lesions on the seedlings, and microscopic examination of inoculated seedlings demonstrated that the fungus invaded the vascular tissues of the young seedlings. Culture filtrates of T. viride were found to contain a heat‐stable factor that caused a decrease in the growth of the roots of young cucumber, pepper and tomato seedlings. In greenhouse experiments, the fungus did not affect germination or seedling fresh weight of young cucumber seedlings in soil‐ peat‐ or rockwool‐based germinating media, but 10% of seedlings germinated in rockwool showed signs of infection. This is the first report of T. viride being pathogenic on pepper and tomato.
A varied population of cucumber mosaic virus from peppers
Authors: PERRY K. L. , HABILI N. , DIETZGEN R. G.
Published: April 2007

A varied population of Cucumber Mosaic Virus (CMV) isolates is reported from peppers (Capsicum annuum) in Australia. Isolates representing both CMV subgroups (serogroups) I and II have been obtained from the same field at the same sampling time. The CMV isolates were typed into subgroup I (eight isolates) and subgroup II (two isolates) using both a nucleic acid hybridization assay and an immunological assay with monoclonal antibodies. The immunological assay described allows the typing of strains in crude sap extracts, obviating the need for purified virions. The spatial and temporal coincidence of both CMV subgroups presents a situation in which pseudorecombinants with reassorted genomic components might arise.
Commelina agraria: a new host ofPyricularia grisea
Authors: PURCHIO A. F. , MUCHOVEJ J. J.
Published: April 2007

A new disease ofCommelina agrariaassociated withPyricularia griseais described. The fungus is compared withPyricularia ebbelsiifromCommelina africana.
The occurrence in Denmark of black root rot of pea caused by Thielaviopsis basicola
Authors: BØDKER L. , LEROUL N. , SMEDEGAARD‐PETERSEN V.
Published: April 2007

Thielaviopsis basicola has been shown to be a root pathogen of pea of considerable importance in Denmark. The fungus is only found in fields with one or more previous pea crops in the field history. In the dry and warm growing season of 1989 the fungus was found in 0·6% and 3·2% of the fields in two separate areas in Denmark. In the fields where T. basicola was detected the average disease severity index in plant samples was 51·8, whereas the average disease severity index in plant samples without the fungus was 27·0. The average yield of green peas was reduced from 5167 to 4171 kg/ha when T. basicola was present. For detection and isolation of T. basicola it is important to use a technique combining microscopic examination, a semi‐selective medium and a dilution plate method.
Rhizoctonia foliar blight of Rosmarinus officinalis
Authors: KALRA A. , PARAMESWARAN T. N. , RAVINDRA N. S.
Published: April 2007

Symptoms of severe leaf blight observed on rosemary (Rosmarinus officinalis) at Bangalore, India, were demonstrated to be caused by Rhizoctonia solani (anamorph of Thanatephorus cucumeris). This is thought to be the first recorded incidence of this pathogen causing disease on rosemary.
Examination of the relationships between vegetative compatibility groups and races in Fusarium oxysporum f.sp. dianthi
Authors: ALOI C. , BAAYEN R. P.
Published: April 2007

The feasibility of identifying races of Fusarium oxysporum f.sp. dianthi by tests for vegetative compatibility type was investigated. Nitrate non‐utilizing nitl and NitM mutants were generated from 51 isolates of F. oxysporum f.sp. dianthi, 18 isolates of f. oxysporum from Dianthus spp. not belonging to f.sp. dianthi and, for comparison, 11 isolates of F. proliferatum from Dianthus spp. Vegetative compatibility groups (VCGs) among the isolates were identified by pairing all nitl with all NitM mutants.

Vegetative compatibility was found between isolates of F. oxysporum f.sp. dianthi races 1 and 8 (VCG 0022), races 2, 5 and 6 (VCG 0021) and race 4 (VCG 0020), and wilt‐causing isolates previously classified as F. redolens from D. caryophyllus (VCG 0023) and D. barbatus (VCG 0024), Three self‐compatible wilt‐causing isolates were vegetatively incompatible with all other isolates (VCGs 0025,0026 and 0027), Two VCGs were found among isolates of F. oxysporum from D. caryophyllus not belonging to f.sp. dianthi; six non‐pathogenic isolates were self‐compatible but vegetatively incompatible with all other isolates. The foot‐rot‐associated isolates of F. proliferatum from D. caryophyllus constituted a separate VCG.

Virulence analyses revealed at least four new races among VCGs 0023 to 0027, New Isolates could be categorized as races as a result of VCG analysis and VCG classification correctly indicated that the race identities previously ascribed to two old isolates had been incorrect. Vegetative compatibility tests offer the prospect for rapid identification of races, although inoculation tests continue to be necessary to differentiate races that belong to a single VCG.
Mechanisms of resistance to Phytophthora cinnamomi in clonal, micropropagated Eucalyptus marginata
Authors: CAHILL D. M. , BENNETT I. J. , McCOMB J. A.
Published: April 2007

Plants of the eucalypt. Eucalyptus marginata. selected through a glasshouse screening procedure for resistance or susceptibility to Phytophthora cinnamomi, were established in tissue culture and micropropagated. After inoculation with P. cinnamomi, root lesions in clonal lines selected as resistant (RR) to P. cinnamomi were restricted and became contained within four days after inoculation while lesions in roots of those lines susceptible (SS) to P. cinnamomi continued to extend rapidly. Activity of phenylalanine ammonialyase (PAL) was increased above controls in root segments of the RR lines 48 h after inoculation with P. cinnamomi while activity in unselected seedlings and the SS lines was reduced or unchanged. After inoculation, lignin concentration was increased and reached high levels compared with uninoculated control levels in roots of the two RR lines tested. Constitutive levels of phenolics in roots of the RR lines were up to 94% higher than in seedling roots and levels were further increased after inoculation. Levels of phenolics in the other lines and seedlings were unaltered by inoculation. A line derived from resistant seedlings from a susceptible family (RS) had the highest constitutive levels of lignin, which were further increased after inoculation. Resistance to P. cinnamomi in clonally propagated E. marginata seedlings is based on similar mechanisms to those of field resistant species.