bluuebunny/crossref_metadata_2025 huggingface dataset:
Identities and pathogenicities of phytophthora spp. causing root rot of red raspberry
Authors: DUNCAN J. M , KENNEDY DIANA M. , SEEMULLER ERICH
Published: April 2007

Phytophthora syringae, P. drechsleri, P. cactarutn, P. cambiuora and P. megasperma were isolated from the roots of red raspberry plants affected by severe root and crown rot with associated cane death. Phytophthora megasperma occurred most frequently and consisted of two types of isolates which differed in colony morphology, growth rates, and oogonial, oospore, sporangial and zoospore size, and pathogenicity to a range of plants. One type with large oospores was typical of P. megasperma var. megasperma, and was non‐pathogenic to red raspberries, while the other with smaller oospores and which grew more slowly in culture than the first, was highly pathogenic, producing symptoms similar to those observed in the field. Highly pathogenic isolates from Germany and the USA were of this type.

All red and black raspberry cultivars tested were susceptible to the pathogenic type, although North American cultivars were generally less affected than British ones. Inoculated plants had reduced shoot and root weights, stem lesions and wilted and yellowed leaves. The blackberry × raspberry hybrid Tayberry and its blackberry parent were immune.

Phytophthora drechsleri, P. cactorum and P. cambivora produced small to moderate amounts of root rot on red raspberry, and P. cambivora also caused slight symptoms on shoots.
The effects of chemicals on developmental stages of Plasmodiophora brassicae (clubroot)
Authors: NAIKI T. , DIXON G.R.
Published: April 2007

Modes of action of benomyl, calcium cyanamide, quintozene, trichlamide (NK 483/WL105305) and EF 70513 for control of Plasmodiophora brassicae Wor. (clubroot) have been studied. Materials were selected because of known activity against P. brassicae and provided a range of chemical structures and requirements for field application. All experiments were made in the glasshouse using seedlings of Brassica campestris ssp. pekinensis cv. Granaat and chemical concentrations in the range 100‐2000 mg a.i./kg compost or soil. The effects of chemicals on pathogen development, symptom severity, host growth, secondary infection and resting spore survival were quantified and residual activity of each chemical at times after application was assessed. Pathogen development was quantified up to 14 days after inoculation in terms of primary root hair invasion and the development of primary plasmodia, mature zoosporangia and partially and fully evacuated zoosporangia. Club development and severity were assessed up to 35 days after inoculation. All chemicals were associated with reductions in pathogen invasion and subsequent symptom development. Benomyl and trichlamide were most effective at inhibiting root hair infection and in reducing club development. Colonization from secondary zoospores was inhibited most effectively by benomyl. Residual activity was most apparent with trichlamide, followed by EF70513, benomyl, quintozene and calcium cyanamide. Only calcium cyanamide possessed fungicidal effect which increased in proportion to the interval between incorporation and planting. Germination of P. brassicae spores was inhibited by calcium cyanamide, EF70513 and trichlamide but only to a limited extent by benomyl and quintozene. Phytotoxicity was not apparent with trichlamide and quintozene; EF70513 produced severe effects at high concentrations, at which benomyl also reduced plant height. Calcium cyanamide was phytotoxic only when seedlings were planted within 7 days of application or when high concentrations were used.
Influence of aldicarb on root lesion nematodes, leaf disease and root rot in wheat and barley
Authors: KIMPINSKI J. , JOHNSTON H. W. , MARTIN R. A.
Published: April 2007

The effects of aldicarb on populations of root lesion nematodes (primarily Pratylenchus penetrans) and on grain yields of spring barley and wheat were examined in the field over 3 years, 1981*83. The incidence of barley net blotch (Pyrenophora teres), wheat leaf blotch (Leptosphaeria nodorum), and common root rot (Cochliobolus sativus) was also recorded in 1982 and 1983. Aldicarb treatments reduced the size of root lesion nematode populations in soil and roots in all years, except in the mid‐season soil sample in 1983. The severity of leaf disease was decreased only in 1982, but the incidence of root rot was not significantly affected by the nematticide. Although aldicarb increased cereal grain yields by approximately 15% there was no significant relationship between numbers of root lesion nematodes in roots and soil and fungal disease symptoms on barley and wheat.
Cultural management of tomato yellow leaf curl disease in Cyprus
Authors: IOANNOU N.
Published: April 2007

Cultural management of tomato yellow leaf curl virus (TYLCV) by roguing old, overwintered tomato crops was investigated in a small, isolated production centre in the southern coastal zone of Cyprus. Control measures were applied on an area‐wide basis during March‐April, before emergence of adult whitefly (Bemisia tabaci Genn.) vectors, for three consecutive years (1980‐82). In all three years, primary virus spread to spring plantings was almost completely prevented, while further secondary spread to summer plantings was kept below 5%, compared with 40‐50% in 1978 and 1979. When control measures were discontinued disease incidence increased to 15% in 1983 and 40% in 1984. The disease could also be controlled by early transplanting in the spring or by late transplanting in the autumn. Several cultural practices were evaluated to prevent or reduce infection of seedlings before transplanting. Seedlings produced in the summer in a coastal region were infected by TYLCV (virus incidence 7‐42%), with a higher incidence in seedbeds situated near infected tomato crops. Infection was significantly reduced by covering seedbeds with an insect‐proof tunnel, and was completely prevented by producing seedlings in inland areas, where no commercial tomato crops were grown. The use of healthy transplants delayed subsequent disease development in the field but had little effect on final disease incidence.
Triadimenol drenches and residues in tobacco seedbeds improve growth and disease control in transplants
Authors: COLE J. S. , ZVENYIKA Z.
Published: April 2007

Triadimenol residues in sandy and clay soils, following applications of up to 1 g/m2 in previous seasons to tobacco seedlings 2 days before they were transplanted, had little effect on seedling emergence and growth. Residues were beneficial to transplants; they improved growth and controlled stem and root infection caused by Rhizoctonia solani and Fusarium solani. During the first 4 weeks after transplanting, stem infection was negatively correlated with loge of the pre‐sowing rate of triadimenol and with loge of the soil concentration in seedbeds at pulling. Plant growth increased linearly according to the equation l/Y=a+b/(x‐c), where Y = plant dry mass (g/plant), .x = triadimenol pre‐sowing (mg/m2) and c= ‐ 1 1, determined iteratively, r2= 0‐94; P < 0.001. Triadimenol applications to bare soil increased the soil concentration by 1 μ/g per 50 mg/m2 applied.
Investigation of the host ranges of the leaf blotch pathogens of onion (Cladosporium allii‐cepae) and leek (C. allii)
Authors: JORDAN MARY M. , MAUDE R. B. , BURCHILL R. T.
Published: April 2007

Inoculation of a range ofAlliumspecies and two non‐alliaceous species with isolates ofCladosporiumallii‐cepaeandC. allii, obtained from onion and leek, respectively, demonstrated that the two pathogens had distinct host ranges. Conidia ofC. allii‐cepae,applied either dry or in aqueous suspension, infectedA. altaicum, A. fistulosum(Japanese bunching onion), A.cepa(bulb onion),A. cepavar.ascalonicum(shallot),A. galanthum, A. pskemense and A. vavilovii. Dry conidia ofC. alliiapplied at a high concentration caused atypical necrosis onA. altaicum, A. fistulosum, A. cepavar.ascalonicum, A. galanthum, A. pskemense, A. vavilovii, A. sativum(garlic),A. ampeloprasumandA. porrum(leek).Only A. ampeloprasumandA. porrumbecame typically infected following inoculation with conidia applied dry at low concentration or in aqueous suspension. Isolates ofC. alliifrom leek failed to infectA. vineale,the type host. The length of conidia of a single isolate ofC. allii‐cepaevaried significantly on differentAlliumspp.
Spread of Phoma exigua var. foveata to healthy potato plants
Authors: CARNEGIE S. F. , ADAM J. W. , CAMERON A. M.
Published: April 2007

Contamination of stem‐cutting bait plants exposed at various locations in and around a potato crop was greatest within the crop, less outside it and least at a site c. 20 km from commercial crops. Within the crop about half the stem infection and tuber contamination detected had occurred before haulm destruction. The incidence of contamination on tubers of bait plants placed within the crop was similar to that on tubers from the surrounding plants. Phoma exigua var. foveata was recovered from green leaves sampled at intervals between June and early September. In one year contamination by P. exigua var. foveata of tubers sampled from healthy plants surrounding a diseased plot was greatest in samples adjacent to the plot and decreased progressively away from it. This pattern was less apparent in two other years. These results are discussed in relation to the spread of airborne inoculum.
Is celery yellow net c used by parsnip yellow fleck virus
Authors: SINGH H. , FROST R. R.
Published: April 2007

Celery yellow net w s described by Hollings (1964) s severe dise se of celery (Apium graveolens L. var. duke (Miller) DC.) that could be transmitted by grafting nd occasionally by mechanical inocul tion with leaf extracts. Pemberton & Frost (1986) observed similar symptoms in celery crops. but were unable to isolate the causal agent.

During recent attempts to isolate the causal gent of celery yellow‐spot, another disease previously reported by Hollings (1964) and Pemberton & Frost (1986), we found that two of our samples from crop in Cheshire contained different virus. As well as yellow spots, these two plants also had yellow‐net symptoms on the older leaves, and one of the plants was stunted with some distortion of the young leaflets. The two virus isolates appeared identical from extensive testing on range of herbaceous indicator plants, so one of them, CV506, w s selected for further study
Application of Trichoderma and Gliocladium in alginate pellets for control of Rhizoctonia damping‐off
Authors: LEWIS J. A. , PAPAVIZAS G. C.
Published: April 2007

Alginate pellets were prepared from wet fermentor biomass of 11 isolates of Trichoderma spp. and Gliocladium virens, with wheat bran as a food base carrier. Pellets with eight of the isolates reduced survival (34‐78%) of Rhizoctonia solani in infested beet seed in soil. Pellets containing a T. harzianum isolate (Th‐58) and a T. hamatum isolate (TRI‐4) were the most effective. All isolates significantly reduced growth of the pathogen from infested beet seed into natural soil. Populations of isolates proliferated in soil to 106−1011 colony‐forming units/g (cfu) from propagules within the pellets. Pellets with TRI‐4 reduced pathogen survival and growth (>70%) in six different soils and were effective against six R. solani isolates in a natural loamy sand. Survival of R. solani in infested beet seed was not reduced when TRI‐4 pellets were added to soil 1‐6 weeks before the pathogen; however, saprophytic growth was prevented. Small amounts of biomass (3.0–7.5 g wet weight) in pellets were as effective as a large amount (300 g) in suppressing the pathogen. The storage of pellets for more than 6 weeks at 5 or 25C reduced their effectiveness against R. solani. Pellets prepared with four and three of the 11 isolates prevented damping‐off of cotton and sugar beet in the greenhouse, respectively.
Stratified distribution of Fusarium and Bipolaris on wheat and barley with dryland root rot in South Australia
Authors: FEDEL‐MOEN RITA , HARRIS J. R.
Published: April 2007

Dryland root rot of wheat and barley in South Australia is a syndrome from which the associated fungi Fusarium equiseti, F. acuminatum, F. oxysporum and Bipolaris sorokiniana were isolated consistently. Fusarium infections were concentrated on the subcrown internodes, crown roots and culm bases, and occurred with equal frequency on wheat and barley. Bipolaris infections were more numerous on barley than on wheat, and were concentrated on culm bases and subcrown internodes. Recoveries of each of the four fungi showed a pattern of infection that was neither randomly nor evenly distributed. Each fungus had preferences for certain sites which resulted in a stratified distribution over the roots and crown. When two barley cultivars were compared, the patterns of infection were different; the subcrown internode was attacked more severely, and there was a substantial increase in the amount of infection by all four fungi on one of the cultivars. Pathogenicity tests on barley and oats showed that all four species of fungi were capable of causing damage to roots, but there were differences between isolates of each fungus and differences in their ability to damage barley and oats.
Effect of crown rust on regrowth, competitive ability and nutritional quality of perennial and Italian ryegrasses
Authors: POTTER L. R.
Published: April 2007

Infection of susceptible cultivars of perennial (Lolium perenne) and Italian (Lolium multiflorum) ryegrasses with crown rust (Puccinia coronata) reduced yield measured 6 weeks after infection and at two regrowth cuts. In perennial, but not Italian, ryegrass, rust infection of mixed swards of a resistant and a susceptible cultivar reduced the contribution to yield made by the susceptible cultivar and increased that of the resistant cultivar. This effect persisted for three regrowth cuts. The trend in effect on the number of tillers, but not plant height, was similar.

Infection increased leaf protein in susceptible perennial ryegrass but had little effect in Italian ryegrass. In both species, rust reduced water‐soluble carbohydrate and the predicted digestibility of susceptible and resistant cultivars, but had no effect on quality of regrowth.
Positive correlations between in vitro growth rate and pathogenesis in Ophiostoma ulmi
Authors: BRASIER C. M. , WEBBER J. F.
Published: April 2007

In vitro radial growth rate was found to be positively correlated with pathogenicity in two experiments involving NAN aggressive isolates of O. ulmi. One of the correlations was detected in a sample of B mating‐type, but not in equivalent A mating‐type isolates. Another was detected in a sample of pathogenic phase, but not in comparable saprophytic phase isolates. The significance of these results for the vascular wilt syndrome and population biology of O. ulmi is discussed.
Susceptibility of winter and summer crops to root and crown infection by Bipolaris sorokiniana
Authors: WILDERMUTH G. B. , McNAMARA R. B.
Published: April 2007

The susceptibility of 24 winter and 17 summer crops to infection by Bipolaris sorokiniana was tested in a glasshouse experiment by growing them in soil amended with wheat‐barley grain colonized by B. sorokiniana (0.2 g per 100 g soil). At anthesis, infection of both lesioned and randomly selected segments of roots and of crowns was determined by plating them on modified Czapek‐Dox Agar. Incidence of infection in winter crops was higher than in summer crops. Guar, mung bean, soybean and sunflower were the least infected of the summer crops while chickpeas and safflower were the least infected of the winter crops. Amongst the taxonomic groups tested, the highest incidence of infection occurred in the gramineous species and the lowest in the leguminous species.

Five summer crops growing in the field were sampled and infection by B. sorokiniana confirmed. Cultivars of wheat, barley, triticale and oats were also screened in a field experiment. Amongst these winter cereals, oats was the least susceptible in both field and glasshouse experiments. Differences between cultivars in susceptibility to common root rot, measured by the degree of lesion development in the subcrown internode, were identified in wheat, triticale and oats but not in barley.
Occurrence of potyvirus and potexvirus infections in black bryony (Tamus communis) in Devon, UK
Authors: VETTEN H. J. , LESEMANN D. E. , ALLEN D. J.
Published: April 2007

Leaf samples of black bryony (Tamus communis L.) from Devon, UK, showing various virus‐like symptoms contained potyvirus‐like particles (normal length c. 790 nm) and cytoplasmic cylindrical (pinwheel) inclusions. In immunoelectron microscopy, particles of most samples reacted with antiserum to dioscorea greenbanding mosaic virus, a potyvirus isolate from Dioscorea rotundata in Togo which is related to yam mosaic virus from the Ivory Coast. Potyvirus particles were not transmitted by sap or aphids (Myzuspersicae) from infected black bryony to black bryony seedlings or Nicotiana benthamiana. One sample from a symptomless plant of black bryony contained a potexvirus which formed massed virion aggregates in the cytoplasm of cells of black bryony, Nicotiana benthamiana and N. megalosiphon. Virions of the potexvirus (normal length 553 nm) contained a coat protein with an apparent molecular weight of 27.7 kd. The potexvirus differed from an Italian potexvirus isolate from black bryony by a serological differentiation index of 4 and gave only weak or no reactions with 23 other antisera to potexviruses, including dioscorea latent virus. The potexvirus caused systemic symptoms in only a few host plants and could be transmitted back to black bryony in which it caused no symptoms. It is provisionally named tamus latent virus.
Genetic analysis of factors for resistance to downy mildew (Bremia lactucae) in species of lettuce (Lactuca sativa and L. serriola)
Authors: FARRARA B. F. , ILOTT T. W. , MICHELMORE R. W.
Published: April 2007

Simultaneous genetic analysis of resistance in species of lettuce (Lactuca sativa and L. serriola) and a virulence in Bremia lactucae were made to characterize the genetic basis of resistance to downy mildew in 11 host cultivars and accessions. Four new downy mildew resistance genes (Dm13, Dm14, Dm15 and Dm16) were characterized. Other resistance phenotypes were conditioned by combinations of these or previously described Dm genes. New resistance genes, Dm 16 (from LSE/18), Dm14 (from Gelber Winterkonig) and Dm15 (from PIVT 1309), mapped to Dm linkage group I (Dm1, Dm2, Dm3 and Dm6) while Dm13 from Pennlake segregated independently of the three previously characterized linkage groups and therefore belongs to a fourth linkage group. Characterization of new resistance genes requires simultaneous consideration of host and pathogen genetics.
Witches' broom disease on cocoa in Rondonia, Brazil: pod infection in relation to pod susceptibility, wetness, inoculum, and phytosanitation
Authors: RUDGARD S. A. , BUTLER D. R.
Published: April 2007

Infection of cocoa pods by Crinipellis perniciosa was examined in the field in relation to pod susceptibility and variations in inoculum and climate over 2 years. The disease was incubated for 13 or 14 weeks in pods inoculated when 2 and 4 weeks old, and for 12 weeks in pods inoculated 6‐12 weeks old. Pods were uniformly susceptible to natural infection during the 12 weeks after pollination. Over 75% of rain showers started between 12.00 and 02.00 h, providing sufficient water to rehydrate basidiocarps as well as to wet pods. Pods remained wet after rainfall for decreasing periods when rain occurred after 13.00 h. Incidence of pod disease was shown to be related to the number of wetness periods longer than 4 h, and to the number of open turgid basidiocarps occurring 12 weeks earlier. Wetness periods had a greater influence on disease. Pod infection was modelled by assuming that infection was limited by either wetness periods or turgid basidiocarp numbers; critical numbers of wetness periods when both factors were of equal weight were defined by an exponential equation. The model was used to predict reductions in pod disease associated with different amounts of broom removal in each year.
Witches' broom disease of cocoa in Rondonia, Brazil: infection of vegetative flushes and flower cushions in relation to host phenology
Authors: RUDGARD S. A.
Published: April 2007

Formation of vegetative brooms and cushion infections were assessed in relation to host phenology and fructification of Crinipellis perniciosa over 2 years. Vegetative growth occurred in distinct periods or‘flushes’based on an endogenous cycle of 8 weeks. Correlation analysis showed that growth patterns of the sample trees were very similar. There were four main flushes in 1984, three in 1985, and the first two in each year coincided with periods of fruiting of the fungus. Total yearly infection increased from 13% in 1984 to 32% in 1985 when there were more periods considered suitable for infection and production of basidiocarps. Many infections on young vegetative tissue produced more than one hypertrophied shoot (broom) and 11 new infections were produced from every fruiting broom in 1984 compared with 3.2 in 1985. The total number of vegetative brooms increased from about 160 per tree in September 1983 to about 650 in September 1985, despite natural broom loss of 68% every 12 months. Infection of flower buds (cushions) was related to flowering intensity and periodicity, and a small proportion of infected cushions produced brooms. The implications of these results are discussed in relation to methods of control.
Complementation between genes for resistance to race 1 of Fusarium oxyspomm f.sp. ciceri in chickpea
Authors: SINGH HARJIT , KUMAR J. , SMITHSON J. B. , HAWARE M. P.
Published: April 2007

The reactions of parents and F1 and F2 generations of crosses of chickpea cultivars K‐850 with C‐104 and JG‐62 and F3 progenies of K‐850 × C‐104 to race 1 of Fusarium oxysporum f.sp. ciceri were studied. The results indicate that K‐850 carries a recessive allele for resistance at a locus different from and independent of that carried by C‐104 and recessive alleles at both loci together confer complete resistance. The possible contribution of this recessive gene to late wilting in K‐850 is discussed. These observations have important implications in breeding for resistance to wilt in chickpea.
Genetic aspects of polyacrylic‐acid‐induced resistance to tobacco mosaic virus and tobacco necrosis virus in Nicotiana plants
Authors: DUMAS E. , GIANINAZZI S. , CORNU A.
Published: April 2007

Among the Nicotiana tabacum cultivars and hybrids tested, polyacrylic acid (PAA) only induced resistance to tobacco mosaic virus (TMV) and tobacco necrosis virus (TNV) in the cultivars Xanthi‐nc (NN) and Xanthi (nn) respectively. This varietal response to the PAA treatment could be sexually transmitted. The complete genetic analysis of the inheritance of the PAA response is reported for the first time, demonstrating that the response is a dominant character with a Mendelian segregation which occurs independently of either the N gene responsible for resistance to TMV or the PRb‐protein genes. Possible relationships between the N gene, the gene for the PAA response and the PRb genes are discussed.
Induction and expression of systemic resistance to the anthracnose disease in bean
Authors: CLOUD A. M. E. , DEVERALL B. J.
Published: April 2007

Development of anthracnose symptoms in trifoliate leaves of Phaseolus vulgaris inoculated with Colletotrichum lindemuthianum was greatly restricted when the primary leaves had been inoculated with the same pathogen 1 week earlier. Penetration from appressoria was inhibited and hyphal growth in epidermal cells was sometimes decreased in preinoculated plants. The response of preinoculated plants also differed: wall appositions and encroachment of nuclei at attempted penetration sites occurred more frequently, and earlier cell death often followed successful penetration. Resistance in trifoliate leaves was also induced by injection of primary leaves with conidia or culture filtrates of the pathogen or a dialysis retentate of these filtrates. Resistance in epicotyls and primary leaves was induced by inoculation of the hypocotyl 1 week earlier. Inoculated cotyledons abscissed, and failed to alter the susceptibility of primary or trifoliate leaves to subsequent inoculation. The results are discussed in relation to a hypothesis to explain the process of induced systemic resistance.
Paclobutrazol and other plant growth‐retarding chemicals increase resistance of melon seedlings to fusarium wilt
Authors: COHEN R. , YARDEN O. , KATAN J. , RIOV J. , LISKER N.
Published: April 2007

Studies were made of plant growth retardation and effects on resistance of melon to fusarium wilt by soil application of paclobutrazol, other ergosterol biosynthesis inhibitors, the fungicide benomyl and the herbicide dinitramine. Paclobutrazol and ancymidol delayed the onset of wilting and were the most effective in reducing wilt incidence. A relationship between effectiveness in retarding seedling elongation and increasing resistance to fusarium wilt was observed. No chemical had a significant effect on pathogen population level in the plant, as determined by stem colonization and direct assessment tests in seedlings grown in soil treated with the chemicals. Excluding benomyl, and to a lesser extent dinitramine, leaf and stem extracts had no inhibitory effect on conidial germination. Gibberellins GA4+7, when applied to seedlings inoculated after germination in paclobutrazol‐treated soil, nullified growth retardation and increased disease incidence. We suggest that disease incidence reduction by paclobutrazol is due to an effect on plant metabolic processes and not to direct fungitoxicity of the compound.
Adaptation of Septoria nodorum to wheat or barley on detached leaves
Authors: OSBOURN A. E. , CATEN C. E. , SCOTT P. R.
Published: April 2007

Single‐spore cultures of wheat‐ and barley‐adapted isolates of Septoria nodorum were serially passaged through detached leaves of wheat or barley. Rare instances of change in host adaptation were observed after passaging but associated changes in other characters, including heterokaryon compatibility, identified the changed isolates as contaminants. Inoculation of progressively more dilute spore suspensions to detached leaves revealed that some isolates were highly infective to the host to which they were adapted, with a high probability of a single spore initiating infection. Inocula deliberately contaminated with a small proportion of spores of opposite host adaptation revealed changes when passaged on wheat that mimicked the rare changes observed on passaging pure wheat‐ or barley‐adapted isolates. These results suggest that adaptation to wheat or barley is a stable property of pure cultures of S. nodorum and that the occasional changes in host adaptation observed on passaging result from selection of contaminants.
Studies of dormancy in sclerotia of Sclerotium cepivorum
Authors: COLEY‐SMITH J. R. , PARFITT D. , TAYLOR I. M. , REESE R. A.
Published: April 2007

Sclerotia of Sclerotium cepivorum formed on onion bulbs in soil were shown to undergo a period of constitutive dormancy lasting 1–3 months during which they failed to respond maximally to the germination stimulant diallyl disulphide. Even after the breakdown of constitutive dormancy sclerotia were subject to exogenous dormancy from which they were only released by the presence of species of Allium or of germination stimulants known to be produced by them.
Specificity, interaction and additivity in host‐pathogen systems
Authors: VANDERPLANK J. E.
Published: April 2007

In the literature of plant pathology, unspecific interaction, as statisticians use the word, is commonly called ‘specificity’ or ‘race specificity’. Specificity, in the sense used by Flor, is confused with interaction, defined statistically. Admittedly, specificity in Flor's sense implies statistical interaction. But the converse is not true. Statistical interaction does not necessarily imply Flor's specificity.

This confusion prompted me to inquire into the concepts of what seem to me to be the three major systems of host‐pathogen relations: additivity, interaction, and specificity. I suggest definitions, the definitions of additivity and interaction following standard statistical usage and the definition of specificity following Flor's sense. Further, I examine briefly tests to distinguish (unspecific) interaction from specificity, and additivity from interaction.

Interaction, as the word is used by statisticians, arises from the variation in row differences from column to column or in column differences from row to row (Adams, 1955). Put differently, interaction is measured by the failure of effects to be additive (Snedecor, 1956).

Additivity is the antithesis of interaction. There is no significant variation in row differences from column to column or in column differences from row to row.

Specificity in a gene‐for‐gene system refers to complementary one‐for‐oneness. Flor's hypothesis reads: “for each gene conditioning resistance in the host there is a specific complementary gene conditioning pathogenicity in the parasite”. Flor's use of the word specific goes back to 1942 when his hypothesis was still embryonic; “The data in the present paper indicate that the range of pathogenicity of a physiologic race of Melampsora lini is determined by pathogenic factors specific for each resistance factor possessed by the host” (Flor, 1942).

Specificity is a form of interaction. There is specific interaction, i.e. interaction with complementary one‐for‐oneness, and unspecific interaction, i.e. interaction without one‐for‐oneness.
Evaluation of antisera raised against Phytophthora fragariae for detecting the red core disease of strawberries by enzyme‐linked immunosorbent assay (ELISA)
Authors: MOHAN SUDESH B.
Published: April 2007

Antiserum was raised against pooled mycelial suspensions from five isolates (designated Pf 1, Pf 2, Pf 3, Pf 10 and Pf 11) representing five physiologic races of Phytophthora fragariae. In enzyme‐linked immunosorbent assay (ELISA), this antiserum detected homologous soluble antigens at protein concentrations as low as 2 ng/ml.

Fungal antigens could also be detected in extracts of strawberry plants infected with P. fragariae. Root extracts prepared from the alpine strawberry Fragaria vesca and F. ananassa cv. Cambridge Favourite infected with any of the five isolates studied produced strong reactions in ELISA. In F. vesca, ELISA‐positive material was detectable 6‐8 days after inoculation before macroscopic symptoms appeared. The cultivar Red Gauntlet, which is resistant to Pf 1, 2 and 3 but susceptible to Pf 10 and 11, reflected this differential response in ELISA; the absorbance produced by extracts of plants infected with virulent isolates was significantly higher than that obtained with the corresponding extracts of plants inoculated with a virulent isolates. The recently introduced cultivars Hapil, Ostara and Providence were found to be susceptible to all isolates in this study: the corresponding root extracts were also positive in ELISA.

The antiserum also detected P cactorum infections. Nevertheless, the ELISA test described should prove valuable in screening certified strawberry stocks.
Phytophthora cryptogea as a cause of root rot of raspberry in Australia; resistance of raspberry cultivars and control by fungicides
Authors: WASHINGTON W. S.
Published: April 2007

Phytophthora cryptogea was isolated from field plantings of the red raspberry cultivars Glen Clova, Canby and Willamette which showed wilting, dieback, stem lesions and root rotting. Pathogenicity of P. cryptogea to raspberry was demonstrated in glasshouse experiments. Twelve cultivars of raspberry were screened for resistance to the disease by growing them in artificially infested soil. Glen Clova and Canby were highly susceptible whilst Chilcotin, Nootka, Haida and Puyallup were resistant. Soil treatments with either metalaxyl, phosphorous acid or fosetyl aluminium controlled the disease. This is the first record of a phytophthora root rot of raspberry in Australia, and the first demonstrating the pathogenicity of P. cryptogea to raspberry.
Studies on the inheritance of resistance to metalaxyl in Bremia lactucae and on the stability and fitness of field isolates
Authors: CRUTE I. R. , HARRISON JUDITH M.
Published: April 2007

One hundred and eighty‐one sexual progeny isolates from three F1, one F2, five BC1 and one BC2 generations of crosses involving two metalaxyl‐resistant and two metalaxyl‐sensitive isolates of Bremia lactucae were assessed for response to metalaxyl. In most cases, isolates were also tested for virulence phenotype and sexual compatibility type. Isolates could be classified into three phenotypes (sensitive, resistant and intermediate) on the basis of their response to fungicide. Sensitive progeny isolates were similar to the sensitive parents and did not sporulate on lettuce seedlings grown in the presence of > 1.0 μg/ml metalaxyl. Resistant progeny isolates, in common with the resistant parents, sporulated as readily on lettuce seedlings grown in the presence of 100 μg/ml metalaxyl as on untreated seedlings. Progeny isolates which expressed an intermediate phenotype not observed in field samples were also recovered. This phenotype was more variable but isolates so classified were able to sporulate on seedlings grown in the presence of 100 μg/ml metalaxyl but exhibited a latent period (time from inoculation to appearance of sporulation) which was on average twice as long as that observed on seedlings grown in the absence of fungicide.

Segregation patterns suggested that response to metalaxyl is controlled at a single locus exhibiting incomplete dominance but that the expression of response in the heterozygous condition may be affected by modifier genes. There was evidence that the metalaxyl‐resistant parental field isolates were heterokaryotic (possibly carrying nuclei homozygous and heterozygous at the locus controlling metalaxyl response). After 10‐30 asexual generations in the absence of fungicide, the response to metalaxyl of resistant field isolates began to approach that of an intermediate type. This phenomenon did not occur with a resistant sexual progeny isolate (presumed homokaryotic) and is additional evidence for the heterokaryosis of field isolates. The relative fitness of a range of isolates was examined by observing changes in the proportions of spores over three asexual generations after they were initially mixed in a 1:1 ratio with mutant isolates carrying a microscopically visible genetic marker (large lipid droplets). Most field isolates were more fit than the mutant isolates used, regardless of whether they were resistant or sensitive to metalaxyl, and there was no evidence that resistant isolates carried any fitness deficit in comparison with the sensitive isolates examined. In contrast, sexual progeny isolates (particularly from BC1 generations) were often less fit than the mutant isolates used, but there was no evidence that this was associated with response to fungicide. These findings are discussed in relation to the mode of action of metalaxyl and disease control strategy.
Field performance of Rendezvous, a wheat cultivar with resistance to eyespot (Pseudocercosporella herpotrichoides) derived from Aegilops ventricosa
Authors: HOLLINS T. W. , LOCKLEY K. D. , BLACKMAN J. A. , SCOTT P. R. , BINGHAM J.
Published: April 2007

Rendezvous is a new cultivar of winter wheat with potent eyespot resistance derived from Aegilops ventricosa. In 11 field experiments conducted over 6 years with both natural and artificial inoculum, Rendezvous was significantly more resistant than other commercial wheat cultivars, many of which have resistance derived from Cappelle‐Desprez. It was also more resistant than its parent VPM 1, the donor of the potent eyespot resistance, suggesting that it possesses resistance genes from both Ae. ventricosa and Cappelle‐Desprez.

In severe eyespot epidemics, Rendezvous lodged less and had a greater mean yield than the moderately resistant cultivar Norman. Treatment with fungicide reduced disease and increased yield in both cultivars, so that they were equal in yield. Rendezvous should not need routine fungicidal treatment for eyespot control, but under exceptional disease pressure may benefit from treatment.
Susceptibility of cultivars of garlic to Sclerotium cepivorum
Authors: COLEY‐SMITH J. R. , ENTWISTLE A. R.
Published: April 2007

Five garlic cultivars, including one claimed to be resistant to Allium white rot, were similar in their effects on the germination of sclerotia of Sclerotium cepivorum. There was no evidence of resistance to the pathogen in any of the cultivars when tested under field conditions.
The influence of cultivar and mechanical damage on the relationship between inoculum concentration of Phoma exigua var. foveata on potato tubers and gangrene development
Authors: BAIN R. A. , LENNARD J. H. , WASTIE R. L.
Published: April 2007

In an experiment to examine the influence of cultivar and tuber damage on the relationship between inoculum concentration and potato gangrene development, the extent to which cultivars differed in their response to increased inoculum concentration depended on the type of damage which the tubers received. There was considerable variation in cultivar response in terms of lesion frequency when tubers were inoculated by damaging them on a commercial grader, whereas when they were uniformly wounded or left undamaged cultivar differences were small. The relationship between the number of detectable wounds on tubers and gangrene incidence was not consistent for the three cultivars. Lesion size was shown to increase linearly with increasing concentrations of pycnidiospores when tubers of cultivars of different susceptibilities were point‐inoculated.
Integrated control of Rhizoctonia solani and fusarium solani in tobacco transplants with Trichoderma hurziunum and triadimenol
Authors: COLE J. S. , ZVENYIKA Z.
Published: April 2007

Trichoderma cultures were isolated locally from soils and screened on potato‐dextrose agar against Rhizoctonia solani. Several isolates of T. harzianum reduced the growth and build up of populations of R. solani and to a lesser extent of Fusarium solani in sterilized soil. In field experiments, biological control of R. solani and F. solani infections in tobacco transplants was achieved by adding T. harzianum (T77) to methyl‐bromide‐fumigated seedbeds before seed was sown. There was also increased growth and leaf yield that was not directly correlated with disease control. Triadimenol fungicide, integrated with the Trichoderma treatment, enhanced disease control.
Thrips as a probable cause of severe fruit distortion in late‐season strawberries
Authors: BUXTON J. H. , EASTERBROOK M. A.
Published: April 2007

Late‐season strawberries have suffered severe fruit distortion in several areas of the UK leading to downgrading of the fruit and financial loss to growers. In trials in 1984 and 1986 in Kent and Cheshire, frequent sprays of pyrethroid insecticides significantly reduced the percentage of distorted fruits. The distortion was attributed to the feeding of various species of thrips, including Thrips atratus, T. major and Frankliniella intonsa.
Occurrence of Mycosphaerella graminicola, teleomorph of Septoria tritici, on wheat debris in the UK
Authors: SCOTT P. R. , SANDERSON F. R. , BENEDIKZ P. W.
Published: April 2007

Ascocarps of Mycosphaerella graminicola regularly developed in debris of wheat crops from eastern England after natural weathering. Identity with the Septoria tritici anamorph and pathogenicity to wheat were demonstrated by isolation and inoculation. Ascospores were present from autumn onwards and were most frequent in December and January. They may contribute to the primary inoculum for epidemics on autumn‐sown wheat.
Root rot of cabbage caused by Phytophthora drechsleri
Authors: THOMPSON A. H. , PHILLIPS A. J. L.
Published: April 2007

A root rot of cabbage is reported from South Africa. The causal pathogen was identified as Phytophthora drechsleri, based on morphological characters and electrophoretic patterns of soluble proteins.
Soft rot of Peruvian carrot due to Erwinia carotovora in Brazil
Authors: ROMEIRO R. S. , SOUSA R. M. , MUCHOVEJ J. J. , KIMURA O.
Published: April 2007

Peruvian carrot soft rot occurs quite frequently in Minas Gerais State, Brazil, either under field conditions or after harvested roots have been stored. The etiology of the disease was investigated and the disease was found to be induced by Erwinia carotovora. This appears to be the first report of this disease.
Importance of the proportion of grassy weeds within legume crops in the perpetuation of Gaeumannomyces graminis var. tritici
Authors: COTTERILL P. J. , SIVASITHAMPARAM K.
Published: April 2007

Various grass species susceptible to infection by Gaeumannomyces graminis var. tritici were mixed‐sown into a legume crop in order to assess their influence on density of inoculum and take‐all disease in a subsequent crop of wheat.

In a pot experiment take‐all inoculum increased (P< 0.001) in all treatments containing a proportion (from 20 to 100%, in increments of 20%) of grass in subterranean clover. In a plot trial, most severe take‐all occurred in the 20% legume/80% grass stands and least in the 100% legume and 80% legume/20% grass stands. Total grain weight was highest (P<0.1) after the 100% legume stands. There was no difference in severity of take‐all after pure stands of medic, subterranean clover and lupin, but there was more severe take‐all after the grass‐infested medic stands than after those of subterranean clover (P< 0.1) or lupin (P < 0.05). No significant differences (P > 0.1) in yield occurred in wheat following any of the legumes or mixed stands.
Relative importance of root rots of subterranean clover caused by Aphanomyces euteiches and Phytophthora clandestina
Authors: GREENHALGH F. C. , MERRIMAN P. R , KEANE P. J.
Published: April 2007

In a growth‐cabinet experiment, Aphanomyces euteiches caused more severe root disease and greater reductions in root and shoot weights of subterranean clover cv. Mount Barker than Phytophthora clandestina in pasteurized sandy loam flooded with water for a 24‐h period each week. A. euteiches also reduced plant growth more than P. clandestina in untreated sandy loam. In a similar experiment, both fungi caused the same amount of disease and reduction in growth of cv. Yarloop in pasteurized clay loam flooded for 24 h each week, and P. clandestina caused more disease and a greater decrease in plant growth than A. euteiches when the soil was flooded for 4 h each week. The pathogens did not interact positively in either soil. In an irrigated pasture, soil drenches with the fungicides metalaxyl and fenaminosulf together reduced both root rots to low levels and increased subterranean clover dry matter by 1 96, 0.50 and 1 20 t/ha in the autumn, winter and spring of 1985, respectively, and by 0.59 t/ha in the autumn of 1986. Results suggest that P. clandestina caused most of these losses in yield.
Differences in the extent of fungal development, host cell necrosis and symptom expression during race‐cultivar interactions between Phaseolus vulgaris and Colletotrichum lindemuthianum
Authors: O'CONNELL R. J. , BAILEY J. A.
Published: April 2007

The cellular reactions of excised hypocotyl segments of 31 cultivars of Phaseolus vulgaris to infection by two races of Colletotrichum lindemuthianum were surveyed. Consistent differences in the extent of fungal development and host cell necrosis were used to establish six infection categories.

Extreme susceptibility (category 5) involved initial formation of infection vesicles in living epidermal cells and a prolonged period of intracellular biotrophic development prior to necrotrophic growth and production of spreading lesions. Extreme resistance (category 0) involved rapid death and browning of penetrated epidermal cells, without formation of infection vesicles or a detectable biotrophic phase. Fungal growth and host necrosis were limited to single epidermal cells. Intermediate reactions (categories 1 to 4) initially resembled category 5, but after a biotrophic phase of varying duration, infected cells and some adjacent uninfected cells died and became brown, and fungal growth ceased. Symptoms ranged from flecks (small groups of dead cells) to large areas of necrosis (limited lesions). Similar intermediate reactions also occurred in normally susceptible hypocotyls which were transferred from 17 to 25°C, or which retained cotyledons.

The finding that resistance is expressed at different stages of infection is discussed in relation to the regulation of cultivar specificity.
Resistance of lettuce and related species to anthracnose (Microdochium panattonianum) in Australia
Authors: GALEA V. J. , PRICE T. V.
Published: April 2007

All 35 commercial lettuce cultivars available in Australia, two cultivars of chicory, one cultivar of endive and single accessions of Lactuca saligna, L. serriola and Sonchus oleraceus were tested for susceptibility to Microdochium panattonianum under glasshouse and field conditions. Under controlled environmental conditions log lesion density on cv. Cos Verdi was linearly related to log inoculum concentration. Inocula from L. saliva and L. serriola were cross‐infective but did not infect the single accessions of L. saligna and S. oleraceus tested. All lettuce cultivars were susceptible. Some cultivars showed a relatively greater increase in susceptibility than others at an increased inoculum concentration. Latent periods for different cultivars ranged from 3 to 7 days under glasshouse conditions and from 8 to more than 17 days in a field trial. There was poor correlation between glasshouse and field trials for the disease rating of cultivars. Chicory, endive and the L. saligna accession were immune (symptomless) and the L. serriola accession was highly resistant. The results indicate that L. saligna, L. serriola. endive and chicory are possible sources of genes for resistance to M. panattonianum.
Cultivar reactions and the genetic basis of resistance to alternaria stem canker (Alternaria alternata f.sp. lycopersici) in tomato
Authors: VAKALOUNAKIS D. J.
Published: April 2007

The reactions of several tomato cultivars and the genetic basis of resistance to an isolate ofAlternaria alternata f. sp. lycopersici were examined. Among the 105 cultivars tested only two, Regal and Toper, were susceptible, while the remainder were highly resistant. The resistant cultivar ACE 55 VF (P;) was crossed with the susceptible cultivar Earlypak No. 7 (P1)‐ When F1, F2, F3, BC1, BC1 selfed, F2 X P2 and BC1P2 x P1 progenies were inoculated at the two‐leaf stage with a suspension of spores of the pathogen, the ratios of resistant to susceptible plants indicated that resistance was conferred by a single dominant gene.
Resistance to thiabendazole in isolates of Helminthosporium solani, the cause of silver scurf disease of potatoes
Authors: HIDE G. A. , HALL SHARON M. , BOORER KATHRYN J.
Published: April 2007

Isolates of Helminthosporium solani were obtained from potato tubers and cultured on agar containing thiabendazole. Some grew on agar containing 100 mg/l and these were classified as resistant, whereas sensitive isolates produced no mycelial growth on agar containing 5 mg/l. Isolates were also found that were intermediate in their sensitivity to the fungicide. All isolates from Scottish virus tested stem cutting stocks (VTSC) on two farms were resistant whereas those from another farm were sensitive to the fungicide. The proportion of resistant isolates from eight English once‐grown seed stocks ranged from 0 to 96%. There has been no previous report of fungicide resistance in H. solani and the possible reasons for these results and their implications are discussed.
Virus infection and furanocoumarins in celery
Authors: LORD K. M. , EPTON H. A. S. , FROST R. R.
Published: April 2007

Celery infected with celery mosaic virus or parsnip yellow fleck virus contained the furanocoumarins angelicin, bergapten, psoralen, trimethylpsoralen and xanthotoxin in concentrations from 0.3 to 3.6 μg/g fresh mass. They were not detected in celery plants grown in aseptic culture, and only occasionally found in apparently healthy plants in the glasshouse.