Survival and Fluctuation in Density of Myrothecium roridum in Mulberry Field Soil

The density of Myrothecium roridum increased in field soil from June to October and decreased from February to April in 1996–1998. The fluctuation in density of M. roridum in the surface soil was affected by the average temperature. In the greenhouse, mulberry leaves were infected by conidia that splashed from soil artificially infested with conidia of M. roridum at 10³ or more conidia/g soil. Disease incidence on mulberry increased when soil was amended with the fallen leaves and when mulberries were planted densely in soil artificially infested with a high conidial density of M. roridum. Received 9 December 1999/ Accepted in revised form 21 July 2000     

Effects of Host and Microbial Factors on Development of Clonostachys rosea and Control of Botrytis cinerea in Rose

Development of Clonostachys rosea in rose leaves and petals and control of Botrytis cinerea by the agent were investigated. C. rosea germinated, established endophytic growth, and sporulated abundantly whether the tissues were mature, senescent or dead when inoculated. Germination incidence was moderate on mature and senescent leaves (47% and 35%) and petals (31% and 43%), and high (>98%) on dead tissues. Sporulation of C. rosea in tissues inoculated when mature, senescent or dead averaged 41%, 61%, and 75% in leaves, and 48%, 87% and 53% in petals. When leaves were wounded with needles before inoculation, germination of C. rosea increased from 45–56% to 90–92%, but sporulation became high (>75%) regardless of wounds. When leaves were inoculated with C. rosea at 0–24h after wounding and subsequently with B. cinerea, germination of the pathogen was reduced by 25–41% and sporulation by 99%. A humid period prior to inoculation of senescent or dead leaves promoted communities of indigenous fungi, reduced sporulation of C. rosea and B. cinerea, and, in dead leaves, increased control of the pathogen associated with C. rosea. Applied at high density, isolates of indigenous Penicillium sp. and Alternaria alternata from rose interacted with C. rosea and reduced control of the pathogen by 16% and 21%, respectively. In conclusion, C. rosea markedly suppressed sporulation of B. cinerea in rose leaves and petals regardless of developmental stage, minor wounds, and natural densities of microflora. This versatility should allow C. rosea to effectively control inoculum production of B. cinerea in rose production systems.     

Development ofClonostachys rosea and interactions withBotrytis cinerea in rose leaves and residues

The effect of microclimate variables on development ofClonostachys rosea and biocontrol ofBotrytis cinerea was investigated on rose leaves and crop residues. C.rosea established and sporulated abundantly on inoculated leaflets incubated for 7–35 days at 10°, 20° and 30°C and then placed on paraquat—chloramphenical agar (PCA) for 15 days at 20°C. On leaflets kept at 10°C, the sporulation after incubation on PCA increased from 60% to 93% on samples taken 7 to 21 days after inoculation, but decreased to 45% on material sampled after 35 days. A similar pattern was observed on leaves incubated at either 20° or 30°C. The sporulation ofC. rosea on leaf disks on PCA was not affected when the onset of high humidity occurred 0, 4, 8, 12 or 16 h after inoculation. However, sporulation was reduced to 54–58% on leaflets kept for 20–24 h under dry conditions after inoculation and before being placed on PCA. The fungus sporulated on 68–74% of the surface of leaf disks kept for up to 24 h at high humidity after inoculation, but decreased to 40–51% if the high humidity period before transferral to PCA was prolonged to 36–48 h. The growth ofC. rosea on leaflets was reduced at low inoculum concentrations (10³ and 10⁴ conidia/ml) because of competition with indigenous microorganisms, but at higher concentrations (10⁵ and 10⁶ conidia/ml) the indigenous fungi were inhibited. Regardless of the time of application ofC. rosea in relation toB. cinerea, the pathogen’s sporulation was reduced by more than 99%. The antagonist was able to parasitize hyphae and conidiophores ofB. cinerea in the leaf residues. AsC. rosea exhibited flexibility in association with rose leaves under a wide range of microclimatic conditions, and in reducingB. cinerea sporulation on rose leaves and residues, it can be expected to suppress the pathogen effectively in rose production systems.     

Conidial production and viability of Calonectria pseudonaviculata on infected boxwood leaves as affected by temperature,wetness, and dryness periods

Calonectria pseudonaviculata causes lesions on boxwood leaves and twigs. Controlled-environment experiments were conducted to determine the effects of temperature and leaf wetness period on C. pseudonaviculata sporulation on diseased (cv. Suffruticosa) leaves and of dryness periods and high temperature on conidial survival. Infected leaves were incubated in moist chambers and subjected to six temperatures (9, 13, 17, 21, 25, and 29°C) and six leaf wetness periods (0, 12, 24, 40, 48, and 72 h). Spore production was influenced significantly by wetness period, temperature, and their interaction. Increasing duration of leaf wetness and increasing temperature generally increased sporulation, with no sporulation occurring at 29°C or 9 and 13°C, except at 72 h of wetness exposure, while it was optimal at 21°C. Detached leaves with profuse conidia were subjected to a range of drying (relative humidity at 65%) times (0, 2, 4, 6, and 8 h) at two temperatures of 21 and 29°C. Conidia were then harvested and plated on water agar. Germinating conidia were counted to measure the spore viability. Spore mortality increased with increasing dryness duration at both temperatures but occurred more quickly and severely at 29 than 21°C. Overall, this study extended biological knowledge of conditions required for crucial stages of the C. pseudonaviculata disease cycle and the obtained results will be vital for developing boxwood blight forecasting and management tools.     

Effect of interrupted leaf wetness periods on suppression of sporulation ofBotrytis allii andB. cinerea by antagonists on dead onion leaves

Saprophytic antagonists were evaluated for suppression of sporulation ofBotrytis allii andB. cinerea on artificially killed segments of onion leaves that were pre-inoculated with the pathogens. During incubation of the antagonisttreated leaf segments in moist chambers, periods of leaf wetness and leaf dryness were alternated to simulate conditions in the field. Interruption of humid conditions with dry periods had a differential effect on antagonists.Alternaria alternata, Chaetomium globosum, Ulocladium atrum andU. chartarum suppressed sporulation ofB. allii almost completely under continuously wet conditions, and when the leaf wetness periods were interrupted with drying periods of 9h imposed 16, 40, and 64 h after the antagonists were applied. When leaf wetness was interrupted 16 h after antagonist application, the number of conidia ofB. allii produced cm^–2 leaf surface after eight days was under the detection limit of 5.2 × 10³ conidia on leaves treated with these antagonists compared to 3.7 × 10⁵ conidia on leaves that were not treated. On the other hand,Gliocladium roseum, G. catenulatum andSesquicillium candelabrum, all highly efficient under continuously wet conditions, were of low to moderate efficiency when leaf wetness periods had been interrupted 16 h after application of the antagonists. The antagonists showed the same differentiation and sensitivity to interrupted wetness periods when tested withB. cinerea.     

Sporulation of Pyrenopeziza brassicae (light leaf spot) on oilseed rape (Brassica napus) leaves inoculated with ascospores or conidia at different temperatures and wetness durations

In controlled environment experiments, sporulation of Pyrenopeziza brassicae was observed on leaves of oilseed rape inoculated with ascospores or conidia at temperatures from 8 to 20°C at all leaf wetness durations from 6 to 72 h, except after 6 h leaf wetness duration at 8°C. The shortest times from inoculation to first observed sporulation ( l ₀), for both ascospore and conidial inoculum, were 11–12 days at 16°C after 48 h wetness duration. For both ascospore and conidial inoculum (48 h wetness duration), the number of conidia produced per cm² leaf area with sporulation was seven to eight times less at 20°C than at 8, 12 or 16°C. Values of Gompertz parameters c (maximum percentage leaf area with sporulation), r (maximum rate of increase in percentage leaf area with sporulation) and l ₃₇ (days from inoculation to 37% of maximum sporulation), estimated by fitting the equation to the observed data, were linearly related to values predicted by inserting temperature and wetness duration treatment values into existing equations. The observed data were fitted better by logistic equations than by Gompertz equations (which overestimated at low temperatures). For both ascospore and conidial inoculum, the latent period derived from the logistic equation (days from inoculation to 50% of maximum sporulation, l ₅₀) of P. brassicae was generally shortest at 16°C, and increased as temperature increased to 20°C or decreased to 8°C. Minimum numbers of spores needed to produce sporulation on leaves were ≈25 ascospores per leaf and ≈700 conidia per leaf, at 16°C after 48 h leaf wetness duration.     

Myrothecium leaf spot of mulberry caused by Myrothecium verrucaria

A fungus that formed white colonies with greenish black spore masses was isolated from diseased mulberry leaves in Gunma Prefecture, Japan, in 1995, 1999, and 2000. It was pathogenic to mulberry. The fungus was identified with Myrothecium verrucaria. It has been added to the list of pathogens that cause Myrothecium leaf spot of mulberry and is identified for the first time as a plant pathogen in Japan.     

Multidrug-resistance plasmid of <Emphasis Type="Italic">Enterobacter cloacae</Emphasis>: transfer to <Emphasis Type="Italic">Erwinia herbicola</Emphasis> on the phylloplane of mulberry and weeds

A mulberry epiphytic Enterobacter cloacae MUL1 harbors plasmid pMUL1 encoding five drug-resistance genes. This plasmid was examined upon its conjugal transfer into epiphytic Erwinia herbicola on the phylloplane of mulberry and 12 species of weeds. The plasmid was transferred into Er. herbicola at a frequency of 10^–5–10^–3/recipient in mulberry and Lolium multiflorum LAM. 1–8 days after wound inoculation with 10⁶–10⁸/ml suspensions. In Chenopodium album L. and C. album L. var. centrorubrum, however, it was transferred only after wound inoculation with a 10⁸/ml suspension, but not with 10⁷/ml or 10⁶/ml suspensions, owing to the weak epiphytic fitness of Ent. cloacae on these weeds. Transconjugants were also obtained for seven other species of weeds in the case of inoculation with a 10⁸/ml suspension. In contrast, when bacterial suspensions were sprayed on mulberry leaves with or without fresh wounds, transconjugants were obtained only in wounded leaves, which were considered suitable for bacterial conjugation. These findings suggest that epiphytic bacteria, including Ent. cloacae and Er. herbicola, may be carriers of drug-resistance genes distributed among plant pathogenic bacteria in nature.     

Relationships of aphid and mite infestations to control ofBotrytis cinerea byClonostachys rosea in rose(Rosa hybrida) leaves

Infestations of aphids(Macrosiphum rosae L.) and of twospotted spider mites(Tetranychus urticae Koch) were examined in relation to growth and sporulation ofClonostachys rosea andBotrytis cinerea, and to suppression of the pathogen by the agent, in green rose leaves. Leaves were infested artificially with 10 aphids/leaflet for 3 h, or naturally with 15-30 aphids/leaflet for 7-12 days or with undetermined numbers of mites for 10-12 days. Leaves that had or had not been infested were inoculated withC. rosea, withB. cinerea, or withC. rosea plusB. cinerea. Germination incidence and germ tube growth ofC. rosea andB. cinerea on the phylloplane in most instances were much greater in leaves previously infested with aphids or mites compared with noninfested leaves. After combined inoculation,C. rosea suppressed germination ofB. cinerea from 47% to 19% in noninfested leaves, but in leaves that had been infested the agent was ineffective and germination incidence of the pathogen increased to 75-93%. Previous infestation with naturally introduced aphids or mites, but not brief infestations of artificially introduced aphids, markedly increased sporulation ofC. rosea after the leaves died during an initial 7-15 days of incubation on a paraquat agar medium, regardless of whether or notB. cinerea was present. Sporulation ofB. cinerea was similarly increased when inoculated alone. After 15-20 days, however, conidiophores of the agent or pathogen covered most of the leaf surface in these treatments. In leaves inoculated withC. rosea plusB. cinerea, the agent suppressed sporulation of the pathogen almost completely in both previously infested and noninfested leaves. Thus, aphid and mite infestations did not compromise the ability ofC. rosea to suppress inoculum production byB. cinerea in the leaves. Increased nutrient availability on the phylloplane through exudation or as honeydew or frass is proposed as a basis to explain effects of the pest infestations onC. rosea andB. cinerea.     

Activity of the New Fungicide Benthiavalicarb Against Plasmopara viticola and its Efficacy in Controlling Downy Mildew in Grapevines

Benthiavalicarb is a new fungicide active against Oomycetes fungal plant pathogens. The present study shows that benthiavalicarb is effective for controlling the Oomycete fungal pathogen Plasmopara viticola, which causes downy mildew in grapevines. The fungicide did not affect zoospore discharge from sporangia of P. viticola, but strongly inhibited zoospore encystment, cystospore germination in vitro and mycelial growth, together with sporangial production in vivo. Benthiavalicarb showed strong prophylactic and local activity in intact plants or detached leaves and low translaminar activity. The compound was not translocated from leaf to leaf in either a acropetal or basipetal direction. Benthiavalicarb applied at 1, 3 and 6 days post-inoculation protected grapevine plants against downy mildew and inhibited sporulation of the pathogen. Similar results were obtained on leaf disks if benthiavalicarb was applied up to 96 h post-inoculation. Benthiavalicarb diminished the sporulation of P. viticola when applied to established disease in the tissue. Benthiavalicarb remained active on leaves for a period up to 28 days. Two foliar applications of benthiavalicarb, 2 weeks apart, to field-grown grapevines inhibited downy mildew development and were as effective as the standard metalaxyl-Cu treatment in controlling the disease. A formulated mixture of benthiavalicarb + Folpet was similar or superior in performance to metalaxyl-Cu and the new strobilurin trifloxystrobin in controlling downy mildew. The effectiveness of benthiavalicarb makes it well suited for integration into a control programme against downy mildew disease in vineyards, and as a component to delay resistance buildup.     

Rhizopus Rot of Mulberry-grafted Saplings Caused by Rhizopus oryzae

A new disease on stocks of mulberry-grafted saplings was found in Tsukuba in 1999. A representative isolate of the Rhizopus species that was consistently isolated from rotted tissues was pathogenic to healthy mulberry stocks. The causal fungus was identified morphologically as Rhizopus oryzae Went & Prinsen Geerligs. Rhizopus rot (“Naefuhaibyou” in Japanese) was proposed for the name of the disease. This is the first report on a mulberry disease caused by R. oryzae. Received 30 March 2001/ Accepted in revised form 4 June2001     

Resistance assessment of grapevine leaves to downy mildew with sporulation area scoring

The use of resistant individuals obtained through a breeding program, aimed at decreasing chemical treatments, is one of the most promising strategies for control of downy mildew caused by Plasmopara viticola in grapevine. In this study, 869 hybrid grape individuals, obtained by crossing the resistant Regent grape cultivar with sensitive Alphonse Lavallée, were tested after artificial inoculation of detached leaves by drops of the pathogen inoculum. Sporulation severity, as visual evaluation of sporulation density including necrosis, and sporulation incidence were scored to assess resistance level, then the sporulation area (mm²) was measured for each individual. The criterium of sporulation incidence could not describe all resistance levels. Sporulation area made it possible to measure the entire area in detail for how the pathogen spread at the inoculation site. Sporulation area was not fully consistent with sporulation severity. In this context, a new scale for sporulation area was developed to determine resistance level to the pathogen by taking into account the distribution of sporulation area values within those obtained from sporulation severity scales. Six categories ranging from 0 to 0.05 mm² (extremely resistant-ER) to ≥15.1 mm² (extremely sensitive-ES) were defined. 43 of the 869 individuals tested through the three evaluation criteria, in which no sporulation was observed, and 18 additional individuals with sporulation area of <0.05 mm² were scored in the ER group. Microscopic analysis confirmed findings for the ER group and other resistance levels. The authors suggest that the scale of sporulation area will be useful for assessment of resistance to downy mildew on grapevine leaves.

     

Movement of <Emphasis Type="Italic">Cucumber Mosaic Virus</Emphasis> Is Restricted at the Interface between Mesophyll and Phloem Pathway in <Emphasis Type="Italic">Cucumis figarei</Emphasis>

Viral movement in the leaf tissues of a resistant host, Cucumis figarei, inoculated with the pepo strain of Cucumber mosaic virus (CMV) and incubated at 24°C or 36°C was investigated by fluorescence in situ hybridization (FISH), leaf-press blotting, tissue printing and immunogold-silver staining techniques. Observation by FISH revealed that at 24°C most infection sites with CMV at 0.01 mg/ml or 0.1 mg/ml were limited to a single cell during the incubation period, that the number of infection sites increased from 24hpi (hours post inoculation) to 80 hpi in the leaves inoculated with CMV at 0.5 mg/ml, and that the size as well as the number of infection sites rapidly increased with time in the leaves inoculated with CMV at 2.0 mg/ml. These results suggested that one factor for the resistance of C. figarei at 24°C might be an inhibition of viral movement in and out of the infection sites. Leaf-press blotting and tissue blotting indicated that CMV remained in the infection sites at 24°C, whereas it spread from the inoculated leaves to other parts of the plants through vascular systems at 36°C. Immunogold-silver staining demonstrated that at 24°C CMV infected bundle sheath (BS) cells in minor veins, whereas at 36°C it invaded not only BS cells, but also phloem parenchyma (PP)/ companion cell (CC) or PP/intermediary cell (IC) complexes in minor veins in the regions with chlorotic symptoms. These results indicated that at 24°C CMV had difficulty in passing through the interface between BS and PP/CC or PP/ IC complexes and that viral entry from mesophyll to the phloem pathway was inhibited in the inoculated leaves. Received 26 August 1999/ Accepted in revised form 14 December 1999     

Host and biotic factors affecting sporulation ofstemphylium botryosum f. sp. lycopersici on tomatoes and ofalternaria porri f. sp. sol ani on potatoes

Factors known to inhibit sporulation of bio trophic fungal pathogens were found to enhance sporulation of two necrotrophic fungi. The sporulating potential ofStemphyliurn botryosum f. sp.lycopersici on tomatoes and ofAlternaria porri f. sp.solani on potatoes increased with necrotization, reaching a maximum on dead leaves. Wetting the dead leaves for the whole period of incubation with increasing concentrations of glucose resulted in progressively decreasing sporulation of both pathogens. However, application of glucose during the first half of the incubation period inhibited sporulation ofS. botryosum f. sp.lycopersici on tomatoes only a little, and increased that ofA. porri f. sp.solani on potatoes. The capacity ofS. botryosum f. sp.lycopersici to sporulate on leaves lasted for 12 weeks at 29°C, and ofA. porri f. sp.solani for 12 weeks at 29°C and for over 21 weeks at 20°C. The results emphasized basic differences in sporulation between biotrophic and necrotrophic parasites. Specific techniques useful for studying sporulationin vivo are discussed.     

Magnaporthe oryzae conidia on basal wheat leaves as a potential source of wheat blast inoculum

Wheat blast caused by Magnaporthe oryzae Triticum causes significant losses on wheat during outbreak years in several South American countries. Despite reports of wheat blast leaf lesions on some wheat cultivars, the importance of inoculum originating from leaves in severely affected commercial fields is disputed. It is generally considered that leaf lesions and/or sporulation on leaves do not usually appear before the occurrence of spike blast in wheat. The purpose of this study was to (i) determine the occurrence of wheat blast on basal leaves, (ii) estimate the number of conidia produced on these leaves, and (iii) determine the impact of current fungicide application practices on inoculum produced from sporulating lesions on basal wheat leaves. Inoculations at the three‐leaf stage showed that certain cultivar and isolate combinations caused more disease on old wheat leaves than young expanding leaves. Under optimum conditions, M. oryzae had the potential to produce tens to hundreds of thousands of conidia on small amounts of wheat basal leaves. A mean of 1 669 000 conidia were produced on 1 g dry basal leaves of a highly susceptible cultivar under optimum conditions for sporulation. Conidia production on leaves coincided with spike emergence under both greenhouse and field conditions. When field studies were conducted under natural epidemic conditions, foliar fungicide applications reduced the amount of M. oryzae conidia on basal leaves by 62–77% compared to non‐sprayed controls. An earlier application of foliar fungicides might reduce inoculum if conidia from basal leaves contribute to wheat spike blast development.     

Effects of host and pathogen genotypes on inducibility of resistance in tomato (Solanum lycopersicum) to Phytophthora infestans

Thirteen tomato (Solanum lycopersicum) accessions were tested for inducibility of resistance against two isolates of Phytophthora infestans using BABA (dl ‐3‐amino butyric acid) as the inducing agent. In a more detailed trial, six of the accessions were assessed for inducibility of resistance to six P. infestans isolates on three leaves of different age per plant. Plants were inoculated 1 week after treatment with BABA. Area under the disease progress curve (AUDPC), sporulation capacity (SC) and infection efficiency (IE) were all affected by treatment with BABA. On leaves of all ages AUDPC was most affected by induction (43–100% reduction on the youngest leaves) followed by SC (14–100%) and IE (0–100% reduction). Tomato genotypes varied significantly in inducibility of resistance against P. infestans and the degree of induction generally decreased with increasing leaf age, whilst the absolute susceptibility with respect to AUDPC and SC rarely changed. The level of induction was not always related to the resistance level of the tomato accession and it was significantly influenced by the pathogen isolate used for challenge inoculation. The results show that inducibility of resistance is a selectable trait that is, however, isolate‐specific.     

Radiochemical distribution and decline studies with bromoxynil octanoate in wheat

Bromoxynil octanoate labelled with ¹⁴C in the ring or in the cyano-group was applied to wheat seedlings at the two-leaf or fully-tillered stage and at rates equivalent to up to 16 oz a.i./acre. The plants were grown either in environmental chambers under controlled conditions for up to 28 days, or outdoors under field conditions for various periods up to harvest. Initially, elimination of radioactivity occurred more rapidly with bromoxynil-cyano-[¹⁴C]-octanoate than with bromoxynil-ring-[¹⁴C]-octanoate, indicating metabolic attack on the cyano group. Under outdoor conditions with ring-[¹⁴C]-herbicide applied at the two-leaf stage, only 12% of the radioactivity was retained after 28 days, principally in the treated leaves. When application was made at fully-tillered stage, about 33% of the ¹⁴C was retained after 56 days, almost entirely in the treated senescent leaves at the base of the plant. There was very little translocation of the herbicide or of any major metabolite. The level of radioactivity in harvested grain and in straw more than 7.5 cm above the ground was very low, even after very late application of ring-[¹⁴C]-labelled herbicide. The amount of bromoxynil octanoate, together with any metabolite retaining part of the aromatic ring, did not collectively exceed the equivalent of approx. 0.01 parts/million bromoxynil octanoate.     

Effects of R gene‐mediated resistance in Brassica napus (oilseed rape) on asexual and sexual sporulation of Pyrenopeziza brassicae (light leaf spot)

The phenotype of the R gene‐mediated resistance derived from oilseed rape (Brassica napus) cv. Imola against the light leaf spot plant pathogen, Pyrenopeziza brassicae, was characterized. Using a doubled haploid B. napus mapping population that segregated for resistance against P. brassicae, development of visual symptoms was characterized and symptomless growth was followed using quantitative PCR and scanning electron microscopy on leaves of resistant/susceptible lines inoculated with suspensions of P. brassicae conidia. Initially, in controlled‐environment experiments, growth of P. brassicae was unaffected; then from 8 days post‐inoculation (dpi) some epidermal cells collapsed (‘black flecking’) in green living tissue of cv. Imola and from 13 to 36 dpi there was no increase in the amount of P. brassicae DNA and no asexual sporulation (acervuli/pustules). By contrast, during this period there was a 300‐fold increase in P. brassicae DNA and extensive asexual sporulation in leaves of the susceptible cv. Apex. However, when leaf tissue senesced, the amount of P. brassicae DNA increased rapidly in the resistant but not in the susceptible cultivar and sexual sporulation (apothecia) was abundant on senescent tissues of both. These results were consistent with observations from both controlled condition and field experiments with lines from the mapping population that segregated for this resistance. Analysis of results of both controlled‐environment and field experiments suggested that the resistance was mediated by a single R gene located on chromosome A1.     

Fitness characteristics of the European lineages of Phytophthora ramorum

As an introduced pathogen, Phytophthora ramorum exists as four near-clonal evolutionary lineages, of which only EU1 and EU2 are established in the UK. EU1 has become widespread since the first findings in 2002 whereas EU2, detected in 2011, has a more limited distribution. Both lineages are epidemic in plantation-grown larch, sporulating asexually on needles, but also causing heavy dieback and mortality. To understand whether EU1 and EU2 pose different threats to forest health, we compared their growth characteristics on agar, pathogenicity on several hosts, and sporulation on Japanese larch needles. When pathogenicity was evaluated by measuring colonization at 20 °C in mature bark (phloem) of Japanese and European larch (Larix kaempferi and L. decidua), English oak (Quercus robur), and beech (Fagus sylvatica), Japanese larch was the most susceptible and oak the least susceptible. On average, EU2 isolates produced significantly larger lesions than EU1 isolates in Japanese larch and oak although not in the other hosts. With tests using young saplings of Japanese and European larch, damaging bark lesions formed at both 10 °C and 20 °C, but EU2 was significantly more pathogenic at 20 °C on both hosts compared with EU1. In contrast, both lineages caused similar amounts of necrosis on inoculated leaves of rhododendron (Rhododendron ponticum). Moreover, EU2 isolates usually sporulated less abundantly on larch needles compared with EU1 isolates, suggesting a trade-off in pathogenicity and sporulation between lineages. As EU2 tends to have smaller sporangia than EU1, this could also reduce the inoculum potential of EU2.