Honey bee dispersal of the biocontrol agent Trichoderma harzianum T39: effectiveness in suppressing Botrytis cinerea on strawberry under field conditions

Botrytis cinerea, which causes grey mould, is a major pathogen of many crops. On strawberry, isolates of Trichoderma spp. can effectively control B. cinerea, but frequent application is necessary. Bees can be used to disseminate biological control agents to the target crop. We tested the ability of honey bees to disseminate Trichoderma harzianum T39 to control B. cinerea in strawberry in the field during the winter in Israel over two consecutive seasons. We used the recently developed ‘Triwaks’ dispenser for loading the bees with the T. harzianum inoculum. During both years, grey mould developed in late January in untreated control plots; at low to medium disease levels it was partially controlled by fungicide treatment, and was best controlled in bee-visited plots. At high disease levels neither chemical nor biological control was effective. To assess the spatial distribution of inoculum by bees, we sampled flowers up to 200 m from the hives and found effective levels of T. harzianum even at 200 m. The approach used in this study provides an effective control of grey mould in strawberry in conditions of low to medium grey mould incidence.     

Epidemiology of Grey Mould in Annual Waiting-bed Production of Strawberry

The epidemiology of Botrytis cinerea was studied in five annual strawberry crops using waiting-bed transplants, a system widely adopted in the Netherlands. On dead leaves of transplants the incidence of B. cinerea varied from 26.7% to 52.6%, but the leaf area with potential sporulation was low (3.5–15.6%). During each crop cycle, the availability of necrotic leaf substrate for spore production of B. cinerea was generally low and varied between seasons and with the quality of transplants. B. cinerea sporulated on a maximum of 15.5 cm² of leaf area per plant, measured as potential sporulation. The aerial concentration of B. cinerea conidia in untreated plots did not differ from the concentration in plots where all dead leaves had been removed, nor from the concentration at 25–50 m distance from the strawberry plots. B. cinerea incidence on flowers ranged from 5% to 96%, but no correlation was found with the potential spore production on necrotic leaves. Grey mould at harvest varied from 1.4% to 11.3% and was correlated with the average precipitation during the harvesting period but not with B. cinerea incidence on flowers. Post-harvest grey mould ranged from 2.1% to 32.6% and was correlated with petal colonisation by B. cinerea. The results suggest that in the annual cropping system with waiting-bed transplants, necrotic leaves are not a significant source of B. cinerea inoculum, unlike in other strawberry production systems. Therefore, control measures of grey mould in this annual system should focus on protection of flowers and young developing fruits, and not on the reduction of inoculum production on leaf debris.     

Assessing host specialization of Botrytis cinerea on lettuce and tomato by genotypic and phenotypic characterization

This study tested the hypothesis that Botyrtis cinerea shows host specialization on tomato and lettuce, using phenotypic and genotypic tools. Strains were isolated from tomato and lettuce grown together in the same greenhouse. Forty‐four lettuce strains and 42 tomato strains were investigated for their genetic diversity and their aggressiveness. Both gene diversity and allelic richness were significantly higher in lettuce strains than in tomato strains (P = 0·01). Cluster analysis revealed a clear division of the strains under study into two clusters. However, this structure did not separate the strains according to their host of origin. Tomato strains were significantly more aggressive than lettuce strains when inoculated on tomatoes (P = 0·001), but no significant differences in aggressiveness were observed when the strains were inoculated on lettuce (P = 0·17) or on apple (P = 0·87). The results suggest an absence of clear host specialization of B. cinerea on tomato and lettuce.     

Relative importance of seed‐tuber and soilborne inoculum in causing black dot disease of potato

Controlled‐environment and field experiments were done to quantify the individual contribution of seed‐tuber and soilborne inoculum of Colletotrichum coccodes in causing black dot disease of potato tubers. Seed‐tuber and soilborne inocula of C. coccodes were quantified using an existing real‐time PCR assay and related to subsequent incidence and severity of disease. In four field trials, a controlled‐environment experiment and through the monitoring of 122 commercial crops, seed‐tuber inoculum was found to be relatively less important than soilborne inoculum in causing black dot, and the level of seed‐tuber inoculum did not significantly affect either the incidence or severity of disease or the percentage of progeny tubers deemed unmarketable. By contrast, soilborne inoculum had the potential to result in high levels of disease and the level of C. coccodes soil infestation (pg DNA g^?1 soil) was found to have a significant effect. At soil infestation levels below 100 pg DNA C. coccodes g^?1 soil, 7% of commercial crops had an incidence of black dot greater than 20%, increasing to 40% and 57% of crops at levels of 100–1000 pg g^?1 and >1000 pg g^?1 soil, respectively. These arbitrary threshold levels for soilborne inoculum related to disease risk are discussed. Interpretation of disease risk based on inoculum levels must, in the future, be informed by agronomic variables and potential control strategies.     

Persistent,symptomless, systemic,and seed-borne infection of lettuce by <Emphasis Type="Italic">Botrytis cinerea</Emphasis>

Experiments are presented which show that Botrytis cinerea, the cause of grey mould disease, is often present in symptomless lettuce plants as a systemic, endophytic, infection which may arise from seed. The fungus was isolated on selective media from surface-sterilised sections of roots, stem pieces and leaf discs from symptomless plants grown in a conventional glasshouse and in a spore-free air-flow provided by an isolation propagator. The presence of B. cinerea was confirmed by immuno-labelling the tissues with the Botrytis-specific monoclonal antibody BC-12.CA4. As plants grew, infection spread from the roots to stems and leaves. Surface-sterilisation of seeds reduced the number of infected symptomless plants. Artificial infection of seedlings with dry conidia increased the rate of infection in some experiments. Selected isolates were genetically finger-printed using microsatellite loci. This confirmed systemic spread of the inoculating isolates but showed that other isolates were also present and that single plants hosted multiple isolates. This shows that B. cinerea commonly grows in lettuce plants as an endophyte, as has already been shown for Primula. If true for other hosts, the endophytic phase may be as important a component of the species population as the aggressive necrotrophic phase.     

Genetic structure and fungicide sensitivity of Botrytis cinerea populations isolated from grapevine in northern Italy

Grey mould, caused by Botrytis cinerea, is a disease severely affecting grape production in northern Italy. However, little information is available on the variability of B. cinerea populations associated with grapevine. The mode of reproduction, sensitivity to fungicides, and for the first time in Italy, the genetic structure of B. cinerea populations isolated from grapevine in a northern Italian region are reported. Botrytis cinerea isolates (317) were completely genotyped for six microsatellite loci and characterized for the presence of the transposable elements Boty and Flipper, for the mating type and for resistance to cyprodinil, fludioxonil, boscalid and fenhexamid. All the isolates were found to belong to B. cinerea Group II, indicating the absence of B. pseudocinerea in the investigated areas. The populations possess a high genotypic diversity, different frequencies of transposable elements and a mixed mode of reproduction. At a regional level, B. cinerea populations belong to a large and interconnected pathogen population that includes the major grape‐growing districts. The populations were generally sensitive to fungicides, with a low proportion (8%) of isolates resistant to cyprodinil, fludioxonil and boscalid. A small genetic distance was found between B. cinerea populations. However, the populations geographically isolated from the others by a mountain range showed a small but statistically significant genetic differentiation and a different pattern of fungicide resistance. The results show that northern Italian B. cinerea populations possess a high evolutionary potential and adaptive capacity.     

The effect of post‐harvest storage conditions on the development of black dot (Colletotrichum coccodes) on potato in crops grown for different durations

The effects of post‐harvest curing and storage temperature on severity of black dot, caused by Colletotrichum coccodes, were investigated for potato crops grown for different crop durations (days from 50% emergence to harvest) in soils that posed a low, medium and high risk of disease. In field trials over four growing seasons (2005–8), black dot severity at harvest increased with increasing crop duration, within the range 103–146 days from 50% emergence to harvest (P < 0.05). In field trials over three growing seasons (2006–8), black dot severity on tubers at harvest increased significantly with increasing soil inoculum in each year, within the range 43–4787 pg C. coccodes DNA/g soil (P < 0.05). Storage trials were conducted to measure the influence of accumulated post‐harvest temperature on black dot. In 2005, no difference in black dot severity was observed on tubers stored for 20 weeks at 2.5 and 3.5 °C. In 2006 (but not 2007), increasing the duration of curing after harvest from 4 to 14 days increased black dot severity on tubers from 8.9 to 11.2% (P < 0.01) in long duration crops (>131 days after 50% emergence) grown under high (>1000 pg C. coccodes DNA/g soil) soil inoculum. The number of days of curing did not affect disease severity for shorter duration crops grown at high soil inoculum, or on crops grown at medium or low (100–1000 and <100 pg C. coccodes DNA/g soil, respectively) soil inoculum concentrations. Soil inoculum and crop duration together provided a reasonable prediction of black dot severity at harvest and after a 20‐week storage period.     

Failure to detect highly resistant strains in dicarboximide resistant field populations of Botrytis cinerea1

Field isolates of Botrytis cinerea with moderate levels of resistance to dicarboximide fungicides (ED50 1.0–4.9 μg ml^?1) and to dicloran were obtained from glasshouses where vinclozolin and iprodione failed to control grey mould. From sensitive and moderatcly-resistant cultures, laboratory isolates were selected on dicarboximide-amended medium, which were highly resistant to these fungicides (ED50 125->3000 μg ml^?1). Conidia of all the resistant isolates germinated well on media amended with 100 μg ml^?1 of the dicarboximides vinclozolin, iprodione, procymidone and myclozolin and with 5 μg ml^?1 of metomeclan. However, the spores of the moderately resistant isolates did not germinate on 100 μg ml^?1 metomeclan while the spores of the highly resistant isolates germinated well. Using media with 100 μg ml^?1 of metomeclan to distinguish between the two phenotypes, no highly resistant strain was detected among 312 resistant samples from five cucumber glasshouses with a high frequency of moderately resistant strains. From air-borne inoculum of five glasshouses with 100% resistant populations, 1604 colonies were recovered on vinclozolin-amended (100 μg ml^?1) medium and none on metomeclan-amended (100 μg ml^?1) medium. It is concluded that strains of B. cinerea highly resistant to dicarboximides are absent from field populations.     

Colonization of lettuce cultivars and rotation crops by Fusarium oxysporum f. sp. lactucae,the cause of fusarium wilt of lettuce

The severity of fusarium wilt is affected by inoculum density in soil, which is expected to decline during intervals when a non‐susceptible crop is grown. However, the anticipated benefits of crop rotation may not be realized if the pathogen can colonize and produce inoculum on a resistant cultivar or rotation crop. The present study documented colonization of roots of broccoli, cauliflower and spinach by Fusarium oxysporum f. sp. lactucae, the cause of fusarium wilt of lettuce. The frequency of infection was significantly lower on all three rotation crops than on a susceptible lettuce cultivar, and the pathogen was restricted to the cortex of roots of broccoli. However, F. oxysporum f. sp. lactucae was isolated from the root vascular stele of 7·4% of cauliflower plants and 50% of spinach plants that were sampled, indicating a greater potential for colonization and production of inoculum on these crops. The pathogen was also recovered from the root vascular stele of five fusarium wilt‐resistant lettuce cultivars. Thus, disease‐resistant plants may support growth of the pathogen and thereby contribute to an increase in soil inoculum density. Cultivars that were indistinguishable based on above‐ground symptoms, differed significantly in the extent to which they were colonized by F. oxysporum f. sp. lactucae. Less extensively colonized cultivars may prove to be superior sources of resistance to fusarium wilt for use in breeding programmes.     

A molecular epidemiology study reveals the presence of identical genotypes on grapevines and ground cover weeds and the existence of separate genetic groups in a Botrytis cinerea population

Botrytis cinerea, the grey mould agent, is one of the most important pathogens of grapevine, due to the great yield losses caused and the economic costs related to disease control. Ground cover plants are assumed to have a role in the complex epidemiology of the pathogen, even if no information on the genetic variability of the strains is available. In this study, a molecular epidemiology approach, based on the comparative analysis of the nucleotide sequences of multiple genes (ITS1-ITS2, G3PDH, NEP1, NEP2, BC-hch, and sdhB), was used to evaluate whether B. cinerea isolated from herbaceous species contributes to grey mould diffusion on grapevines. From 330 samples collected in two vineyards in Lombardy, Italy, 63 B. cinerea strains were isolated from tissues of grapevine with symptoms (50 strains) and spontaneous ground cover plants (13 strains). Capsella bursa-pastoris, Cardamine impatiens, Lamium purpureum, and Crepis tectorum were identified as novel B. cinerea hosts. Sequence analysis and phylogeny showed that the same genotypes were present on both grapevines and herbaceous plants, with no fitness (estimated from growth and sporulation on potato dextrose agar) or pathogenicity (on grapevine leaves and berries, and tomato leaves) penalties. This confirms that ground cover plants can be a source of inoculum for B. cinerea on grapevine. Moreover, phylogenetic analysis of the BC-hch gene allowed the identification of two genetically distinct clusters, characterized by vegetative incompatibility and different distributions of the mating types, fitness, and pathogenicity. Therefore, B. cinerea seems to be composed of two diverging subpopulations that do not differ for host specialization.     

In vitro and In vivo Activity of Cyprodinil and Pyrimethanil on Botrytis cinerea Isolates Resistant to other Botryticides and Selection for Resistance to Pyrimethanil in a Greenhouse Population in Greece

No cross-resistance was observed between pyrimethanil or cyprodinil and the fungicides benomyl, iprodione or carbendazim + diethofencarb. In vitro, both anilinopyrimidine fungicides were effective against strains of Botrytis cinerea resistant to benzimidazoles and/or dicarboximides and against a wild type strain insensitive to diethofencarb (EC₅₀ values ranged between 0.03–0.19 and 0.006–0.054gml^–1 for pyrimethanil and cyprodinil, respectively). Preventive applications of anilinopyrimidines completely protected young cucumber plants and fruits that were inoculated with all strains of B. cinerea. The effectiveness of pyrimethanil against grey mould was studied in greenhouse grown tomatoes in relation to (a) the type of infection and the progress of the disease on different plant parts and (b) the response of the naturally occurring B. cinerea population to the selection pressure caused by eight successive applications of this fungicide. Pyrimethanil effectively controlled grey mould on leaves, fruits and stems but did not significantly reduce the number of dead plants and fruits with 'ghost spot' symptoms. The selection pressure caused by the consecutive applications of pyrimethanil resulted in reduction of its effectiveness on leaves that became apparent after the sixth application. This was correlated with a shift of the B. cinerea population (not previously exposed to anilinopyrimidines) towards reduced sensitivity, probably due to the development of a low level of resistance (R _L = 7.7). Pyrimethanil delayed the onset of the disease but it did not reduce the infection rate.     

Relationship between Spongospora subterranea f. sp. subterranea soil inoculum level,host resistance and powdery scab on potato tubers in the field

The relationship between initial soil inoculum level of Spongospora subterranea f. sp. subterranea (Sss) and the incidence and severity of powdery scab on potato tubers at harvest was investigated. In all experiments soil inoculum level of Sss (sporeballs/g soil) was measured using a quantitative real‐time PCR assay. Of 113 commercial potato fields across the UK, soil inoculum was detected in 75%, ranging from 0 to 148 Sss sporeballs/g soil. When arbitrary soil inoculum threshold values of 0, <10 and >10 sporeballs/g soil were set, it was observed that the number of progeny crops developing powdery scab increased with the level of inoculum quantified in the field soil preplanting. In four field trials carried out to investigate the link between the amount of inoculum added to the soil and disease development, disease incidence and severity on progeny tubers was found to be significantly (P < 0·01) greater in plots with increasing levels of inoculum incorporated. There was a cultivar effect in all years, with disease incidence and severity scores being significantly greater in cvs Agria and Estima than in Nicola (P < 0·01).     

Inoculum potential of Sclerotinia sclerotiorum sclerotia depends on isolate and host plant

The soilborne fungus Sclerotinia sclerotiorum infects many important crop plants. Central to the success of this pathogen is the production of sclerotia, which enables survival in soil and constitutes the primary inoculum. This study aimed to determine how crop plant type and S. sclerotiorum isolate impact sclerotial production and germination and hence inoculum potential. Three S. sclerotiorum isolates (L6, L17, L44) were used to inoculate plants of bean, carrot, lettuce, oilseed rape (OSR) and potato, and the number and weight of sclerotia per plant quantified. Carpogenic germination of sclerotia collected from different hosts was also assessed for L6. Production of sclerotia was dependent on both crop plant type and S. sclerotiorum isolate, with OSR and lettuce supporting the greatest number (42–122) and weight (1.6–3.0 g) of sclerotia per plant. The largest sclerotia were produced on OSR (33–66 mg). The three S. sclerotiorum isolates exhibited a consistent pattern of sclerotial production irrespective of crop type; L6 produced large numbers of small sclerotia while L44 produced smaller numbers of large sclerotia, with L17 intermediate between the two. Germination rate and percentage was greatest for larger sclerotia (4.0–6.7 mm) and also varied between host plants. Combining sclerotial production data and typical field crop densities suggested that infected carrot and OSR could produce the greatest number (3944 m^?2) and weight (73 g m^?2) of S. sclerotiorum sclerotia, respectively, suggesting these crops potentially contribute a greater increase in inoculum. This information, once further validated in field trials, could be used to inform future crop rotation decisions.     

Synthesis and antifungal activity of imidazole-1-carboxylates

A series of imidazole-1-carboxylates was prepared by reacting various alcohols with trichloromethyl chloroformate and imidazole or N,N'-carbonyl-diimidazole. They were tested for fungitoxic activity in vitro against two phytopathogenic fungi, Botrytis cinerea (grey mould) and Gibberella fujikuroi, and for preventive efficacy against grey mould on cucumber leaves. 1-(4-Substituted phenoxymethyl)-2,2-dimethylpropylimidazole-1-carboxylates showed excellent in-vitro activity against B. cinerea, and moderate activity against G. fujikuroi, and some of them also effectively controlled grey mould in vivo. A 1H-1,2,4-triazole derivative corresponding to an imidazole derivative did not have any activity, while a thiocarboxylate corresponding to an imidazole carboxylate showed excellent activity against both B. cinerea and G. fujikuroi.     

Biological and integrated control of grey mould of grapevine: results in Italy1

Three experimental trials were carried out in Northern Italy during 1985 and 1986 in order to control grey mould of grapevine (Botrytis cinerea) by using isolates of Trichoderma spp. resistant to several fungicides commonly sprayed against grapevine pathogens, alone or in alternation with benzimidazoles or dicarboximides, in vineyards where fungicide-resistant strains of B. cinerea are frequent. The antagonists alone partially controlled the pathogen on cv. Moscato ?Asti. In one case, the integration of chemical and biological control measures showed slightly better results than for the fungicide alone (for benomyl but not for vinclozolin), but further trials are needed to investigate the full potential for using fungicide-resistant Trichoderma in alternation with fungicides. Trichoderma spp. performed very poorly on cv. Barbera.     

Induced resistance to foliar diseases by soil solarization and Trichoderma harzianum

The effect of soil solarization and Trichoderma harzianum on induced resistance to grey mould (Botrytis cinerea) and powdery mildew (Podosphaera xanthii) was studied. Plants were grown in soils pretreated by solarization, T. harzianum T39 amendment or both, and then their leaves were inoculated with the pathogens. There was a significant reduction in grey mould in cucumber, strawberry, bean and tomato, and of powdery mildew in cucumber, with a stronger reduction when treatments were combined. Bacillus, pseudomonad and actinobacterial communities in the strawberry rhizosphere were affected by the treatments, as revealed by denaturing gradient gel electrophoresis fingerprinting. In tomato, treatments affected the expression of salicylic acid (SA)‐, ethylene (ET)‐ and jasmonic acid (JA)‐responsive genes. With both soil treatments, genes related to SA and ET – PR1a, GluB, CHI9 and Erf1 – were downregulated whereas the JA marker PI2 was upregulated. Following soil treatments and B. cinerea infection, SA‐, ET‐, and JA‐related genes were globally upregulated, except for the LOX genes which were downregulated. Upregulation of the PR genes PR1a, GluB and CHI9 in plants grown in solarized soil revealed a priming effect of this treatment on these genes' expression. The present study demonstrates the capacity of solarization and T. harzianum to systemically induce resistance to foliar diseases in various plants. This may be due to either a direct effect on the plant or an indirect one, via stimulation of beneficial microorganisms in the rhizosphere.     

Chitosan Stimulates Defense Reactions in Grapevine Leaves and Inhibits Development of Botrytis Cinerea

Chitosan (β-1,4-linked glucosamine oligomer) derived from crab shells conferred a high protection of grapevine leaves against grey mould caused by Botrytis cinerea. Under controlled conditions, it was shown to be an efficient elicitor of some defense reactions in grapevine leaves and to inhibit directly the in vitro development of B. cinerea. Treatment of grapevine leaves by chitosan led to marked induction of lipoxygenase (LOX), phenylalanine ammonia-lyase (PAL) and chitinase activities, three markers of plant defense responses. Dose-response curves show that maximum defense reactions (PAL and chitinase activities) and strong reduction of B. cinerea infection were achieved with 75–150 mg l⁻¹ chitosan. However, greater concentrations of chitosan did not protect grapevine leaves with the same efficiency, but inhibited mycelial growth in vitro. Present results underlined the potency of chitosan in inducing some defense responses in grapevine leaves which in turn might improve resistance to grey mould.     

Non‐pathogenic rhizosphere bacteria belonging to the genera Rhizorhapis and Sphingobium provide specific control of lettuce corky root disease caused by species of the same bacterial genera

Lettuce corky root (CR) is caused by bacteria in the genera Rhizorhapis, Sphingobium, Sphingopyxis and Rhizorhabdus of the family Sphingomonadaceae. Members of this family are common rhizosphere bacteria, some pathogenic to lettuce. Sixty‐eight non‐pathogenic isolates of bacteria obtained from lettuce roots were tested for control of CR caused by Rhizorhapis suberifaciens CA1^T and FL1, and Sphingobium mellinum WI4^T. In two initial screenings, 10 isolates significantly reduced CR induced by one or more pathogenic strains on lettuce seedlings in vermiculite, while seven non‐pathogenic isolates provided significant CR control in natural or sterilized field soil. Rhizorhapis suberifaciens FL11 was effective at controlling all pathogenic strains, but most effective against R. suberifaciens CA1^T. The other selected isolates controlled only pathogenic strains belonging to their own genus. In a greenhouse experiment, a soil drench with selected biocontrol agents (R. suberifaciens FL11, Sphingomonas sp. NY3 and S. mellinum CA16) controlled CR better than seed treatments or application of alginate pellets. In microplots infested with R. suberifaciens CA1^T, seed treatment with R. suberifaciens FL11 provided complete control and a soil drench with FL11 significantly reduced the disease. Pathogenicity tests with FL11 on 23 plant species in 10 families resulted in slight yellowing on roots of lettuce and close relatives; similar yellowing appeared on some roots of non‐inoculated lettuce plants. This research showed that biocontrol agents can be genus‐specific. Only one isolate, FL11, provided more general control of various pathogenic strains causing CR even in field soil in pots and microplots.     

A Polymerase Chain Reaction (PCR) Assay for the Detection of Inoculum of Sclerotinia sclerotiorum

The development of a polymerase chain reaction (PCR) assay for the detection of inoculum of the plant pathogenic fungus Sclerotinia sclerotiorum is described. The PCR primers were designed using nuclear ribosomal DNA internal transcribed spacer sequences. Specific detection of DNA from S. sclerotiorum was possible even in the presence of a 40-fold excess of DNA from the closely related fungus Botrytis cinerea. PCR products were obtained from suspensions of untreated S. sclerotiorum ascospores alone, but DNA purification was required for detection in the presence of large numbers of B. cinerea conidiospores. Specific detection of inoculum of S. sclerotiorum was possible in field-based air-samples, using a Burkard spore trap, and from inoculated oilseed rape petals. The assay has potential for incorporation into a risk management system for S. sclerotiorum in oilseed rape crops.     

Passive heat treatment of sweet basil crops suppresses white mould and grey mould

Sweet basil white mould (BWM, Sclerotinia sclerotiorum) and grey mould (BGM, Botrytis cinerea) are important diseases in Israel and other basil‐growing regions. The impact of microclimate on BWM and BGM and on plant sensitivity to these diseases was studied. Disease incidence was evaluated in three field experiments, each consisting of 10–12 polyethylene‐covered tunnels. BWM and BGM incidences were correlated with air temperature, relative humidity (RH) and soil temperature data. The incidence of BWM was negatively correlated with high (above >25 or >30 °C) air temperatures, RH > 50% and RH > 75% and high (>21 or >24 °C) soil temperatures. BGM incidence was negatively correlated with high (>25 °C) air temperatures and high (>21 or >24 °C) soil temperatures, and positively correlated with RH >65% or >75%. Shoots harvested from plants grown in the walk‐in tunnels were inoculated with S. sclerotiorum or B. cinerea under controlled conditions. Severity of BWM and BGM on those shoots was negatively correlated with tunnel air temperatures of >25 and >30 °C and soil temperatures >18 °C. Thus, high temperatures were related to reduced disease incidence and to reduced sensitivity to the pathogens. Experiments involving potted plants revealed that heating only the root zone suppresses canopy susceptibility to BWM and BGM. These findings indicate that the effect of high greenhouse temperatures involves an indirect systemic effect that renders the host less susceptible to disease. This effect was also observed in harvested shoots that were no longer at the high temperatures, and the effect was systemic.