Variations among field isolates of Botrytis cinerea in their sensitivity to antifungal compounds

Seventeen field isolates of Botrytis cinerea were compared by determining their radial growth on synthetic media containing various amounts of 21 antifungal compounds. Twelve of these compounds were fungicides that are recommended for the control of Botrytis infections. There were marked differences between the isolates in their sensitivity to the compounds. Individual isolates displayed high levels of resistance to some of the fungicides, including benomyl, carbendazim, iprodione, thiabendazole, thiophanate-methyl, vinclozolin and zineb. The most potent growth inhibitors were benomyl and carbendazim (ED₉₅ values for most isolates <0.1 μg fungicide ml^?1 media), dichlofluanid, iprodione, nystatin, thiabendazole, thiophanatemethyl and vinclozolin (ED₉₅ values for most isolates < 1.0 μg ml^?1), and captan, chlorothalonil, dicloran and thiram (ED₉₅ values for most isolates < 6.0 μg ml^?1). Zineb was much less potent than the other recommended anti-Botrytis fungicides; it was no more effective than carboxin, dinocap and mancozeb (ED₉₅ values for most isolates > 25 μg ml^?1).     

Laboratory studies on benzimidazole resistance in Septoria tritici1

A technique is described for testing isolates of Septoria tritici from winter wheat for resistance to benzimidazole fungicides. Secondary spores from 23 isolates were tested on Czapek Dox V-8 agar amended with benomyl at 1–10 μg ml. Twenty-one isolates were recovered from eight crops in England in 1984 and two (PBI isolates) were obtained in 1973. Thirteen isolates, including both PBI isolates, were sensitive to benomyl at 1 μg ml^?1 and nine were resistant at 10 μg ml^?1. The remaining isolate had a low proportion (1:3.7 x 10⁴) of resistant spores. The minimum inhibitory concentration for sensitive isolates was 0.2–0.4 μg ml ¹ benomyl and for resistant isolates was more than 1000 μg ml ¹. Benomyl-resistant isolates were cross-resistant to carbendazim, thiabendazole and thiophanate-methyl, but not to 12 other fungicides with different modes of action. The implications of these findings are discussed.     

Characterization of a dicarboximide-fungicide-resistant laboratory isolate ofMonilinia laxa

Monilinia laxa, the incitant of blossom blight in stone fruits in Israel, is sensitive to 5μg/ml of the dicarboximide fungicides vinclozolin and iprodione in the growth medium. When a large number of spores, from an isolate never exposed to these fungicides, was seeded on a medium containing 15 μg/ml iprodione, spontaneous resistant mutants appeared at 10^-5 frequency. These mutants showed cross resistance to the dicarboximide fungicides vinclozolin, procymidone, l-(3,5-dichloro-phenyl)-3-propen(2)-pyrrolidin-2,5-dion (Co 4462), l-(3,5-dichlorophenyl)-3-methoxymethyl-pyrrolidin-2,5-dion (Co 6054), and to dicloran. Growth rate on fungicide-free medium was similar to that of the parental sensitive strain but sporulation was much reduced. Growth rate on media supplemented with dicarboximide fungicides decreased gradually with increasing fungicide concentrations. The resistance has been stable for more than one year in the absence of fungicides. Artificial inoculation of cherry, apricot and plum fruits previously treated with 500 μg/ml vinclozolin, iprodione, procymidone or Co 6054, with a resistant strain, resulted in brown rot; similar treatments provided full protection of the fruits against the sensitive strain.     

Field strains of Stemphylium vesicarium with a resistance to dicarboximide fungicides correlated with changes in a two-component histidine kinase

In Stemphylium vesicarium, four phenotypes were recognized according to their in vitro responses to dicarboximide fungicides: S (sensitive), S₊ (low resistant to iprodione and procymidone but moderately resistant to vinclozolin), R₁ (moderately resistant to iprodione and vinclozolin but highly resistant to procymidone), R₂ (highly resistant to all dicarboximides). Cross-resistance was observed between dicarboximides and aromatic hydrocarbon fungicides in all cases while cross-resistance to phenylpyrroles was only detected in R₂ phenotype. Moreover, no changes were noted in sensitivity to oxidative and osmotic stress inducers. An osmosensing histidine kinase gene, homologous to OS1 from Neurospora crassa, was sequenced from several field isolates of Stemphylium vesicarium. This gene is predicted to encode a 1,329 amino acid protein, comprising a conserved histidine-kinase domain in the C-terminal region and six tandem repeats of about 90 amino acids at the N-terminal end. In S₊ and R₁ phenotype isolates, a single amino acid substitution was observed in the first amino acid repeat; F267L and L290S respectively. For the R₂ isolates, the exchanges T765R or Q777R were located within the histidine-kinase domain.     

The advantage of tbz + iprodione treatment for control of gray mold decay of celery caused by the heterogenic spore population ofBotrytis cinerea in Israel

A combined TBZ — iprodione treatment was more effective in inhibiting growthin vitro ofBotrytis cinerea isolates obtained from decayed celery than either of the fungicides applied separately. This was exhibited for both TBZ-resistant and TBZ-sensitive isolates. TBZ at 500 (μg ml^-1 plus iprodione at 1000 μg ml^-1 reduced celery decay beyond the reduction obtained by each fungicide alone. When applied prior to inoculation, the combined treatment prevented decay by the TBZ-sensitive/iprodione-resistant isolates and reduced initial decay by the TBZ-resistant/iprodione-sensitive isolates to 3–10% of the level without treatment. Under natural infection conditions iprodione showed better decay control than TBZ, and at 1500 μg ml^-1 it reduced initial decay during prolonged storage to 3% of the no-treatment level. Although TBZ (500 μg ml^-1) or iprodione (1000 μg ml^-1) applied separately reduced decay significantly, the combination of lower concentrations of each fungicide was sufficient to eliminate decay development almost totally. The combined treatment also inhibited decay bySclerotinia sclerotiorum, which contributed 3% of the total soft rot in stored celery.     

Resistance to polyoxin AL and other fungicides in Botrytis cinerea collected from sweet basil crops in Israel

A total of 568 B. cinerea isolates were collected from diseased sweet basil plants and the air in 10 sweet basil greenhouses. Mycelial growth tests were used to evaluate the sensitivity of these isolates to benomyl, fenhexamid, iprodione, polyoxin AL and pyrimethanil. EC₅₀ values for polyoxin, the main botryticide on sweet basil in Israel, ranged from 0.4 to 6.5 μg ml^?1 and had a bimodal distribution; the EC₅₀ values for sensitive isolates ranged from 0.4 to 1.5 μg ml^?1 and the EC₅₀ values for low-level resistant isolates ranged from 4 to 6.5 μg ml^?1. Among populations that had not been exposed to polyoxin treatments, 20 to 35 % of the collected isolates were low-level resistant for polyoxin. Polyoxin treatments in an experimental greenhouse shifted the equilibrium in favour of low-level resistant isolates, and the change occurred rapidly: from a frequency of 20 % low-level resistant isolates in the population that had never been treated with polyoxin to a frequency of 72 % after a few treatments over two seasons. Prolonged use of polyoxin in Israeli basil crops (in some sites for more than 10 years) does not appear to have led to the development of high-level resistance, but low-level resistant isolates were found in commercial greenhouses with the frequency of up to 73 %. High-level resistance to benzimidazoles was common (60 to 80 % of isolates) in greenhouses with a history of benzimidazole treatments; whereas 15–25 % of the isolates from greenhouses in which fungicides were not used were resistant. Low-level resistance to dicarboximides was fairly widespread (frequency of 30 to 80 % depending on the greenhouse) and a few cases of moderate resistance to dicarboximides were also noted (frequency of 0 to 9 %). Neither high- nor low-level resistance to anilinopyrimidines was common in sweet basil commercial greenhouses (0 to 7 %). However, 34 % of the isolates were strongly resistant in the experimental greenhouse, following a few treatments with anilinopyrimidine fungicides during the previous season. Before those treatments, the proportion of anilinopyrimidines resistant isolates had been 1 %. About 3 % of the isolates exhibited low-level resistance to fenhexamid and no isolates were found to be strongly resistant to fenhexamid. Low-level resistance to one fungicide was often associated with low-level resistances to other fungicides. Thirty-two phenotypes exhibiting resistance to one or more of the tested fungicides were noted among B. cinerea isolates. Resistant isolates showed similar or reduced fitness parameters in comparison to wild-type isolates.     

Dicarboximide resistance in Botrytis cinerea in protected lettuce

In surveys of protected lettuce crops in the Humberside area of the UK during 1984-5, 47.3% of Botrytis cinerea isolates were resistant to dicarboximides and 25% to benomyl. Dicarboximide-resistant isolates obtained direct from the field had a moderate degree of resistance with ED₅₀ values for mycelial growth on agar of 1.0-2.4 μg/ml vinclozolin for all except two of 30 isolates.
Isolates which were resistant to vinclozolin were also resistant to iprodione, myclozolin and procymidone. Thirty dicarboximide-resistant isolates obtained direct from the field were capable of infecting cucumber cotyledons sprayed with field-strength Ronilan (250 μg/ml vinclozolin) whereas sensitive strains were not. Strains showing different degrees of resistance to dicarboximides developed after incubation of sensitive and resistant strains on agar supplemented with vinclozolin. Some of these strains had ED₅₀ values for mycelial growth on agar of more than 100 μg/ml vinclozolin. No highly resistant isolates were obtained direct from the field. Resistance to dicarboximides in field isolates was stable.     

Resistance profiles of Botrytis cinerea populations to several fungicide classes on greenhouse tomato and strawberry in Lebanon

Tomato and strawberry are the most important protected crops in Lebanon and are seriously affected by grey mould disease, caused by Botrytis cinerea. In the present study, the fungicide sensitivity assays revealed medium to high frequencies of B. cinerea isolates resistant to benzimidazoles, dicarboximides, and anilinopyrimidines on tomato and strawberry. Fludioxonil- and boscalid-resistant mutants were uncommonly found at generally low frequency on both crops. Resistance to fenhexamid was detected in only one site on tomato but in most sites on strawberry with high frequencies, and the occurrence of resistance to QoI fungicides was ascertained on both crops. The majority of the tested isolates (>90%) exhibited multiple fungicide resistance, and isolates resistant to the seven antibotrydial fungicide classes were detected on strawberry in three locations. A high level of resistance was shown by B. cinerea mutants resistant to boscalid, fenhexamid, and QoI fungicides, while two levels of moderate and high resistance to anilinopyrimidines were identified. Genetic analysis revealed point mutations in the target genes commonly associated with resistance in B. cinerea isolates, with all mutants resistant to dicarboximides, fenhexamid, boscalid, and QoI fungicides carrying single-nucleotide polymorphims in BcOS1 (I365S/N, Q369P, and N373S), Erg27 (F412V/I), SdhB (H272R/Y), and cytb (G143A) genes, respectively. The general incorrect use of fungicides has caused the development and spread of fungicide resistance as a widespread phenomenon on protected tomato and strawberry in Lebanon. The implementation of appropriate antiresistance strategies is highly recommended.     

Sensitivity of populations ofBotrytis cinerea to triazoles,benomyl and vinclozolin

Sensitivity of field isolates (121) ofBotrytis cinerea from France (1992), Germany (1979–1992), Israel (1990) and the Netherlands (1970–1989) to the triazoles tebuconazole and triadimenol, the benzimidazole benomyl and the dicarboximide vinclozolin were tested in radial growth experiments. Resistance to benomyl (in 21 to 100% of isolates tested) and vinclozolin (in 25 to 71% of isolates tested) was common in most countries. EC₅₀s (concentrations of fungicides inhibiting radial mycelial growth ofB. cinerea on B5-agar by 50%) for tebuconazole and triadimenol ranged between 0.01–1.64 and 0.4–32.6g ml^–1, respectively, and were log-normally distributed. The variation factor (ratio between EC₅₀s of the least and most sensitive isolate tested) amounts 164 and 82 for tebuconazole and triadimenol, respectively. These values are comparable to those for azole fungicides applied in control of other pathogens. Hence, variation in sensitivity to triazoles can probably not explain limited field performance of triazoles towardsB. cinerea. Isolates from south west Germany (1992) were significantly less sensitive to tebuconazole than isolates collected earlier in Germany, Israel and the Netherlands. Such less sensitive populations may contribute to the limited field performance of DMI fungicides towardsB. cinerea. The sensitivity of isolates from south west Germany to tebuconazole was similar to that of DMI-resistant mutants generated in the laboratory. These mutants displayed stable resistance with Q-values (ratio between EC₅₀ of resistant mutant and wild type isolate) between 5 and 20. Sensitivity of field isolates and laboratory mutants to tebuconazole and triadimenol was correlated.     

Effects of certain herbicides on the fate of sporangiospores of Mucor piriformis and conidia of Botrytis cinerea and Penicillium expansum

The effects of several herbicides used in pome fruit orchards on the germination of spores and growth of mycelia of Botrytis cinerea, Mucor piriformis and Penicillium expansum in vitro and the survival of propagules of these fungi in soil were studied. Diuron in agar at 4–128 μg ml^?1 reduced germination of spores of B. cinerea and M. piriformis, and 2,4-D and paraquat at 32 μg ml^?1 similarly affected B. cinerea and P. expansum. Several herbicides at 128 μg ml^?1 in agar reduced growth of B. cinerea and M. piriformis but were ineffective against P. expansum. Propagule survival levels of the three fungi generally were lower in both autoclaved and non-autoclaved soil amended with herbicides than in non-amended soil. This effect was greatest in non-autoclaved soil, suggesting involvement of microbial antagonists. The most effective herbicides for reduction of fungal propagules in soil were 2,4-D, diuron, and paraquat.     

Effect of chlorothalonil on resistance of Botrytis cinerea to dicarboximides in cucumber glasshouses1

Failures to control grey mould by dicarboximides on winter-grown cucumbers in glasshouses in Israel were attributed to the development of resistance to these fungicides in populations of Botrytis cinerea. A survey of 18 glasshouses in the winter of 1983-84 revealed that resistance is widespread where dicarboximides have been used extensively. During the summer, resistant B. cinerea populations often shift back to sensitivity; however, following few dicarboximide sprays in the subsequent winter, resistant strains reappear, increase rapidly and become dominant in the pathogen population. In two out of three glasshouse experiments, combination of chlorothalonil and dicarboximides in spray programmes slowed down the increase of resistant strains, whereas in a third experiment such a programme had no effect. The usefulness of chlorothalonil in fungicide-alternation programme to suppress dicarboximide resistance is dicussed in relation to the fitness properties of established versus newly-appearing resistant mutants.     

灰葡萄孢多药抗性菌株的筛选和鉴定

从浙江杭州市售草莓上分离得到83个灰葡萄孢菌株,测定了这些菌株对苯醚菌酯、多菌灵和异菌脲的敏感性,筛选出对这3种药剂同时产生了抗性的两个菌株HZ021和HZ054,其在马铃薯葡萄糖琼脂(PDA)平板上的菌丝生长和产孢量与敏感菌株相比无显著差异,在黄瓜叶片上均表现出很强的致病力。结果表明,HZ021和HZ 054有很高的适合度。通过对抗性菌株中细胞色素b (CYT b)、双组份组氨酸激酶(OS-1)和β-微管蛋白(TUB 2)基因序列进行分析发现,HZ021和HZ054对多种药剂的抗性是由于其药剂靶标基因上的点突变所致。     

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.     

Multiple resistance of Botrytis cinerea from kiwifruit to SDHIs,QoIs and fungicides of other chemical groups

BACKGROUND: Botrytis cinerea Pers.: Fr. is a high‐risk pathogen for fungicide resistance development that has caused resistance problems on many crops throughout the world. This study investigated the fungicide sensitivity profile of isolates from kiwifruits originating from three Greek locations with different fungicide use histories. Sensitivity was measured by in vitro fungitoxicity tests on artificial nutrient media. RESULTS: Seventy‐six single‐spore isolates were tested for sensitivity to the SDHI fungicide boscalid, the QoI pyraclostrobin, the anilinopyrimidine cyprodinil, the hydroxyanilide fenhexamid, the phenylpyrrole fludioxonil, the dicarboxamide iprodione and the benzimidazole carbendazim. All isolates from Thessaloniki showed resistance to both boscalid and pyraclostrobin, while in the other two locations the fungal population was sensitive to these two fungicides. Sensitive isolates showed EC₅₀ values to boscalid and pyraclostrobin ranging from 0.9 to 5.2 and from 0.04 to 0.14 mg L^?1 respectively, while the resistant isolates showed EC₅₀ values higher than 50 mg L^?1 for boscalid and from 16 to > 50 mg L^?1 for pyraclostrobin. All QoI‐resistant isolates carried the G143A mutation in cytb. Sensitivity determinations to the remaining fungicides revealed in total eight resistance phenotypes. No isolates were resistant to the fungicides fenhexamid and fludioxonil. CONCLUSION: This is the first report of B. cinerea field isolates with resistance to both boscalid and pyraclostrobin, and it strongly suggests that there may be a major problem in controlling this important pathogen on kiwifruit. Copyright © 2010 Society of Chemical Industry     

Impact of fludioxonil resistance on fitness and cross-resistance profiles of Altrenaria solani laboratory mutants

Sensitivity and inherent resistance risk of Alternaria solani to fludioxonil, cross-resistance profiles and the potential implications of resistance mutations on fitness parameters were investigated. Fludioxonil was highly effective against a wild type A. solani field strain both in vitro (EC₅₀?=?0.05 μg/mL) and in preventive applications on artificially inoculated tomato fruit. Mutants with low [Resistance factor (Rf): 15 based on EC₅₀], medium (Rf: 150–300) and high (Rf: > 1000) levels of phenylpyrrole resistance were isolated from the wild type strain at high frequencies following mutagenesis with UV irradiation and selection on fludioxonil containing medium. Resistant isolates retained their resistance levels even after 9 subcultures on fungicide-free growth medium while they could express their resistant phenotypes in planta. Investigation of cross-resistance relationships showed that fludioxonil resistance mutations also reduce the sensitivity of mutant strains to the aromatic hydrocarbon fungicide quintozene as well as the dicarboximides iprodione and vinclozolin. No cross-resistance was observed between fludioxonil and fungicides with different modes of action such as the sterol biosynthesis inhibitors (DMIs) imazalil and flusilazole and the carboxamide boscalid. All fludioxonil resistant isolates were more sensitive to the anilinopyrimidine pyrimethanil, while only two isolates were less sensitive to the QoI pyraclostrobin compared to the wild-type strain. Study of fitness determining parameters showed that resistance mutation(s) had no adverse effects on mycelial growth, conidial germination and sensitivity to osmotic stress while they had a pleiotropic effect on virulence and conidia production in resistant mutants. Results of the present study indicate that fludioxonil is a highly effective fungicide against A. solani, while the risk of resistance development to this fungicide is considered to be medium making fludioxonil an ideal alternative to high risk fungicides such as boscalid and pyraclostrobin whose performance against early blight has already been compromised by resistance development.

     

Evolution of resistance to different classes of fungicides in <Emphasis Type="Italic">Botrytis cinerea</Emphasis> from greenhouse vegetables in eastern China

Between 2003 and 2005, 337 isolates of Botrytis cinerea collected from greenhouse vegetables were characterized for resistance to fungicides. A low level of chlorothalonil resistance was detected and in these resistant isolates there was cross-resistance to captan and thiram. To the best of our knowledge, this is the first report of chlorothalonil resistance in B. cinerea from vegetables in China. The sub-population of B. cinerea highly resistant to benzimidazoles developed quickly during the years 2003 to 2005. Rapid spread of double resistance to benzimidazoles and diethofencarb was also observed. Resistance to dicarboximides was of low-level character and no highly resistant isolates were detected. In contrast, emergence of resistance to pyrimethanil, the only anilinopyrimidine fungicide used in China at present, was detected in 2003 just 3 years after pyrimethanil introduction. Pyrimethanil-resistant isolates demonstrated fitness comparable with that of wild sensitive isolates. These results suggest that pyrimethanil has a high risk of leading to resistance development in B. cinerea in greenhouse vegetables.     

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.     

Detection of resistance to sterol demethylation-inhibiting (DMI) fungicides in<Emphasis Type="Italic">Cercospora beticola</Emphasis> and efficacy of control of resistant and sensitive strains with flutriafol

Single-lesion isolates ofCercospora beticola (n=150) were collected in 1998 from sugar beet fields in the area of Serres, N. Greece. In this area, sterol demethylation-inhibiting (DMI) fungicides have been used for almost 20 years to control sugar beet leaf spot. The sensitivity of these isolates to the DMI fungicides flutriafol and difenoconazole (EC₅₀ values) was determined on the basis of inhibition of mycelial growth at several fungicide concentrations. The relative growth (RG) of isolates was correlated at all tested concentrations with the respective EC₅₀ values, indicating that RG provides a reliable estimate for the sensitivity of the isolates. The highest correlation coefficients were obtained for concentrations of 1 μg ml⁻¹ flutriafol and of 0.05 μg ml⁻¹ difenoconazole, respectively. Consequently, they are proposed for monitoring of DMI sensitivity inC. beticola populations, as single discriminatory concentrations in a simplified test method. Based on the RG values at the discriminatory concentration of 1 μg ml⁻¹ flutriafol,C. beticola isolates were classified as either resistant or sensitive. The efficacy of flutriafol, applied at the commercially recommended dose, in controlling Cercospora leaf spot was examined in field experiments conducted during 1999 and 2000. Disease incidence in plots artificially inoculated with resistant isolates and treated with flutriafol was significantly higher than in similar plots inoculated with sensitive strains. These results suggest that poor disease control after application of flutriafol may be based on the presence of resistant strains within the pathogen population in northern Greece. This emphasizes the risk of the development of practical resistance if there is increased frequency of such strains within the population. http://www.phytoparasitica.org posting July 13, 2003.     

Survival of dicarboximide-resistant strains ofBotrytis cinerea in plant debris during summer in Israel

Survival- ofBotrytis cinerea was monitored during two summer seasons. Mycelium and conidia were found dead on the surface of plant debris within 2 months of incubation, whereas a high level of viability was detected in thallus of the pathogen which was 1–2 mm inside the dry host tissue. Of the 148 samples of infected senescing cucumber female fruits, 8% survived seven warm months; half of these isolates ofB. cinerea were resistant to dicarboximides (5 (μ/ml iprodione). Of the stems of cucumber infected withB. cinerea in winter, 18% yielded the pathogen at the beginning of the following winter; 15% of the surviving isolates were resistant to dicarboximides. Cucumber seedlings artificially infected byB. cinerea did not yield the pathogen longer than 9 weeks after establishment of infection, even when incubated in the shade. Plant debris with symptoms of gray mold were kept in the shade during the summer; at the beginning of winter it was possible to establish infection ofB. cinerea from the dry debris.     

Fungicide resistance in diseases of vegetables growing under plastic in Crete1

Serious fungicide resistance problems have been encountered in several major vegetable pathogens in glasshouses in Crete. Botrytis cinerea populations are now widely resistant to either or both benzimidazoles and dicarboximides. Pseudoperonospora cubensis very rapidly became resistant to metalaxyl, with cross resistance to other acylalanines. Didymella bryoniae has shown some benzimidazolc resistance. Sphaerotheca fuliginea, against which a great diversity of fungicides is used, has mostly not given problems. However, strains with resistance to benomyl, triforine and ditalimfos have been found in experimental plots. Ways of managing resistance in Crete are discussed.