In vitro Selection of Strains of Phytophthora cactorum Resistant to Metalaxyl

Isolates of Phytophthora cactorum resistant to the systemic fungicide metalaxyl were obtained by exposing them to sequentially increased concentrations of metalaxyl. A linear relationship was observed between the concentrations of metalaxyl and percentage inhibition of mycelial growth of P. cactorum. The stability of metalaxyl-resistant isolates 150R and 250R was confirmed after six serial transfers on corn meal agar without fungicide. The in vitro metalaxyl-resistant isolate (Ph10) was less aggressive on apple rootstocks compared with the Ph07 isolated from metalaxyl-treated trees and the Ph03 isolated from untreated trees. Metalaxyl-resistant and sensitive isolates remained sensitive to the chemically unrelated fungicide fosetyl-Al at high concentration (600 μg/ml), to mancozeb, and to a mixture of metalaxyl + mancozeb. Significant differences in resistance to metalaxyl existed among P. cactorum field isolates.     

Evaluation of fungicides to control potato late blight (Phytophthora infestans) in the plains of Nepal

Fungicide application is an effective management option to control late blight of potato (caused by Phytophthora infestans). Field experiments were conducted to evaluate the efficacy of recently introduced and previously used fungicides on late blight management and potato yields in the western plains of Nepal in 2015 and 2016 crop seasons. Fungicides and a non-treated control (NTC) were replicated three times in a randomized block design planted with late blight susceptible cultivar Cardinal. Chlorothalonil, copper oxychloride, dimethomorph, fenamidone + mancozeb, mancozeb and metalaxyl were sprayed in 2015. In 2016, carbendazim was used instead of chlorothalonil. The area under disease progress curve (AUDPC) was consistently reduced in years by dimethomorph (90% and 65% in 2015 and 2016, respectively), fenamidone + mancozeb (68% and 62%) and mancozeb (40% and 47%) compared with the NTC. Similarly, tuber yield was increased with the application of dimethomorph (266% and 146% in 2015 and 2016, respectively), fenamidone + mancozeb (211% and 155%) and mancozeb (136% and 116%) compared with the NTC. Chlorothalonil reduced AUDPC by 43% and increased tuber yield by 170% in 2015. Other fungicides either had inconsistent results or did not reduce late blight severity and consequent effects on potato yield. The overall benefit–cost ratio was highest for dimethomorph in both years. These results show efficacy of dimethomorph, fenamidone + mancozeb and mancozeb in reducing late blight severity and increasing potato tuber yield in the plains of Nepal.     

Effects in vitro of nine fungicides on growth of entomopathogenic fungi

The effects of nine fungicides were evaluated in vitro on the entomopathogenic fungi Beauveria bassiana, Conidiobolus coronatus, C. thromboides, Metarhizium anisopliae, Paecilomyces farinosus, P. fumosoroseus, Scopulariopsis brevicaulis and Verticillium lecanii. The susceptibility of the fungi to the fungicides varied. The dithiocarbamate derivations zineb + copper oxychloride, and mancozeb completely inhibited germination of C. coronatus, C. thromboides, B. bassiana, P. farinosus, M. anisopliae and V. lecanii. The fungicides triadimefon, copper oxychloride, metalaxyl, sulfur, sulfur + nitrothal‐isopropyl and hymexazol exhibited various effects on the fungi. Usually, fungistasis was more pronounced at 15°C than at 25°C and the inhibitory effects were in direct proportion to the dosage of active ingredient (recommended field rate, 10‐fold higher and 10‐fold lower). In a few combinations, fungi partially overcame or even recovered from the initial inhibition of growth which might have resulted from delayed germination. In other cases, inhibition of growth occurred only after a delay and its intensity increased with time. Stimulation of fungal growth when it occurred was rarely permanent. Generally, adverse effects were much greater against the entomophthoraleans C. coronatus and C. thromboides than against the Hyphomycetes. Extrapolation of the results to practice and to the field situation is difficult. Nevertheless, the data presented give an idea of possible side‐effects in nature.     

Effects of Selected Fungicides and the Timing of Fungicide Application on Beauveria bassiana-Induced Mortality of the Colorado Potato Beetle (Coleoptera: Chrysomelidae)

Four fungicides used for controlling foliar diseases of potato (Solanum tuberosum) were evaluated under field and laboratory conditions for their effects on the infectivity and sporulation of Beauveria bassiana when used as a control for the Colorado potato beetle, Leptinotarsa decemlineata (CPB). We investigated the direct effects of fungicides on B. bassiana-induced CPB mortality and the effect of time between fungicide and B. bassiana application. Effects of fungicide on conidial survival in the soil and on foliage were examined in the field. Significantly more larval mortality was observed when larvae were sprayed with B. bassiana than with the water control. Fungicide had no significant effect on larval mortality in the field. In the laboratory, survival of larvae was significantly lower among larvae fed fungicide-treated foliage. B. bassiana-induced mortality in the laboratory was observed only when larvae were fed foliage treated with copper hydroxide or water. Larvae fed mancozeb- or chlorothalonil-treated foliage experienced high mortality regardless of B. bassiana treatment. While there was no significant effect of fungicide on B. bassiana sporulation on cadavers in the field, a pattern emerged that indicated higher proportions of cadavers producing conidia in plots sprayed with water or copper hydroxide than in plots sprayed with chlorothalonil or mancozeb. Survival of B. bassiana conidia in the soil and on foliage was significantly greater in plots treated with copper hydroxide or water than in plots treated with mancozeb or chlorothalonil. Fungicides such as copper hydroxide may be less deleterious to the fungus than mancozeb and chlorothalonil.     

Reduced sensitivity of tomato early blight pathogen (Alternaria solani) isolates to protectant fungicides,and implication on disease control

The sensitivity of Alternaria solani isolates to the fungicides mancozeb and chlorothalonil was evaluated, to determine if inadequate disease management by these fungicides could be attributed to reduced sensitivity of A. solani isolates to these fungicides. The sensitivity of 60 isolates of A. solani was assessed using the inhibition of radial mycelial growth (RG) method, using fungicide concentrations of 0, 1.0, 10, 100, 500 and 1000 μg a.i ml^?1 medium. EC₅₀ was calculated for each isolate and fungicide combination. The EC₅₀ values of different A. solani isolates to mancozeb ranged from 9.05 to 712.65 μg ml^?1. EC₅₀ values of different isolates to chlorothalonil ranged from 4.25 to 849.4 μg ml^?1. The percentage of isolates with reduced sensitivity was 46.7 and 53.3% for mancozeb and chlorothalonil, respectively. Results of the in vivo tests demonstrated decline in disease control by the two fungicides with the reduced-sensitivity isolates compared to the sensitive ones.     

Characterization of Beauveria bassiana and Metarhizium anisopliae isolates for management of tarnished plant bug,Lygus lineolaris (Hemiptera: Miridae)

Selected morphological and physiological characteristics of four Beauveria bassiana (Balsamo) Vuillemin isolates and one Metarhizium anisopliae (Metschnikoff) Sorokin isolate, which are highly pathogenic to Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), were determined. There were significant differences in conidial size, viability, spore production, speed of germination, relative hyphal growth, and temperature sensitivity. Spore viability after incubation for 24h at 20 degrees C ranged from 91.4 to 98.6% for the five isolates tested. Spore production on quarter-strength Sabouraud dextrose agar plus 0.25% (w/v) yeast extract after 10 days incubation at 20 degrees C ranged from 1.6x10(6) to 15.5x10(6)conidia/cm(2). One B. bassiana isolate (ARSEF 1394) produced significantly more conidia than the others. Spore germination was temperature-dependant for both B. bassiana and M. anisopliae. The time required for 50% germination (TG(50)) ranged from 25.0 to 30.9, 14.0 to 16.6, and 14.8 to 18.0h at 15, 22, and 28 degrees C, respectively. Only the M. anisopliae isolate (ARSEF 3540) had significant spore germination at 35 degrees C with a TG(50) of 11.8h. A destructive sampling method was used to measure the relative hyphal growth rate among isolates. Exposure to high temperature (40-50 degrees C) for 10min had a negative effect on conidial viability. The importance of these characteristics in selecting fungal isolates for management of L. lineolaris is discussed.     

Leaf Disc Inoculation, a Fast and Precise Test for the Screening of Metalaxyl Tolerance in Sunflower Downy Mildew

A new method, based on leaf disc inoculation, was developed for the screening of metalaxyl tolerance in field isolates of Plasmopara halstedii . High-pressure liquid chromatography (HPLC) was used to determine the fungicide concentration in the inoculation medium and in the incubated leaf tissue over the test period. These measurements revealed that the fungicide concentration inside the leaf tissue within 24 h had adjusted to the concentration in the outer medium and remained constant for the time of cultivation over a period of more than 11 days. In contrast to whole seedling tests with application of the fungicide via seed dressing, the leaf disc method allows precise quantification of the effective fungicide concentration at the site of infection and is less space and time consuming. Metalaxyl tolerance of P. halstedii isolates was gradually determined according to the sporulation of the pathogen on sunflower leaf discs in the presence of increasing fungicide concentrations. Isolates collected in South Germany showed no tolerance and sporulation was prohibited when tests were carried out at 0.02  μ g (a.i.)/ml of metalaxyl or more. In contrast, a tolerant French isolate developed sporangia on leaf discs incubated in a metalaxyl solution of 100  μ g (a.i.)/ml.     

Potential of some Metarhizium anisopliae isolates for control of Culex quinquefasciatus (Dipt., Culicidae)

Abstract: The potential of some isolates of Metarhizium anisopliae and Beauveria bassiana for use in the integrated management of Culex quinquefasciatus was evaluated. Metarhizium anisopliae isolate 1037 was selected in initial bioassays with a 50% lethal concentration (LC₅₀) of 1.97 × 10⁴ conidia/ml. This fungus caused higher mosquito larva mortality when applied as a conidial suspension to the surface of the water than as dry conidia, with a time to 50% lethal (LT₅₀) of 1 day compared with 3.6 days for the dry conidial application. However, results with UV- and heat-inactivated conidia did not confirm a possible role of fungal toxins in causing mortality when ingested by C. quinquefasciatus larvae. Metarhizium anisopliae did not remain active for as long as the bacterium Bacillus sphaericus isolate 2362. At 24 h after application, the fungus-induced mortality on mosquito larvae was significantly lower than the mortality caused by the bacterium. By the second day, almost no activity by the fungus was observed. Results suggest that M. anisopliae isolate 1037 has potential for use in mosquito control programmes.     

Management of entomopathogenic fungi in cultures of Tenebrio molitor (Coleoptera: Tenebrionidae)

Larvae of mealworms Tenebrio molitor L. (Coleoptera: Tenebrionidae) have been used as animal feed, but fungal pathogens rapidly downsize the populations, resulting in economic losses. In this work, we established an effective management strategy for fungal pathogens. An entomopathogenic fungus, Beauveria bassiana, was isolated from mealworm cadavers. The bioassay of some isolates of this species at >90% relative humidity revealed that the ERL1575 isolate had the highest virulence. At 20–30% RH, ERL1575 conidia when ingested produced 80% mortality but when sprayed topically produced only <10% mortality. Mealworms that had ingested conidia were exposed to 20, 25, 30 and 35°C and high humidity (>95%) for 5 days. This experiment produced about 90% mortality except at 35°C where mortality was <20%. When 40 fungicides were assayed against ERL1575, fluazinam (1000‐fold) and mancozeb (667‐fold) significantly inhibited conidial germination and/or hyphal growth. When fluazinam and mancozeb were added to the mealworm diet of conidia‐inoculated wheat bran, most were alive 3 days post application. However, 100% mortality resulted 3 days post application in the conidia‐inoculated wheat bran without any fungicides. In conclusion, B. bassiana isolates are pathogenic at <30°C when they are ingested by mealworms but fluazinam and mancozeb can be used for management to control the pathogen in their cultures.     

Comparative impact of artificial selection for fungicide resistance on Beauveria bassiana and Metarhizium brunneum

Hypocreales fungi such as Beauveria bassiana (Balsamo) Vuillemin and Metarhizium brunneum Petch can be negatively affected by fungicides thereby reducing their biocontrol potential. In a previous study, we demonstrated enhanced fungicide resistance in B. bassiana through artificial selection. However, it is not clear if the enhanced resistance was because of improved germination, vegetative growth, or both. Additionally, the enhanced fungicide resistance has only been demonstrated in B. bassiana, and therefore it is of interest to investigate the potential to enhance resistance in other fungi. Thus, the objectives in this study were to determine the potential to enhance fungicide resistance in M. brunneum through artificial selection, and investigate if selection is based on germination, vegetative growth, or both in B. bassiana and M. brunneum. Selection for resistance to fenbuconazole, and triphenyltin hydroxide was assessed through inhibition evaluations on solid media, and germination and mycelial growth in liquid media. Increased resistance after selection was observed for all fungicide-fungus combinations on solid and or liquid media. Selection resulted in increased resistance to fenbuconazole in both fungi in solid and liquid media; in liquid culture fungicide resistance in B. bassiana was manifested by increased germination and mycelial growth, whereas in M. brunneum fungicide resistance concerned only mycelial growth. Selection for resistance to triphenyltin hydroxide varied in the different media. For B. bassiana, triphenyltin hydroxide resistance was enhanced on solid media but not in liquid, whereas enhanced resistance of M. brunneum was detected in both media. Fungicide sensitivity and selection potential differs based on the medium and fungal species. Selection for fungicide resistance, had negative effects on other beneficial traits when fungicide pressure was removed, for example, some selected populations showed decreased germination or growth, relative to their nonselected control populations. Additionally, reduced virulence to the greater wax moth, Galleria mellonella (L.), was observed in all fungal populations that were exposed to fungicide resistance regimes. We conclude that it is possible to use genetic selection to enhance fungicide resistance in B. bassiana and M. brunneum, but before use the resulting populations should be screened for inadvertent negative impacts on beneficial traits.     

Insecticidal and antifeedant activities of proteins secreted by entomopathogenic fungi against Spodoptera littoralis (Lep., Noctuidae)

Abstract:  Entomopathogenic fungi are a poorly exploited source of insecticidal proteins, which may be used for the development of new natural insecticides and as alternative molecules for transgenic deployment. The crude soluble protein extracts in Adamek's liquid medium of 25 fungal isolates belonging to the fungal species Metarhizum anisopliae , Beauveria bassiana , Beauveria brongniartii and Scopulariopsis brevicaulis were screened by per os toxicity on Spodoptera littoralis larvae. Whilst extracts from two M. anisopliae and two B. bassiana isolates gave significant mortalities when applied either on alfalfa leaf discs or incorporated into artificial diet, the one from M. anisopliae 01/58-Su isolate was the only most toxic that showed promise for S. littoralis control. In leaf disc assays, this extract exhibited strong dose-related toxic and antifeedant activity against the larvae. At 10, 20 and 40  μ g protein/insect, the extract gave 61.3%, 96.6% and 100.0% mortality, respectively, and average survival time of 5.7, 4.3 and 3.1 days respectively. Not only the antifeeding index was dose-related, but it significantly increased over time in a dose-related manner. Longer exposure times led to a dose-related significant increase in larval mortality. The exposure times for 50% mortality were 91.3 h and 62.1 h for 20 and 40  μ g protein/insect respectively. The crude extract when exposed to higher temperature or protease treatment lost toxicity, indicating that toxicity was protein mediated. In addition, the liquid medium composition did not influence its insecticidal activity. The effects of the protein extract on midgut cells of second instar larvae of S. littoralis were investigated by using both light and electron microscopy. A progressive bleeding of the midgut epithelium into the gut lumen was observed along with lysis of the epithelium and deterioration of the microvilli.     

Evaluation of fungicides on Indian isolates of Phytophthora colocasiae causing leaf blight of taro

Leaf blight caused by Phytophthora colocasiae is the most destructive disease affecting taro (Colocasia esculenta) worldwide including India. Fungicides (primarily metalaxyl) remain as an important strategy to manage taro leaf blight in India over decades. It is important to monitor isolate sensitivity to identify build-up of fungicide resistance and thereby modify fungicide usage strategies. P. colocasiae isolates representing four different geographical regions of India were evaluated for their sensitivity to metalaxyl and three other commercially available fungicides viz. Samarth, Biofight and Akoton by poisoned media technique. All the isolates tested were sensitive to metalaxyl, nevertheless there is an increase in the effective concentration compared to the previous reports. Among the other fungicides, Samarth was found to be superior in completely inhibiting mycelial growth at 0.05% followed by Biofight at 1%. Metalaxyl and Akoton^® shared a common inhibitory concentration at 2%. The most effective fungicide determined by the in vitro method was evaluated in vivo for studying the pattern of inhibition before and after the disease development in detached taro leaf. The results of the study revealed that build-up on metalaxyl resistance in P. colocasiae is in its course and caution should be taken while administering against taro leaf blight. Fungicide Samarth could be used as an alternative to metalaxyl for management of taro leaf blight.     

The potential for enhanced fungicide resistance in Beauveria bassiana through strain discovery and artificial selection

Our objectives were to determine the (1) natural variation in fungicide resistance among Beauveria bassiana strains, (2) potential to increase fungicide resistance in B. bassiana through artificial selection, and (3) stability of virulence in selected B. bassiana strains. Fungicides included dodine, fenbuconazole, and triphenyltin hydroxide, which are commonly used in pecan and other horticultural crops. Comparison of seven B. bassiana strains indicated some are substantially more resistant to fungicides than others; a commercial strain (GHA) was less resistant than all wild strains isolated from pecan orchards. Artificial selection resulted in enhanced fungicide resistance in the GHA strain but not in a mixed wild strain. Removal of selection pressure for three passages did not reduce the enhanced fungicide resistance. Sub-culturing with exposure to fungicides did not affect the GHA strain's virulence to pecan weevil, Curculio caryae, larvae, whereas fungicide exposure increased virulence in a mixed wild population of B. bassiana.     

The effect of fungicides, irrigation and plant density on the development of Peronospora sparsa, the cause of downy mildew in rose and blackberry

Downy mildew of rose (Rosa spp.) and blackberry (Rubus fructicosus), caused by Peronospora sparsa, can cause significant losses in production. In a series of experiments, fungicides with different modes of action to the commonly used phenylamide‐based products were examined for efficacy on both crops. Cymoxanil + mancozeb + oxadixyl and fluazinam gave good downy mildew control on both rose and blackberry. On outdoor, container‐grown rose, high volume sprays of fosetyl‐aluminium were also effective, but on young micropropagated blackberry plants, application as a drench treatment was better than as a spray. Good control was also achieved on blackberry with chlorothalonil and with metalaxyl in formulation with either thiram or mancozeb. There was no evidence of loss of control with phenylamide fungicides due to resistance. Irrigation regimes were also examined on blackberry and sub‐irrigation of plants in propagation on a sand bed led to significantly lower disease levels than those found where plants had been irrigated by overhead sprinklers. Reducing the density of container‐grown rose plants had a measurable effect on the progress of downy mildew, though this was small and temporary when compared with the effect of fungicide treatment. Fungicide programmes which gave season‐long control of rose downy mildew resulted in significantly improved extension growth.     

Disease Development and Buildup of Resistance to Oxadixyl in Potato Crops Inoculated with Phytophthora infestans as Affected by Oxadixyl and Oxadixyl Mixtures: Experimental and Simulation Studies

Simulator predictions for the effect of oxadixyl and oxadixyl mixtures on the control of late blight in potato crops inoculated with Phytophthora infestans and the buildup of fungal resistance to oxadixyl were compared with data obtained in field experiments. The simulator, which considered fungus, fungicides and crop variables, predicted accurately the effect of fungicide sprays (oxadixyl, oxadixyl mixed with mancozeb, and oxadixyl mixed with mancozeb and cymoxanil) on blight development. The model predicted accurately both resistance buildup and infection in non-treated crops and in crops treated with oxadixyl alone or in a mixture with mancozeb (SAN 518F), but overestimated the control efficacy of the three-way mixture Pulsan.     

Deleterious effect of soil‐applied metalaxyl and mancozeb on the mycoparasite Pythium oligandrum

Pythium oligandrum was recovered, identified and quantified from air‐dried soil plated on 1.5% water agar containing 0.1% glucose. Isolations of P. oligandrum over 2 years from soils treated with single applications of metalaxyl plus mancozeb were consistently lower than those from untreated soil from the same fields. In three fields in the first year P. oligandrum was reduced from a range of 43.3–115.0 to 17.0–43.2 isolates g^‐1 soil. In the second year, results from 11 fields showed reductions from 27.8–141.8 to 2.8–44.5 isolates g^‐1 soil. P. oligandrum was sensitive to both metalaxyl and mancozeb, with median effective dose (ED₅₀) values of 0.13 ± 0.02 μg m^‐1 and 3.33 ± 0.12 μg ml^‐1, respectively. In a pot test with three soils treated with metalaxyl, mancozeb or the combination of fungicides, levels of P. oligandrum declined over 3 months, with effects first recorded 2 weeks after treatment. Levels of P. oligandrum were reducd by differing degrees in the three soils. Isolate counts from untreated soils declined from a mean of 58.0 g^‐1 soil at the start of the experiment to 27.5 g^‐1 after 3 months, whereas fungicide treatments caused further reductions to 11.1 (metalaxyl), 9.7 (mancozeb) and 4.8 isolates g^‐1 (metalaxyl plus mancozeb).     

Activity of Ten Fungicides against Phytophthora capsici Isolates Resistant to Metalaxyl

Pepper Phytophthora blight (PPB), caused by Phytophthora capsici, is an important disease of pepper in China. The extensive application of metalaxyl has resulted in widespread resistance to this fungicide in field. This study has evaluated the activities of several fungicides against the mycelial growth and sporangium germination of metalaxyl‐sensitive and metalaxyl‐resistant P. capsici isolates by determination of EC₅₀ values. The results showed that the novel carboxylic acid amide (CAA) fungicide mandipropamid exhibited excellent inhibitory activity against PPB both in vitro and in vivo, with averagely EC₅₀ values of 0.075 and 0.004 μg/ml in mycelial growth and sporangium germination, respectively, and over 88% efficacy in controlling PPB. The other three CAA fungicides also provided over 70% efficacy in controlling PPB. The mycelial growth was less sensitive to quinone outside inhibitor (QoI) fungicides azoxystrobin and trifloxystrobin than that of sporangium germination in P. capsici isolates. However, azoxystrobin and trifloxystrobin provided over 80% efficacy in controlling PPB. It was noted that propamocarb and cymoxanil did not exhibit activity against the mycelial growth or sporangium germination of P. capsici isolates in the in vitro tests, with over 70% efficacy in controlling PPB. The new fungicide mixture 62.5 g/l fluopicolide + 625 g/l propamocarb (trade name infinito, 687.5 g/l suspension concentrate (SC)) produced over 88% efficacy in controlling PPB caused by both metalaxyl‐sensitive and metalaxyl‐resistant isolates. The data of this study also proved that there was obviously no cross‐resistance between metalaxyl and the other tested fungicides. Therefore, these fungicides should be good alternatives to metalaxyl for the control of PPB and management of metalaxyl resistance.     

Pathogenicity of Beauveria bassiana,Metarhizium anisopliae (Deuteromycotina: Hyphomycetes), and other entomopathogenic fungi against Lygus lineolaris (Hemiptera: Miridae)

The pathogenicity of 32 fungal isolates from the genera of Beauveria, Verticillium, Paecilomyces, Metarhizium, Mariannaea, and Hirsutella to second-instar tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was tested under laboratory conditions. These isolates originated from various insect hosts and substrates from France, Denmark, Austria, Italy, Turkey, Syria, and the United States. A single exposure concentration (1 x 10(7) conidia/ ml) assay for each isolate was first conducted by immersing the insects in 10 ml of a fungal suspension for 5s. These were followed by concentration-mortality assays on five of the most pathogenic isolates using four test concentrations ranging from 2 x 10(4) to 2 x 10(7) conidia/ml. B. bassiana 726 (Bemisia-passaged GHA strain) was used as a standard for comparison in all of the assays. Among the test isolates, three produced mortality not significantly different from the water control. Mortality ranged from 35 to 98% among the other 29 isolates. The LC50 values of the five most pathogenic isolates ranged from 0.8 to 5.0 x 10(5) conidia/ml. The LT50 values for these isolates ranged from 6.0 to 6.9, 3.1 to 5.1, and 2.5 to 4.0 d for concentrations of 2 x 10(5), 2 x 10(6), and 2 x 10(7) conidia/ml, respectively. Two strains of B. bassiana (ARSEF 1394,5665) and one M anisopliae (ARSEF 3540) were more pathogenic to the nymphs than the standard, having significantly lower LC50 and LT50, values. Our results demonstrated that several genera of entomopathogenic fungi have promise as microbial control agents against L. lineolaris.     

In vitro compatibility of Beauveria bassiana strain ATCC 74040 with copper fungicides

Copper fungicides and mycoinsecticides based on entomopathogenic fungi Beauveria spp. are the most common pesticides used in organic crop production systems. The in vitro effects of the copper fungicides copper oxide, copper hydroxide, copper oxychloride, copper sulphate, dicopper chloride trihydroxide and tribasic copper sulphate were investigated for mycelial growth, sporulation and conidial germination of the ATCC 74040 commercial strain of Beauveria bassiana. Mycelial growth was evaluated on potato dextrose agar plates with 100%, 75%, 50%, 25%, 12.5%, 6.25% and 0% of the recommended application rates of each fungicide at 15 and 25°C. Sporulation and conidial germination were determined at the recommended field doses of each fungicide at 25°C. All copper fungicides had fungistatic or fungicidal effects on B. bassiana that varied according to the dose. Only in two cases, copper oxide at 15°C and copper hydroxide at 25°C, at the lowest concentration of 6.5%, was mycelial growth not statistically significantly inhibited. Inhibition of mycelial growth depended both on the fungicide and its concentration, and partly on temperature. Both sporulation and conidial germination of B. bassiana were significantly inhibited by all fungicides. All fungicides inhibited the sporulation in a similar way (99.8%–100%). With the exception of copper oxychloride (inhibition, 13.6%), the other fungicides showed high detrimental effects on conidial germination (inhibition, 91.7%–100%). The fungus was strongly affected by some fungicides even at the lowest doses. The biological index used for the B. bassiana with copper fungicides ranged from 0.6 (copper sulphate) to 18.1 (copper oxychloride). Therefore, the tested fungicides were classified into the upper half of the highly toxic (T) category and are considered incompatible with the entomopathogenic fungus B. bassiana strain ATCC 74040 under in vivo experimental conditions. These results need to be further verified in vitro under both greenhouse and open-field conditions.