Compatibility of entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) Sorokin with fungicide thiophanate-methyl assessed by germination speed parameter.

摘要

The biocontrol agent Metarhizium anisopliae is efficient to combat more than three hundred species of insect pests and can be used in biologicalchemical combinations with chemical defensives maintaining the inoculum source of fungi in the field. Studies of conidiogenesis in M. anisopliae are fundamental, considering that conidia are the main form of inoculum for biological control. Among the pesticides applied in pastures for pest control, to prevent and control plant diseases, is thiophanate-methyl. Due to the importance of M. anisopliae as a microbial agent of a wide variety of insect pests, it is of critical importance to evaluate the effect of chemical products on this fungus, considering the conidia germination speed parameter, which is directly associated with virulence. Therefore, this study aimed to verify the effect of different concentrations of thiophanate-methyl on the conidia germination speed of MT (Mato Grosso) strain of M. anisopliae. Conidia were incubated with thiophanate-methyl in concentrations of 200 micro g/ml (T1), 20 micro g/ml (T2), 2 micro g/ml (T3) and 0.2 micro g/ml (T4) at 28 degrees C and sampled throughout 24 hours. The control was performed without the pesticide. Bayesian analysis showed an inhibition of conidia germination in the presence of 200 and 20 micro g/ml of thiophanate-methyl. The curve of conidia germination speed showed that until 14 h of incubation, there was an increase in the germination speed of control and all treatments. Shortly afterwards, this speed decreased in T2 and T3 but it remained stable for C and T4. A stronger inhibition of conidia germination was caused by T1. The compatibility observed in concentrations of 20 and 2 micro g/ml indicates that this fungicide could be mixed with M. anisopliae in biological-chemical combinations, maintaining the viable fungal inoculum after its application. To confirm it, third-instar larvae of sugarcane borer (Diatraea saccharalis) were infected with a combination of a conidia solution of MT strain and thiophanate-methyl in concentration of 20 micro g/ml. As controls, water, conidia solution and the fungicide were applied separately. Food was offered ad libitum and larvae were monitored daily throughout 7-12 days at 25 degrees C and the factors of living larvae, larvae in pupal stage and dead larvae were evaluated. As results, the thiophanate-methyl did not affect the D. saccharalis larvae, but when these larvae were treated with M. anisopliae conidia mixed with the pesticide, it was observed a reduction of larvae mortality of 26.8% when compared with the use of M. anisopliae only (without pesticide).