Mutagenic effects of low-energy N+ ion implantation on the propamocarb-tolerance of nematophagous fungus Lecanicillium attenuatum

Lecanicillium attenuatum is an important nematophagous fungus with potential as a biopesticide for control of plant-pathogenic nematodes. However, relatively low fungicide-tolerance limits its application in the field. To improve the propamocarb-tolerance of L. attenuatum , a low-energy N + ion implantation-based mutagenesis system was established. In the first round of N + ion implantation, a proper conidial lethality rate (87.2–88.8%) and the highest positive mutation rate (11.2–11.4%) were achieved, and the highest propamocarb-tolerant mutant LA-I-R1-T7-M1 and LA-I-R1-T7-M2 were isolated in the experiment 1 and experiment 2 respectively, having a median effective concentration (EC 50 ) value of 1223.6 and 1173.6 μg/ml respectively. Multiple rounds of N + ion implantation were further employed, but fungal propamocarb-tolerance had not been significantly enhanced until the fifth-round of ion implantation. The LA-I-R5-M1 was the highest tolerant to propamocarb among all the mutants, whose EC 50 value was increased 2.54-fold compared to wild-type strain, reaching to the 1298.7 μg/ml. Its EC 50 value was significantly increased with continuous passaging, which was stable from the fifth- to fifteenth-generation, and then declined. However the EC 50 value of the twentieth-generation strain was still higher than the EC 50 (1298.7 μg/ml) of the first-generation strain. The colony growth, conidia yield and conidial germination of mutants on plates, and their parasitism in the nematode eggs of Meloidogyne incognita and Heterodera glycines were not significantly changed in both single- and multiple-round of N + ion implantation. In conclusion, we had succeeded in improving the propamocarb-tolerance of L. attenuatum through this low-energy N + ion implantation-based mutagenesis system. The improved strain LA-I-R5-M1 could be potentially applied in combination with propamocarb in the field.