Abstract: 【Aim】This study aims to explore the endophytic colonization potential of Lecanicillium lecanii strain JMC-01 in cabbage (Brassica oleracea var. capitata), its physiological impacts on the host plant and the repellent effects of induced cabbage volatile compounds against  Myzus persicae. 【Methods】 The L. lecanii strain JMC-01 spore suspensions at the concentrations of 1×10⁸, 1×10⁷ and 1×10⁶ spores/mL were inoculated to cabbage plants using the leaf spraying method and root drenching method, respectively. The colonization rates were determined using the PDA plate detection method on the 1st, 3rd, 7th, 10th, 14th and 21st day after inoculation. The growth promoting effect of L. lecanii strain JMC-01 on cabbage was investigated by measuring the plant height, root length, fresh weight, dry weight, stem diameter and chlorophyll content of the cabbage on the 21st day after inoculation. The insect Y-tube olfactometer was used to detect the behavioral selection of the wingless adults  and day-1 1st instar nymphs of M. persicae to the cabbage plants at 24 h after inoculation with the spore suspension of L. lecanii strain JMC-01 at the concentration of 1×10⁸ spores/mL. Gas chromatography-mass spectrometry (GC-MS) was used to identify differential volatile compounds from the cabbage inoculated and uninoculated with the spore suspension of L. lecanii strain JMC-01 at the concentration of 1×10⁸ spores/mL. The insect Y-tube olfactometer was used to detect the repellent effects of these differential volatile compounds induced by L. lecanii strain JMC-01 against the wingless adults and day-1 1st instar nymphs of M. persicae. 【Results】 The L. lecanii strain JMC-01 inoculated with leaf spraying method exhibited superior colonization efficiency in cabbage plants to that with root drenching method, achieving 100% colonization rates in cabbage across all the three concentrations on the 1st day post inoculation with leaf spraying method, with detectable colonization signals persisting on the 21st day after treatment with L. lecanii strain JMC-01 spore suspension at the concentration of 1×10⁷ spores/mL. Growth promotion experiments demonstrated that L. lecanii strain JMC-01 spore suspensions at the concentrations of 1×10⁸ and 1×10⁷ spores/mL significantly enhanced the plant height, root length, stem diameter and biomass accumulation, with the L. lecanii strain JMC-01 spore suspension at the concentration of 1×10⁷ spores/mL showing the most pronounced promoting effect on chlorophyll synthesis. The total chlorophyll content in the cabbage treated with L. lecanii strain JMC-01 spore suspension at the concentration of 1×10⁷ spores/mL reached 37 mg/g. The L. lecanii strain JMC-01 spore suspension treatment on the cabbage plants exhibited repellent effects on the wingless adults and day-1 1st instar nymphs of M. persicae. GC-MS analysis identified 12 differential volatile organic compounds induced by L. lecanii strain JMC-01 colonization in cabbage, among which n-hexadecane and 3-methyl-2-oxyindole exhibited repellent effects on the wingless adults and day-1 1st instar nymphs of M. persicae. The wingless adult M. persicae showed stronger olfactory response to the standard substances n-hexadecane and 3-methyl-2-oxyindole than the day-1 1st instar nymphs. The repellent effect of n-hexadecane on the day-1 1st instar nymphs increased with the spore suspension concentration increasing. 【Conclusion】 This study reveals that the L. lecanii strain JMC-01 can endophytically colonize in the cabbage plants, and can achieve a growth-promoting effect on the cabbage through endophytic colonization. At the same time, it can also induce the plant to produce volatile compounds to repel M. persicae, providing a theoretical basis for the application of entomopathogenic fungi in biological control strategies.

Key words: Myzus persicae; Lecanicillium lecanii; Brassica oleracea var. capitata, endogenous colonization, growth promotion, repellent effect