Abstract:

In order to obtain a dual functional biocontrol strain with excellent antagonistic effect against Fusarium oxysporum in potato and promoting the growth of potato plants，the inhibition effect of secondary metabolites produced by strain L19 on the growth of Fusarium oxysporum was determined by the plate confrontation method. The lipopeptides and volatile compounds released by strain L19 were detected and identified by PCR and gas chromatography-mass spectrometry（GC-MS），respectively. The greenhouse pot experiment and chlorophyll fluorescence detection technology were used to explore the effect of strain L19 on the promotion of potato plants growth and leaf photosynthesis，respectively. The results showed that a total of 25 biocontrol strains were isolated，among which strain L19 could significantly inhibit the growth of Fusarium oxysporum hyphae. According to morphology and gyrB sequence analysis，the strain was identified as Bacillus amyloliquefaciens. The secondary metabolites produced by strain L19 caused the deformation of hyphae，such as twisting，adhesion，expansion and bubbling. The hyphae treated with B. amyloliquefaciens L19 metabolites lost penetration. With fermentation liquid concentration increasing，the spore germination rate of F. oxysporum was lower. B. amyloliquefaciens L19 contained lipopeptide synthesis genes such as sfp，ituA，fenB，bacD and mycB. Moreover，B. amyloliquefaciens L19 produced 12 volatile compounds，among them，the aromatic content accounted for 47.42%，followed by alcohols and ketones. 2-Ethyltoluene was the main volatile compound，with relative content of 20.91%. B. amyloliquefaciens L19 showed the ability to produce cellulase. The pot experiment showed that compared to the control group，the growth index of potato plants significantly increased after applying different concentrations of L19 fermentation broth. The growth rate of root circumference was as high as 78.57%，and the root morphology was better treated by 5 × 10⁷ CFU · mL^-1 L19 fermentation. The analysis of chlorophyll fluorescence parameters showed that there were significant differences in the fluorescence intensity of OJIP curve at O，J（2 ms），I（30 ms）and P points between the treated groups and the control groups. After the application of different concentrations of fermentation broth，the absorption of light energy per unit reaction center（ABS/RC），the energy captured by the unit reaction center for reduction of QA（TRo/RC），and the heat dissipation per unit area（DIo/CSo）of potato leaf photosynthetic index increased by 16.32%-28.38%，respectively，B. amyloliquefaciens L19 fermentation liquid can improve the light energy utilization rate of plant leaves. Therefore，the secondary metabolites secreted by B. amyloliquefaciens L19 showed strong inhibition effect on F. oxysporum，and the fermentation broth also had the growth promoting effect on potato plants. Moreover，B. amyloliquefaciens L19 could improve the photosynthesis of plant leaves and has good application prospects.

Key words: potato, Fusarium wilt, Fusarium oxysporum, Bacillus amyloliquefaciens, antagonism, growth promoting effect, biological control