Abstract:

【Objective】 Previous studies have shown that Bacillus cereus NJSZ-13 strain has the best effect on Pinus massoniana growth. To further analyze and evaluate the underlying biological and control mechanism of the strain on Bursaphelenchus xylophilus, NJSZ-13 strain was added to the insect and egg liquid to study the killing effect of the strain on B. xylophilus and its oviposition, egg hatching and reproduction activities.【Method】 NJSZ-13 strain was divided into suspension, fermentation broth and fermentation filtrate by centrifugation, and then mixed into the original solution, with 5, 10, 100 and 1 000 dilutions. The concentrations of suspension and fermentation broth were 3×10 ⁸ cfu/ mL, and sterile water and NB medium were used as the control. ①The nematocidal effects of NJSZ-13 strain on B. xylophilus in 24 and 48 hours were determined by the immersion method. ②Ten pairs of female and male fourth instar larvae with good growth were selected and placed in a 1.5 mL centrifuge tube. After being treated with NJSZ-13 strain for 24 h, the eggs were washed from the centrifuge tubes into 35 mm culture dishes, and the amounts of eggs laid in each treatment counted. ③Sterile egg solutions (1 mL, containing about 400 eggs) and NJSZ-13 strains were placed into 35 mm dishes for the counting of the numbers of hatched worms at 12, 24 and 36 h. ④The mixtures of nematode solution (100 μL) (containing 500 B. xylophilus) and 100 μL NJSZ-13 strains were put into 60 mm culture dishes of Botrytis cinerea. The nematodes were isolated and counted using the behrmann method after being cultured in a 25 ℃ incubator for five days. 【Result】 ①The nematocidal rate of NJSZ-13 was 100% after 24 h of treatment, while the killing rate of NJSZ-13 strain was only 81.47% after 48 h of treatment. ②NJSZ-13 strain could inhibit the oviposition of B. xylophilus significantly, and the inhibition decreased with an increase in dilution ratio. ③The 10-fold dilution of the NJSZ-13 strain inhibited the hatching of the eggs significantly at 12 h, with a significant level achieved at 24 h, only the fermentation broth and fermentation filtrate exhibited significant inhibition at 36 h. When treated with the 100-dilution for 12 h, the fermentation broth and fermentation filtrate had significant differences when compared with the control, with no significant differences at the other treatment time points. ④ There were significant differences in fecundity between NJSZ-13 strain and the control group (P < 0.05). When 10-dilution solution was used to treat B. xylophilus, the bacterial suspension had no significant effect on B. xylophilus fecundity.【Conclusion】 Bacillus cereus NJSZ-13 strain had nematocidal effects on B. xylophilus. Among them, the nematocidal effects of fermentation broth and fermentation filtrate were more significant; NJSZ-13 strain could inhibit B. xylophilus oviposition, egg hatching and reproduction, and the inhibitory effects of fermentation broth and fermentation filtrate were more obvious than those of the bacterial suspension.

Key words: Bursaphelenchus xylophilus, Bacillus cereus, oviposition, hatching, reproduction