Effects of Bacillus cereus on Survival, Fecundity, and Host Adaptability of Pine Wood Nematode

To clarify the role of bacteria in PWD, three PWNs with different virulence (strongly virulent strain AMA3, normally virulent strain AA3, and weakly virulent strain YW4) were selected as research objects, and three strains of Bacillus cereus (nematode-associated bacteria GD1, Pinus massoniana endophytic bacteria GD2, and P. elliottii endophytic bacteria NJSZ-13) at different concentrations were used to determine their effects on the survival and fecundity of the nematodes. The results showed that strains GD1 and GD2 could significantly improve the survival and fecundity of PWNs at three different concentrations, while NJSZ-13 showed the opposite effects. The inoculation experiments showed that the disease index of P. massoniana under different treatments was as follows: AMA3 < a mixture of AMA3 and GD1 < a mixture of AMA3 and GD2. Similar results were shown in the Larix kaempferi inoculation experiment. Further, using RNA-sequencing analysis, we found that the up-regulated genes in PWN were sHsp 21, Hsp 70, and Hsp 72 after being treated by strains GD1 and GD2. The longevity regulatory pathways, MAPK signaling pathways, glutathione metabolic pathways, and cytochrome P450 metabolic pathways related to these genes are clearly enriched. These results show that the bacteria can improve the host adaptability of PWN, and endophytic bacteria of pine trees may be more effective in improving the host adaptability of nematodes than the associated bacteria of nematodes.