Interaction Mechanism Between Soil Bacteria-Feeding Nematodes And Plant Pathogenic Bacteria

Plant diseases pose a serious threat to global food security and production.Using antagonistic organisms in the natural environment to control pathogenic bacteria is a research hotspot in recent years.Some studies have shown that plant resistance to pathogens is related to the enrichment of specific rhizosphere microorganisms(especially bacteria)in the soil.Bacteria-feeding nematodes as a key nutrient level in soil ecosystem,can affect plant growth by affecting the number and community structure of rhizosphere microorganisms.However,the mechanism by which bacteriafeeding nematodes participate in plant disease inhibition by regulating pathogens and rhizosphere bacteria is still unclear.Caenorhabditis elegans,the model nematode,and Protorhabditis sp.,the dominant indigenous nematode,were used in this study.And five plant pathogenic bacteria Xanthomonas oryzae pv.oryzae、Ralstonia solanacearum,Pectobacterium carotovorum subsp.carotovorum 、 Pseudomonas syringae pv.lachrymans and Clavibacter michiganense subsp.sepedonicum 、two antagonistic bacteria Pseudomonas protegens Pf-5 and Bacillus R-4 of R.solanacearum as experimental materials.The main research contents include the following three aspects:1)The feeding behavior of bacteria-feeding nematodes on plant pathogenic bacteria,and the effects of pathogenic bacteria on physiological characteristics,movement,body length and body width of nematodes;2)The feeding preference of nematodes to antagonistic bacteria from Ralstonia solanacearum,and the effects of antagonistic bacteria on the physiological characteristics(reproduction and longevity)of nematodes;3)Effects of bacteria-feeding nematodes’ secretions on pathogens and antagonists.The main results are as follows:1.Feeding preference tests for five plant-pathogenic bacteria and E.coli OP50 showed that C.elegans and Protorhabditis sp.showed no preference for pathogens.2.The pathogens significantly reduced the reproduction and prolonged the life span of C.elegans,but did not affect the Protorhabditis sp..Most of the pathogens had no effect on movement of C.elegans.The pathogens could significantly inhibit the growth of C.elegans,but had no effect on body length and body width of Protorhabditis sp..3.Feeding preference tests of R.solanacearum and its antagonistic bacteria Pf-5and R-4 showed that C.elegans and the Protorhabditis sp.had a preference for antagonistic bacteria.And nematodes showed a preference for antagonistic Pf-5 over OP50.Antagonistic R-4 could prolong the life span of C.elegans by about 40%.However,there was no significant effect on the longevity of Protorhabditis sp..4.The secretions of C.elegans、Protorhabditis sp.and two other common native bacteria-feeding nematodes Acrobeloides sp.、Panagrolaimus sp.could enhance the antagonistic effect of Pf-5 and R-4 against R.solanacearum.The secretions of C.elegans and Protorhabditis sp.had a significant inhibitory effect on the number of R.solanacearum at a specific concentration,but they could significantly increase the number of antagonistic bacteria Pf-5 and R-4.In conclusion,bacteria-feeding nematodes do not prefer plant pathogens,so it is less likely to help plants resist pathogens by feeding on pathogens.However,bacteriafeeding nematodes prefer to feed on antagonistic bacteria of pathogens,and the secretions of nematodes can enhance the bacteriostasis ability and quantity of antagonistic bacteria at a specific concentration.This may be an effective way for bacteria-feeding nematodes to indirectly help plants resist disease.