Inhibition of Citrus Huanglongbing Disease by <i>Paenibacillus polymyx</i> KN-03 and Analysis with Transcriptome and Microflora

Soil drench treatment using <i>Paenibacillus polymyxa</i> strain KN-03 was applied to citrus plants infected with <i>Candidatus</i> Liberibacter asiaticus (<i>C</i>Las). The infection status was assessed using PCR and a real-time quantitative PCR detection system (qPCR). The application of KN-03 resulted in a notable reduction in <i>C</i>Las levels in citrus plants. Specifically, by the 257th day post treatment commencement, following 24 KN-03 applications, the negative rates of <i>C</i>Las in the vein, root tip, and shoot tip were 50%, 0%, and 50%, respectively. After 24 cycles, KN-03 application significantly enhanced plant growth and stimulated reactive oxygen production in citrus leaves compared to control plants. Transcriptome analysis identified specific upregulated pathways. Furthermore, flora analysis revealed an increased abundance of microorganisms possessing potential utilization value, including <i>Burkholderia-Caballeronia-Paraburkholderia</i>, <i>uncultured_bacterium_o_Acidobacteriales</i>, <i>uncultured_bacterium_f_Gemmatimonadaceae</i>, and <i>Rhodanobacter</i>, in the root zone. Moreover, the BugBase analysis indicated that KN-03 treatment increased the abundance of beneficial rhizosphere bacteria associated with biofilm formation, element mobilization, and stress tolerance. These findings support the utility of <i>Paenibacillus polymyxa</i> KN-03 as an effective plant-growth-promoting bacterium for <i>C</i>Las management, with additional benefits for plant growth and soil health, specifically offering detoxification resources for shoot tip grafting.