Application of Paclobutrazol Altered the Soil Bacterial Diversity and Richness of Mango Orchards: A Metagenomic Study

The soil microbiome regulates plant and soil health by cycling nutrients, reconstructing soil, degrading xenobiotics, and regulating growth. Paclobutrazol (PBZ) is a plant growth regulator that is commonly used to induce flowering, particularly in alternate bearers such as mangoes. However, the long-term persistence of PBZ in the soil causes alteration in the soil microbial community and other living species. In the present study, high-throughput whole metagenome sequencing (WMS) through IlluminaNovaseq 6000 was carried out to ascertain the alteration in microbial diversity in control (T1) and PBZ (T2) contaminated soil of mango orchards. The HTS technology revealed that the PBZ application in the soil specifically recruits and improves the abundance of some specific bacterial groups that are known for their own antimicrobial, xenobiotics degradation, and plant growth-promoting rhizobacteria (PGPR) features. The relative abundance of Proteobacteria, Acidobacteria and Actinobacteria in the soil was found to be greatly improved with the application of PBZ. Shannon, Simpson and InvSimson reflect the bacterial diversity, found to be higher in T1, while Ace and Chao diversity indices showed that the soil bacterial richness was significantly higher in T2. The biological buffering of soils by Actinobacteria, nutrient cycling by Acidobacteria, nitrogen fixation and degradation of high molecular weight compounds like PBZ was evident from this study, indicating microbial bioremediation of PBZ in mango orchards. Further, this study establishes altered community composition of the rhizospheric microbiome due to PBZ treatment, which is the trigger for the recruitment of bacteria supporting growth regulatory activities that subsequently may regulate arboreal phenology.