ORIGINAL ARTICLE The effect of paclobutrazol on soil bacterial composition across three consecutive flowering stages of mung bean Jimmy Kuo 1,2 & Yen-Wen Wang 3 & Michael Chen 3 & Georgia Fuh 4 & Chorng-Horng Lin 5 Received: 23 March 2018 /Accepted: 22 August 2018 # Institute of Microbiology, Academy of Sciences of the Czech Republic, v.v.i. 2018 Abstract Paclobutrazol, (2RS, 3RS)-1-(4-chlorophenyl)-4, 4-dimethyl-2-(1H-1,2,4-triazol-1-yl) pentan-3-ol, is a plant growth retardant that mainly inhibits gibberellins (GAs) biosynthesis. In agricultural practice, paclobutrazol is applied to arrest vegetative growth so as to increase the reproductive growth of many orchard fruit, as well as grain crops. However, due to its over-application and chemical stability, paclobutrazol accumulates in soil and inhibits the growth of subsequent crops, especially those grown for vegetative purposes. The present study focused mainly on the changes in the soil bacterial community following application of paclobutrazol. Mung bean (Vigna radiata) plants were treated with paclobutrazol and cultivated for three consecutive seasons. Soil samples were collected and analyzed by denaturing gradient gel electrophoresis (DGGE) using 16S rDNA gene fragments and clone library analyses. The results obtained through clustering and clonal sequencing analysis showed that the bacterial community was affected by paclobutrazol, and in addition, was more diverse in the third stage of mung bean plant cultivation. The results of the study showed that paclobutrazol affected bacterial composition, and the population of bacteria varied greatly across time. Introduction Paclobutrazol is a widely-employed plant growth regula- tor and fungicide that stunts growth by inhibiting gibber- ellins (GAs) synthesis. It has been shown to retard pri- mary growth in numerous plant species without decreas- ing crop yield (Jacyna and Dodds 1999); however, the benefits of paclobutrazol to agriculture must be weighed against a known consequence, prolonged soil retention (Grimstad 1993; Sharma and Awasthi 2005). Empirical studies have demonstrated that residual paclobutrazol limits the growth of future plantings in some species (Jacyna and Dodds 1995). In one of the few studies investigating the effect of paclobutrazol on the soil microbiome, Silva et al. (2003) applied a plate-counting technique, and found that paclobutrazol decreased bacterial biomass in mango or- chard soil by 58%. However, the impact of paclobutrazol on the diversity of soil bacterial communities remains poorly understood. There are few studies in this area, and the results have mainly been inconclusive (Lin et al. 2010). This study examined the impact of paclobutrazol on the bacterial community in soil cultivated with mung bean plants. Changes in bacterial composition and diver- sity were studied under prolonged and controlled paclobutrazol exposure using denaturing gradient gel electrophoresis (DGGE), the unweighted pair group method with arithmetic mean (UPGMA) clustering, and 16S rDNA sequence analysis. Yen-Wen Wang and Michael Chen contributed equally to this paper. * Chorng-Horng Lin clin@mail.dyu.edu.tw; clin86@hotmail.com 1 Department of Planning and Research, National Museum of Marine Biology and Aquarium, Pingtung, Taiwan 2 Institute of Marine Biotechnology, National Dong Hwa University, Pingtung, Taiwan 3 Institute of Molecular Biology, DaYeh University, Changhua, Taiwan 4 College of the Atlantic, Bar Harbor, ME 004609, USA 5 Department of Bioresources, DaYeh University, Changhua, Taiwan Folia Microbiologica https://doi.org/10.1007/s12223-018-0644-x