**3.1 Isolation and identification of antagonistic bacteria against** *X. oryzae* **pv.** *oryzae*

Rice plant samples were collected from 40 districts of Bangladesh representing 30 AEZs during boro seasons 2018–2019 and aman seasons 2018–2019. In total 300 bacterial isolates and 100 fungal isolates were isolated and purified from rice plant samples during boro season, 2018. Some selected representative bacterial species were shown in **Figure 1**. Out of 300 bacterial isolates, eighteen were identified as antagonist against *X. oryzae* pv. *oryzae* and inhibited the growth of *X. oryzae* pv. *oryzae in vitro* which was ranged by 28.39–76.19% (**Table 1** and **Figure 2**). The maximum (76.14%) growth inhibition of *X. oryzae* pv. *oryzae in vitro* was recorded by BDISOB05P while the minimum (28.59) growth inhibition was exhibited by

#### **Figure 1.**

*Representative photographs of purified bacterial isolates obtained from rice phylloplane and rhizosphere. BDISOB05P: an isolate from Mymensingh, BDISOB01R: an isolate from Mymensingh and BDISOB21R: an isolate from Chattagram.*

BDISOB272R. These antagonistic bacterial isolates were identified by sequencing of PCR products of 16SrDNA gene (**Figure 3A**). The identified bacterial species were BDISOB04P (*P. putida*), BDISOB05P (*P. putida),* BDISOB98P (*Stenotrophomonas maltophilia*), BDISOB241P (*Burkholderia* sp.), BDISOB242P *(B. gladioli),* BDISOB219R (*P. taiwanensis*)*,* BDISOB220R (*Serratia* sp.), BDISOB221R (*Pseudomonas* sp.), BDISOB222R (*P. plecoglossicida*)*,* BDISOB258R (*P. putida*), BDISOB272R (*Stenotrophomonas maltophilia*), BDISOB275R (*P. putida*), BDISOB186R (*Pseudomonas* sp.), BDISOB283R (*Pseudomonas fluorescens*), BDISOB306R (*P. putida*), BDISOB53R (*P. putida*), BDISOB61R (*Delftia tsuruhatensis*) (**Table 1**). In total 400 bacterial isolates and 40 fungal isolates were isolated and purified from rice plant samples collected in aman season, 2018. Seventeen bacterial isolates were identified as antagonist against *X. oryzae* pv. *oryzae* and inhibited the growth of *X. oryzae* pv. *oryzae in vitro* which was ranged by 38.33–60.66% (**Table 2**). The highest (60.66%) growth inhibition of *X. oryzae* pv. *oryzae* was exhibited by BDISO147Pand the lowest (38.33%) growth inhibition was shown by BDISO135P.These antagonistic bacterial isolates were identified by sequencing of PCR products of 16SrDNA gene (**Figure 3B**). The bacterial species were BDISO04P (*P. putida*), BDISO45P (*Bacillus paramycoides*), BDISO356P (*P. hibiscicola*), BDISO198P (*Serratia plymuthica*), BDISO135P (*Bacillus sp.*), BDISO148P (*Serratia marcescens*), BDISO92P (*Serratia marcescens*), BDISO237P (*Alcaligenes faecalis*), BDISO12P (*Alcaligenes faecalis*),


*Potential Role of Rice Plant Growth Promoting Phylloplane and Rhizospheric Bacteria… DOI: http://dx.doi.org/10.5772/intechopen.99854*

#### **Table 1.**

*List of antagonistic bacterial isolates identified by homology search ofsequences of 16SrDNA by BLAST program obtained from plant samples collected in boro season 2018.*

BDISO196P (*Alcaligenes faecalis*), BDISO145P (*Serratia marcescens*), BDISO09P (*Serratia marcescens*), BDISO21R (*Serratia marcescens*), BDISO154P (*P. taiwanensis*), BDISO154P (*P. taiwanensis*), BDISO147P (*Serratia marcescens*)*,* BDISO158R (*Serratia marcescens*), BDISO0R (*B. amyloliquefaciens*). In boro season 2019, 300 bacterial isolates were isolated and purified. In boro season 2019, out of 400 bacterial isolates fourteen were identified as antagonist against *X. oryzae* pv. *oryzae* and inhibited the growth of *X. oryzae* pv. *oryzae in vitro* which was ranged by 20.83– 60.87% (**Table 3** and **Figure 3C**). The maximum (60.87%) growth inhibition of *X. oryzae* pv. *oryzae in vitro* was recorded by BDISOB37R while the minimum (20.83%) growth inhibition was exhibited by BDISOB14R. The bacterial species identified were BDISOB37R [*Pseudochrobactrum asaccharolyticum*], BDISOB16R [*Pseudochrobactrum asaccharolyticum*], BDISOB91R [*Pseudochrobactrum asaccharolyticum*], BDISOB17R [*Limnolyngbyacircumcreta*], BDISOB15R [*Pseudochrobactrum asaccharolyticum*], BDISOB86R [*Enterobacteraerogenes*], BDISOB30R [*Pseudochrobactrum asaccharolyticum*], BDISOB92R [*Pseudomonas fluorescens*], BDISOB178R [*Serratia marcescens*], BDISOB11R [*Pseudochrobactrum asaccharolyticum*], BDISOB21R [*Stenotrophomonas maltophilia*], BDISOB24R [*P. asaccharolyticum*], BDISOB23R [*Pseudochrobactrum asaccharolyticum*] and BDISOB14R [*Pseudochrobactrum asaccharolyticum*] by sequencing of bacterial 16SrDNA. In aman season 2019, 400 bacterial isolates were isolated and purified. In aman season 2019, out of 400 bacterial isolates fourteen were identified as antagonist against *X. oryzae* pv. *oryzae* and inhibited the growth of *X. oryzae* pv. *oryzae in vitro*which was ranged

#### **Figure 2.**

*Representative photographs of*in vitro *growth inhibition of* X. oryzae *pv.* oryzae *by different potential bacterial isolates. BDISOB04P: an isolate from Cox's Bazar, BDISOB05P: an isolate from Mymensingh and BDISOB221R: an isolate from Chattagram.*

by 50.83–61.545% (**Table 4**). The maximum (61.54%%) growth inhibition of *X. oryzae* pv. *oryzae in vitro* was recorded by BDISOB54R while the minimum (50.93%) growth inhibition was exhibited by BDISOB12R. These antagonistic bacterial isolates were identified by sequencing of 16SrDNA gene (**Figure 3D**). The bacterial species were BDISOB70R [*Serratia marcescens*], BDISOB54R [*B. gladioli*], BDISOB08R [*Serratia marcescens*], BDISOB31R [*Serratia marcescens*], BDISOB06R [*Serratia marcescens*], BDISOB171R [*Alcaligenes faecalis*], BDISOB46R [*Serratia marcescens*], BDISOB09R [*Serratia marcescens*], BDISOB33R [[*Serratia marcescens*], BDISOB11R [*Serratia marcescens*], BDISOB36R [*Serratia marcescens*], BDISOB07R [*Serratia nematodiphila*], BDISOB172R [*B. aerophilus*] and BDISOB12R [*Serratia marcescens*] by sequencing of bacterial 16SrDNA.
