Isolation and identification of endophytic bacteria in potato leaves and their virulence to Phthorimaea operculella

【Objective】To study insecticidal activity of endophytic bacteria in potato leaves against Phthorimaea operculella larvae,and to provide theoretical basis for biological control of P. operculella.【Method】Leaves of 2 main potato varieties Lishu No.6 and Hui-2 in Yunnan Province were used as materials. Endophytic bacteria in the potato leaves were isolated and cultured on LB solid medium. Species of endophytic bacteria were identified based on the morphological characteristics and 16S rDNA sequence. Virulence of fermentation broth,fermentation supernatant and bacterial suspension to the 3^rd instar larvae of P. operculella were determined by leaf immersion feeding method.【Result】Bacillus thuringiensis QL1 and Rhodococcus fascians YH2 with insecticidal activity against P. operculella 3^rd instar larvae were isolated from the leaves of the Lishu No.6 and Hui-2,respectively. P. operculella 3^rd instar larvae were treated with strains QL1 and YH2 fermentation broth at 1.5×10⁹ CFU/mL on the 7^th day,and the cumulative mortality rates were 81.67% and 65.00%,and the LT₅₀were 3.03 and 5.58 d,respectively. P. operculella 3^rd instar larvae treated with strain QL1 fermentation broth at the 3^rd,5^th and 7^th d,and their LC₅₀were 7.99×10⁸,3.21×10⁶ and 2.73×10³ CFU/mL,respectively. The strain YH2 bacteria did not obviously affect mortality of P. operculella 3^rd instar larvae. At 1.5×10⁹ CFU/mL,insecticidal activity against P. operculella 3^rd instar larvae of strains QL1 and YH2 fermentation broth were stronger than of fermentation supernatant and bacterial suspension. Furthermore,as time went on,the cumulative mortality rates increased gradually after P. operculella 3^rd instar larvae were treated with strains QL1 and YH2 fermentation broth,fermentation supernatant and bacterial suspension.【Conclusion】Fermentation broth,fermentation supernatant and bacterial suspension of strains B. thuringiensis QL1 and R. fascians YH2 from endophytic bacteria in potato leaves have insecticidal activity against the 3^rd instar larvae of P. operculella,therefore,they can be developed as potential strains of the P. operculella biological control agent.