Isolation and characterization of endophytic bacteria from tomato foliage and their in vitro efficacy against root-knot nematodes

Fifteen endophytic bacteria were isolated from leaves and stems of Solanum lycopersicum and Solanum pimpinellifolium collected from different locations of the Jorhat district of Assam and characterized by morphological, cultural, biochemical and molecular approaches. An in vitro study was carried out to evaluate their potentiality as biological control agents against second stage juvenile of the root-knot nematode, Meloidogyne incognita race2. Thirty second stage juveniles (J₂) of M. incognita race 2 were exposed to cell free culture filtrates of all the 15 bacterial endophytes in a sterile cavity block at a concentration of S(100%), S/2(50%), S/4(25%), S/6(17%) and S/10(10%) for a duration of 6, 12, 24, and 48 hr. The results revealed that all the isolates had the potentiality to significantly increase the mortality of the second stage juveniles (J₂). The percent mortality was directly proportional to the duration of exposure time and the concentration of the culture filtrate. The isolate BETL2 showed the best result with 81.47% mortality of juveniles followed by isolates BETL4 (81.43%), BETLI (79.07%), BETS2 (78.87%), and BETL6 (78.17%). The 16S rRNA sequence amplification results indicated that these isolates were Bacillus marisflavi (BETL2), Bacillus altitudinis (BETL4), Microbacterium arborescens (BETL1), Exiguobacterium indicum (BETS2), and Bacillus marisflavi (BETL6). The four most efficient isolates were structurally analyzed using a scanning electron microscope and this revealed that the length and breadth of isolates—BETLI, BETL2, BETL4, and BETS2 were 701.70 nm × 348.30 nm, 954.10 nm × 303.10 nm, 984.10 nm × 332.90 nm and 1422.00 nm × 742.00 nm, respectively. The result of the present study indicated that the above four novel strains of endophytic bacterial isolates enhance the mortality of J₂ of M. incognita race2 and has the potentiality as biological control agents against M. incognita.