Abstract
Out of 39 isolates of rhizobacteria, recovered from economic plants grown in 8 locations in Egypt, 6 isolates were able to produce Hydrogen Cyanide (HCN). 16S rRNA sequence analysis identified these isolates as: Pseudomonas japonica strain NBRC 103040, Bacillus megaterium strain CtST3.5, Pseudomonas sp. strain Gamma-81, P. tolaasii strain ATCC 33618, P. chlororaphis strain Lzh-T5, and P. mosselii strain CV25. These HCN producers were able to inhibit growth of Agrobacterium tumefaciens and affect viability of Meloidogyne incognita juveniles in vitro. The isolates of P. japonica and Pseudomonas sp. Gamma-81 prevented the gall formation on tomato plants by A. tumefaciens, regardless of the presence of M. incognita. The isolates of B. megaterium, P. chlororaphis, P. tolaasii, and P. mosselii decreased the weight and number of galls produced by A. tumefaciens in the presence or absence of M. incognita. The 6 HCN producers decreased the population of M. incognita and the number of nematode galls than the positive control, when used against M. incognita. A similar effect was achieved against mixed infections with M. incognita and A. tumefaciens. The HCN-producing rhizobacteria, in the presence of A. tumefaciens and/or M. incognita, caused obvious increment in all growth parameters of tomato than the negative control and healthy plants. The only exception was found in case of Pseudomonas sp. Gamma-81 against M. incognita and against mixed infection, where growth parameters of tomato were decreased. Although the isolates were naturally isolated from the rhizosphere of economic plants, it must be cautiously considered since the isolate identified as P. japonica has been reported as a human pathogen. Also, P. tolaasii was reported causing a bacterial blotch on cultivated mushrooms under certain environmental conditions. Further investigations are needed.
Highlights
Crown gall disease caused by Agrobacterium tumefaciens is a major bacterial disease in nurseries and orchards and is being considered one of the most important disorders that causes high losses in nurseries (Pulawska 2010)
The results showed that A. tumefaciens showed (98.41%) similarity with A. tumefaciens strain IAM 12048 and A. tumefaciens strain NCPPB2437
The 6 hydrogen cyanide (HCN) producing isolates were isolated from rhizosphere soil of guava plants grown in Behiera governorate (BR11 and BR13), peach plants grown in Giza governorate (GA21), potato plants grown in Ismailia governorate (SW1 and SW4), and corn plants grown in Beni-Seuf governorate (BW3)
Summary
Crown gall disease caused by Agrobacterium tumefaciens is a major bacterial disease in nurseries and orchards and is being considered one of the most important disorders that causes high losses in nurseries (Pulawska 2010). Biological control of crown gall is more effective in controlling the disease rather than chemical control (Tolba and Soliman 2013). The search for biological means for controlling root-knot. Cyanide forms stable complexes with the essential elements (Cu2+, Fe2+, and Mn2+) for the protein function and is considered a toxic substance to most living. Abd El-Rahman et al Egyptian Journal of Biological Pest Control (2019) 29:41 organisms. Hydrogen cyanide (HCN) is a volatile secondary metabolite that is synthesized by many rhizobacteria and has a powerful effect on many organisms. HCN inhibits the electron transport and disrupts the energy supply to the cell, which leads to death of living organisms. Many bacterial genera have the ability to produce HCN including species of Alcaligenes, Aeromonas, Bacillus, Pseudomonas, and Rhizobium (Alemu 2016)
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