Antagonistic microorganisms have been used as biological control agents to reduce the use of chemical fungicides in the control of crop diseases. The present work was conducted to determine the antagonistic potential of Bacillus sp. isolates against the soil-borne fungus Cochliobolus sativus, the causal agent of barley common root (CRR) disease. Out of 525 isolates, 40 were showed in vitro antagonistic activity against the virulent C. sativus isolate CRR16. On the basis of 16S rRNA gene sequencing Bacillus sp. isolates are identified as B. atrophaeus, B. subtilis, Paenibacillus polymyxa, B. amyloliquefaciens, B. simplex and B. tequilensis. Results showed that Bacillus sp. had significant (P<0.05) antagonistic activities against the C. sativus where the percentage of radial growth inhibition of the fungi colonies ranged from 59 to 92%, compared to the untreated control. The B. subtilis isolate SY41B had the highest inhibition effect on the vegetative growth zones as compared with the other species isolates. In view of these, our results indicate that the antagonistic effect of the Bacillus sp. isolates may be important contributors as a biocontrol approach that could be employed as a part of integrated CRR management system.

Non-choice laboratory experiments were conducted to estimate the influence of host density and viability of codling moth eggs on the superparasitism behavior of Trichogramma principium Sug. et Sor and T. cacoeciae Marchal (Hymenoptera: Trichogrammatidae). There was a strong effect of number of emerged offspring of T. principium and T. cacoeciae and host density on the mean number of parasitized eggs. The tendency of T. principium and T. cacoeciae females to oviposit was increased when high number of Cydia pomonella was available. The results presented that the host density influenced in the percentage of superparasitized eggs. The superparasitism appeared to be more noticeable when sterile C. pomonella was offered. Superparasitism behavior was noticed in both parasitoids species, regardless of host density and viability. The study demonstrates the success of T. principium and T. cacoeciae in the existence of high host density and in an integrated program employing the sterile insect technique for C. pomonella management.

Background: Fusarium culmorum and Fusarium solani are economically important fungal pathogens of many plant species causing significant yield losses worldwide. Frequent uses of fungicides are hazardous to humans and the environment. Therefore, in vitro antagonistic activity of diverse Bacillus species isolates with biological potential activity to control these both pathogens should be investigated. Objective: The objectives were to isolate and identify the Bacillus spp., which are potential controls of F. culmorum and F. solani, and to characterize molecularly, at the species level, those isolates that have potential as biocontroller of the pathogens. Methods: The in vitro antagonistic potential of 40 Bacillus isolates against F. culmorum and F. solani was evaluated on the basis of fungal growth inhibition on nutrient broth culture. The colony morphology and the 16S rRNA gene sequencing of Bacillus spp. were used to identify the isolates. Results: Bacillus sp. isolates were identified as B. atrophaeus, B. subtilis, Paenibacillus polymxa, B. amyloliquefaciens, B. simplex and B. tequilensis. They had significant (P<0.05) antagonistic activities against F. culmorum and F. solani isolates as compared to the untreated control. The antagonistic effects varied depending on the Fusarium sp. The bacterial B. subtilis isolates SY116C and SY SY118C provided the most noteworthy result as both strongly inhibited mycelial growth of F. solani by 97.2%, while the B. tequilensis isolate SY145D was the most effective in the formation of inhibition zones against F. culmorum by 75%. Conclusion: It is apparent that Bacillus sp. isolates play an important role in the inhibition of growth of F. culmorum and F. solani, and that the B. subtilis isolates SY116C and SY118C had the highest biological potential activity against these fungi. These antagonistic effects may be important contributors as a biocontrol approach that could be employed as a part of integrated soil pathogen management system.

Quorum sensing in Gram-negative bacteria is regulated by diffusible signal molecules called N-acyl-L-homoserine lactones (AHLs). These molecules are degraded by lactonases. In this study, six Bacillus simplex isolates were characterized and identified as a new quorum-quenching species of Bacillus. An aiiA gene encoding an AHL-lactonase was identified based on evidence that: (i) it showed high homology with other aiiA genes of Bacillus sp.; (ii) the deduced amino acid sequence contained two conserved regions, , characteristic of the metallo-b-lactamase superfamily; and (iii) the protein had zinc-dependent AHL-degrading activity. Additionally, the expression of the aiiA gene was significantly up-regulated by 3-oxo-AHL. The AHL-lactonase inhibited multiplication of the 3-oxo-C6-AHL-producing plant pathogen Erwinia amylovora sy69 both in vitro and in planta. The results provide support for the use of the quorum-quenching functionality of B. simplex in the integrated control of the devastating fire blight pathogen.

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