**Abstract**

Biological control is a potential nonchemical method to manage plant pathogens by beneficial microorganisms. To improve antagonistic potential of biocontrol agents, mutation by radiations, chemicals, and genetic manipulations has been used. Genetic techniques and ionizing radiation containing direct or indirect emissions play the greatest role for selection of useful microorganisms to enhance the efficiency of biological systems. Indeed, genetic engineering has a main role in increasing antimicrobial metabolites, host colonization ability, and endurance in micro-ecosystem. Genetic improvement can be achieved by protoplast fusion, genetic modification (GM), and chemical (genotoxic agents) and physical mutations. However, ultraviolet light and ionizing radiations can induce modifications in the genome of an organism. Irradiation, particularly gamma rays, is also applied for controlling postharvest diseases. Indeed, irradiation cannot completely eliminate pathogens, but it might result in cell injury and directly damage the chromosomal DNA of a living cell. This technology has been used for many reasons including disinfestation of foods, reducing foodborne pathogens, and extending shelf life many fruits, vegetables, and nuts. In the current review, we discuss advances in the radiation and molecular genetic techniques with the aim to improve antagonistic potential of microorganisms as it is applied to the suppression of plant pathogens.

**Keywords:** biocontrol agents, genetic engineering, ionizing radiations

#### **1. Introduction**

The risks associated with chemical residues on the leaves and fruits have highlighted the need for more useful and safer alternative control treatments. Biological control is a potential nonchemical mean to manage plant pathogens including fungi, bacteria, nematodes, or weeds by beneficial microorganisms such as fungi, yeast, or bacteria [1]. The virulence of pathogens probably changes if genetic mutations occur in the genes related to pathogenicity of microorganisms upon mutagenic treatments [2]. It is quite obvious that the application of ionizing radiations such as gamma rays and X-rays and genetic methods plays the greatest role in the development of techniques for the selection of useful microorganisms

[3]. Indeed, irradiation is the process of exposing an amount of energy in the form of speed particles or rays for improving food safety and reducing microorganisms that destroy agricultural crops. For instance, studies on transcriptional changes of *Salmonella typhimurium* using gamma irradiation showed that the expression of the virulence genes in irradiated mutants was reduced in comparison with non-irradiated controls [4]. It has been also shown that gamma irradiation alone or in combination with other methods can improve the microbiological safety [5]. Likewise, the wholesomeness (lack of teratogenicity, mutagenicity, and toxicity) of irradiated products has been studied extensively, in which food irradiation has not provided any evidence of increased threat of mycotoxin formation in irradiated food [6]. There is an increasing interest in commercial application of genetically modified microorganisms with improved biocontrol properties toward plant pathogens [7]. To that end, this chapter is an advanced survey reviewing the radiation and molecular genetic techniques with the aim to improve antagonistic potential of microorganisms as it is applied to the suppression of plant diseases.
