Plant Pathology Science

 Plant pathogenic bacteria have evolved specialized strategies to infect their hosts. In this regard, the key virulence factors are effector proteins, cell wall degrading enzymes, toxins, extracellular polysaccharides and phytohormones. The interactions between plant pathogenic bacteria and their hosts have resulted in an evolutionary system between host defense responses and pathogen virulence factors. Pathogenic bacteria are continually under pressure to diversify their mechanisms to prevent host defenses and optimize nutrient availability. In turn, these virulence mechanisms have shaped the evolution of plant innate immunity. In this paper, the pathogenicity and virulence factors of plant pathogenic bacteria are discussed.

 Aflatoxin contamination of pistachio nut is a health challenge that can affect the economic value of the largest Iranian non-oil exports. This potent hepatocarcinogen mycotoxin is produced by some species of Aspergillus, particularly by A. flavus, under certain conditions during fruiting, harvesting, transportation and storage. Infection of pistachio to the fungus in the orchard is the key factor in its contamination with aflatoxin. This situation occurs with the formation of early splited pistachios and mechanical damages that caused by biotic and abiotic factors. The environmental temperature and relative humidity and the moisture content of pistachio, during the different stages of pistachio production and processing, have significant roles in the incidence and distribution of fungal contamination as well as the increasing of aflatoxin production. The inhibition of these factors is possible with applying of some agronomic, mechanical, physical and biological methods. Orchard establishment based on principles of gardening like optimal plant spacing, uniformity of cultivars, good pruning, proper irrigation method and nutrition along with on time harvesting, proper processing and storage, can guarantee the production of a healthy and valuable product. Biological controls using nontoxinogenic strains of A. flavus and yeasts are also recorded as successful strategies for reducing the pistachio aflatoxin.