Plant Pathology Science

 Proteases cleave the peptide bonds in proteins and in this way prevent protein activity by degrading them. Proteases are classified into four categories: serine proteases, cysteine proteases, aspartic proteases and metalloproteases. Plant pathogens utilize these vital molecules in plant infecting process. In the other hand, the activity of proteases is inhibited by protease inhibitors of plants. Serine is one of the protease inhibitors. The plants produce the materials inhibiting pathogenic proteases. These molecules are produced in plant cells during pathogenic microorganisms and viruses attack. Protease inhibitors are divided into several families based on sequence similarity and structure. Because the risk of pathogen resistance to this defense strategy is low, it seems these molecules could be use for biological control against plant pathogens.

 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.

Iranian Pistachio is one of the most important horticultural product in export market. Crown and root rot caused by Phytophthora species is the most serious disease of plant, which annually destroys a considerable number of mature and young trees. This disease has been reported from all provinces of Iran. The pathogen is soil-borne and is distributed by sporangia or the released zoospores and infects the healthy trees. In the most Pistachio orchards, the key factors of disease development are the sensitivity of pistachio crown to Phytophthora and the flooding method of irrigation. The symptoms of the disease are include blight in early spring, drying of the green leaves during the growing season, gum exudation from the crown of tree  and the root rot. Gummosis can be successfully controlled by integrated disease management including orchard constructing in non-infected areas, using resistant or tolerant cultivars, using healthy rootstocks, improving the irrigation methods and avoiding the direct contact of water with tree crown, isolating the contaminated parts of the orchard from the healthy parts, using suitable fungicide, and biological control based on Trichoderma and Bacillus species.