Plant Pathology Science

Most crops are propagated by seed. A large number of pathogenic fungi can transmitted by seed and cause epidemy of destructive plant diseases. Treatment of seeds has been shown to prevent plant disease epidemics caused by seedborne fungal pathogens. In this paper, morphological characteristics of ten pathogenic fungi belong to the genera, Alternaria, Aspergillus and Bipolaris, which can decay or reduce the germination of seeds or cause the brown leaf spot disease of cereals, has been described.

 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.

Introduction: Early blight caused by Alternaria species is one of the most important tomato diseases in the world. The disease has been reported from most areas in Iran with up to 90% infection. This study was conducted to investigate the effect of nano-chitosan on the severity of the ‎disease and its use as a replacement‎ of the chemical fungicide, chlorothalonil. Materials and Methods: Diseased tomato plants of fields and greenhouses of Fars province in southern Iran were sampled. Pathogens were isolated from diseased tissues, purified and identified by studying their morphological characteristics. The effect of nano-chitosan at three concentrations of three, five and seven grams per liter and the fungicide chlorothalonil were tested before and after inoculation of two pathogens. The disease severity indexes were measures in Sunseed and 16 cultivars of tomato under greenhouse conditions using a factorial experimental in completely randomized design with four replications. The data were analyzed with comparing the means. Results: The isolated pathogens were identified as A. solani and A. alternata. Results of the greenhouse experiment showed that A. solani was more aggressive than A. alternata and the cultivar 16 was more resistant to the disease. Nano-chitosan at 5 and 7 mg/ l significantly reduced disease severity indexes when use before pathogen inoculation, and at 7 mg/l when use after pathogen inoculation. Conclusion: Nano-chitosan can be used as a bio-fungicide to replace chlorothalonil as a chemical fungicide for disease management.