نشریه دانش بیماری شناسی گیاهی
پیاپی 2 (بهار و تابستان 1391)

Genetic engineering has begun about 160 years ago with discover inheritance laws of biological traits, isolation and purification of DNA from inner cell, replication and propagation of its pieces with polymerase chain reaction in vitro, identification and purification favorable genes and transfer them with Agrobacterium tumefaciens bacterium, or directly to plants cell, by gene gun, and produce whole transgenic plant, from gene modified cell with tissue culture methods innovation and fully developed in recent 4 decades. With this technology transfering favorable genes, without accompaniment with unwanted genes, into plants is possible, and resistance transgenic plants to fungal, bacterial, viral and nematodes, and tolerant to environmental stress produced. Genetic engineering has created hope for better plants diseases management and increase agricultural production to meet food needs of a growing human population.

Early blight is an important worldwide disease of tomato that farmers must have frequent spray chemicals to control it. One way to reduce the use of pesticides, costs of production and the risk of environmental pollution, spraying based on forecasting of TOMCAST system, which is based on the time of wet leaves and temperature during tomato growing season in each region, predict disease severity, and determine suitable time of spraying. Application this system, in some countries considerably reduced pesticides usage on tomato. This system predict time of spraying when needed and has maximum effect. By using this forecasting method in Iran, can reduce pesticides usage on this freshly consume fruit, efficiency of using pesticides, and increase yield.

Citrus gummosis disease cause canker accompanied by gum exudates, crown and root rot, twig dieback, and decline of citrus trees. This disease has been reported from Khuzestan and Fars provinces, now infected by in parts of Kohgiluyeh and Boyerahmad province (southwest Iran), namely: Molabarfi, Bidestan, Posht-e-koh, Tol-e-mavizi, Bidzard, Chaharbish-e-olia and Chaharbish-e-sofla from Gachsaran town and Cheshm-e-belghis, Dehborji, Spar and Marin from Kohgiluyeh town. Sour lemon, sweet lemon, big sour lemon and orange were more infected respectively. Pathogen identified as Phytophthora nicotianae. As it is epidemic in this province for planting diseased seedlings, incorrect planting method, stalk sensitivity, incorrect irrigation method, can manage by planting healthy certified seedlings on sour orange stalk, correction planting and irrigation methods, chemical control, and biological control with antagonistic fungi or bacteria.

Trichoderma form-species are among of the important antagonists of plant pathogenic fungi and also induce resistance in field crops. Therefore their isolation and identification could be helpful for applying them in biological control. They isolate by pour soil diluted suspension on Dawet, Peptone – Rose Bengal, or modified Potato- Dextrose-Agar mediums. Species can identify based on colony characteristics, growth characteristics and morphological characteristics of conidiophores, phialids, and conidia. Eighty-five isolates of Trichoderma from 25 soil samples, from 8 regions of the Fars province sugar beet fields, isolated and purified with this method. With studied their characteristics eight form-species of Trichoderma identified with names: T. asperellum, T. atroviride, T. brevicompactum, T. harzianum, T. longibrachiatum, T. spirale, T. tomentosum and T. virens. Methods of isolation, identification and morphological characteristics of these fungi described.

Fusarium ear rot is one of the most important diseases of corn in Iran. This disease cause by Fusarium moniliforme fungus. Its symptoms are pink to red spots on ear, cause it completely rot and eventually loss of yield quantity and quality. Identification and cultivation resistant or semi-resistant corn hybrids is the best management method of this disease. Artificial infection of maize hybrids with fungal suspension of causal agent is an affective method to study their reactions, determine base on disease severity index (%DS). According to research conducted in Iran, between 12 planting hybrids, 2 hybrids K3493 / 1 × K18 and KLM 77029/8-1-2-3-2-3 × MO17 are resistant, and 9 are semi- resistant. With extension, cultivation of these hybrids, can manage the disease and increase the quality and quantity of maize hoped.

Root and crown rot is an important disease in Kohgiluyeh and Boyerahmad province peach orchards. Its signs are wilting, general weakness, loss of foliage and sometimes sudden wilt and death of the tree. To isolate the pathogen, used corn meal-agar with antibiotics, Delvasid, Ampicillin and rifampicin medium. Pathogen is Phytophthora cactorum. For pathogenesis test, 2 inoculation methods, to a tree branch or contaminated soil around the roots and crown of seedling is used. Inoculation roots and crowns of seedlings and saplings of six varieties of peaches with this pathogen, showed that Takheh is resistant, Alberta, Redhoon and Mashhad red peach are semi-resistant, Angiri and J.H.Hill are sensitive to the disease.

The soft rot causal bacteria, species of Pectobacterium and Dickeya, are important pathogens of plants, which have worldwide distribution. These bacteria are very broad host range and cause plant tissues rot. Diseases caused by these bacteria in the form of soft rot, black stem, bulb rot and leaf spot of corn, rice, canola, sugar beet, potatoes, banana, dates, carrots, cabbage, onions, turnips, peppers, philodendron, pandanus, dieffenbachia, Cyclamen, Iris, Aglaonema, Dracaena, Gladiolus, Ficus, ornamental cactus, and Orobanche have been reported from Iran. Some varieties of field crops such as corn, tomatoes, potatoes and sugar beet, as tolerant to these bacteria in Iran.