نشریه دانش بیماری شناسی گیاهی
پیاپی 1 (پاییز و زمستان 1390)

Arbuscularfungi are root symbiontsof 80% of plants, such as most field crops and fruit trees. They establish in root tissue, arbuscule in endodermis cells, and an extramatrical fine hyphal net. These fungi byincreasing absorption of water and nutrient elements for plants, making changes in chemical constituents of plant tissues, competition with pathogens for nutrients and establishment site, structural changes in roots, alleviation of environmental stresses, and increasing population of useful bacteria in soil, help management of diseases caused by fungi, fungal like organisms, nematodes, bacteria, phytoplasmas and physiological disorders. Collection, identification, purification, propagation, and inoculation of these useful fungi to plants, can decrease usage of chemical fertilizers and pesticides that are harmful to consumers of agricultural products as well as to the environment.

In order to control plant parasitic nematodes, in spite of chemical costs, some may have residue in yield, some kill the natural enemies of nematodes, and many of them may pollute the environment. Based on research carried out by oil, seed kernel extract and powder, and meal of neem, complete bead-tree seed extract and powder, yarrow aerial parts extract and powder, can cause mortality of these onstage juveniles of the root-knot nematode Meloidogyne incognita. The effect of these plants materials on the nematode mortality compared with control and showed statistically significant difference at the level of 1%. Application of these plants materials maybe reduces of chemical pesticides and risks of their using.

Banana is one of the important fruit in tropical humid areas. In Iran it grows under plastic cover in the Mazandaran and Golestan provinces. Bacterial leaf spot and necrosis disease of banana have been reported from these provinces. Symptoms of this disease are seen as necrotic spots on central young leaves. Spreading these spots, the diseased leaves become completely rotten and the plant growth will stop. Causal pathogen is the bacterium, Xanthomonas campestris pv. musacearum, which produces yellow mucoid colony. This is agram-negative, non-fluorescent, oxidase negative and catalase positive bacterium. Pathogenicity test of bacterium can be proven by its inoculation to banana leaves. Disease symptoms, sampling, isolation and methods of pathogenicity test of the bacterium, and disease management have been described in detail.

Increasing world population and food demand in recent decades, as well as the importance of environmental health, most researchers focused attention to the use of microorganisms to improve the crops yields. Some species of Trichoderma are known to be plant growth promoters. It is believed that Trichoderma species, not only decrease the pathogens in the soil, but also increase growth of underground or aerial parts of the plants with establishment and abundant sporulation in soil, especially around roots of field crops, vegetables, cucumber, and ornamental plants, by bio-chemical mechanisms. With respect to isolation and reports of many Trichoderma species from soils of Iran, importance of researches on plant growth promoting effects of these fungi highlighted more than the past.

The importance of plant protection is increasing with the need of optimizing the quality of agricultural yields. This is essential to search for suitable and appropriate microorganisms for biological control and also study and practice on how to use the optimal conditions for the successful management of plant diseases. One of these microorganisms is the fungus-like, Pythium oligandrum that live saprophytic in the soil. This microorganism has antagonistic and hyper parasitic effects on some of soil borne pathogens. This is not virulent on the 12 species of plants, belonging to six families and only present on their root surface. It is used for control of the wide range of pathogens of the field crops and also can stimulate plant growth, result in increasing the yield.

In some wet areas of Iran, mancozeb is widely used for control of the downy mildew of cucumber which is harvesting shortly after spray application. Therefore residual detection of this fungicide in the cucumber fruit is important, considering the consumer's health. Residual amount of this fungicide is detecting in the randomly collected cucumber fruit samples. In this regards, fruit samples in 100 gram weight is taken and the juice extracts using N-hexane solvent in the succulent apparatus. Then the extract examine at the light with wave length of 280 nm by spectrophotometer. The relationship between amount of the light absorption by the extract and concentration of mancozeb active ingredient is determined, using the linear diagram. The maximum allowed residual level for cucumber fruit, is 2 mg/kg.

Cultivation of bell-pepper has been developed in Esfahan province, due to its nutritional value and consumption amount. In a survey, fields and greenhouses investigated for foliar diseases of this plant and diseased plants were collected. The collected plant materials were kept in clean plastic bags and transferred to lab. Studying the diseases symptom and isolation, purification, and morphological characterization of pathogens, five common diseases of aerial parts of bell-pepper including downy mildew, powdery mildew, Sclerotinia stem rot, Alternaria blight and gray mold, were identified. Causalfungi were Peronospora tabacina, Levielulla taurica, Sclerotinia sclerotiorum, Alternaria alternate and Botrytis cinerea, respectively. Methods of sampling, isolation and purification of pathogens, diseases symptoms and morphological characteristics of pathogens illustrated.