نشریه دانش بیماری شناسی گیاهی
سال سوم شماره 1 (پیاپی 5، پاییز و زمستان 1392)

Metabolomics or analysis of the whole cellular metabolites is a new and powerful tool that provides a quick view to the large numbers of small molecules (metabolites) within the cell and indicates dynamics of these molecules under different conditions. Quantitative and qualitative measurements of these metabolites provide some useful information on biochemical status of the cell so can be used to monitor the gene functions. Nowadays, metabolomics has a wide range of application in agriculture. Metabolomics is mainly used for the study of plant responses to a wide range of biotic or abiotic stresses including plant storage diseases as well as the resistance of plants to the pathogens. Since metabolites are final products of gene expression and all changes in gene expression is reflected in metabolite profiles, hence metabolite profiles provide a good comprehensive understanding of plant defense mechanisms against plant pathogens. This is a rapid, simple and accurate tool for identifying the metabolites associated with resistance as a biomarker for screening the resistant cultivars against plant diseases. In addition, understanding the resistance mechanisms at molecular level provide a better understanding of resistant gene function and pyramiding suitable resistant gene in elite cultivar. This is a review article on different methods of studying the plant metabolites and their administrative problems in plant pathology.

Plant nutrients are generally applied to increase the crop production and improve their quality. Many of these elements can improve the level of tolerance or resistance in plants. Improving and balancing the soil nutrients can be considered as an effective method in plant disease control and subsequently in sustainable agriculture. Plant nutrition is the first and the most important barrier against the plant pathogens, so can be affect the other parts of the disease triangle. They can satisfactorily decrease the diseases severity, or make a considerable reduction in their density, so the other control measures successfully can be carried out with a lesser costs of plant disease management. In this review we tried to explain the most recent data collected about the influence of mineral nutrients on plant disease resistance and tolerance, histological or morphological changes of plants and the virulence or survival of plant pathogens.

Fungal diseases of plants are major treats for agricultural products. Lots of fungicides are widely used to control the plant pathogens. Incidence of resistance to the fungicides in the pathogenic fungi is a main limitation in their use. With some exceptions, in general, there are more reports on the resistance of fungi to systemic fungicides than the non-systemic ones. This review discusses the mechanisms of resistance to chemical fungicides (e.g. altering the target site, reducing the fungicide uptake, fungicide removal, detoxification or metabolism of the fungicide) in some phytopathogenic fungi at the molecular level and describes the methods (e.g. RFLP-PCR, and allele specific real-time PCR) used in molecular detection of resistance to the fungicides.

Alfalfa downy mildew, caused by Peronospora trifoliorum, is one of the limiting factors in alfalfa production. Under favorite conditions in spring, the disease is prevalent after first moving and the plant leaves turn to yellow followed by drying. The standard greenhouse experiments and field screening methods are applicable to select the resistant ecotypes of alfalfa to this disease. In greenhouse tests, seven days old seedlings of alfalfa are inoculated with spore suspension. After completion of incubation period and the first symptoms were observed, the percentage of the symptomless seedlings are comparing with resistant control. Field experiments must be carried out for different alfalfa ecotypes in locations with suitable conditions for natural occurrence of disease, using an appropriate statistical design with minimum three replications. The response of cultivars evaluate based on disease severity. In Iran, the cultivars KS224 and Saranac showed resistance to downy mildew and some ecotypes like Kiseverdai, Nikshahri, Gharghlooogh, Malek-Kandi and Gharghloogh known as tolerant to disease.

Yellow rust is a major disease of wheat in Iran. Airborne spores of the fungal pathogen are the primary source of contamination. Temperature, humidity, intensity and direction of wind, cultivars response to disease, existence of volunteer wheat in summer, planting time and level of nutrition, are main factors which affect the disease epidemic. In forecasting model based on the disease tracing and its severity in a particular year, some effective agents such as climatic factors, cultivars response and plant growth stage, are determining the numbers of fungicide application. In this review, the importance of disease in the world and Iran as well, disease symptoms, causal agent, effective factors in disease spread, forecasting model and its executive steps and also the suitable fungicides for disease control have been described.

Salicylic acid basically is one of the phenolic acids compounds which are necessary for inducing systemic acquired resistance is produced in plants in response to a large number of plant pathogens. Salicylic acid is responsible for expression of the pathogen related proteins. This is produced in plants in connection with hypersensitive reaction and systemic acquired resistance. Some changes which inhibit the salicylic acid production as well as its deactivation in plants, can increase the disease susceptibility to plant pathogens. The role of salicylic acid and the required pathways in inducing systemic acquired resistance and final yield increase have been described.

Most of the symbiotic fungi can improve the growth of the host plants by increasing in water and nutrients absorption. Among the symbiotic fungi, Piriformospora indica or Piri have a good potential in symbiotic relation with plants and well known for its effect on host plants by increasing adventitious roots and growth stimulation in above and below ground parts of the plants. The effects of this fungus on vegetative growth of some medicinal plants and accumulation of the secondary metabolites have been discussed.