نشریه دانش بیماری شناسی گیاهی
سال چهارم شماره 1 (پیاپی 7، پاییز و زمستان 1393)

Barley is one of the world`s most widely consumed cereal. Rhynchosporium commune، the causal agent of barley leaf scald، is one of the most deleterious pathogens of barley which can cause up to 40% yield loss، under favorable conditions. Primary infection takes place by spores produced on infected plant debris. The secondary infection can be repeated by spore dispersal by rain and wind. Although the teleomorphic stage is unknown، high levels of genetic diversity have been observed within and between populations of this pathogen، attributed to some mechanisms such as gene flow، parasexual cycle and asexual recombination. The management of this disease is mainly achieved through cultural and chemical measures of control and use of resistant cultivars. In this paper، different aspects of pathogen symptoms، taxonomy and biology of pathogen، and management of disease are discussed.

Endomycorrhizae or arbuscular mycorrhizal fungi، play an important role in the life of field crops، flower and fruit gardens and vegetables. They increase nutrient uptake and yield of plants and resistance to soil-borne pathogens of plants as well. As these beneficial fungi، are obligate root symbiotic، mass production of their inoculum is only possible on the living tissue of root. The first method for this purpose was pot culturing، then the hydroponic، aeroponic and root organ culture have been devised. Methods and factors affecting the mass production of these beneficial fungi are described and discussed here.

Plant pathogenic bacteria have evolved specialized strategies to infect their hosts. In this regard، the key virulence factors are effector proteins، cell wall degrading enzymes، toxins، extracellular polysaccharides and phytohormones. The interactions between plant pathogenic bacteria and their hosts have resulted in an evolutionary system between host defense responses and pathogen virulence factors. Pathogenic bacteria are continually under pressure to diversify their mechanisms to prevent host defenses and optimize nutrient availability. In turn، these virulence mechanisms have shaped the evolution of plant innate immunity. In this paper، the pathogenicity and virulence factors of plant pathogenic bacteria are discussed.

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.

Mycorrhizal fungi increase water and nutrient elements absorption to the plant and plant provide carbohydrates for the fungus and this is beneficial for both parties. Many plants need to these fungi for absorption some mineral elements and resistance to environmental stresses such as drought، soil contamination to heavy metals such as lead، zinc and cadmium. Some soil borne bacteria have been identified as third part of the mycorrhiza، which cause improving the performance of this symbiotic relationship، and have been named as mycorrhiza helper bacteria.

Chitosan is a biodegradable natural compound derived from the bark of crabs and shrimp which have antimicrobial role against fungi and bacteria. Chitosan has directly effects on morphology of treated pathogens which reflect its fungistatical and fungicidal activity. It has been shown that chitosan increases production of glucanohydrolase، phenolic compounds and specific phytoalexin synthesis with antifungal activity and reduces enzymes such as polygalacturonase، pectin methyl-esterase that related to soft rot. In addition، chitosan can develop structural barriers via lignin synthesis. Therefore chitosan is considered as a new non-toxic biological material، inducer resistance of plants against diseases.