نشریه دانش بیماری شناسی گیاهی
سال دوم شماره 1 (پیاپی 3، پاییز و زمستان 1391)

Powdery mildew fungi are important obligate parasites of plants. They produce white cover on aerial parts of host plants, which then turn to yellow. The diseased plant becomes yellow and then wilted result in reducing quality as well as quantity of products in field and vegetable crops and also fruit trees. Among all of the control measures against powdery mildew, the most common method is application of the chemical fungicides, after disease incidence. Regarding to the hazards of agrochemicals and also considering the probability of incidence of resistant races of the pathogen, the biological control is considered as a safe and useful method for controlling the disease. The fungi Ampelomyces quisqualis, Pseudozyma flocculosa and Lecanicillium longisporum; the bacterium Bacillus subtilis; the mite Tydeus lambi and twenty-spotted lady beetle Psyllobora vigintimaculata, have been used effectively against the powdery mildew of cucumber, squash, tomato, pepper, grape and rose. Some of these biological agents have been introduced to the market, commercially.

There are some strategies for adaptation to environmental changes in plants, including a range of molecular-biochemical and also intent or induced mechanisms. The proper response of plant is occurred when it receives extracellular signals and transfers those inside the cell. Ethylene, identified as a plant hormone which regulates the plant reactions under some circumstances. Ethylene production has been enhanced in response to biological stresses like plant infection by pathogens or herbivores attack. Most of induced defense genes are regulated by transduction pathways signal. The biosynthesis pathway of ethylene from the amino acid methionine has been studied well. In this pathway, the produced ethylene activates the resistant genes resulting to incidence of plant resistance. The responsible genes in rice and also the ethylene-expressed resistance genes have been discussed in this review.

Regarding to the need of improving the quality and quantity of agricultural products, the science of plant protection has been taken under consideration. Accurate identification and detection of plant pathogens is one of the best ways for successful plant disease management. One of the useful methods is analysis of the volatile organic compounds, which spread from diseased plants. In this method, specificity of the volatile organic compounds and also the factors that affect the identifying of plant diseases and effective methods on these compounds are important. First, these compounds should be collected and then be analyzed. The best method for analysis of these compounds is dynamic sampling followed by gas chromatography and using the proper probes. Although the high costs of the tools make it difficult to apply this method for agricultural purposes, but by using the statistical methods and estimations the costs can be decrease.

DNA microarrays technology is a method for studying the gene expression in large scale, based on investigations of probes and targets hybridization. This technology can also be used for identification of different organisms. DNA microarrays are a set of probes linked to a solid phase as microscopic spots. After hybridization of targets to probes, hybridization level is calculated by means of different methods such as measuring refulgence of fluorescent dyes to determine gene expression level. A microarray examination has different steps: making DNA chips, preparing targets, performing hybridization, and gathering and analyzing data. DNA microarrays technology can be used in different fields of plant pathology such as identification of different species of fungi, bacteria, nematodes and viruses, and to study plant-pathogen interaction.

Most nematodes are free-living. They live in oceans, fresh waters and soil and feed on bacteria, fungi and other nematodes. Some are predators and some are parasites of plants and animals. Some of the latter group are insect-associated. There are different types of relations between insects and nematodes. Beneficial nematodes that cause disease in insects are referred to as “entomopathogenic” and have the ability to kill the insects. Entomopathogenic nematodes from the genera Stein¬ernema and Heterorhabditis have proven to be the most effective as biological control organisms. Only the infective juvenile stage of entomopathogenic nematodes will survive in the soil, find and penetrate insect pests. In this paper, different types of association between nematode and insect with emphazing on entomopathogenic nematode species have been reviewed.

Sexual reproduction of fungi is governed by the mating type (MAT) locus. Because two alternate forms (alleles) are completely dissimilar sequences and encoding different transcription factors, this locus is structurally unusual, yet they occupy the same chromosomal position. Genomic analyses facilitate the definition of MAT locus sequences in many species, so the knowledge of MAT locus structure and evolution has been significantly advanced in recent years. This important genomic feature has been studied most extensively in the largest phylum of the fungi, Ascomycota, which is the largest group of the plant pathogenic fungi. In this article we discuss the different aspects of mating type genes and their structure and organization in Ascomycota. Knowledge on the mating type genes may provide a great assistance to understanding the potential of phytopathogenic fungi for sexual cycle and consequently on genetic diversity in fungal populations. The proper data on sexual reproduction and genetic diversity of phytopathogenic fungi might be useful in different aspects of plant disease management.