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In the course of its evolution, plants have developed various mechanisms that act on the local and systemic levels and which role is to adapt plants to the environment they live in. One of these mechanisms is widely recognized plant defense system directed against biotic factors, to which belongs, among the others, pathogen attack. The first line of the defense against pathogen attack is so called structural constitutive resistance determined by plant anatomical structure and chemical constitutive resistance consisting of unfavorable effect of plant secondary metabolites against the pathogens. Epidermis and periderm play a main role in structural constitutive defense. Layers and waxes are present in epidermis and there are trichomes and thorns on its surface, and on the surface of roots hairy roots. Cell wall itself is also a very important structural barrier. Lack of the continuity of epidermis, caused by wounding or the presence of the natural openings (stomata, spiracles and hydathodes that are the potential places of the pathogen attack), enables pathogens to overcome the first line of defense. Systemic acquired resistance (SAR) and induced systemic resistance (ISR) constitute the second line of plant defense system. Induced systemic resistance has been studied in respect of mechanism of its development and in respect of signaling pathways that transmit the ISR signal to distant plant tissues and organs. The main reason of research, however, is prospect to exploit this phenomenon as the plant protection system against pathogens. Utilization of ISR in agriculture could possibly at least significantly decrease the amount of chemical pesticides. The largest group among plant pathogens is fungal pathogens, mainly necrotrophic fungi including grey fungus Botrytis cinerea, Fusarium oxysporum, Alternaria species and pathogenic oomycetes Phytophthora infestans. B. cinerea infection causes grey mold disease, seedling blight and the death of stem in many plant species in pot plants and crops as well as in conifer and broadleaved trees and shrubs. Fungi of Alternaria genus cause potato or tomato alternariosis, blight of tomato seedlings and infest vegetables and black spot disease in crucifers. Fusarium wilt caused by F. oxysporum is the most destructive disease of potato and tomato, while P. infestans causes potato blight. Necrotrophic fungi can infect living tissues, but their development and reproduction take place only on death tissue. Necrotrophic fungi secrete specific enzymes and mycotoxins during the penetration of host tissues. These substances cause the death of host cells and enable pathogen to feed in the host`s death tissue. Plant diseases caused by described above necrotrophic fungi are very often epidemic, and lead to destruction of entire field causing significant yield losses in agriculture, horticulture and fruit farming. Plant protection against infection of necrotrophic fungi is currently based on keeping the agrotechnical rules regarding soil quality, term of planting, use of fertilizers and chemical protection. At the beginning of 90` last century it has been reported on ISR induction by inoculation of cucumber rhizosphere with bacteria of Pseudomonas genus against Colletotrichum orbiculare, that causes anthracnose in cucumbers. Further research has shown, that this kind of resistance was induced by plant growth-promoting rhizobacteria (PGPR), which colonizing plant roots promote plant growth, rhizoremediation and soil fertilization (Azospirillum, Herbaspirillum, Enterobacter, Acetobacter, Azotobater i Pseudomonas). On the other hand it reduced disease symptoms caused by pathogens and herbivorous insects (Bacillus, Pseudomonas i Serattia). In this paper, we describe molecular mechanisms of ISR induced against necrotrophic fungal pathogens in a light of the current results of research. We provide also examples of ISR induction by nonpathogenic Pseudomonas strains that belong to PGPR. Selected Pseudomonas factors responsible for ISR induction have been divided into direct and indirect factors. Direct factors constitute a competition for iron and antibiotics production and indirect factors bacterial lipopolysaccharide (LPS), Pseudomonas metabolites massetolide A, N-alkylated benzylamine derivative (NABA) and N-acyl-L-homoserine lactone (AHL).

The Editorial Board
Andrzej Łukaszyk - przewodniczący, Zofia Bielańska-Osuchowska, Szczepan Biliński, Mieczysław Chorąży, Aleksander Koj, Włodzimierz Korochoda, Leszek Kuźnicki, Aleksandra Stojałowska, Lech Wojtczak

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