Abstracts |
Natural soil salinity, or salinity resulting from salt-rich irrigation water, not only poses a threat to crop production, but also it affects the distribution and severity of the soil- and air-borne diseases. Under these circumstances, salinity may interact with the pathogens in the soil or in irrigation water; as a result, salinity may either result in reduction in the effectiveness of fungi through the reduction of sporulation and conidial germination or lead to an increase in the virulence of pathogens through stimulation of enzymatic activities such as cellulase, pectin lyase, and polygalacturonase produced by the microorganisms. In some cases, salinity may have an additive negative effect on fungal-infected plants without interacting with the fungal pathogens.
In the first case, the negative effect of salinity may prevent the pathogenic propagules from reaching the root infection sites and reduce the efficacy of the pathogens by means of a reduction in protein and enzyme syntheses. Therefore, salinity may negatively affect the prevalence and distribution of the pathogen. In the second case, salinity may have a positive effect on pathogen growth. It may increase the development of motile zoosporangia, spores, conidia, and the germ tube formation of the fungi as well as result in increased enzymatic activities. Thus, the fungi may grow better and become more virulent. After an adaptation period, halophytic races of the fungi may also appear and cause a threat to crop production in nonsaline and saline soils. Under these circumstances, development of symbiotic bacteria and mycorrhizal fungi also may be negatively affected through the reduction of colonization capacity. In the third case, the combined effect of both salt (even low concentrations) and the pathogen may cause a more serious problem than those of either the negative effect of salt or the pathogen alone. Under such conditions, additional energy may be required due to an additional effect of stress resulting from the fungi. Therefore, plant growth is significantly retarded and crop production is seriously reduced, as well as a deterioration in fruit quality. The strategy, therefore, should be to aim to develop new disease-resistant and salt-tolerant plants that can thrive in spite of the effects of both pathogens and salinity; this is because the behavior and the characteristics of plant pathogens constantly change under salinity and adapt to the conditions of salt-tolerant plants.
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