Evaluating the resistance of Potato tubers under different temperatures related to Potato bacterial soft rot disease control

Background and objectives
Potato bacterial soft rot is considered one of the most common bacterial diseases of Potato.Soft rot of potatoes was caused by a range of bacteria worldwide, such as Pectobacterium carotovorum subspecies carotovorum, Pectobacterium atrosepticum, and Dickeya species.The bacteria mainly attack the fleshy storage organs of their hosts (tubers, corms, bulbs, and rhizomes), they also affect succulent buds, stems, and petiole tissues. Controlling the disease is not always so effective, sanitary practices in production, storing, and processing which can be done to slow the spread of disease and protect yields. Little information is available on the effect of temperature on pathogen interaction with plants and the induction of PR genes. In the present study, an attempt was made to establish a relationship between the accumulation of PR proteins and the development of resistance obtained by infecting Potato tuberculosis cells with bacterial pathogens at different temperatures to  effectively control potato bacterial soft rot disease.
Materials and methods
Pectobacterium carotovorum, strains A₂ and A₁₄, Pectobacterium atrosepticum, strains A₂₁ and A₃₆, and Dickeya-dadantii ENA49 were used. Potato cultivars Scarab, Vetraz, and Odyssay, were used for the bacterial infection. The experiment was factorial with three replications based on a completely randomized design. The macerated tissue weight was measured in mg per disc. In other experiment, the relative value of mRNA copies of studying genes was determined in potato tuber cells of two semi resistant and susceptible cultivars which infected with bacterial strains of Pectobacterium carotovorum 2A, Pectobacterium atrosepticum 36A, and Dickeya dadantii ENA49 which were incubated under temperatures of 18, 28 and 33 ^{° C}.
Results
Odyssay cultivar of Potato as a susceptible cultivar and Scarb cultivar as a semi-resistant cultivar to Potato pathogens under different temperatures (18^°С, 28^°С and 33^°С) were identified. When potatoes are infected with pectolytic bacteria, the genes PR-3, PR-5t and   PR-10 were expressed. In tubers and leaves of resistant potato cultivars, the level of PR-5t gene expression is significantly higher than that of susceptible cultivars, when infected with bacteria and without infection. There is a correlation among expression levels of PR-5t gene in the tissues of potato tubers with their resistance to bacterial soft rot.
Discussion
Several pathogens usually attack plants. Different defence pathways in plants have evolved in reaction to the pathogens. These defence mechanisms can be stimulated and activated by some microorganisms or chemicals. Temperature can be considered a virulence factor. It has a significant effect on the pathogenicity of pectolytic bacteria Pc, Pa, and Dd. Plant resistance to pathogens is directly related to pathogenesis expression related genes and defence response genes. When potatoes are infected with pectolytic bacteria, the induction of pathogenesis related genes and Potato defence response genes occurs which is in consistent to other researchers' findings on plant resistance mechanisms to pathogens through the induction of defence response genes. The experimental results showed that when potatoes are infected with pectolytic bacteria, the induction of several PR genes occurs, especially PR-3, PR-5t, and PR-10. The induction of the PR-10 gene is stimulated by the infection of Pc and Pa at low temperature (18 ^{° C}).