Highly Targeted Detection of Priority Phytopathogen Pectobacterium brasiliense: From Obtaining Polyclonal Antibodies to Development and Approbation of Enzyme-Linked Immunoassay and Lateral Flow Immunoassay

<i>Pectobacterium brasiliense</i> is a bacterial phytopathogen that causes soft and black rot and actively spreads worldwide. Our study is the first development of immunoassays for detecting <i>P. brasiliense</i>. We immunized rabbits and obtained serum with an extremely high titer (1:10⁸). Isolated polyclonal antibodies were tested by enzyme-linked immunosorbent assay (ELISA) using 18 closely related strains and 5 non-related bacterial pathogens. No cross-reactivity was found concerning the tested pathogens. The ELISA of <i>P. brasiliense</i> was developed in a double-antibody sandwich format with a detection limit of 1.5 × 10⁴ cells/mL. A lateral flow immunoassay (LFIA) for <i>P. brasiliense</i> was also developed in a double-antibody sandwich format with a detection limit of 1 × 10⁵ cells/mL. The results of <i>P. brasiliense</i> cells testing with LFIA in plant matrix showed a high correlation (R² = 0.932) between concentrations of added and revealed cells. When testing potato seed material, ELISA and LFIA confirmed 75 and 66% of positive samples according to real-time PCR, respectively. For negative samples, ELISA showed 84% coincidence, and LFIA coincided with PCR for 89% of samples. Thus, the developed immunoassays can be used to evaluate plant material in poorly equipped conditions or under field testing.