Temperature-dependent interaction between Erwinia persicina and Pectobacterium brasiliense enhances potato soft-rot severity

Abstract Potato soft rot is associated with pectolytic bacteria in the genera Pectobacterium and Dickeya, but mixed bacterial infections may intensify disease severity. Since 2018, potato tubers with soft rot and distinct pink discoloration have been repeatedly observed in seed stocks from several regions of the Russian Federation, suggesting involvement of atypical pathogens. During surveillance conducted from 2018 to 2023, 32 pink-pigmented bacterial isolates were recovered from symptomatic potato tubers. Five isolates collected between 2021 and 2023 (EP01–EP05) were selected purposively for detailed characterization to represent variation in colony pigmentation, hypersensitive-reaction intensity, soft-rot severity, collection year, and geographical origin. Phenotypic, biochemical, and multilocus sequence analyses of the 16 S ribosomal RNA (rRNA), gyrB, and rpoD genes identified all five isolates as Erwinia persicina. Pathogenicity and hypersensitive-reaction assays confirmed their ability to cause soft rot in potato tubers. Co-inoculation with Pectobacterium brasiliense, P. atrosepticum, P. versatile, P. parmentieri, and P. carotovorum showed the largest co-inoculation-associated increase with P. brasiliense; responses with other species were variable. At 24 °C, the lesion diameter increased by approximately 14.4% with P. brasiliense combined with E. persicina strain 1790, and by 33.9% with potato isolate EP04. For the E. persicina × P. brasiliense combination, the increase was temperature-dependent, with lesion size rising by 17.0–29.0% at 5–20 °C and by 34.2–73.4% at 25–35 °C compared to P. brasiliense alone. Some other pairings also showed changes in lesion diameter (Table 3); the results therefore do not establish an exclusively P. brasiliense-specific interaction. These results suggest E. persicina can serve as an accessory to the potato soft-rot complex under these conditions, with the temperature-dependent severity increase specifically observed in the EP04 × F126 strain pairing.