Fermentation: an Unreliable Seed Treatment for Bacterial Fruit Blotch of Watermelon
Acidovorax citrulli is a seed-borne pathogen that causes bacterial fruit blotch (BFB), a global threat to watermelon production. Treating watermelon seeds to eliminate A. citrulli is a critical component of BFB management and several strategies have been evaluated to mitigate the impact of the disease. In China, watermelon seed producers routinely incubate seeds in watermelon juice (fermentation) to reduce the risk of seed infection by A. citrulli and seedling transmission of BFB. However, there has been limited effort to evaluate the efficacy of fermentation in mitigating A. citrulli seed infection. The current study first showed that fermented watermelon fruit juice could inhibit A. citrulli population growth, and further demonstrated that the low pH conditions, not the dynamic of temperature, generated during the fermentation process might play a major role in inhibition of growth of A. citrulli and could induce the viable but non-culturable (VBNC) state in A. citrulli. We developed an effective method that was based on PMA-PCR to detect viable A. citrulli cells under low pH conditions or in fermented watermelon fruit juice. We also provided evidence that VBNC A. citrulli cells induced by fermented watermelon fruit juice could not be resuscitated and did not retain their virulence on watermelon seedlings. However, VBNC A. citrulli cells could be resuscitated in LB medium. Based on these observations, we conclude that fermentation in watermelon fruit juice may not be an effective seed treatment for BFB as it may increase the seed infection by A. citrulli.