Every year, up to 30% of the potato crop is lost due to soft rot caused by bacteria of the genera Pectobacterium and Dickeya. Treating the storage area with pesticides and chlorine compounds is dangerous and can lead to poisoning. RUDN University biologists proposed to fight soft rot with the help of bacteriophages that destroy specific types of bacteria but do not harm potato cells or people. The results are published in Viruses MDPI.

Mixtures of various bacteriophages, or phage cocktails, are used in agriculture against plant diseases. Thanks to them, it is possible to reduce economic losses due to product damage. But so far, attempts to protect potatoes from soft rot do not go beyond laboratory tests and model strains, and such conditions differ from real ones. To solve these problems, it is necessary to clearly define the list of pathogenic bacteria harmful to potatoes, select the phages that cope with them best, isolate and clean their culture, establish the technology of use in storage conditions and create methods for evaluating the results. This was done by biologists from RUDN University, who tested the technology in the storage facility in 2019-2020.

"To apply a phage cocktail against soft rot on an industrial scale, we need to answer a lot of questions about the genomics of Pectobacterium bacteria and viruses that specialize in them, and better understand the molecular and biological basis of their interaction. We also need to understand the technical details — the production of the cocktail and the form of its use, and get permission at the legislative level. Our research will help solve these problems,” said Prof. Alexander Ignatov, D.Sc. in Biology, from the Department of Agrobiotechnology at RUDN University.

RUDN University biologists together with colleagues from the Research Center "PhytoEngineering", Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, and Moscow State University, collected affected potato samples from industrial storage facilities to determine the main pathogenic bacteria. The strains were distinguished by a PCR test and by variations in the 16S rRNA gene sequence. The researchers found that the strains that looked like Pectobacterium carotovorum belonged to the newly identified species Pectobacterium versatile. In addition to it, the most common strains were brasilense Pectobacterium and Pectobacterium polaris, which are often found in the fields of Central and Eastern Europe. But Pectobacterium atrosepticum and representatives of the genus Dickeya, which caused outbreaks of diseases in the early 2000s, were not in the samples.

Microbiologists tested 50 bacteriophages on these strains and selected the most effective varieties. At the same time, scientists have identified viruses that destroy bacteria, and not just infect them, integrate into their genome and go to "sleep mode". The cocktail was tested in an industrial potato storage facility in the Rogachevo Agropark. Potatoes were treated once a week for six months. As a result, the growth of phytopathogenic bacteria on tubers decreased by 10-12 times.

"Precautions in potato warehouses, for example, low temperatures, cannot give one hundred percent guarantee of crop safety. During the experiment, no significant outbreaks of the disease occurred at the control storage facilities, so in the future, we want to understand exactly what concentration of bacteria and under what conditions leads to spoilage of potatoes. We have successfully tested the technology for crop protection and developed a convenient and fast method for monitoring the population of bacteriophages so that they can be used on an industrial scale,” said Prof. Alexander Ignatov, D.Sc. in Biology, from the Department of Agrobiotechnology at RUDN University.

Journal Link: Viruses 2021, 13(6), 1095