Evaluation of Ukrainian potato varieties and breeding material for resistance to pathotypes of Synchytrium endobioticum occurring in Georgia and Ukraine

Aim: To evaluate new Ukrainian potato breeding material for resistance to the common pathotype 1(D1) of the potato wart pathogen Synchytrium endobioticum. Furthermore, to re-evaluate during 2021–2023 seventeen Ukrainian potato varieties for the validity of previously determined resistance towards the common pathotype 1(D1), and also to assess resistance to 4 virulent pathotypes present in Ukraine and one virulent pathotype occurring in Georgia. This all to introduce new sources of resistance in Ukrainian breeding programs and to use resistant material (more) effectively in disease foci in the respective countries. Materials and Methods: In our present study 971 samples of potato breeding material were used in the first year of laboratory testing and 306 samples in the second year. The breeding material used originated from of the Institute of Potato Research of the NAAS of Ukraine (IPR NAAS), and its Polissia Experimental Department (PED). Seventeen Ukrainian potato varieties (Table 3) were used for field studies to validate the earlier assessment of resistance to S. endobioticum common pathotype 1(D1), and to evaluate resistance to virulent pathotypes present in Ukraine (11(M1), 13(R2), 18(Ya), 22(B1)), and one virulent pathotype found in Georgia (38(N1)). The resistance to the potato wart pathogen was assessed under laboratory conditions against an artificial infectious background, using winter and summer zoospores for the breeding material and a natural infectious background in some foci of the pathogen in Ukraine and Georgia, according to EPPO Standard PM 7/28(2) and the national methodology harmonized with the EU requirements. Results: Resistance to winter zoospores of the common pathotype 1(D1) was determined in 949 out of 971 samples (97.7%) in the first year of testing and in 300 out of 306 samples (98%) in the second year, using summer zoospores. Resistance to 11(M1) was present in 14 varieties (82.4%): Alians, Glazurna, Khortytsia, Podolianka, Rodynna, Shchedryk, Skarbnytsia, Slauta, Slovianka, Solokha, Strumok, Tyras, Vzirets, and Zhytnytsia. Resistance to 13(R2) was also present in 13 varieties (76.5%): Alians, Aria, Glazurna, Khortytsia, Kniahynia, Rodynna, Shchedryk, Skarbnytsia, Slauta, Solokha, Strumok, Tyras, and Vzirets. Resistance to 18(Ya) was present in 8 varieties (47.1%): Aria, Glazurna, Kniahynia, Rodynna, Skarbnytsia, Slauta, Vzirets, and Zhytnytsia. Resistance to 22(B1) was found in 12 varieties (70.6%): Alians, Charunka, Glazurna, Khortytsia, Kniahynia, Rodynna, Shchedryk, Solokha, Strumok, Tyras, Vzirets, and Zhytnytsia. The most virulent pathotype was found to be 38(N1), re-confirming unpublished results of the authors. Only two varieties (11.8%), Kniahynia and Rodynna, were resistant to this pathotype, proving the need for enhanced detection and breeding work to determine the distribution of this pathotype and to adequately control it, once found. The variety Polisska Rozheva, used as a susceptible control, was affected by all pathotypes, which confirms its high susceptibility to the pathogen. Conclusions: In an evaluation for resistance of new Ukrainian breeding material against the common pathotype 1(D1) of S. endobioticum, c. 98% was found to be resistant, when subjected to inoculation with winter, as well as summer spores. Potato varieties that are resistant to one or more pathotypes can be recommended to be used in foci where the occurrence of that pathotype or those pathotypes is known. In case of not fully tested foci, the planting of varieties Glazurna (resistant to all 5 pathotype known to occur in Ukraine, but sensitive to pathotype 38(N1), till now only reported to be established in Turkey, Bulgaria and Georgia) or Rodynna (resistant to all six tested pathotypes) should be enforced. The data on resistance of our testing can be used in further breeding programs. Finally, it is strongly recommended that molecular methods such as marker assisted selection and microsatellite diagnostics are incorporated in Ukrainian and Georgian breeding activities.