Biological features of the vegetative and flowering phenophase onsets among diploid plum species in Northwestern Russia

   Background. Monitoring of phenological rhythms in plants is one of the stages in the study of new genotypes. The adaptive potential of a genotype at the northern border of the area of plum distribution is the main criterion characterizing a cultivar. The main role in the formation of the assortment of diploid plum species in Russia is played by cherry plum, Chinese plum, and Russian plum.   The goal of this study was to identify the factors affecting the dates of the growing season and flowering onsets for diploid plums under the conditions of Northwestern Russia.   Materials and methods. The dates of the onsets of the vegetative and flowering phases in 50 accessions of cherry, Russian and Chinese plums in 1986–2020 served as the material for the study under the conditions of collection plantations at Pushkin and Pavlovsk Laboratories of VIR.   Results and conclusion. All the species demonstrated a tendency towards a shift of phenodates to earlier dates with an average rate of 1-2 days/10 years caused by warming. The conditions of the year had the greatest effect on phenodates, as they determined 67.0–68.3 % of the variability in the phenophase onset dates; the impact of the species factor was manifold less: 0.5–1.1 %. Russian plum occupied an intermediate position between cherry plum and Chinese plum in the onsets of both the vegetative and flowering phases. No differences were observed between the species in the duration of the period between the onsets of the vegetative phase and flowering. According to the long-term observations, the most adaptive cultivars were cv. ‘Podarok Sankt-Peterburgu’ (k-41445) of Russian plum, with medium dates of both the vegetative and flowering phase onsets, and with a 20-day difference in years in the onsets of these phases, cv. ‘14-1-14’ (k-7375А) of Russian plum, and cherry plum cvs. ‘Pchelnikovskaya’ (k-41446) and ‘Krasnaya 25-29’ (k-15792А).