No significant differences have been observed between introduced (American and European) and Moldavian ones according to the time of initiation and characteristics of the differentiation of flower buds. American varieties Rival, Robada, Lorna, Katy, do not have an acceptable resistance of flower buds to the winter low (-15 - -20 oC during 7-10 days) temperatures. Only some studied American genotypes have the earliest beginning of blooming (1-2 days) in comparison to the Moldavian ones. There have been found some Romanian varieties with late blooming period. The period of flowering of CR-263, NJA-42, Paterson, Tilton coincide with the principal Moldavian varieties (Bucuria, Krasnoshciokii, Nadejda, Detskii), serving as good pollinators for them. The most of American varieties are more susceptible to the attack of Monillinia laxa than Moldavian ones.