Tree mortality was recorded in a selection orchard of maintenance breeding of cv. Bergeron LE-2 in 1993–2002. The beginning of blossoming was examined in individual trees in the same orchard in 1999–2002. Considering the effect of year, a maximum difference in the average beginning of blossoming was 10 days in the whole set of trees. The beginning of blossoming of individual trees was not identical in the same year. A difference in the onset of phenophase “beginning of blossoming” between early and late blossoming trees was 1–4 days in the particular years. The trees maintained their early or late blossoming for the whole period of evaluation. No tree died in the orchard by 1998. From 1999 to 2002 50% of early blossoming trees died and only 2.38% of late blossoming ones (average of three replications). Two thirds of early blossoming trees died during vegetation, a third died during vegetation rest. No commercially important viroses were proved to be present. It is the reason why viruses could not be a potential cause of the above-mentioned facts. The presence of phytoplasm (ESFY) was confirmed by the method NESTED PCR in one case in a randomly selected early blossoming tree. The test was negative in two randomly selected late blossoming trees from underplanting. The early beginning of blossoming did not influence productivity. Correlations between the beginning of tree blossoming and blossom abundance, or between the beginning of blossoming and productivity, were insignificant (r = 0.12 or
r = –0.13). Even though the causative agent of higher mortality in early blossoming trees was not confirmed unambiguously, it is desirable to select the best individuals only from the group of late blossoming ones during maintenance breeding of cv. Bergeron. These individuals should be used as prebasic material in a certification process and as basic material after prescribed repeated testing.