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The objects of research are sixteen cultivars nectarines and elite, which data were reported for the period 2019-2021 on the territory of the Fruit Growing Institute - Plovdiv. The purpose of the study is to group and evaluate according to the degree of frost on their flowers. For this purpose, single factor analysis of variance and Tukey’s test were applied for difference estimation as well as hierarchical cluster analysis. It was established that during the three years of research, the Sunfree cultivar freezes 100%, which made it the most susceptible variety to temperature effects. The least consequences of negative temperatures on the flowers are the least in the Gergana variety for 2019 (33%), the Morciani 90 for 2020 (84%), and the El. 4-151 in 2021 (72.66%). As a result of the studies, it was established that the resistance to low temperatures in different cultivars and elites is largely determined by the degree of coincidence of the phenological stages: early bloom and full bloom with those negative temperatures. [ABSTRACT FROM AUTHOR]

This study investigated the changes at the values of fertile eggs (%), hatchability of set eggs (%) and hatchability of fertile eggs (%) during the period 2009–2017 in five lines of hens. The changes of the values at these traits during different years were represented by mathematical models. Regarding the values of fertile eggs (%) in the studied years from 2009 to 2017 varied at diferent extent in the five hen genotypes. It was found that in the studied years 2009–2017 fertility of eggs (%) has the highest coefficient of determination in line STR (76%), and in hatchability of set eggs (%) – in line GN (75%). In the different years from 2009 to 2017, the hatchability of fertile eggs (%) was statistically closest values at the eggs of line E (80%). Third-order polynomial regression models depicted the values of these parameters of the different years in the best way. They represented wave-like patterns of parameters’ time course and instability in all lines of hens. [ABSTRACT FROM AUTHOR]