Evaluation of plant growth regulators for control of dormancy in apricot (Prunus armeniaca L.)

In an environment where fruit production is increasingly affected by unpredictable weather patterns, it is important to look for ways to minimise the impact of climate change on production. Under Central European condi-tions, a limiting factor for apricot (P armeniaca L.) growing in certain years is the occurrence of late spring frosts. One measure to eliminate their impact is to delay the actual flowering of the trees. This can be done by breeding or just by applying various plant growth regulators (PGRs). According to our results the varieties with a long dormancy period in the conditions of the Czech Republic are `Velika Luka' (dormancy break 79 days from the beginning of December), then `Bai Gon' with the same values, `Chuang zhi hong' (dormancy break 73 days from the beginning of December) and hybrid form Lednice `Pozdne kvetouci,' which had an average dormancy break 70 days from the beginning of December, even though in most years in field conditions it often blooms as one of the last genotypes. Next, we tested the effect of 6 active substances in 16 different concentrations on their ability to delay flowering. The results show that the application of Ethrel-based mixtures (concentrations of 0.05 and 0.5%) had the greatest influence, delaying flowering by up to 3-5 days, but also had the most destructive effect on tree health. The application of the commercial prod-uct Rhodofix (NAA-1-Naphthaleneace tic acid (NAA)-0.3%) and the application of a proprietary mixture based on NAA 1.0% did not have a very significant effect, with a delay in flowering of just 2 to 3 days. One interesting finding was that the application of the above products had a statistically significant effect on the ripening date of apricot fruit, with a difference of up to 4 days. Based on the results, the application of PGRs can affect the flowering time, but not in a completely fundamental way. Thus, protection against late spring frosts is therefore dependent on a combination of several approaches.