Abstract
The aim of the research is to determine in the moderately cold climate of Tyumen the timing of the onset and duration of the vegetation phases of red clover cultivars developed in other climatic regions of Russia and abroad. The studies were conducted in a collection nursery in the 2nd year of plant life (2017, 2019–2024). Studied were 39 cultivars characterized as diploid one-cut, diploid double-cut, and tetraploid double-cut. Based on the dates of flowering and seed ripening, 17 cultivars were classified as early-ripening and 22 as late-ripening. The beginning of flowering of early-ripening cultivars was noted in the 2nd and 3rd decades of June – 1st decade of July with the sum of effective temperatures (> 5 °C) of 461–722 °C, late-ripening ones – in the 1st and 2nd decades of July at 545–898 °C. The flowering and seed maturation phases of early-ripening cultivars began, on average, 15 days earlier than those of late-ripening ones. The total duration of the growing season was 99–127 days for early-ripening cultivars, and 123–148 days for late-ripening ones. A significant effect of moisture conditions during the mass flowering phase of plants in July on the maturation time of seeds of late-ripening cultivars was noted (r = 0.76; 0.90). With sufficient and excess moisture (HTC from 1.08 to 1.75), the seeds of late-ripening cultivars ripened no earlier than September, while with HTC values ≤ 1 (from 0.28 to 0.90), they ripened during August. The sum of effective temperatures at the seed ripening date of early-ripening red clover cultivars was 1138–1375 °C (average 1278 °C), while for late-ripening ones it was 1357–1516 °C (average 1489 °C). Correlations between the length of the growing season and agroclimatic parameters during the field season were weak. Collection cultivars from one and the same maturity group can be used in breeding work as parental forms in polycross nurseries.