| Summary: | Flax (Linum usitatissimum L.) is grown in different climatic zones as both a spring and winter crop. Adaptation to different growing conditions produced genotypes with different growth durations and degrees of photosensitivity. It was always of great importance for breeders to create varieties with rapid development, in particular, early-flowering ones. The evaluation of lines from the VIR flax genetic collection revealed a wide intraspecific diversity in the duration of growth phases, the number of leaves on the stem (physiological indicator of early flowering), and the degree of photosensitivity. Line gc-109, early flowering under the long-day conditions, but greatly photosensitive, was found to possess the wf1 (white flowers) gene, associated with early flowering and a small number of leaves. This line was crossed to the late-flowering but low-photosensitive line gc-375, which had reddish purple flowers. The analysis of segregation in F2 held under the long (19 hours) and short (12 hours, daylength at the equator) day conditions showed that the number of leaves on the plant stem was associated with the flowering time and controlled by close genetic systems only under the long-day conditions. In addition, no relationship between the flowering time and petal color was found under the short-day conditions. Thus, different groups of genes are active in different light schedules. More than 200 lines of the 6th generation of inbreeding were obtained from the plants of the hybrid population. Their field testing under the long-day conditions showed that although the majority of the lines with white petals flowered early and had a small number of leaves, some of them bloomed later and were leafier. On the contrary, the early flowering and less leafy lines appeared among the lines with colored flowers. Therefore, it is reasonable to assume that a crossover between the gene participating in the control of early flowering, which came from the gc-109 line, and its wf1 gene occurred in meiosis of F1. The linkage between the genes controlling early flowering and white petals suggests that flower color can serve as a marker of early flowering in the selection of early breeding material.
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