Ecological plasticity and sustainability of cotton in the Southern Steppe of Ukraine

Depending on the length of the cotton growing season, the area of cultivation and its highest productivity potential are determined, and the prompt ripening of raw cotton allows for home-grown harvesting and high-quality soil preparation. The purpose of this study was to identify samples adapted to the conditions of the Southern Steppe of Ukraine from the cotton gene pool. The study used methods of plant variety expertise: phenological observations, morphological studies, and evaluation of breeding material for valuable traits. Based on the study results, parental components were selected to expand the process of forming early-ripening forms and productivity of raw cotton. The ability of cotton plants to grow in extreme conditions of the Southern Steppe of Ukraine was assessed and its homogeneity or stability, the index of growing conditions, the coefficient of variation – the difference in the numerical values of the trait duration of the period “germination – beginning of flowering” of plants in varieties with different growing season and their fluctuations around the average value were determined. It was found that according to the determined plasticity (bi), the variance of stability (𝑆𝑖 2 ), and the coefficient of variation of the duration of “germination – the beginning of flowering” higher tolerance to environmental factors was characterised by ultra-early ripening varieties. The average regression coefficient (bi ) was -0.36; the variation in the duration of the period by year was 10.1%, which is significantly lower compared to early-ripening varieties – -0.77% and 12.9%, mid-ripening varieties – -0.80% and 15.0%, and late-ripening varieties – -1.30% and 16.6%, respectively. The maximum average productivity to frosty raw cotton of 49.4 g/plant was formed by the sample Pidozerskyi 4 (UF0800003), the duration of the period “germination – beginning of flowering” was 47 days, and “germination – full ripening” – <103 days. The lowest raw cotton productivity of 21.2 g/plant was demonstrated by the late-ripening sample Joloten 32 (IU14056549) of Turkmen selection, the duration of the growing season of which was 145 days on average over the years of research. The findings of this study will be used in further breeding to create high-yielding cotton varieties with increased environmental plasticity and stability and highquality fibre