N. Valkova, M. Koleva*
Field Crops Institute, 6200 Chirpan, Agricultural Academy, Sofia, Bulgaria
(Manuscript received 14 October 2021; accepted for publication 16 January 2022)
Abstract. The norm of reaction in qualitative aspect was studied in 31 Bulgarian and foreign cotton cultivars. The results of competitive variety trial carried out at the Field Crops Institute in town of Chirpan during the period 2016 – 2019 were used. The type of their dynamic regression (of their regression curve) and the structure of ecological environments in their dynamic rows were determined, on five traits, in order to characterize the reaction norm of the studied genotypes. It was found that the studied cultivars had in most cases another reaction norm differing considerably from that of the standard variety. The specificity of their reaction was manifested to a smaller extent in regard to its type and more strongly in the structure of ecological environments in their dynamic rows. As regards the individual traits, the reaction norm of cultivars was expressed to varying degrees, depending on their peculiarities. In terms of type of reaction, cultivars 791-169 (similar to the standard variety in 4 characters), Philipopolis, Kris, Darmi, Natalia and T-08 (similar in 3 characters) were the closest to the standard variety. Cultivars Boyana, Nelina, Colorit and C-9070, in which there was no similarity of traits with the standard variety, and other 13 cultivars, similar in only one trait, were the furthest from it. Cultivars from these two groups could be included in one selection program to create new genotypes with a convex type of reaction for most of the traits. The convex type of regression, with the exception of Helius variety, occurred in all cultivars and traits, which was a prerequisite for an effective selection of genotypes with high adaptive ability. With high adaptability and very valuable for the cotton breeding programs were found the cultivars: IPTP Veno and Tabladila-16, with a convex type of dynamic regression in four traits – seed cotton yield, boll weight, fiber ginning out turn and fiber length; Kris, Stoneville 112 and Dorina with a convex type of regression for three traits.