Determination of the growing season duration of popcorn lines (Zea Mays L. everta Sturt.) according to the FAO classification

Topicality. The of the growing season is the main breeding trait, which determines the practical use of the initial material of popcorn in a particular agroclimatic zone. Thus, so the differentiation of samples on this trait is important and relevant. Issues. Most methods for determining FAO index of popcorn lines and hybrids (Zea Mays L.) are based on the standard with a certain maturity group, while for maize (Zea Mays L. everta Sturt.) such standards are not available. Purpose. To determine the FAO index of new popcorn lines on three indicators: the number of leaves per a plant, the effective temperature sum during the growing season, and the growing season duration. Materials and Methods. The initial material was 46 popcorn lines in S5, which were developed in the Food Maize Breeding Laboratory at the Institute of Grain Crops of NAAS of Ukraine. The field trials were carried out at the Synelnykove Breeding and Research Station during 2020–2021. The FAO index of popcorn lines was determined according to Adryushchenko and Kryvytsky’s method. Results. We have determined the growing season duration of new popcorn lines according to the FAO classification by three indicators: the number of leaves per a plant, the effective temperatures sum during the growing season and the number of days until full ripening. Conclusions. It was noted that the indicator values that determine the maturity group of S5 popcorn lines can vary with growing conditions. Therefore, when only one indicator is used, we cannot obtain the accurate results. It is possible to reliably identify the maturity groups of initial material by the means of the proposed method of FAO determination on three indicators. Based on the results of the research, the new popcorn lines were divided into 3 groups. It was found that the mid-early ripening group (FAO 240-250) includes 4 lines in S5 - IKR 2-1, IKR 11-9, RV 3 and RV 1; to the mid-ripening group (FAO 320-390) – 32 lines in S5, including RR1, RR11, RS 13, RB 3, RK 43, RK 32, IKR 11-3, etc.; to the mid-late ripening group (FAO 400 - 410) - 10 lines in S5, including RV 18, RV 11, RP 61, RS 3, RV 6, etc.. It is proposed to select the lines of mid-early and mid-ripening groups for developing the new popcorn hybrids with full-value food popcorn grain. The formed working collection includes 80.4 % of samples of these maturity groups. Key words: breeding, popcorn, line, FAO maturity index, growing season, effective temperature sum.