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To evaluate the yield of dual-purpose grain-forage sorghum promising lines, a factorial experiment was conducted in a randomized complete block design with three replications in four places (Karaj, Mashhad, Isfahan, Birjand, Shiraz, and Gorgan) during 2017-2018. Experimental factors included harvest time at four levels (milk stage, soft dough stage, hard dough stage, and physiological maturity of grain) and dual-purpose grain-forage sorghum genotypes at seven levels (promising lines of KDFGS4, KDFGS6, KDFGS9, KDFGS10, KDFGS16, MDFGS1, and MDFGS2). The results of combined analysis of variance showed that the effect of year, place, year × place, place × genotype, and year × place × genotype on the grain yield was significant (P≤0.01), and the effect of genotype on this trait was significant (P≤0.05). The highest and lowest grain yields (6.67 and 5.04 t ha-1) were obtained by KDFGS6 and KDFGS16 lines, respectively. The maximum and minimum 1000-grain weights (34.9 and 22.1 g) were observed in KDFGS6 and MDFGS2 lines, respectively. The results of combined analysis of variance showed that the effect of place, year × place, genotype, year × genotype, place × genotype, year × place × genotype, harvest time, genotype × harvest time, year × harvest time, place × harvest time, year × place × harvest time, year × genotype × harvest time, place × genotype × harvest time, and year × place × genotype × harvest time were significant on the dry forage yield. The highest and lowest dry forage yields (29.65 and 22.66 t ha-1) were obtained by MDFGS1 and KDFGS16 lines, respectively. Between different harvest times, the maximum and minimum dry forage yields (28.31 and 22.08 t ha-1) were obtained at the grain physiological maturity and milk stages, respectively. The maximum content of digestible organic matter in the dry matter was obtained by harvesting the KDFGS9 and KDFGS16 lines in the milk stage. The highest crude protein content (118 g kg-1) was obtained by harvesting the MDFGS1 line in the grain milk stage, and the highest metabolizable energy (2.58 Mcal kg-1) was obtained by harvesting the KDFGS16 line at this stage. Also, according to the results of grain and forage yield stability analysis, the KDFGS10 and KDFGS6 lines were identified as the most stable dual-purpose grain-forage sorghum genotypes, and the MDFGS1 line was identified as the best single-purpose forage genotype. Overall, considering all the quantitative and qualitative aspects of forage and grain production and yield stability, among the genotypes, the KDFGS6 promising line is introduced as the superior dual-purpose grain-forage genotype, and the MDFGS1 line is introduced as the superior single-purpose forage genotype. Also, among the harvest times studied, forage harvesting at the soft dough stage will be recommended.Keywords: Sorghum, Genotype, Harvest time, Grain, Dry matter, Forage quality.
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