Effect of harvest time on morphological traits and yield of dual-purpose sorghum (Sorghum bicolor L. Moench) promising lines

To assess the productivity potential of dual-purpose (grain-forage) sorghum promising lines at different harvesting times, a field experiment was carried-out using randomized complete block design with three replications in six locations (Karaj, Mashhad, Isfahan, Birjand, Shiraz, and Gorgan) Iran, during 2017 and 2018 growing seasons. Morphological traits and yield of seven dual purpose sorghum promising lines (KDFGS4, KDFGS6, KDFGS9, KDFGS10, KDFGS16, MDFGS1, and MDFGS2) were evaluated at four harvest stages (milk, soft dough, hard dough, and physiological maturity). The results showed that the lowest silage forage yield and the highest dry forage yield in all sorghum promising lines were obtained at the physiological maturity stage. The highest dry forage (34.32 ton.ha-1) and grain yield (7.39 ton.ha-1) were recorded in Shiraz and Isfahan.  The lowest forage and grain yield were produced in Birjand and Gorgan, respectively. The highest (6.67 ton.ha-1) and lowest (5.04 ton.ha-1) grain yield (obtained from KDFGS6 and KDFGS16 lines, respectively. The highest silage forage yied and dry forage yield, the tallest plant height, and the shortest panicle length belonged MDFGS1 line. Considering the suitable dry matter content for silage forage production, the soft dough stage was identified as appropriate stage to harvest sorghum forage. The highest grain yield stability belonged to MDFGS2, KDFGS6, and KDFGS10 lines, repectively. While, the highest forage yield stability belonged to KDFGS9, KDFGS6, and MDFGS1 lines, respectively. Based on the results of this study and considering the yield and yield stability, KDFGS6 line was identified as the superior dual-purpose (grain-forage) sorghum genotype, and MDFGS1 promising line was more suitable for forage production.