Photoperiodic effects on primary and ratoon growth in three varieties of grain sorghum

Abstract

Effects of photoperiodic treatments on the primary crop and the carryover effects of the short-day treatment from the primary crop to the ratoon crop of grain sorghum were investigated during 1966. These investigations were conducted at Texas A & M University, College Station, Texas. Grain sorghum varieties, 60-Day Milo, 80-Day Milo and Texas Blackhull Kafir were used. Two photoperiods, normal daylength and 10-hour daylength, were employed. The primary crop was considered as the growth from planting to blooming. After blooming, the primary crop was clipped at 2 heights: ground level and combine height. The ratoon crop was considered as the growth from clipping to blooming. The results obtained from these studies show that the short-day treatment has profound effects on the growth and development of these grain sorghum varieties. In the primary crop under short-day treatment both floral initiation and blooming were significantly hastened in all 3 varieties. The residual effects of the short-day treatment on the flowering of the ratoon crop were, however, determined by the height and time of clipping. The 3 varieties also differed in their responses to photoperiods. The 2 milo varieties responded significantly to the short-day treatment, but the kafir did not. When plants were clipped at the same time, the tillers from the plants exposed to the short-day treatment had earlier floral initiation and blooming than the tillers in the long-day treatment. The enhancement in blooming due to the short-day treatment was even greater when the plants were clipped at combine height. But when the plants in the 2 photoperiods were clipped at different times, according to their blooming time, tillers of the plants exposed to the short-day treatment required a longer period than the tillers in the long-day treatment. ...