GERMINATION UNDER CONTROLLED TEMPERATURE AND FIELD EMERGENCE OF 13 SORGHUM CULTIVARS

Temperature and cultivar strongly influence the establishment of dryla nd sorghum [Sorghum bicolor (L) Moench]. Little is known about the ext ent of variability in germination and emergence among different sorghu m cultivars as affected by temperature. Our objective was to monitor c ultivars for germination under different temperature regimes in the la boratory, and subsequently to test their performance in the field for emergence. Sorghum seeds were screened for germination during 10 d in polyethylene growth pouches held in the dark at constant temperatures of 10, 15.5, 21, 26.5, 32, or 37.5 degrees C. In the field study, 13 h ybrids were planted on 4, 13, 21, and 26 June 1991, and observed for e mergence. Germination percentage significantly (P < 0.05) increased as temperature of treatment increased from 15.5 to 26.5 or 32 degrees C when averaged across the cultivars, with no germination at 10 degrees C. As temperature increased from 15.5 to 37.5 degrees C the average ti me to germination decreased significantly (P < 0.05). Cultivar Richard son-9112 had the greatest germination percentage (98%) and DK-46, as w ell as DK-42, had the least (79%) when averaged across the five temper atures. For 80% or above of the seeds to germinate, it required 7 d at 15.5, 3 d at 21, 2 d at 26.5 and 32, and 1 d at 37.5 degrees C temper ature. An optimum temperature of the cultivars investigated varied bet ween 26.5 and 32 degrees C. Mean held emergence was significantly (P < 0.05) greatest (83%) with Richardson-9112 and least (36%) with DK-42Y as well as DK96 compared to nine cultivars. Relative mean emergence i n the held regressed with relative mean germination in the laboratory yielded a significant (P < 0.05) correlation (r(2) = 0.77). This study demonstrates the cultivar differences for response to temperature and information concerning variability in germination, and emergence.