| Abstrakt: |
Nonsenescence and sweet culms are being incorporated into cultivars of grain sorghum [Sorghum blcolor(L.) Moench.] for potential improvement in yield. Clarification of carbohydrate production and accumulation patterns within the culm during grain filling is needed for guidance in breeding. Data on culm carbohydrate levels are also needed to evaluate blomass for possible energy uses. A senescent, hybrid, cultivar designated 37 and three non senescent, hybrid, cultlvars designated PS, 65, and 6R were harvested at three stages of maturity: (i) 15 days post anthesls (PA), (il) black layer (BL), and 15 days post black layer (PBL). Panicles on some plants within each replicate were also removed at BL Glucose, fructose, sucrose, and starch concentrations were determined on the culms. Culm and total plant weight, kernel weight, and grain per panicle were also measured. Culm glucose levels at PA were 90.5, 48.1, 39.5, and 12.6 mg/g oven dry weight (ODW), respectively, for PS, 6R, 65, and 37. Glucose levels declined at each successive harvest except in cultivar 65. A similar pattern was obtained for fructose at PA with values of 78.8, 44.2, 43.7, and 21.1 mg/g ODW for the same cultivar sequence. Levels of sucrose decreased from PA to BL by 66.8 and 21.9 mg/g ODW, respectively, for P5 and 65, and then increased to 124.6 and 173.3 mg/g. Sucrose increased in 6R at each maturity stage and a significant increase to 303 mg/g ODW was obtained in PBL. Slight increases of sucrose occurred in 37 during the successive maturing stages. Starch levels increased at all stages in 6R, but declined from PA to BL in PS, 65, and 37, then increased by PBL. Weight/100 kernels was 2.86, 2.80, 2.17, and 1.91g at PBL, and grain weight/panicle was 66.7, 66.5, 55.3, and 48.2g, respectively for PS, 65, 6R, and 37. These results suggest that sweet culms do not reduce grain weights. Culm sugar accumulation patterns differed among cultivars. Patterns exhibited by P5 and 65 appeared to be desirable for grain production and possibly as biomass for energy use since the culms continued to fill with sugar after BL. The nonsenescing cultlvars contained significantly more carbohydrates at all maturity stages than the senescing one. Plants with panicles removed at BL had accumulated more culm carbohydrates at PBL than reported above in most cases. |
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