Descriptive Comparison of Senescent and Nonsenescent Sorghum Genotypes

Under normal field conditions, leaves of many typical sorghum [Sorghum bicolor (L.) Moenchl lines such as BT×378, RT×7000, RT×2536, and SC 214(IS 1598C) senesce after grain maturity. In the field, several upper leaves of three partially converted lines [SCOO56 (IS 12568), SC0599 (Rio), and SCO170 (IS12661)] from the sorghum conversion program remained green and apparently vigorous after grain maturity. This phenomenon of green leaf retention after the grain reached physiological maturity was termed “nonsenescence”. The purpose of this study was to compare standard (senescent) and nonsenescent lines to determine Characteristics which describe differences between the two genotypes and to define desirable qualities of the nonsenescent lines. Senescent and nonsenescent lines were evaluated in the field for three growing seasons, 1974 to 1976, at College Station, Texas. The soil type was Ships clay (Udertic Haplustoll) intergrading toward a Norwood clay loam (Typic Udifluvent). Several plant characteristics (growth parameters, yield and yield components, basal tiller production, stem diameter, ercent basal stem sugar concentration, and total leaf glade chlorophyll content) were measured to characterize genotypic differences. Experimental design was a randomized complete block with four replications. Growth data were recorded during the reproductive stage of development. The nonsenescent genotype required 2 days longer to reach 50% anthesis, averaged 3 to 4 cm shorter height, produced two to three more basal tillers per plant, had larger stem diameters, maintained higher basal stem sugar concentrations, and produced higher leaf blade chlorophyll contents than did the senescent genotype. Data involving leaves (green leaf number and weight, senesced leaf number and weight, leaf area index, leaf area duration, and leaf area ratio) favored the nonsenescent genoty e. The grain-leaf ratio of the senescent genotype exceeddthat of the nonsenescent genotype 30 days after anthesis because of a consistent reduction in leaf area due to senescence. Except for test weight (which was higher in the nonsenescent genotype), yield and yield components were generally inconsistent between genotypes. Parameters which could reasonably be measured in a breeding program to select for nonsenescent genotypes might include stem diameter and stem sugar concentration, tiller counts of a ratoon crop, and number of green leaves retained after grain maturity. Leaf area and chlorophyll measurements after the grain has reached physiological maturity might provide more conclusive Information on nonsenescence capability, but would probably not be feasible in a breeding program.