Utilization of Alternate Cytoplasms to Evaluate Combining Ability in a Diverse Group of Sorghum B-Lines

Conversion of sorghum [ Sorghum bicolor (L.) Moench] maintainer lines to male-sterility is an expensive and time consuming process. To test for combining ability, B-lines are traditionally converted to male-sterile A-lines before crossing to a restorer (R) line. Most of the lines are then discarded in the hybrid testing process. A method to test the lines before conversion would greatly increase efficiency in a breeding program. The objective of this study was to evaluate the potential of R-lines, sterilized in an alternate cytoplasm, as testers for B-lines. A combining ability study was conducted in which ten genetically diverse male-sterile restorer lines were crossed to a diverse group of maintainer lines. The R-lines were sterilized in four different cytoplasms. The hybrids and lines were tested in separate experiments at two locations in 1988. Twelve normal cytoplasm hybrids were also included for comparison to the alternate cytoplasmic counterparts. Combining abilities of the lines and testers were calculated. Correlations were calculated between the yield of the hybrids and lines as well as the hybrids derived from different cytoplasms. Generally, hybrids produced in an alternate cytoplasm did not yield as high as the normal cytoplasm, but gave a similar relationship. Line yields did predict the general combining ability of the hybrid. It was concluded that one should utilize a tester that has shown a high correlation in hybrid combinations to the line yield. The utilization of alternate cytoplasm male-sterile restorer lines to test maintainer lines appears to be a useful strategy in a sorghum breeding program.