Registration of KLS_30 and KSS_30 Populations of Maize

KLS_30 (Reg. no. GP-454, PI 636488) and KSS_30 (Reg. no. GP-455, PI 636489) are dent maize (Zea mays L.) populations that were released in 2003 by the Nebraska Agricultural Experiment Station, University of Nebraska-Lincoln. Both populations were developed by W.A. Compton using 30 cycles of divergent mass selection for seed size from the open-pollinated variety, Krug Yellow Dent. This variety was derived from the three-way cross, (a Nebraska strain of Reid Yellow Dent 3 Goldmine) 3 an Illinois strain of Reid Yellow Dent. The same selection procedure was used to develop all cycles of each population. Between 1200 and 1500 plants of each population were grown in separate isolations, and an equal number of kernels from open-pollinated ears with the consistently largest (KLS) or smallest (KSS) kernels were bulked to form the next cycle. The proportion of individuals selected in all cycles and for both populations was 1%. Additional details on the method of selection were provided by Odhiambo and Compton (1987). Odhiambo and Compton (1987) evaluated the base population (cycle 0) and cycles 2, 7, 12, and 20 of each population for kernel weight, seed yield, and other agronomic traits. Through cycle 20, 100-kernel weight (on a dry-weight basis) had increased in KLS at a linear rate of 0.5 g cycle and decreased in KSS by 0.7 g cycle. Averaged across the two populations, nearly 98% of the variation among cycles was attributable to a linear model. The 100-kernel weights of cycle 0,KLS_20, andKSS_20were 28.5, 36.9, and 12.2 g, respectively. KLS_30 and KSS_30 were evaluated for kernel weight at Lincoln, NE, in 2002 (two different planting dates) and in 2004 at Lincoln and Wood River, NE, and at Ames, IA. Check inbreds, B73 and Mo17, also were evaluated in 2004 at Lincoln and Ames, and the check hybrid, B73 3 Mo17, was evaluated at Lincoln in 2004. For both populations approximately 50 fullsib ears were produced at each location by making controlled pollinations; for the checks, ears were produced by controlled selfor sib-pollinations. One hundred kernels were sampled from the middle of each ear, dried in a forced-air oven at 608C for 7 d, and then weighed. Across all environments, the average 100-kernel weights of KLS_30 and KSS_30 were 44.8 and 8.6 g, respectively. This difference and the difference at each environment was highly significant (Table 1). Also, the 100-kernel weight of KLS_30 was significantly greater than the weight of each of the checks at both Ames and Lincoln in 2004, whereas the 100-kernel weight of KSS_30 was significantly in 2004 less than the checks at both locations. The ratio of the KLS_30 to KSS_30 100-kernel weights across locations was 5.2, compared to a ratio of only 3.0 reported by Odhiambo and Compton (1987) between the cycle 20 populations. This difference in the ratios suggests that additional gains from selection have been realized over the last 10 cycles. Additional divergence betweenKLS andKSS could be obtained by new cycles of selection only if genetic variation exists in either or both KLS_30 and KSS_30. The variance among the KLS_30 full-sib ears for 100-kernel weight was significantly greater than the variance among ears within each of the genetically homogeneous check entries at both Ames and Lincoln in 2004. The variance among the KSS_30 ears was significantly less than the variance of each check at Ames and not significantly different from each check at Lincoln. However, when variability was measured by coefficient of variation (CV), there was some indication that variability within both populations was greater than existed with the check entries (Table 1). At Lincoln in 2002 and 2004, the average number of days from planting to anthesis of both KLS_30 and KSS_30 was 82, which was not significantly different from the average days to anthesis of B73. Neither KLS_30 nor KSS_30 has been evaluated for grain yield or any other agronomic traits. However, through 20 cycles, seed yield was significantly decreased by selection for small kernel size but not significantly changed by selection for large kernel size (Odhiambo and Compton, 1987). KLS_20 was 65% higher in yield than KSS_20. KLS_30 and KSS_30 were released primarily because of their potential use as germplasm in research to investigate the inheritance and physiology of kernel size in maize. Seed will be maintained by the Department of Agronomy and Horticulture at the University of Nebraska-Lincoln. Small quantities of seed of each population may be obtained from the corresponding author on written request.