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Combining Ability Related to Reduced Gene Flow among Maturity Groups within Maize Populations

ESCA Genetics Corp., 830 Bransten Road, San Carlos, CA 94070-3305
Crop and Weed Sciences Dep., 329 Walster Hall, North Dakota State Univ., Fargo, ND 58105
SIGCO Res., Inc., Box 289, Breckenridge, MN 56520

^* Corresponding author.

Little is known concerning the genetic consequences of reduced gene flow among early, medium, and late flowering plants that occurs within maize (Zea mays L.) synthetics. This study was conducted to investigate if genes become stratified into subpopnlations associated with flowering time within synthetics [as indicated by differences in average heterosis of hybrids between plants from various subpopulations and in estimates for their general combining ability (GCA) and specific combining ability (SCA)]. Three independent diallel sets of crosses, each among eight elite synthetics were produced by intercrossing plants of varying maturities within each synthetic: early x late (GI), medium x medium (GIII), and late x early (GIII). Average performance of Gil hybrids (as the standard) was compared to hybrids from GII and GIII. The eight synthetics, which varied in maturity from AES100 to AES400, were evaluated for GCA and SCA by each of the three diallel sets. Field experiments were grown during 3 yr in up to nine environments in North Dakota. The rankings of GCA effects from each diallel were compared using two nonparameteric statistical methods, the Mann-Whitney test and Spearman rank correlation coefficients. Results indicated that diallels GI, GII, and GIII gave similar average performance for all traits and similar estimates of GCA and SCA for eight of nine traits evaluated. For all traits studied, GCA mean squares were greater than SCA mean squares, indicating a predominance of additive variation. The Mann-Whitney test indicated that GCA effects for all traits from the three diallels had similar distribution functions, and except for test weight, Spearman rank correlation tests ranked the GCA effects for GI, GII, and GIII in similar orders. Results indicated that gene flow was not greatly restricted among different maturity groups in the synthetics studied.

Received for publication September 21, 1988.