Combining Ability Among Four‐Clone Alfalfa Synthetics¹

Abstract

Two groups of experimental alfalfa ( Medicago sativa L.) synthetics were produced, 36 synthetics from 10 related parents in one group and 24 synthetics from nine unrelated parents in the other. Combining ability variances were estimated for spring growth, yield, recovery after the first harvest, fall growth, stand, and frost damage in a field experiment, and for reaction to seven pathogens in greenhouse experiments. Significant general combining ability variance was detected for spring growth, yield, recovery after the first harvest, and for reaction to Colletotrichum trifolii Bain and to Pseudopeziza medicaginis (Lib.) Sacc. in both groups of synthetics. General combining ability variance for stand, and reaction to Phoma herbarum West f. medicaginis West ex. Rab., Uromyces striatus Schroet. var. medicaginis (Pass.) Arth., and to Corynebacterium insidiosum (McCull.) Jens, were significant in one or the other of the two groups. Significant specific combining ability variance was observed for yield, stand, frost damage, and reaction to C. trifolii , U. striatus , and C. insidiosum in one or the other of the groups. Significant combining ability variances were not detected for reaction to Stemphylium botryosum Wallr. and Leptosphaerulina briosiana (Poll.) Graham and Luttrell in either group of synthetics. We concluded that specific combining ability variations in the four‐clone alfalfa synthetics in both groups were so small that breeding procedures that operate on additive gene action would be more effective in development of improved synthetics than attempting to utilize specific combining ability effects by screening numerous experimental synthetics.