ABSTRACT
Summary Interspecific compatibilities were investigated among genotypes of Trifolium sarosiense Hazsl., used as females, and T. pratense L. (red clover), used as males. This research was undertaken to introduce the perenniality of T. sarosiense into T. pratense by hybridization and thus to increase the longevity of stands of red clover for hay, pasture, and soil improvement. Objectives 166of the study were to further the knowledge of interspecific hybridization barriers in Trifolium and to isolate clones of T. sarosiense and T. pratense that could aid in their eventual hybridization, either directly or by embryo rescue. Twenty-three clones of T. sarosiense were used as females to cross with 8 clones of T. pratense as males. Plants were maintained in a growth chamber at 15°-18°C at a photoperiod of 16 hours, so that all plants flowered continuously for 3 years. Seeds were dissected from pods and visually classified into four categories of seed size. Class I seeds were largest and, based on grow-out tests, were considered to be selfs. Parent genotypes were significantly different in seed set, but no combination produced hybrid seeds that would germinate in vivo. T. sarosiense x T. pratense interaction effects, while significant, were not as important as the female effects. T. sarosiense and T. pratense clones that produced relatively large amounts of class II hybrid seeds (the largest among the hybrid seeds) also tended to produce the largest amounts of class III seeds (the next largest) but did not often produce large amounts of class IV seeds (the smallest). It was inferred that production of class II and class III shriveled seeds was of greater importance than producion of class IV seeds. Class II and III embryos, although not capable of germinating in vivo, were capable of being rescued via tissue culture because of their delayed abortion. Recurrent selection for viable seeds probably would be effective for interspecific hybridization. In the present hybrid, however, recurrent selection is not necessary since embryos are being produced that are sufficiently developed for rescue by tissue culture.
