Crossing and Morphological Relationships among Species Closely Related to Arrowleaf Clover¹

Abstract

Isolation barriers were examined by making all possible crosses including reciprocals among arrowleaf clover (Trifolium vesiculosum Savi), T. mutabile Portenschl. and T. leiocalycinum Boiss. & Spruner. No evidence of sterility was indicated by cross seed set. All F1 cross seed germinated readily but yellow seedlings were produced by crosses of T. mutabile and T. leiocalycinum with T. vesiculosum. F1 plants from reciprocal crosses of these species were normal green. The yellow condition disappeared as plants matured. Most F1 plants from crosses between accessions produced less stainable pollen than plants from crosses within accessions. All species had 16 somatic chromosomes and chromosome associations at metaphase I of meiosis were similar for all parents and F1 progenies. We concluded that T. mutabile and T. leiocalycinum are quite closely related and are slightly differentiated from T. vesiculosum. Therefore, the three taxa must be isolated under field conditions to prevent crossing.