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Diploid Interspecific Hybrids of Tripolium pratense L.,T. diffusum Ehrh., and Some Related Species¹

Pollen from Trifolium hirtum All., T. diffusum Ehrh., and T. pallidum Waldst. & Kit. on pistils of T. pratense L. germinated and the tubes grew through the styles to the vicinity of the ovules. Likewise, pollen from T. pratense on pistils of T. diffusum and T. pallidum germinated, and the resulting tubes grew to the vicinity of the ovules. Compatible matings within T. pratense resulted in vigorous pollen tube growth, similar to that of the interspedfic combinations.

Matings of T. pratense with T. pallidum and T. hirtum produced no mature seeds. Embryos were collected at 7 days of age, but no hybrids were satisfactorily grown in embryo culture. Many hybrids were produced by mating T. pratense x T. diffusum, but none were obtained from the reciprocal mating. Hybrids were generally chlorotic in the seedling stage, and chlorosis was observed on young leaves in older plants. Most floral and vegetative characteristics of hybrids were intermediate to the parents.

All F₁ hybrids of T. pratense x T. diffusum were 2n = 15 and meiosis was very irregular. Univalents and bivalents at MI averaged 1.6 and 1.3 per cell, respectively. The remainder of the chromosomes were associated in complex multivalents of 3 to 15 members. Most multivalents were chains, and bivalents were rods. Up to three bridges with fragments were found at AI, and bridges were also seen at All. These chromosomal abnormalities indicate the presence of translocations and paracentric inversions. It was concluded that T. pratense and T. diffusum had complex differences in chromosome structure.

The F₁ of T. pratense x T. diffusum was nearly sterile. However, backcrosses to T. pratense produced a few plants that may have been polyploids. The BC₁ plants flowered and were partially fertile.

Key Words: Clover species • Hybrid sterility • Hybrid meiosis • Structural hybridity • TriIolium pallidum • Trifolium hirtum

² Formerly Graduate Research Assistant (Now, Head, Plant Science Field Research, Eli Lilly International Corp., Greenfield Laboratories, Greenfield, Ind.), and Associate Professor of Plant Breeding, The Pennsylvania State University, University Park, Pa., respectively.

Received for publication August 2, 1971.