Interspecific in <i>Trifolium</i> L. Sect. <i>Trifolium</i> Zoh. II. Fertile Ployploid Hybrids Between <i>T. medium</i> L. and <i>T. sarosiense</i> Hazsl¹

Interspecific hybrids of Trifolium medium L. ✕ T. sarosiense Hazsl. and reciprocal hybrids were produced by hand pollinations in a greenhouse. Hybrids of T. medium ✕ T. sarosiense were normal green and intermediate betweenthe two parents for morphological traits, but the reciprocal hybrids showed chlorophyll deficiencies including mottling and chimeras. Seed set from interspecific crosses was lower than from intraspecific crosses, but the small reduction in seed set represents only a minor isolation barrier between the species. All hybrids and both parents were self‐incompatible. Hybrids of T. medium 2n=72 ✕ T. sarosiense 2n=48 and the reciprocal hybrids had 2n=60 chromosomes except for two plants which had 2n=58 chromosomes. Meiotic analysis of chromosomes of T. medium and T. sarosiense revealed mean frequencies of 7.40 I, 32.30 II and 1.34 I, 23.33 lI respectively per PMC at metaphase I of meiosis. The hybrids (2n=60) of T. medium ✕ T. sarosiense and reciprocal exhibited mean frequencies ot 5.30 I, 27.29 II and 4.68 I, 27.66 II, respectively, per PMC at metaphase I. However, the two 2n=58 hybrids had a reduction in bivalents to 25.96 and 26.00, respectively. Mean pollen stainabillty of the two parents was greater than 95%, whereas mean stainability of all hybrids was 89%. Other lines of T. medium were later identified with 2n=64, 68, 70, 72, and 80 chromosomes. The 2n=64 and 80 lines showed mostly 32 II and 40 II, respectively, but cytotypes with 68, 70, and 72 chromosomes had 32 II and an increasing number of univalents. Although the complexity of ploidy level in the T. medium taxa complicates any conclusions concerning phylogenetic relationships, our results indicate strong evolutionary links between T. sarosiense and T. medium .