Variation of morphological and agronomic traits in hybrids of Trifolium pratense × T. medium and a comparison with the parental species

Trifolium pratense L. is a high-yielding and high-quality fodder crop. However, it shows low persistence, which may be overcome by hybridisation with species that produce rhizomes. Hybrids between T. pratense L. and T. medium L. were previously obtained by embryo rescue. The aim of this study was to evaluate 16 characteristics (stem weight, stem length, internode number, length/width ratio of a central leaflet of the trifoliate leaf on the 4th internode, stem thickness on the 4th internode, average leaf area of the trifoliate leaf, weight of dry plant, plant length, stem and head number per plant, head number per stem, seed weight per plant, seed weight per head and dry matter per stem) in the hybrid plants derived from F1 hybrids and in both parental genotypes. The characteristics were evaluated in 500, 745 and 112 hybrid plants in the years 2006, 2008 and 2009, respectively. The significance of the morphological differences was determined by the general linear model and generalised linear model with Poisson distribution with two factors, genotype and year. Some of the examined traits were intermediate in the hybrids. There were significant differences between the hybrids and T. pratense in nearly all the analysed characteristics, except for the following ones: length/width ratio of a central leaflet of the trifoliate leaf on the 4th internode under the top head, plant weight and head number per plant. The stem number per plant was significantly higher in the hybrids compared to both parental species, which could have a positive impact on the yield. Short rhizomes were observed in the hybrids after the harvest of plants in the second harvest year. The stability of this trait and its impact on the perenniality of the hybrids will be investigated in the next years.