Abstract:

Medicago ruthenica is a leguminous forage crop with strong resistance to various stress factors and rich genetic diversity， which can be used as a cross breeding parent within the same forage genus as a source of rich genetic resources. Identification of a procedure to obtain true hybrids is an important component of cross breeding and heterosis utilization. In this study， in order to obtain new germplasm materials of M. ruthenica with more abundant genetic characters， two hybrid combinations were made by reciprocal crosses， using M. ruthenica cv. ‘Zhilixing’ with upright growth form and high yield， and a yellow-flowered variant of wild M. ruthenica var. Sojak with strong stress resistance as parents. 85 true hybrids were identified from 118 F₁ hybrids by sequence-related amplified polymorphism （SRAP） molecular marker technique. F₂ material was obtained from the true cross F₁ plants with excellent performance of M. ruthenica ‘Zhilixing’ ♀×M. ruthenica Sojak ♂， and further heterosis analysis was carried out on the main agronomic characters of 13 F₁ and 20 F₂ plants for traits such as plant height， plant growth form， number of primary branches， approximate leaf area， leaf∶stem ratio and single plant aboveground biomass of single plants. It was found that the coefficients of variation of phenotypic values of F₁ traits ranged from 18.82% to 45.72%， among which the aboveground biomass per plant， leaf∶stem ratio and primary branch number varied most greatly. The parental dominance of each trait ranged from -54.2% to 26.9%， but only the leaf stem ratio （8.22%） showed superparental dominance. The coefficient of variation （19.66% to 41.63%） of each trait in F₂ was lower than that in F₁， and the heterosis （-52.38% to 19.75%） was weakened. In addition， the mid- and super-parent vigor of yield-related traits in F₁ and F₂ were mostly negative and the intraspecific heterosis was weak. This study will provide new germplasm for the improvement of M. ruthenica and other forages of the Medicago genus.

Key words: Medicago ruthenica, sequence related amplified polymorphism molecular markers, hybrid identification, heterosis