Assessment of combining ability and comparison of selected selfed and open pollinated generations clones of alfalfa (Medicago sativa L.) ecotypes

This study was conducted to quantitatively evaluate selfed (S1, S2 and S3) and open pollinated (OP1, OP2 and OP3) generations of alfalfa in terms of inbreeding depression and general combining ability of S2 families of alfalfa ecotypes. Selfing of selected plants to produce three generations of S1, S2 and S3 generations were performed under the field conditions and the clones of each selfed- generations were used for producing of open pollinated- generations.  For comparison of dry forage yield and plant height of selfed (S1, S2, S3) and open pollinated (OP1, OP2, OP3) generations randomized complete block design with three replications was employed in 2015 and 2016 growing seasons at Plant and Seed Improvement Institute, Karaj, Iran.. The results revealed significant differences among ecotypes, generations and growing seasons and their two- way and three-way interactions for dry forage yield. Alfalfa ecotypes reacted differently to selfing, and the highest rate of vigor depression was observed in the S1 generation tropical ecotypes. However, vigor recovery observed in all ecotypes with continuing selfing and vigor remarkably increased in S3 generation. Vigour recovery was observed more in OP2 than OP3. The highest general combining ability for dry forage yield observed for Yazdi and Nikshahri ecotypes which are tropical ecotypes. Therefore, crossing of these ecotypes with ecotypes originated from different climatic conditions could be more effective in improvement of forage yield of synthetic and hybrid (semi or free hybrid) varieties in alfalfa.