Identification of qualitative superior hybrids based on second selfing generation of alfalfa (Medicago sativa L.) using GGE-Biplot analysis

Improvement of forage quality is one of the important purposes of alfalfa breeding in order to develop cultivars with higher feeding values. The objective of this experiment was to evaluate of combining ability and heterosis for forage quality including; leaf to stem ratio, crude protein, soluble carbohydrate, ash, acid detergent fiber and neutral detergent fiber by GGE biplot graphical method. Selected partially inbred lines from the second generation selfing of eight alfalfa ecotypes were evaluated in a half-diallel cross design. Field experiments were performed in a randomized complete block design with three replications, included eight parents and 28 F1 at two locations, Karaj and Arak, Iran, during 2015-2016. Based on the results of Griffing method, mean square of GCA and SCA and SCA by environment interaction were significant for all the traits (p<0.01) and GCA by environment interaction were significant for leaf to stem ratio (p<0.05) and also for ADF and NDF (p<0.01). GGE biplot graphical method showed the highest positive GCA for Silvana and the most negative GCA for Kozare and Rahnani for leaf to stem ratio, crude protein, soluble carbohydrate, ash. Nikshahri showed the highest positive GCA for acid detergent fiber and neutral detergent fiber as the unfavorable traits. SCA was the maximum for two specific parents; Ghahavand and Silvana for all the traits. Results revealed that there were proper diversity and heterosis for forage quality in alfalfa parents, so selfing and crossing between the partially inbreds (S2) could be possible by crossing between best single crosses to produce free hybrids to improve forage quality.