Effect of drought stress on the induction of summer dormancy and dry matter partitioning in alfalfa (Medicago sativa L.) ecotypes

Study of potential of alfalfa ecotypes in biomass partitioning and harvestable and non-harvestable parts as well as induction of summer dormancy under water scarcity can lead to develop adapted cultivars for sustainable farming system andto meet targets of the breeding program. Therefore, this experiment was conducted with 10 alfalfa ecotypes under four irrigation managements at Seed and Plant Improvement Institute (SPII), Karaj, Iran, during 2016-2018. The irrigation treatments included; full irrigation and irrigation withhold for 20, 40 and 60 days. Under stress and on stress conditions, Nikshahri and Yazdi ecotypes had the highest regrowth rate, therefore, these two ecotypes as well as KFA6 ecotype with high stem number demonstrated the highest survival rate under induction of summer dormancy. The highest biomass belonged to normal irrigation with 17.31 t.ha-1 while the maximum unharvestable part yield with 7.02 t.ha-1was measured in irrigation withhold treatment for 40 days. Yazdi and KFA6 ecotypes showed the maximum total biomass (15.71 and 15.76 t.ha-1 respectively) among warm and cold region ecotypes with different fall dormancy scores and can be used as aprentsin alfalfa breeding programs. Regarding to biomass partitioning ratio, KFA17, KFA6 and Yazdi, which are landraces, had greater harvestable part to unharvestable part ratio with 1.63, 1.43 and 1.40, respectively. Therefore, these landraces can be selected for forage production under different irrigation managements. As the leaf to stem ratio has the main role in forage quality, Baghdadi ecotype with leaf: stem ratio of 1.29 had the highest forage quality among studied ecotypes. Baghdadi also maintained its high quality in all irrigation management treatments. In alfalfa breeding programs focused on improvement of forage and unharvestable yield for sustainable production in both optimum and stress environment conditions, Yazdi and KFA6 ecotypes seems to be suitable.