Phenology, leaf gas exchange, growth, and seed yield in contrasting Medicago truncatula and Medicago laciniata populations during prolonged water deficit and recovery

Abstract

The aims of this study were to investigate the effect of prolonged water stress and recovery on phenology, growth, and seed yield in Tunisian contrasting populations of Medicago truncatula and Medicago laciniata . After ample irrigation for 24 days, the plants of each population were divided into two lots: the first lot was irrigated at 100% field capacity (FC), and the second at only 45% FC. After 24 days of treatment, one lot of dehydrated plants was rewatered at 100% FC, while the other was maintained at 45% FC. Interspecific and intraspecific differences were found in phenological responses to water deficit. All growth parameters were more reduced in M. truncatula populations than in M. laciniata populations. The water shortage tolerance of M. laciniata populations was associated with a lower metabolic impairment of photosynthesis and maintenance of relatively higher leaf relative water content. Seed yield was also more reduced in M. truncatula populations compared with M. laciniata populations. In M. laciniata, seed mass was a compensation mechanism to sustain seed yield under drought conditions. Seed yield variation between populations under water deficit was explained mainly by variation in seed number per plant.