Interaction of salinity and temperature on the germination of alfalfa cv CUF 101

Alfalfa, Medicago sativa L is a major forage legume in the arid climate of the Gulf countries where salinity is a serious production problem. A laboratory experiment was initiated to evaluate the effect of salinity - temperature interactions on the germination of alfalfa cv CUF 101. The alfalfa seeds were sown in Petri dishes with saline solutions of varying concentrations (electrical conductivities of 0.01, 6.4, 12.2, 17.4, 22.6, 27.2, 32.1 and 37.2 dSm -1) prepared with NaCl. The germination response of the seeds were determined over a wide range of temperatures (15, 20, 25, 30, 35 and 40 °C) for a period of 8 d. Germination counts, taken every 2 d, were used to compute germination rate index. Generally, germination percentage decreased with increasing salinity and was severely limited at 40 °C. Salinity-temperature interactions were highly significant. The optimum germination temperature was 20-25 °C. Based on these results, the most favourable period to establish alfalfa cv CUF 101 in the Sultanate of Oman and other areas with similar climatic conditions has been proposed.Interaction de la salinité et de la température sur la germination de la luzerne cv CUF 101. La luzerne Medicago sativa L représente une culture fourragère importante dans les régions arides des pays du golfe arabo-persique où la salinité constitue un problème majeur pour la production. Un travail de laboratoire a été initié pour évaluer l'effet des interactions température x salinité sur la germination des semences du cv CUF 101. Des solutions de NaCl (ayant pour conductivités électriques 0,01, 6,4, 12,2, 17,4, 22,6, 27,2, 32,1 et 37,2 dSm-1) sont utilisées pour étudier la germination des semences en boîtes de Petri à des températures variées (15, 20, 25, 30, 35 et 40 °C). L'index de germination est défini par le nombre de semences germées tous les 2 jours. Le pourcentage de germination diminue en fonction de l'augmentation de la salinité pour atteindre une valeur très faible à 40 °C. Les interactions température x salinité sont hautement significatives. La température optimale de germination est comprise entre 20 et 25°C. La meilleure période pour l'établissement de la luzerne cv CUF 101 dans le sultanat d'Oman et dans les zones à climat similaire est suggérée d'après les résultats

Variable salinity responses of 12 alfalfa genotypes and comparative expression analyses of salt-response genes

Twelve alfalfa genotypes that were selected for biomass under salinity, differences in Na and Cl concentrations in shoots and K/Na ratio were evaluated in this long-term salinity experiment. The selected plants were cloned to reduce genetic variability within each genotype. Salt tolerance (ST) index of the genotypes ranged from 0.39 to 1. The most salt-tolerant genotypes SISA14-1 (G03) and AZ-90ST (G10), the top performers for biomass, exhibited the least effect on shoot number and height. SISA14-1 (G03) accumulated low Na and Cl under salinity. Most genotypes exhibited a net reduction in shoot Ca, Mg, P, Fe, and Cu, while Mn and Zn increased under salinity. Salinity reduced foliar area and stomatal conductance; while net photosynthetic rate and transpiration were not affected. Interestingly, salinity increased chlorophyll and antioxidant capacity in most genotypes; however neither parameter correlated well to ST index. Salt-tolerant genotypes showed upregulation of the SOS1, SOS2, SOS3, HKT1, AKT1, NHX1, P5CS1, HSP90.7, HSP81.2, HSP71.1, HSPC025, OTS1, SGF29 and SAL1 genes. Gene expression analyses allowed us to classify genotypes based on their ability to regulate different components of the salt tolerance mechanism. Pyramiding different components of the salt tolerance mechanism may lead to superior salt-tolerant alfalfa genotypes