English abstract
Alfalfa (Medicago sativa L.) is the most important legume forage crop in Oman. Several alfalfa
landraces are being grown in different agro-ecological regions of the country. However, the forage
yield is often low due to the lack of improved varieties and abiotic stresses like salinity. Five
independent experiments were conducted to characterize alfalfa landraces of Omani origin for salt
tolerance; to evaluate the sensitivity of alfalfa genotypes to sodium and chloride salinity, and to
evaluate the influence of nano-sized chitosan-proline, biochar and γ-amino butyric acid (GABA)
application on salt tolerance in alfalfa. In the first experiment, thirty-four (34) alfalfa landraces,
indigenous to Oman, were evaluated at different levels of salt stress. Salt stress caused a reduction
in growth and dry matter yield of alfalfa landraces with exception of some, which responded
positively to the salinity levels of 3 and 6 dS m-1
compared to control. Alfalfa landraces OMA
257, OMA, 245, OMA 270, OMA 315, OMA 211, OMA 117, OMA 56, OMA 239, OMA 148,
OMA 131, OMA 95, OMA 263, OMA 262, OMA 289, and OMA 220 were designated as salt
tolerant based on their overall performance across salinity levels of 6, 9 and 12 dS m-1
. In the second experiment, twenty (20) high yielding alfalfa landraces were exposed to three levels of salt
stress. With an increase in salinity stress levels from 2 dS m-1to 10 dS m-1, there was a decrease
in different morphological traits across the landraces, except forage fresh weight which increased
at both salt stress levels (6 and 10 dS m-1
) compared to control owing to high leaf free proline,
total soluble phenolics, catalase enzyme, and leaf potassium concentration. However, different
biochemical traits and Na+
and Cl−
increased with the increase in salt stress levels (6 to 10 dS m 1
). The level of genetic diversity for the populations from the four regions was moderate (Ad Dhahira) to high (Al-Batinah, Ad-Dakiliya and Ash-Sharqiyah). In the third experiment, salt
stress, irrespective of type and intensity, caused a significant reduction in plant biomass,
physiological, and shoot mineral contents compared to control; however, this reduction was in the
order of NaCl (150 mM) > Na+(150 mM) > Cl−(150 mM). The tested genotypes were more sensitive to Na+toxicity than the Cl−
toxicity, and the contrasting genotypes differed in tissue tolerance of high Na+and Cl−
. In the fourth experiment, the potential of nano-proline seed priming and biochar in improving the salt tolerance in two differentially responding alfalfa genotypes whereas in the fifth experiment, the potential of γ-amino butyric acid in improving salt tolerance
in differentially responding alfalfa landraces. The application of biochar and nano-priming
significantly improved plant growth and carbon assimilation. However, the combined use of nano priming and biochar was more effective in improving salt tolerance than the sole application.
Biochar application instead triggered Na+
and Cl− but contributed to salt tolerance through an
increase in K+
contents, accumulation of proline and activation of the antioxidant defense system.
The GABA application as seed priming followed by root dipping improved the salt tolerance in
alfalfa. In conclusion, there was a significant variation of alfalfa landraces for salt tolerance, which
indicates their potential for cultivation in saline areas and/or use in breeding programs aimed to
develop salt tolerant alfalfa genotypes. The landraces OMA 6, OMA 161, and OMA 285 were
excellent in performance based on morphological and biochemical traits, and tissue mineral
contents under salt stress. The alfalfa genotypes were more sensitive to Na+
toxicity than the Cl−toxicity, and the contrasting genotypes differed in tissue tolerance of high Na+and Cl−. The exogenous application of nano-sized chitosan-proline, biochar and GABA helped in improving salt tolerance in alfalfa.
