Screening for Salinity Tolerance in Alfalfa

Abstract

A lack of salt-tolerant cultivars may be due in part to inadequate evaluation protocols used for selection. Our objective was to develop a greenhouse protocol that is simple and consistently separates genotypes for their relative ability to survive under saline conditions. In 2000 and 2001, 12 alfalfa (Medicago sativa L.) cultivars were seeded in 3.8- by 21-cm cone-shaped containers plugged with capillary matting and filled with silica sand. Six-week-old seedlings were submersed in a NaCl-nutrient solution starting at an electrical conductivity (EC) of 3.0 dS m−1 and increased 3.0 dS m−1 every 1 to 2 wk for 10 to 13 wk. Probit analysis was used to estimate the time and salt dose to reach 50 (LD50) and 75% (LD75) mortality. Probit results were compared with cultivar ranking for mean percentage plant mortality when overall trial mortality reached approximately 50 and 75%. Pearson's rank correlations between 2000 and 2001 at the LD50 and LD75 levels were r = 0.90 (P < 0.001) and r = 0.88 (P < 0.001), respectively. Rank correlations between 2000 and 2001 based on means when overall trial mortality levels were approximately 50 and 75% were r = 0.92 (P < 0.001) and r = 0.85 (P < 0.001), respectively. The correlations between mean percentage cultivar mortality rankings and the probit-based rankings were above r = 0.90 (P < 0.001) in both years. The high correlations verify that this protocol produces repeatable results and provides a method to effectively screen large numbers of plants for survival under saline conditions.