Analysis of the Tolerance of 22 Malus baccata Accessions to Alkali Stress

Alkali stress is an important factor that restricts the growth and yield of crops. Apple ( Malus baccata Borkh.) rootstocks have attracted widespread attention because of their wide distribution and ability to exist in various forms. This study reported the tolerance of several M. baccata accessions to alkaline stress using the sand culture method. Nitrogen (N), phosphorus (P), and potassium (K) contents in the roots of 22 M. baccata accessions decreased after 40 days of alkali stress exposure. N and P contents in the leaves of most M. baccata seedlings decreased, whereas K content increased. In addition, the new leaf number and fresh and dry weights of the M. baccata accessions decreased significantly, indicating that alkali stress inhibits the growth of M. baccata seedlings. The 22 M. baccata accessions were divided into three categories: high, moderate, and low tolerance based on the cluster analysis of the resistance coefficients of six growth indices combined with the average resistance coefficient evaluation of the growth indices. These delineations are important for screening M. baccata resources. This study provides a basis for the growth of the apple industry in areas such as northwest China, which suffer from severe salinization.