Shoot and root growth of castor bean in response to soil salinity

Description

Soil salinity is a serious threat to agriculture worldwide, which is increasing due to natural salinisation and increased irrigation. Castor bean (Ricinus communis L.) is an industrial oilseed crop. This study evaluated root and shoot responses of two castor bean genotypes (Zibo imported from China and Freo from Western Australia) to 0, 100 and 200mM sodium chloride (NaCl) grown in deep PVC tubes in a glasshouse. Salt stress was induced gradually, with 25mM NaCl added every second day from 21 days after sowing (DAS) until the pre-determined salinity level was reached. Plants were harvested for assessments at 112 DAS. In both genotypes, the 200mM NaCl treatment significantly reduced plant height, stem diameter, number of fully expanded leaves, leaf area, shoot and root biomass, total root length, photosynthetic traits, chlorophyll content, K+ concentration, K+/Na+ ratio and increased Na+ concentration, relative to the control. The 100mM NaCl treatment had litter effect on both genotypes indicating their tolerance to moderate salinity stress (100mM NaCl). Castor bean plants showed salinity tolerance mechanisms such as retaining Na+ in old tissues, limiting Na+ uptake by roots, limiting Na+ translocation into shoots, and maintaining high K+/Na+ ratio in young leaves.