Seedling, early vegetative, and adult plant growth of oilseed rapes (Brassica napus L.) under saline stress

Salinity is a major limiting factor for early crop establishment and yield. In this study, 131 Brassica napus genotypes were evaluated for germination and early seedling growth in Murashige & Skoog medium supplemented with NaCl. Selected genotypes were then evaluated for tolerance to salinity at the vegetative and reproductive stages in greenhouse and semi-hydroponic systems using 1.4, 5, 10, 15, 20, and 28 dS m(-1) salt stress. Relative salt tolerance (RST) was calculated and compared with genotype performance under no salt stress (control). The area under the germination progress curve (AUGPC) varied from 53 to 90 in the control and from 6 to 89 under 200 mmol L-1 NaCl stress. The seedling vigor index (SVI) ranged from 200 to 1606 and 10 to 736 in the control and 200 mmol L-1 salt stress treatments, respectively. The RST for germination, root length, shoot length, and SVI ranged from 8% to 97.7%, 2% to 98.3%, 6.5% to 70.8%, and 1.9% to 83%, respectively. Root length was most severely affected by saline conditions, followed by shoot length and AUGPC, when RST percentages of these traits were compared among responses of the 131 genotypes. Genotypes showed varying levels of proline and glucosinolate accumulation under different levels of saline stress. Greater accumulation of proline and glucosinolates was recorded with increased salinity level. This study indicates that variation exists in seedling and adult plant responses to saline stress in B. napus genotypes and that improvement for salinity tolerance requires selection at the seedling, vegetative, and reproductive plant stages.