Salinity Tolerance of Phaseolus Species during Germination and Early Seedling Growth

Salinity tolerance during germination and early seedling growth was evaluated for 24 accessions representing four wild Phaseolus species (P. angustissimus A. Gray, P. filiformis Bentham, P. leptostachyus Bentham, and P. microcarpus Mart.) and four accessions of cultivated common bean (P. vulgaris L.) at 0, 60, 120, and 180 m M NaCl. Salinity stress delayed germination in all accessions to varying degrees. Eight accessions of P. filiformis germinated fastest under high salinity (120 mM NaCl). Additional wild accessions exhibiting rapid germination at 120 m M NaCl were P. angustissimus, PI535272, P. leptostachyus, PI535336, and P. microcarpus, PI430196. Among accessions, median germination time (days to 50% germination, T50) at 120 mM NaCl was correlated positively (r2 = 0.55, P ≤ 0.01) with germination in the control treatments. Seeds that germinated rapidly at 60 m M NaCl also germinated rapidly at 120 m M NaCl. At 180 m M NaCl, several accessions reached 50% germination by 6 d, demonstrating high genetic potential within Phaseolus for salinity tolerance during germination. The biomass of radicles plus hypocotyls decreased with increasing salinity. Cluster analysis separated the accessions into three groups. Group I included salt sensitive accessions with late germination, high sensitivity index (ratio of median germination time at 120 m M NaCl versus control), and reduced seedling growth. Group II included salt tolerant accessions with rapid germination, high sensitivity index, and enhanced seedling growth. Group III included cultivated accessions corresponding to the Mesoamerican and Andean gene pool with rapid germination, low sensitivity index, and intermediate seedling growth. The results confirm that wild Phaseolus species, and in particular P. filiformis, represent a genetic resource for improvement of salinity tolerance in common bean.