Osmotic adjustment segregates with and is positively related to seed yield in F3 lines of crosses between Brassica napus and B.juncea subjected to water deficit

For osmotic adjustment to be used as a selection criterion for adaptation to drought there is a need to demonstrate its segregation and association with seed yield in a population. This study examined osmotic adjustment and seed yield in F3 lines derived from crosses between Brassica napus (cvv. Karoo, Monty) and B. juncea (line JN25). A clear separation of the level of osmotic adjustment was observed among 20 F3 lines of Karoo x JN25 (7 high and 13 low) and 20 F3 lines of Monty x JN25 (8 high and 12 low) under glasshouse conditions. When the 3 parents and 8 selected F3 lines were grown in a low-rainfall environment in the field, the segregation of osmotic adjustment was largely similar to that observed in the glasshouse. Yield reduction, with irrigated plots as controls, was up to 30% for genotypes with low osmotic adjustment but only 10% for those with high osmotic adjustment. Osmotic adjustment was closely correlated with the accumulation of K+ (r = 0.91), soluble sugars (r = 0.90) and proline (r = 0.96), whereas other solutes (Na+, NH4+, Cl-, NO3-, Mg-2(+) and Ca-2(+)) made little or no contribution to osmotic adjustment. Proline concentrations were very low in well-watered plants but sharply increased by 5- to 15-fold in plants subjected to water deficit, and net proline accumulation showed a higher association with total seed number (r = 0.86) and yield (r = 0.89) than did the concentrations of K+ (r = 0.75 to 0.82) or soluble sugars (r = 0.68 to 0.72). The study suggests that leaf proline concentration could be a good indicator of osmotic adjustment in Brassica oilseeds.