Xylem flow rate differences are associated with genetic variation in snap bean pod calcium concentration

Two commercial snap bean (Phaseolus vulgaris L.) cultivars (Hystyle and Lab rador) that differ in pod Ca concentration were grown aeroponically to asse ss physiological factors associated with these differences. Xylem flow rate , Ca absorbed, and Ca concentration in sieve sap and pods (all and commerci al size no, 4) were measured, Flow rate, Ca absorption and pod Ca concentra tion, but not sap Ca concentration, differed between cultivars, and this su ggests that genetic variability in pod Ca concentration is caused mainly by differences in flow rate, rather than differences in sap Ca concentration. 'Hystyle' showed 1.6 times greater flow rate, 1.5 times greater pod Ca con centration, and 1.7 times greater Ca absorbed than 'Labrador'. Flow rate co rrelated positively with Ca absorbed (R = 0.90), Ca concentration in pods o f size no, 4 (R = 0.55), and total pods (R = 0.65). Plant maturity influenc ed sap Ca concentration and Ca translocated increased as plant matured. The se results provide evidence that flow rate differences may cause variabilit y for pod Ca concentration in snap beans.