Quantitative estimation of seed desiccation sensitivity using a quantal response model:: application to nine species of the genus Coffea L.

Seed desiccation sensitivity was studied in nine species of the genus Coffea by measuring seed viability after equilibration over various saturated salt solutions. A quantal response model based on the logistic distribution was developed in order to describe the typical S-shaped patterns observed. The closeness of fit or the desiccation sensitivity model was shown, and the assumption that seed desiccation sensitivity follows a continuous distribution within species was verified. For each species, the water content at which 50% of initial viability was reached, WC(50), and a specific parameter describing the intra-specific variability, beta, were calculated using a non-linear regression. A simplified water sorption model was developed which allowed easy calculation of water activity and water potential corresponding to WC(50) (a(w50) and Psi(50)) for relative humidities ranging between 10 and 100%. Distribution of WC(50) and Psi(50) (or a(w50)) in the genus Coffea was homogeneous within the following intervals: from 0.05 to 0.38 g H(2)O.g(-1) dw for WC(50) and from -168 to -11 MPa for Psi(50). Different classifications of the coffee species studied as regards to their desiccation sensitivity were obtained depending on whether WC(50) or Psi(50) was used for classification. The continuum for desiccation sensitivity observed within the nine species studied confirmed that coffee is an appropriate material for studying desiccation sensitivity.