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 Coffe a by measuring seed viability after equilibration over various saturated sa lt solutions. A quantal response model based on the logistic distribution w as developed in order to describe the typical S-shaped patterns observed. T he closeness of fit or the desiccation sensitivity model was shown, and the assumption that seed desiccation sensitivity follows a continuous distribu tion within species was verified. For each species, the water content at wh ich 50% of initial viability was reached, WC50, and a specific parameter de scribing the intra-specific variability, beta, were calculated using a non- linear regression. A simplified water sorption model was developed which al lowed easy calculation of water activity and water potential corresponding to WC50 (a(w50) and Psi(50)) for relative humidities ranging between 10 and 100%. Distribution of WC50 and Psi(50) (or a(w50)) in the genus Coffea was homogeneous within the following intervals: from 0.05 to 0.38 g H2O.g(-1) dw for WC50 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 WC50 or Psi(50) was used for classificat ion. The continuum for desiccation sensitivity observed within the nine spe cies studied confirmed that coffee is an appropriate material for studying desiccation sensitivity.