Cryopreservation of seeds of four coffee species (Coffea arabica, C-costatifructa, C-racemosa and C-sessiliflora): importance of water content and cooling rate

In the range of water contents studied (0.1-0.4 g H2O g dw(-1)), Coffea arabica seeds were less sensitive to desiccation than C. costatifructa, C. racemosa and C. sessiliflora seeds. At 0.20 g H2O g dw(-1), 53% of C. arabica seeds germinated after direct immersion in LN (rapid cooling, 200 degrees C min(-1)), but none of them developed into normal seedlings. By contrast, in C. costatifructa, C. racemosa and C. sessiliflora, when seeds were dehydrated to the optimal water content (0.19, 0.28 and 0.31 g H2O g dw(-1), respectively), the percentages of seeds which developed into normal seedlings after LN exposure were 26, 78 and 31% of the desiccation control, respectively. Normal seedlings could be recovered from cryopreserved C. arabica seeds only if they were desiccated to 0.20 g H2O g dw(-1) and precooled slowly to -50 degrees C prior to immersion in LN. Precooling seeds at 2 degrees C min(-1) allowed 25% of seeds to develop into normal seedlings. The thawing rate had no effect on the survival of cryopreserved C. arabica seeds. In all cryopreservation experiments, the total germination did not reflect the percentage of seeds which developed into normal seedlings. Examination of excised embryos indicated a partial explanation of this difference since only the shoot apex was destroyed in abnormal embryos, whereas the hypocotyl and radicle were normal.