Survival of the Citrus grandis and Citrus madurensis seeds in liquid nitrogen after dessication using different methods

In Malaysia, citrus fruits are widely cultivated throughout the country mainly for local consumption where it is used as food flavouring, as a drink and a source of medicine. At present, conservation of citrus germplasm is mainly through field gene banks. However, the trees rarely survive more than 15-20 years and are subjected to problems such as exposure to attacks by pests and diseases, natural hazards, as well as high labour costs for maintenance. Although most citruses produce seeds, however, seed conservation is not practical because it does not remain viable when stored for extended period of time. Cryopreservcation is the only safe and cost-effective option for long-term conservation of germplasm of such seeds. However, the success of cryopreservation is highly dependent on the availability of freezable water in order to avoid recrystallization of ice. Desiccation can be achieved through various means and these have been reported to influence viability. Therefore, the present study was undertaken to study the effects of desiccation on viability of C. grandis and C. madurensis seeds with and without exposure to liquid nitrogen. Two desiccation methods werre employed, namely desiccation using the laminar air flow and silica gel whereby seeds were desiccated for 12, 24, 36, 48, 60, 72, 96 and 120 hours. Fresh seeds for both species had high survival of 100%. Upon desiccation the moisture content declined with a faster rate for desiccation using silica gel. Desiccation resulted in reduction in survival especially when desiccated to below 20% moisture content. Seeds with moisture content higher than 30% did not survive liquid nitrogen exposure. Desiccation using silica gel resulted in more damage compared to desiccation. Upon exposure to liquid nitrogen C. grandis has more than 50% survival while the results for C. madurensis were slightly less. It is shown that both C. grandis and C. madurensis have the potential to be cryopreserved. From this study it can be conducted that desiccation is necessary for cryopreservation and that desiccation using LAF is better than using silica gel.