Dessication and freezing tolerance of seeds from select citrus species

إنجليزي. Citrus seeds are classified as intermediate, so seed conservation under conventional storage conditions defined for orthodox seeds cannot be applied. Cryopreservation is the only viable option for long term storage of citrus germplasm. One of the critical factors ensuring success in cryopreservation is the amount of water present in the cell prior to freezing. This study aimed to determine the level of moisture content that would allow seeds of select Citrus species to survive cryopreservation without deleterious effects on seedling recovery. The tolerance of seeds of select Citrus species to dessication and freezing was determined. Surface sterilized seeds excised from mature fruits were dried over silica gel (100 g) in an airtight container for varying time intervals. Dessicated seeds were subjected to rapid freezing in liquid nitrogen, rapid thawing at 50 degC, and cultured onto MS basal medium for seedling recovery and germination. The seed s of five citrus species evaluated were able to tolerate dessication to less than 10% moisture content without deleterious effects on germination, and consequently survived cryopreservation. depending on species and moisture content, percent seedling recovery often cryopreservation ranged from 5.5 to 100%. Seedling recovery after cryopreservation increased with decreasing moisture content of the seeds. Among the different citrus species evaluated, lime (C. aurantiifolia)showed the highest dessication and freezing tolerance followed by Kubot native (native citrus sp.), pummelo (C. grandis) and calamansi (X Citrofortunella microcarpa). These four species exhibited more than 70% survival after cryopreservation. The manadarins 'Szinkum' and 'Ladu'(C. reticulata) showed the least survival after cryopreservation. The results of the study demonstrate for the first time that citrus seeds could be dessicated to less than 10% moisture contentwithout significant reduction in germinatio n, and that cryopreservation by seed dessication technique is an effective and simple method for long-term preservation of Citrus genetic resources.

إنجليزي. Scientific Conference of the Federation of Crop Science Societies of the Philippines Lapasan, Cagayan de Oro City (Philippines) 2-6 May 2005