Effect of water content and temperature on seed longevity of seven Brassicaceae species after 5 years of storage.

Maximising seed longevity is crucial for genetic resource preservation and longevity of orthodox seeds is determined by environmental conditions (water content and temperature). The effect of water content (down to 0.01 g·H2O·g(-1) ) on seed viability was studied at different temperatures for a 5-year storage period in taxonomically related species. Seeds of seven Brassicaceae species (Brassica repanda, Eruca vesicaria, Malcolmia littorea, Moricandia arvensis, Rorippa nasturtium-aquaticum, Sinapis alba, Sisymbrium runcinatum) were stored at 48 environments comprising a combination of eight water contents, from 0.21 to 0.01 g·H2O·g(-1) DW and six temperatures (45, 35, 20, 5, -25, -170 °C). Survival curves were modelled and P50 calculated for those conditions where germination was reduced over the 5-year assay period. Critical water content for storage of seeds of six species at 45 °C ranged from 0.02 to 0.03 g·H2O·g(-1) . The effect of extreme desiccation at 45 °C showed variability among species: three species showed damaging effects of drying below the critical water content, while for three species it was neither detrimental nor beneficial to seed longevity. Lipid content could be related to longevity, depending on the storage conditions. A variable seed longevity response to water content among taxonomically related species was found. The relative position of some of the species as long- or short-lived at 45 °C varied depending on the humidity at which storage behaviour was evaluated. Therefore, predictions of survival under desiccated conditions based on results obtained at high humidity might be problematic for some species.

Comparison of vitrification and encapsulation-dehydration for cryopreservation of Thymus moroderi shoot tips.

Vitrification and encapsulation-dehydration were tested for cryopreservation of Thymus moroderi Pau ex Martínez (Labiatae), an endemic plant from south-eastern Spain. For vitrification, shoot tips were loaded in a solution containing 0.4 M sucrose + 2 M glycerol for 20 min at room temperature, dehydrated in PVS2 solution for 0-105 min at 0 degree C, then immersed in liquid nitrogen (LN) for at least 1 day and rapidly rewarmed. The highest survival (71.4 percent) was obtained after 60 min PVS2 dehydration. Encapsulation-dehydration gave slightly lower results, with up to 50 percent explants survival. In the optimal protocol, donor plants were cold-hardened at 10 degree C for 5 weeks, excised shoot tips precultured for 48 h on MS medium with 0.08 M sucrose, encapsulated, pretreated in medium with 0.75 M sucrose for 19 h, desiccated to 22 percent moisture content (fresh weight basis), and immersed in LN. Vitrification thus appears more suitable than encapsulation-dehydration for cryopreservation of T. moroderi shoot tips.

Cryopreservation of in vitro shoot apices of Oxalis tuberosa Mol.

Oca (Oxalis tuberosa Mol.) is an under-utilized tuber crop from the Andean region. Cryopreservation would allow the safe and long-term preservation of the genetic resources of this crop. A protocol for the cryopreservation of in vitro grown shoots has been developed using the vitrification solution PVS2. Two genotypes were studied (G1 and G27). Nodal segments were cultured on MS medium and incubated at 10 degree C with 16 h photoperiod and 10 mol per square meter per second irradiance, for two weeks. Apices were then excised and cultured on MS+0.15 M sucrose for 3 days at 5 degree C in darkness. Subsequently, apices were immersed in a loading solution (liquid MS medium+2 M glycerol+0.4 M sucrose), and then treated with the vitrification solution PVS2 for 0 to 40 minutes. Cryovials were then immersed in liquid nitrogen. Four weeks after rewarming and culture on recovery medium, genotype G1 showed approximately 60 percent recovery (normal growth) with 20 min PVS2 treatment. Genotype G27 showed lower recovery (30 percent). Differential scanning calorimetry yielded a Tg midpoint for PSV2 solution of ca. -120 degree C. Calorimetric studies on apices at different stages of the cryopreservation protocol showed a change in calorimetric parameters consistent with a decrease in the amount of frozen water as the protocol advanced.

Apex cryopreservation of several strawberry genotypes by two encapsulation-dehydration methods.

This paper presents results from a study to develop cryopreservation procedures for apices of several strawberry genotypes. Five Fragaria x ananassa Duch. cultivars and two wild species (F. chiloensis and F. virginiana) have been screened using the encapsulation-dehydration method and/or a protocol which compromises vitrification and encapsulation-dehydration. Apices were encapsulated in an alginate gel, precultured on media containing high levels of sucrose (0.8 M, conventional protocol), or a combination of 0.4 M sucrose and 2 M glycerol. Recovery rates varied among genotypes (23-63%). The latter method reduced considerably the time needed for the cryogenic procedure by eliminating the pre-treatment with 0.8 M sucrose for 19 h prior to dehydration, as required by the conventional procedure.

Effects of Seed Cryopreservation and Priming on Germination in Several Cultivars of Apium graveolens.

Seed germination of seven celery cultivars was studied after storage in liquid nitrogen for 1 or 30 d. Cryopreservation was also carried out on pelleted and primed seeds. None of the treatments applied reduced germination percentages. T(50) (time for germination to reach 50%) significantly decreased in Florida, Utah and Istar cultivars when priming, alone or in combination with cryopreservation, was used.