title: Increases in the longevity of desiccation-phase developing rice seeds: response to high-temperature drying depends on harvest moisture content.
abstract: OBJECTIVE
  Previous studies have suggested that the drying conditions routinely used by genebanks may not be optimal for subsequent seed longevity. The aim of this study was to compare the effect of hot-air drying and low-temperature drying on subsequent seed longevity for 20 diverse rice accessions and to consider how factors related to seed production history might influence the results.
  
  
  METHODS
  Seeds of rice, Oryza sativa, were produced according to normal regeneration procedures at IRRI. They were harvested at different times [harvest date and days after anthesis (DAA), once for each accession] and dried either in a drying room (DR; 15 % relative humidity, 15 °C) or in a flat-bed heated-air batch dryer (BD; 45 °C, 8 h d(-1)) for up to six daily cycles followed by drying in the DR. Relative longevity was assessed by storage at 10·9 % moisture content and 45 °C.
  
  
  RESULTS
  Initial drying in the BD resulted in significantly greater longevity compared with the DR for 14 accessions (seed lots): the period of time for viability to fall to 50 % for seeds dried in the BD as a percentage of that for seeds dried throughout in the DR varied between 1.3 and 372·2 % for these accessions. The seed lots that responded the most were those that were harvested earlier in the season and at higher moisture content. Drying in the BD did not reduce subsequent longevity compared with DR drying for any of the remaining accessions.
  
  
  CONCLUSIONS
  Seeds harvested at a moisture content where, according to the moisture desorption isotherm, they could still be metabolically active (>16·2 %) may be in the first stage of the post-mass maturity, desiccation phase of seed development and thus able to increase longevity in response to hot-air drying. The genebank standards regarding seed drying for rice and, perhaps, for other tropical species should therefore be reconsidered.
authors.affiliation: T.T. Chang Genetic Resources Center, International Rice Research Institute, Los Baños, Philippines and School of Agriculture, Policy and Development, University of Reading, Earley Gate, PO Box 237, Reading RG6 6AR, UK.
authors.forename: K J
authors.initials: KJ
authors.lastname: Whitehouse
authors.affiliation: T.T. Chang Genetic Resources Center, International Rice Research Institute, Los Baños, Philippines and f.hay@irri.org.
authors.forename: F R
authors.initials: FR
authors.lastname: Hay
authors.affiliation: School of Agriculture, Policy and Development, University of Reading, Earley Gate, PO Box 237, Reading RG6 6AR, UK.
authors.forename: R H
authors.initials: RH
authors.lastname: Ellis
mesh_terms: D002980:Climate; D003890:Desiccation; D006813:Humidity; D012275:Oryza / Q000254:growth & development*; D012639:Seeds / Q000254:growth & development*; D013696:Temperature
keywords: Oryza sativa; Seed longevity; desiccation phase; genebank; harvest moisture content.; rice; seed development; seed drying