To check for maintenance of seed viability, the germination ability of lettuce accessions is monitored according to ISTA procedures at regular intervals (Van Treuren et al., 2013). Accessions are regenerated when seed viability drops below 80% for cultivated material or below 60% for accessions of wild species. Regeneration is also carried out when germination has decreased with at least 15% during a monitoring interval or when the remaining seed quantity has dropped below 1.7 g.
The majority of lettuce accessions are regenerated under controlled greenhouse conditions. Since cultivated lettuce and the majority of its wild relatives are self-fertilising, no protective measures are used to avoid cross-pollination, with the exception of a few outcrossing species. Regenerations are carried out in close cooperation with seven lettuce breeding companies affiliated to the Dutch association for the plant reproduction material sector (Plantum NL). More detailed information about regeneration procedures can be accessed through the link provided in the right margin of this page.