Mating patterns in perennial ryegrass: consequences for seed regeneration

Genebank accessions stored ex situ as seed populations require periodic rejuvenation in order to maintain sufficient numbers of viable seeds. During regeneration the genetic integrity of an accession may be compromised by various factors, including variation in pollination rates between plants. For a rejuvenated accession of Lolium perenne (L.), consisting of 49 parental plants, a paternity exclusion analysis was performed by means of molecular analysis. Investigation of a total of 551 offspring showed that mating within the study population was clearly nonrandom, as 61.9% of the identified pollen donors were located within 1m distance from the mother plant. Observed pollination rates were very well described by an inverse quadratic function of interplant distance between potential mating pairs. However, contamination was considered more threatening to the genetic integrity of the accession than variation in pollination rates between plants. Within the total sample 5 cases of pollen contamination and 4 cases of seed contamination were observed. This indicated the need for improved measures during the rejuvenation of perennial ryegrass germplasm in order to avoid gene flow between accessions.