|Del Rio, Alfonso|
Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2009
Publication Date: 9/29/2009
Citation: Bamberg, J.B., Del Rio, A.H. 2009. Unbalanced Bulk of Parent's Seed is Not Detrimental in Germplasm Regeneration of Two Model Potato Populations. American Journal of Potato Research. 86(5):391-397. Interpretive Summary: Potato is the most important US vegetable, and one of the best hopes for feeding an increasingly hungry world. Breeders need to keep producing better varieties to meet changing needs of the industry and preferences of consumers. Breeders get raw materials from genebanks, so it is in the interest of US Agriculture for the US Potato Genebank at Sturgeon Bay, Wisconsin to maintain the broadest possible array of genes in the collection. We can do so efficiently by determining which genebank activities provide opportunity for genetic losses and which don’t. Periodically, seedlots have to be regenerated by growing up seedlings into parent plants which will produce a fresh supply of seeds. Some have advocated making a separate seedlot composed of an equal number of seeds from each mother plant (i.e., “balanced”) to use as parents for future regeneration cycles. We recorded seedset over 12 cycles of seed multiplication and the presence of 105 DNA markers in two populations noted to have much variation in seed production per plant. Since very few genes would have been significantly better preserved with a balanced seed bulk, we conclude that the extra labor, recordkeeping and storage space needed to make such bulks is probably not worthwhile. Such technical information allows the genebank to increase efficiency and thereby better serve germplasm users who improve the potato crop.
Technical Abstract: Although the potato of commerce, Solanum tuberosum is a clonal crop, genebank preservation of wild and cultivated relatives is commonly done as populations of true seeds. In order to help equalize gamete contribution and prevent genetic drift over seed regenerations, some recommend a bulk of equal number of seeds from each mother plant be used as a source of parents for future rengenerations (an unbalanced overall bulk of the remaining seeds is made for general distribution). To assess whether this technique is an advantage to the genebank, we selected two S. andigena populations with great variation of seed production among mothers. Seed production of each mother was recorded over 12 standard seed regenerations, and genetic indicators were developed in the form of 105 polymorphic RAPD bands. For each polymorphic band, the variation of seed production per mother was used to predict the change in banded egg frequency in regenerations if an overall seed bulk had been made. Assuming pollen success from each mother was equal to egg success, the probability of excluding bands from a 20-plant sample was also calculated and compared before and after regeneration. As anticipated, only a fraction of bands were polymorphic within the populations and thus vulnerable to change in frequency or extinction from the population. Most of the remaining polymorphic bands were present in several mothers, making their vulnerability very low. Of the remaining polymorphic bands vulnerable within one population, most were fixed or nearly fixed in the other. Only 4 bands would have been substantially less vulnerable to loss by making a balanced seed bulk, and the average improvement was only 23% over the original population. Balancing seed from mothers does not control potential differences in male contribution, and it cannot remedy loss of a band from a population when that band is unique to a parent that produces no seeds at all. For balanced bulks to provide a significant preservation advantage, a band must be relatively rare in all populations and associated with mothers that tend to produce significantly fewer seeds. Very few bands appear to meet these conditions. We therefore conclude that the extra organization and resources invested in making balanced seed bulks probably pay back little genetic benefit to the genebank.