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diggin’ in SEED by Doug Boze, Southeast Idaho Area Manager, ICIA, Inc. Potato leaf Roll Virus exhibits symptoms well and all suspect leaf roll-infected plants are confirmed by elisa testing. typically, 550 to 640 individual lots are grown out and tested each year. most lots are represented by a 400 tuber sample. starting in 2009, about 1/3 of the lots were collected, treated and planted in mid- october. this is two weeks earlier than what was customary. the remaining lots were planted in Idaho Mosaic Progress Report Evaluating the ICIA winter test in California baCK in 2007, iDaho seeD anD commercial growers became concerned about unexpected levels of mosaic in some commercial fields, causing the seed growers to reassess how their seed lots are evaluated for virus levels in the post-harvest test. the post-harvest test is required on all certified seed lots and is used to determine eligibility of a lot for recertification. Recertification eligibility means a lot of seed is allowed to be planted in idaho and entered into the Certified seed Program, administered by the idaho Crop improvement association. the post-harvest test is also used by seed and commercial growers to determine suitability of a lot as planting stock for commercial potato production. at a certified seed growers meeting held that fall, idaho seed growers approved a change in testing protocol requiring elisa—enzyme-linked immunosorbent assay—testing for mosaic of all seed lots in the post-harvest test. mosaic is caused primarily by Potato Virus y (PVy), and to a lesser extent, by Potato Virus a (PVa). Prior to this change in protocol, the post-harvest test consisted of planting a representative sample of each certified seed lot in southern California, and visually inspecting the emerged plants for several factors, including mosaic. Plants exhibiting virus symptoms were sampled and lab-tested to verify the visual findings. Varieties considered latent for expression of virus symptoms, such as Russet norkotah and shepody, were leaf-sampled and elisa-tested for mosaic. under the new testing protocol, a representative sample of each certified seed lot is planted in southern California, and leaves from all emerged plants are sampled and lab-tested using the elisa method at the idaho Crop improvement association seed Certification laboratory in idaho Falls. the advantage to testing all emerged plants for mosaic by elisa is that the test detects viruses in plants that are not exhibiting disease symptoms. all other factors determining lot eligibility, including percent Potato leaf Roll Virus and seed-born chemical injury are determined by visual row inspections. early november. leaf sampling takes place during three sampling periods: early and mid-January, and early February. a “Field Day” also takes place in early February, allowing seed growers and representatives of seed buyers an opportunity to visit the test plot and evaluate their test rows. seed buyers often use a combination of lab results and visual observation of test rows when making buying decisions. HOW ARE WE DOING? since instituting the change in winter testing protocol in 2007, steady progress has been made in overall reduction of lots with any mosaic percentage and in lots found to be ineligible for recertification due to excess mosaic. overall incidence, or lots with any mosaic, has decreased by 10 percent, and lots ineligible for recertification have decreased by 14 percent. utilization of this more-sensitive testing method has increased seed growers’ and buyers’ confidence in the winter test readings and has enabled them to make better decisions regarding the suitability of a lot for either planting a commercial field or for recertification purposes. another advantage to this change in testing protocol is improved timeliness regarding reporting of winter test results. as it is no longer necessary to wait until a sufficient numbers of plants have emerged and have reached a size suitable for visual mosaic detection, testing and reporting can begin earlier in the winter. it has been a long-time objective of the certification program to make progress in this area with seed growers and their customers giving it a high priority. elisa testing along with changes in test plot fertility management and split planting times has contributed to achievement of this goal. PG “As it is no longer necessary to wait until a sufficient numbers of plants have emerged and have reached a size suitable for visual mosaic detection, testing and reporting can begin earlier in the winter.” 22 Potato Grower | SEPTEMBER 2010