Potato Grower

May 2018

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WWW.POTATOGROWER.COM 25 PIVOT POINT TO END GUN ASK YOUR NELSON DEALER ABOUT THE BIG GUN® REBUILD PROGRAM 3030 SERIES WITH 3NV NOZZLE: Press, Spin, Click for On, Off, Flush, Line Flush Functions NELSON IRRIGATION CORPORATION OFFERS A FULL RANGE OF WATER APPLICATION SOLUTIONS FOR MECHANIZED IRRIGATION. FROM CONTROL VALVES TO PIVOT SPRINKLERS, AND PRESSURE REGULATORS TO END GUNS — THE PACKAGE IS COMPLETE. TEL: +1 509.525.7660 — NELSONIRRIGATION.COM 169038NelIrr12h.indd 1 10/3/17 1:43 PM genes to produce potatoes with high-quality tubers along with other traits, including resistance to Colorado potato beetle. Screening for beetle resistance is a laborious task involving quantification of insect feeding, and only small numbers of plants can be screened at any one time. The task of selection would be a lot more efficient if the breeder could use genetic information from DNA markers for assistance. Helen Tai is a genomics researcher at AAFC who works on development of more efficient selection tools for potato breeding. Because screening for beetles on whole plants is so laborious, Tai turned to analyzing naturally produced compounds in the leaves to identify a chemical signature in the leaf that could be used to characterize resistance. One important chemical difference was in glycoalkaloids, complex chemical defense compounds synthesized from cholesterol and sugars by the plant's own biosynthetic machinery. In particular, the domesticated potato produces the glycoalkaloids solanine and chaconine. Because solanine and chaconine are toxic to humans, potatoes are bred to have low levels of these compounds in tubers. However, levels of these glycoalkaloids remain high in potato plant leaves. Although Colorado potato beetles have a steady diet of leaves, they are not affected by the toxicity of solanine and chaconine. Jamuna Paudel, a post-doctoral fellow in Tai's lab, researched the effects of artificially reducing solanine and chaconine in domesticated potato and found that feeding rates remained the same, but insects raised on these plants developed more quickly and died earlier. The researchers concluded that Colorado potato beetles had adapted to feeding on a diet of high solanine and chaconine, and that reducing these glycoalkaloids in the diet disturbed the pests' normal development. Tai also found that all wild, Colorado potato beetle-resistant Solanum species had low levels of solanine and chaconine. Further investigation of the wild Solanum revealed that instead of solanine and chaconine, another glycoalkaloid, dehydrocommersonine, was produced. Tai's lab also discovered that the leaves of the domesticated potato not only had higher levels of solanine and chaconine compared to tubers, but they also produced a third glycoalkaloid, solanidenol chacotriose. Further studies showed that leaves of resistant hybrids had high dehydrocommersonine and low solanidenol chacotriose, while susceptible hybrids had the opposite pattern. Armed with this new way of defining Colorado potato beetle resistance, Tai teamed up with Kyle Gardner and used genetic mapping to find DNA markers linked to the region of the potato genome contributing to the resistance trait. These resistance markers can be combined with additional markers linked to other important traits, such as resistance to viruses, for use in selection of superior potato varieties. With recently hired entomologist Chandra Moffat, Tai, Bizimungu and Gardner are investigating how Colorado potato beetles will respond over time to the most promising hybrid crosses produced by the breeding program. As the Colorado potato beetle is a dynamic and notoriously adaptable insect, researchers will need to keep investigating new ways to stay ahead of it by developing more genetic sources of resistance and strategies for integrated pest management.

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