Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2009
Publication Date: August 15, 2009
Citation: Nitzan, N., Boydston, R.A., Batchelor, D., Crosslin, J., Hamlin, L., Brown, C.R. 2009. Hairy Nightshade is an Alternative Host of Spongospora subterranea, the Potato Powdery Scab Pathogen. American Journal of Potato Research. 86:297–303. Interpretive Summary: The disease powdery scab of potato is caused by an unusual fungus. It is a parasitice slime mold. It causes belmishes on the tubers where the spore form of the fungus is formed. Also, it forms galls on the roots where the spore form is also stored. The damage caused by powdery scab is erratic from one field to the next and one year to next. We showed that a common weed can host the powdery scab organism and provide inoculum that will go to potato. This has several implications. First, controlling hairty nightshade efficiently will reduce this source of the disease. Second, even if potato is not being grown, hariy nightshade can maintain damaging levels of powdery scab in the soil that will subsequently cause damage in future potato crops. Understanding how a pathogen becomes available to damage a crop is important in the control of the crop.
Technical Abstract: Structures, similar to galls developing on potato roots infected by the powdery scab pathogen S. subterranea, were observed on roots of hairy nightshades (Solanum physalifolium, formerly S. sarrachoides) collected from commercial potato fields in Washington State where populations of S. subterranea were high. Plants of the susceptible potato cultivars Shepody, Umatilla Russet and Russet Burbank, and hairy nightshade were artificially inoculated in the growth chamber with S. subterranea inoculum originating from potato and hairy night shades. Root galls and root galls like structures were recorded, respectively, on 10 of 12 potato plants, and 13 of 25 hairy nightshade plants that were artificially inoculated with inoculum from potato; and on 2 of 19 potato plants, and 5 of 16 hairy nightshade plants that were artificially inoculated with inoculum from hairy nightshades. S. subterranea specific PCR assessment significantly (P<0.05, R2 = 0.7) correlated to the visual assessment in 34 of 40 samples, whereas 5 of 40 samples were negative visuals with positive PCR out come, and only 1 of 40 samples was positive visual with a negative PCR out come. Root galls developing on potato contained significantly more sporeballs than root galls developing on hairy nightshades. The results of the present study indicated that that the structures observed on hairy nightshades powdery scab root galls. The completion of the Koch postulates indicated that S. subterranea can infect and complete its life cycle on hairy nightshades producing a new generation of spore balls that are infectious on potato. To the author’s knowledge, this is the first report of S. subterranea development on hairy nightshades.