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M A R C H 2 0 1 620 POTATO GROWER sues of tuber. Examples include all potato viruses PVY PLRV PVX PMTV TRV. Dr. Gudmestad indicated that there is a role for regulatory agencies in help- ing control seed borne pathogens. One finds that Type I and Type II pathogens are not regulated. However if they constitute an inva- sive pathogen they are most com- monly regulated via quarantines APHIS or CFIA. Type III and Type IV pathogens are most commonly regu- lated through seed certification regu- lations and occasionally by quaran- tines i.e. PMTV. There is a risk associated with import- ing seed despite the fact that there are valid reasons to buy out-of- stateprovince seed. The most com- mon reason is to access newer vari- eties. However one should carefully weigh the risk of either importing a major disease problem or worse yet importing a pathogen that can do irreparable harm. Examples of serious and urgent problems are the intro- duction on the farm of powdery scab new strains of late blight bacterial ring rot PMTV cyst nematodes and now Dickeya soft rot. Dickeya sp. are a new threat. Recommendations by Dr. Gudmestad were that potato growers if at all pos- sible buy seed locally because the risks that you will buy a problem from out-of-state that does not exist in your statefarm are higher than you think. Seed has been responsible for moving new genotypes of late blight potato cyst nematode pow- dery scabPMTV and now Dickeya. The last recommendation was that if you must buy seed remember to get a NA Plant Health Certificate in advance of purchase. Pectobacterium and Dickeya Dr. Gary Secor NDSU was speaking on a video about bacterial soft rot such as bacterial seed decay Dr. Secor mentioned that Pectobacterium bacte- ria occur in tuber lenticels. They per- sist in the soil less than one year. There are bacteria in all surface waters they move in aerosols enter through lenticels and wounds and are the most common cause for decay during wet conditions. This can be followed by systemic blackleg. There is no chemical control. Blackleg always has a decayed seed piece but a decayed seed piece does not always result in blackleg. If air is cut off from the seed by a film of water preventing it from breathing bacteria will begin to grow on the cut surface or in lenticels causing soft rot. The rate of growth increases with the temperature. Both liquid and dust seed treatment can aggravate the situation if not applied properly. Liquid can be too wet or hygroscopic dust may absorb too much moisture resulting in too wet seed pieces. Pectobacterium sp. can also cause soft rot in stem or tuber. Stem rot often occurs after damaging wind or hail. Tuber rot is most often a secondary pathogen to late blight ring rot pink rot Fusarium. Again bacteria develop faster at higher temperatures. Infections require an entry site and free water. It is good to avoid injuries and wet conditions. Improper han- dling for shipment can be the cause of tuber soft rot. The names of soft bacteria has been changed since 2005. In the US we have Pectobacterium atrosepticum Pectobacterium carotovorum subsp. caro- tovorum and P. brasiliense and P. wasabiae. Dickeya dianthicola has a wide host range and was present but not common on potatoes in the US. Others in the US are D. dadantii and D. zeae. The most virulent species is D. solani which was found as a bio- var3 of D. dianthicola. It is not found in the US. Dickeya symptoms resem- ble blackleg but are not black. The plants collapse in the field while the bacteria are still inside the system. Dickeya is more aggressive but is less hardy. It needs higher temperatures. Potato samples have been identified for Dickeya dianthicola in the US. We need molecular testing to identify whether Pectobacerium or Dickeya is present and what species it is. When Dickeya is suspected the symptoms to look for are stem rot that is drier than that of Pectobacterium and not black inky or wet but with hollow stem and vascular infection. Plants may collapse quickly in the field without obvious wet blackleg symptoms and tubers with internal rot. Plants rot underground and can be picked up easily. The vascular tissue may be black staying inside the stem. Dr. Secor mentioned that a quaran- tine for Dickeya was not expected to be necessary. Sanitation is very important. All disinfectants work. Crop rotation is a good management strategy because the organism does not survive well in the soil but sur- vival in water is important. Certification agencies are in the process of developing a response. Dr. Secor concluded that there is an urgent need for testing as it is being requested by buyers. Testing proto- cols are now being developed and val- idated.