RE SEARCH New Erwinia variants require more knowledge and specific tests So far, field inspections have always determined the inspection results of seed. bly spreads via seed, but spreading via jointly-used machinery or minimal water vapour and rain drops can’t be ruled out. Carotovorum causes bacterial wet rot or soft rot Pectobacterium carotovororum subsp. carotovorum is the most widespread Erwinia subspecies. It is also found in the soil and in many other host plants including weeds. However, there are no signs yet that this subspecies also can cause bacterial infections in the field on its own. During the storage of potatoes, this bacterium can cause wet rot or soft rot. The Dickeya and Pectobacterium variants can do the same. Wet rot or soft rot mainly cause problems when growers don’t store the tubers properly. The bacterium can also cause secondary infection in the field, in which case the disease is primarily caused by a different Dickeya or Pectobacterium species. Dickeya tends to thrive in cold weather Within the Dickeya species, two can be distinguished that cause blackleg in the Netherlands. In the eighties and nineties, Dickeya dianthicola was responsible for around 30 percent of bacterial infections. Today, this bacterium is only sporadically The complex of the Erwinia bacterium Pathogen Pectobacterium atrosepticum Pectobacterium wasabiae Pectobacterium carotovorum subsp. brasiliense Pectobacterium carotovorum subsp. carotovorum Dickeya dianthicola Dickeya solani Erwinia carotovora subsp. carotovora Erwinia chrysanthemi seen. Like Pectobacterium atrosepticum, Dickeya dianthicola thrives in cold weather and the change in climate seems to be a relevant indication here. Since 2000, we’ve often been finding Dickeya solani in diseased plants. This bacterium is also found in fields of hyacinths and sometimes in the surface water, so it could have reached a seed potato crop via infected surface water. This bacterium can be particularly aggressive in high temperatures and can therefore cause many problems in the countries around the Mediterranean. This bacterium species is also often genetically identical. As with the Pectobacterium carotovorum subsp. brasilience, this points to a recent introduction. Knowledge very important Firstly, knowledge about the diversity of Erwinia bacteria is very important during the inspection of the seed. The tests that are used must, naturally, be able to show all the different variants. Meanwhile, reliable molecular tests have been developed based on the detection of DNA. NAK has introduced these tests for Pectobacterium atrosepticum and Pectobacterium wasabiae The Dickeya species can all be traced in a single test. If a Dickeya test is positive, additional tests will show which specifOld name Erwinia carotovora subsp. atroseptica Particulars Dominant in the past, not often found in the last 10 years. Thrives in cold weather. Is often found in seed lots, but not so often in diseased plants. Upcoming problem. Aggressive in both low and high temperatures. Only causes problems in storage. Dominant in the past, not often found in the last 10 years. Thrives in cold weather. Often found in diseased plants. Aggressive in high temperatures. 24 Potato World 2015 • number 4 Pagina 23
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