The re-emergence of Potato Virus Y in potato seed stock is of great concern to farmers because insecticides used to control the aphids that vector PVY do not effectively decrease transmission of the disease.
In response, the U.S. Environmental Protection Agency has granted an Emergency Exemption to the Montana Department of Agriculture for use of BmJ to control PVY on up to 2,675 acres of seed potatoes. Manufactured by Certis USA, BmJ contains Bacillus mycoides isolate J, a bacterium discovered by Montana State University (MSU) that has been shown to trigger a plant’s immune response to pathogenic fungi, bacteria, and viruses. Products that can produce this response (called systemic acquired resistance) represent an advancement in the management of pests and plant diseases.
MSU’s Barry Jacobsen and his colleagues discovered and patented BmJ, which is a naturally occurring bacterium. BmJ, they found, “turns on” specific genes found in most plants. These genes induce the plant to produce defensive reactions that make it more difficult for a pathogen, such as PVY, to infect the plant. BmJ is a resistance activator with no direct effect on the plant pathogen itself. That characteristic makes BmJ a potentially valuable tool for use in fungicide resistance management programs.
Potato Virus Y (PVY) is one of the most damaging potato viruses affecting crop yields and tuber quality. PVY can also affect tomato, capsicum, and some other related species. Symptoms vary depending on viral strains and susceptibility level of host cultivar. They may include mottling, distortion and necrosis of leaves and stems, premature defoliation, tuber necrosis and plant death, or no symptoms at all.
PVY is transmitted by aphids in a non-persistent manner, with Myzus persicae being the most efficient vector. PVY can also be spread by mechanical means, plant-to-plant contact, or with infected planting material such as seed tubers. Disease management of PVY and other potato viruses relies largely on clean planting material and use of resistant crop varieties, but reduction of available virus reservoirs and vector numbers may also be useful.
The emergence of new PVY strains has recently been reported from different areas, including an increase in new tuber-necrotic strains in the U.S. Numbers of co-infecting strains will build up with every crop cycle if PVY infected seed tubers are used, especially if these are moved to different areas where the virus strains they carry may combine with local PVY populations.
Induced (or acquired) systemic resistance (ISR) of plants against pathogens is a widespread phenomenon. It is a host response triggered by a local infection that leads to long lasting disease resistance effective against fungi, bacteria, and viruses. Changes in cell walls, pathogenesis related enzyme modifications and/or production of phytoalexins have been found to be associated, but further defensive compounds are likely to exist.
Bacillus mycoides is a common, ubiquitous soil bacterium assigned to the B. cereus species complex. Strain J, a non-pathogenic, phyllosphere inhabiting isolate, was previously shown to be effective as a biocontrol agent against the fungal cercospora leaf spot (Cercospora beticola) of sugar beet reducing disease incidence by up to 90 percent in both glasshouse and field experiments.