Photo 1: Fusarium wilt resistant and susceptible tomato seedlings. Michelle Grabowski
Although winter still holds Minnesota in its icy grasp, smart gardeners are already pouring over seed catalogs and preparing for the season ahead. There are many factors to consider when choosing which vegetable variety to grow this season. One option available to gardeners is disease resistant varieties. These are varieties that have been specially bred or selected for their ability to remain healthy in the presence of a pathogen. Choosing disease resistant vegetable varieties can save the gardener time and money since they will likely not require fungicide sprays or other control measures to prevent the development of fruit rot, leaf spots or other disease problems.
In order to make educated decisions about purchasing disease resistant seed, there are a few terms that gardeners should be familiar with. According to the American Phytopathological Society, a resistant plant is a plant that possesses properties that prevent or impede disease development. A fully resistant vegetable variety will not become diseased even if the pathogen is present and the environmental conditions favor disease development. Many vegetable varieties are moderately resistant or partially resistant, meaning that they cannot block all disease development but often are able to resist the pathogen enough to remain far healthier than a plant without any resistance. Similarly a tolerant plant is able to endure disease without serious damage or yield loss. For example a powdery mildew tolerant squash variety may have some powdery mildew on its leaves, but is likely to produce a good crop none the less.
Look for resistant varieties on seed packets or plant labels and in plant catalogues. Many companies indicate disease resistance with a series of initials after the variety name or within the description of the plant. For example a pumpkin labeled PMT means that this variety is powdery mildew tolerant. All initials are typically defined somewhere in the catalogue but you may have to flip a few pages to find the list.
Look for varieties that list resistance to a specific disease problem. For example tomatoes are often listed as VF, resistant to Verticillium wilt and Fusarium wilt. This tells you that the variety has been tested with a specific pathogen and found to be resistant to it. The genetic make up that results in a resistant plant is typically specific to one disease only, although it is possible to combine multiple genes for disease resistance into one variety. Broad unspecific claims, like Good Disease Resistance are typically not very useful. This may indicate a plant that is generally vigorous, but it is unlikely that the plant has been tested against any specific disease problem.
Remember not all plant diseases are common in Minnesota. Look for varieties with resistance to diseases that have been a problem in your garden in the past or are common in Minnesota. For some plant diseases there are many varieties to choose from that all have disease resistance. This allows the gardener to choose disease resistant seed and also select for several other characteristics. For example there are now many pumpkin varieties with tolerance, moderate resistance or complete resistance to powdery mildew. These disease resistant pumpkins vary from small to large and ribbed or smooth in their fruit characteristics and may grow as a large vine or a small bush. Unfortunately there are not disease resistant varieties for every plant disease. Some diseases like Septoria leaf spot of tomato plants and common smut on sweet corn occur in Minnesota every year, but no resistant variety has been discovered yet. A very comprehensive list of disease resistant vegetable varieties is available from Cornell University at http://vegetablemdonline.ppath.cornell.edu/Tables/TableList.htm.
Common Diseases in MN
Resistant or Tolerant Varieties
|Asparagus||Rust and Fusarium Crown Rot||Jersey Knight, Jersey Giant, other ‘Jersey’ varieties|
|Green Beans||Several fungal and bacterial leaf spots, several viruses||Many varieties available|
|Cucumber||Powdery mildew, Scab, several viruses||Many varieties available|
|Peas||Powdery Mildew, root rot||PM resistance available in many varieties, ‘Strike’ is resistant to Pythium root rot|
|Sweet Corn||Rust and Smut||Tolerance and moderate resistance to rust available in several varieties. No smut resistance available|
|Mt. Fresh and JTO-99197 offer some resistance to early blight.|
Many varieties resistant to verticillium
|Peppers||Bacterial Leaf Spot||Several varieties available|
|Pumpkins and Squash||Powdery Mildew several viruses||Many varieties available|