Setting the Gold Standard for Tomatoes

Tomatoes susceptible to late blight, on the left, contrast with tomato hybrids resistant to late blight, early blight, and septoria leaf spot. Source: Mike Gloss, Kingbird Farm; Martha Mutschler, Cornell University.

When food lovers choose items for a grocery list or plan a garden plot, tomatoes take the prize. Tomatoes rank first among the top ten most popular vegetables grown in home gardens and fifth among the most profitable vegetables to grow. They also have been named the most purchased vegetable in the United States.

In 2009, airborne fungus late blight, which can spread through a garden or field in just a few days, decimated tomato crops in the Northeast. Some growers in the region reported total tomato crop loss. Scientists stepped up creation of blight-resistant tomato varieties, working with new urgency on research they had begun years before.

In addition to late blight, early blight and septoria leaf spot also threaten Northeastern tomato crops. Martha Mutschler of Cornell University stepped into the ring with a goal of knocking out this fungal triple threat. With a USDA Regional IPM Competitive Grant from the Northeastern IPM Center in her corner, Mutschler prepared to go the distance to combine the winning genetic characteristics for fungal resistance in tomato crops.

Finding Genes that Protect

Mutschler and her team of collaborators—including Tom Zitter of Cornell, Kelly Ivors and Randy Gardner of North Carolina State University’s Mountain Research Station, and many extension partners in New York, West Virginia, Pennsylvania, and North Carolina—learned that plants carrying the genes Ph2 and Ph3 formed the gold standard of late-blight resistance.

Tomato breeds that contain genetic control of all three diseases have little to no need for fungicide applications. They naturally resist the effects of late blight and septoria. Mutschler’s varieties underwent testing in both organic and conventional settings to meet the needs of diverse growing methods.

Ripe tomatoes in the field. Source: USDA Agricultural Research Service Photo Unit, Bugwood.org

Shared Bounty

Mutschler and her collaborators release their tomato lines nonexclusively. All seed companies have access to the triple-resistant tomato lines and the molecular markers for the Ph2 and Ph3 resistance genes. Thus they can add the triple fungal resistant trait to their new varieties. To make selection easier for growers, Mutschler and Zitter developed a list of tomato variety characteristics with their resistance and tolerance capabilities. See the Vegetable MD Online website:

http://vegetablemdonline.ppath.cornell.edu/.

Among the varieties already on the market for the 2013 growing season is the new triple-fungal resistant tomato hybrid “Iron Lady” (High Mowing Organic Seeds). More new hybrids with the trait are expected to be released by several seed companies in the next few years. “The process is moving fast,” says Mutschler. “At this rate, new varieties might come out yearly,” she predicts.

This means there is much work to be done.  Mutschler hopes to breed tomato lines with even stronger resistance to early blight. What’s more, Mutschler is combining genes for different traits to solve other problems. She says she is confident that her team will continue to develop tomato plants that can withstand a wide range of pest insects and diseases spread by them.