The view from Devil’s Courthouse mountain, which Sue and I hiked to on October 6.

This is a very cool article by Carolyn - I completely forgot that she embarked on this sort of project.

Off The Vine Disease Project

Carolyn Male

A few months ago I got an email from Joe Imhof, one of our subscribers, who basically, but very nicely, challenged us to put up or you know what with regard to disease tolerance and susceptibility of heirloom tomatoes. Joe knew that we didn’t want to deal with individual diseases but felt that assessing tolerance in heirlooms would be of great benefit to many people who are now growing heirlooms or would like to. He is absolutely right and I thank him for being the impetus behind this project. Many of us who grow lots of heirlooms have always known that potato leaf types are more tolerant than others to early blight and septoria leaf spot. And I should mention that the correct term is disease tolerance, not resistance; no variety, be it open pollinated or hybrid, is totally resistant to any pathogen (according to most of the tomato pathologists I’ve talked to recently). The type of information we can obtain should be of importance to those companies selling heirloom tomato seed, Seed Savers Exchange members, individual growers and magazines that carry heirloom tomato-related stories. I called a few folks to feel them out about this project and there was uniform encouragement. I must tell you about my chat with Kent Whealy at SSE. I called to see if they would be interested in participating and Kent said that because of disease build up they were opening new ground this year and he wasn’t expecting much disease. To which I responded that I was sorry to hear that! I couldn’t believe I said that..I guess it all depends on what your perspective is on a given issue.

When I mention that potato leaf varieties are more tolerant of early blight I can document that fact. In early 1993 Jon Traunfeld of Baltimore, MD called me and asked if I had any varieties of heirloom tomatoes that I thought were especially disease resistant (whoops!...tolerant). I mentioned about the potato leaf types and sent him seed of Olena, a very nice Ukrainian pink. I believe the field study was done through the Master Gardeners program; the farmer coopters are listed as Marty and Eric Rice of Frederick County, MD. Jon is with the Univ. of Maryland Extension service and administers the Master Gardener program for Maryland as part of his duties. The following information is taken from the report Jon sent me. The two objectives of the study were to (1) determine the relative susceptibility of four tomato cultivars to early blight and (2) compare the early blight susceptibility of potato leaf varieties to regular leaf varieties. The four varieties chosen for study were: 1. Pik Red, a determinate hybrid commercial variety known to be fairly susceptible to early blight; 2. Early Cascade, an indeterminate hybrid, early and small fruited with “purported” early blight tolerance; 3. Brandywine; indeterminate, large fruited, potato leaf, and 4. Olena; indeterminate, large fruited and potato leaf.

There were six randomized blocks, each containing 24 plants, for a total of 144 plants. Spacing was two feet within the rows and six feet between rows. The stake and weave method of support was used and a straw mulch was laid down. The Rices’ farm is a certified organic farm with no sprays or fertilizers used. As can be seen in Table one, the plants were observed five times during the summer to determine the percent of leaves affected with symptoms and the percent leaf defoliation. The data very strongly show that Early Cascade, the hybrid variety with supposed tolerance to early blight, was the most susceptible. It’s an early tomato so that might be expected. Pik Red is not an early tomato and it suffered nearly as much as Early Cascade. Look at the August 10 and August 25 data. Do you now believe? The statistical data are included for those folks who are interested. All good field studies should have a known susceptible variety (Pik Red), a known tolerant variety (Early Cascade), and test varieties (Brandywine and Olena). All good field studies should treat the data statistically. This was a well designed field study. A brief summary of the results was reported in Organic Gardening and I panicked a bit because Olena was mentioned and at that time I was the only person on the face of the earth who had seeds for that variety.

When I read a catalog description of Brandywine this year which said that it was susceptible to disease as were most heirlooms, you can imagine my response. And yes, there are regular leaf varieties which are tolerant to early blight also. The only person to report disease status for some heirlooms is Jeff McCormack at Southern Exposure Seed Exchange; just read his tomato pages!

We can’t do what Jon Traunfeld and his group did. No one expects you to do percentages, etc. And we’re interested in many other diseases than early blight. And we can’t do this the way it should be done, in terms of each of you having known susceptible and tolerant varieties for each disease to be studied. And we can’t control your seed source for each variety. That’s an important factor because a number of diseases can be seedborne, such as bacterial canker, bacterial sport and anthracnose, to name a few. Dr. Helene Dillard at Cornell has studied the effect of fermentation of seeds on the elimination of pathogens and found that while the total amount of pathogens is lessened, they are not totally removed. Commercial seed companies usually do a triphosphate treatment of tomato seeds, but that’s pretty specific for Tobacco Mosaic Virus, which is not a major pathogen of tomatoes. Dr. Dillard and others, whom I’ll mention in the materials to be sent to participants, have helped me generate lists of the most important pathogens for different parts of the country. Right now I’m in envy of California – you poor disease deprived folks!

Here’s the game plan. If you are growing at least two plants each of at least five varieties we’d love to have you participate. Please send me a long self-addressed envelope with 78 cents worth of postage. The first 100 responders will get, as an extra incentive, a very small field guide to tomato diseases published by Ciba-Geigy. The guide is for farmers, has some excellent pictures, and is basically a promotional for Ridomil, one of their products. I’m indebted to Joyce Soltis, a Ciba-Geigy representative, for the donation of 100 of these guides. If we get more than 100 participants and I can’t send you a field guide I’ll assume you’re making a 46 cent donation to the cause because I just don’t have it in me to take the time to write out checks for 46 cents. I’ll send you instructions and data sheets. Using your own knowledge of the diseases listed for your area, and/or the guidance of the field guide, fill in what you can in terms of tolerance and susceptibility. If you don’t feel confident about certain diseases, don’t assess them. Another excellent guide is called “Identifying Diseases of Vegetables” by MacNab, Sherf and Springer. It costs about $18 and is available from Southern Exposure Seed company and Johnny’s Selected Seeds (addresses in the February Off The Vine).

Please participate. This summer we’ll collect as much data as we can, and then refine our methods for next year, and maybe open it up to others. Jon Traunfeld is pretty sure that he can get the cooperation of the Master Gardeners program in the US, and there are other ways of soliciting input from others. But let’s us do the initial work to see how it goes. I need help! I have no experience with computer data-based software. Is there someone out there who would volunteer to computerize the data in a meaningful fashion? If so (pretty please) email me at malec@rosnet.strose.edu and we’ll chat.

I’ve got the tomato field guides now and should finish my research work with tomato pathologists around the country in a few weeks, after I get this issue of Off The Vine mailed. So please send me a long SASE with 78 cents postage (my address is in the masthead on page 2) and I’ll mail you the materials in early July. And I’ll be checking my email to see if we have a volunteer tomato tabulator!

______________

As you will read in a future article, Carolyn got very few takers, so the project never got off the ground. But - this is a great early example of citizen science with respect to a garden project. The lack of volunteers is also a testament to how challenging it is to do this sort of thing.