My favorite garden plant undoubtly is the tomato. Tomatoes embody the jubilant tenor of summer, capturing the very essence of the hot sun in their juicy flesh. They are a literal expression of the vitality of the landscape that produced them. Oddly enough, my earliest memories of those tomato plants were not the fruits but the wonderfully pungent aroma of their foliage. I can remember when I was four years old, going into an old white greenhouse in Thomaston, Connecticut with my dad and buying some tomato plants. From the vantage point of a four year old, my eyes stood even with the tops of those plants. I distinctly remember running my fingers over those plants and inhaling their heady aroma for the first time. It is as though that intense fragrance hermetically seals the experience in my memory.
This year there is little tomato foliage to smell. My own tomato plants have been decimated, as well as countless other gardeners and farmers in the Northeast, by late blight. Late blight is caused by the phycomycete fungus Phytophtora infestans (Mont.) de Bary. Late blight is a highly destructive disease affecting both tomato and potato. This is a disease of historic importance first described on potato in 1845 and on tomato in 1847. The disease appeared in both North America and Europe in the 1830’s and is thought to have originated in Central America. Before the disease appeared in Ireland it caused a devastating epidemic in the early 1840s in the northeastern United States. The same disease is responsible for the infamous Irish potato famine of the 1840’s.
Symptoms of this disease appear on stems and leaves of tomato and potato. They appear as water soaked brown to black blotches on stems and leaves. Stem lesions are brown. These can appear as small spots or can be a few inches long. On leaves and leaflets, late blight lesions are water-soaked looking, brown, and sometimes have yellow margins. When numerous lesions develop they form into brown areas resulting in the leaves drying out and shriveling. These symptoms develop on leaves and can occur on stems, and fruiting tissue. The tomato fruit inhibits the late blight on the stem end or any part of the fruit. These lesions expand and ultimately expand within the tomato. This is followed by secondary soft rot and quick breakdown of the fruit. Gardeners are advised to remove plants as symptoms are detected. It’s best to immediately remove whole plants, put them in plastic bags to avoid carrying the infected plant material and dispose of these materials. Do not compost disease plant materials. Phytophora infestans does not survive in the soil in plant debris. It can survive in infected potato tubers left in the soil.
Subsequently, what happened this summer and how did this come to be? Severe late blight epidemics occur when Phytophora. infestans grows and reproduces rapidly on the host crop, tomato or potato. Reproduction occurs via sporangia that are produced from infected plant tissues and is most rapid during conditions of high moisture and moderate temperatures (60-80 degrees F.) Sporangia disperse to healthy tissues via rain splash or on wind currents. Reproduction is asexual; each sporangium is an exact copy of the one that initiated the parent lesion, and each can initiate a new lesion. Plant pathologists use the term disease triangle to describe necessary conditions for a disease outbreak. All these conditions were present this summer, the pathogen late blight, a host tomato and potatoes and a favorable environment, and plenty of rain, moderate temperatures and high humidity for this disease to take off. This season’s near record rainfall contributed to late blight getting a foothold in backyard garden plots and waterlogged tomato fields. But this is not the whole story.
Chef and restaurant owner Dan Barber writing in the New York Times, You Say Tomato, I Say Agriculture Disasterstates that weather alone doesn’t explain the early severity of the disease this year. Instead he describes two factors: the origins of the tomato plants that are used and the renewed interest in gardening this year. According to plant pathologists, this devastating round of blight spread in part from the hundreds of thousands of tomato plants bought by home gardeners at Wal-Mart, Lowe’s, Home Depot and Kmart stores in April. Julia Morris writing in the New York Times, Outbreak of Fungus Threatens Tomato Crops states that “Bonnie Plants, based in Alabama, had supplied most of the seedlings to the stores and recalled all remaining plants starting on June 26.” Dan Barber asserts that, “Once those infected starter plants arrived at the stores, they were purchased and planted, transferring their pathogens like tiny Trojan horses into backyards and community gardens.” This is perhaps why the Northeast was hit so ferociously. The disease was spread through lots of little backyard gardens.
Another causative factor has been the increased interest encouraging the use of heirloom cultivars of tomatoes. They’re often more flavorful than conventional varieties. Most of my own tomatoes that I grow are heirlooms. But it may be increasingly important to grow non heirlooms too or tomato cultivars that will be bred to resist late blight. Therefore it’s important that research be carried out at land-grant universities (like the University of Connecticut) and their development of new cultivars with natural or manmade resistance to late blight and other diseases. For example Dan Barber mentions that plants like Mountain Magic tomato, an experimental variety developed by Cornell University is being tested at various locations. I gleaned from the Cornell University website three varieties of tomatoes that are listed in a table that are resistant to late blight and include, Golden Sweet, Juliet and Legend. I definitely will try this next year in my garden.
The greater implication here is that natural and manmade disasters threaten the well being of our food production systems. Its one thing for home gardeners to miss a growing season of tomatoes, but it a far bigger problem if agricultural crop failures threaten the well being of the United States. Think of the ramifications of agricultural failures on a grand scale and what it may mean for our food supply. This is why it’s critical that research be carried out to develop tomato plants that are resistant to late blight as well as other disease as well as other environmental factors such as drought tolerance. Plant breeders have traditionally selected for shelf life, uniformity and shipping for a modern industrialized system of agriculture at the cost of a really tasty tomato (that’s why home grown tomatoes are so good-they are delicious!).
The future may mean not only including these traits but fostering a system of food growing that embraces greater variety with increased biodiversity of plant species as well as one adapted to local and regional conditions. Commercial farms of the future may look different then they do now. I am excited about this possibility. These farms will encourage more natural diversity with cropping systems that duplicate how nature does it. Natural diversity is the best ecological insurance to prevent future disasters that we experienced this year in the Northeast. This may be our only ammunition in an arsenal of ways to grow food but yet maintain healthy ecosystems.
Follow the tenants listed in the Gardening with Nature web site. They are small traditions, with cumulative effects, that each of us can do on a daily basis to more closely work with nature and reduce our carbon footprint. I’m hoping next year I’ll be able to smell that tomato foliage in my own gardens. Following the themes that I promote on this web site, I still will grow my favorite heirlooms but will try to put my hands on some seed of that Mountain Magic as well as the other varieties I listed. I’ll probably try a few standard hybrids that I stopped growing, new ones and old ones. The tomato patch will be more inclusive of an assortment of cultivars, inherently insuring a more diverse tomato patch. That’s the best insurance against a repeat of this year. I will have to just wait a year to see what this will look like. But in the meantime I can imagine what that will be like. That’s the fun part of gardening.