Like many greenhouse tomato growers, Michael Bledsoe has long battled Pepino mosaic virus (PepMV). Bledsoe is the vice president for scientific and regulatory affairs for Village Farms, one of the largest greenhouse tomato growers in the world, with operations in West Texas and British Columbia. “Pepino mosaic virus is fairly ubiquitous, certainly,” he says. “To not have Pepino is more rare than to have it.”
But its familiarity doesn’t make PepMV any more palatable. “If it comes in the middle of a cropping cycle, you can lose a whole week’s production,” he says. “A week’s production is $55,000 for a 20-acre greenhouse, and we have 270 acres, so you can see it can be a very devastat-ing problem.”
What makes PepMV even more insidious, says Bledsoe, is that it seems to exacerbate any other problem in the greenhouse. Bledsoe, who designs all of Village Farms’ IPM programs, has seen it time and again. “Pepino makes everything else worse,” he says.
Because of his experience with PepMV, Bledsoe has become a big fan of USDA-Agricultural Research Service (ARS) scientist Kai-Shu Ling, who is attempting to develop a tomato that can stand up to attack by PepMV. For years, Ling has been studying the origins and evolution of PepMV, which can damage tomato fruit, stunt growth, and leave the plant vulnerable to other infections.
Two PepMV strains that infect tomato plants in the U.S. show a distinct genetic divergence from strains that infect tomato plants in Europe. Ling, who works at the ARS U.S. Vegetable Laboratory in Charleston, SC, studied the genetic makeup of some PepMV strains found in South America, where the virus was first found. He wanted to see if he could tease out the relationships between the PepMV strains found in Europe, South America, and the U.S.
When Ling examined the makeup of U.S. PepMV strains, he observed a strong similarity to the South American strains. One U.S. strain exhibited almost 99% of the same DNA sequence as a South American strain. Another U.S. strain shared almost 91% of its genetic traits with a different South American strain. However, European strains only shared from 78% to 86% of the genetic characteristics found in South American strains.
Giving Growers Hope
Ling also identified three varieties of wild tomatoes with a range of genetic resistance to PepMV. He used the most robust of these varieties to generate new progeny that remained symptom-free after they were exposed to PepMV strains found in South America.
Ling will now use this symptom-free variety to see if he can create a tomato plant with genetic resistance to two U.S. PepMV strains. If he succeeds, he will try to develop a tomato type that has a more general resistance to the European strain of PepMV.
Taking No Chances
Village Farms, one of the world’s leading hydroponic tomato growers, takes the doctor’s orders. The doctor in this case is Ling, Ph.D., a USDA-Agricultural Research Service plant pathologist, who recommends that greenhouse growers be very careful when it comes to sourcing their seed. Much more so than with field-grown tomatoes, viruses can really run wild in the greenhouse, so the best way to avoid a virus is to prevent it from ever getting inside in the first place.
“Make sure you source only from reputable companies; don’t buy cheap tomato seed,” says Ling. “Make sure the seed is tested and certified.”
Bledsoe, who holds a doctorate himself, says Ling is one of the leading authorities on such viruses. Because Village Farms doesn’t want to take risk with any of their 270 production acres, he takes Ling’s advice to heart. “Every seed that comes in now gets tested by an independent lab,” says Bledsoe.
If a seed were to test positive for a certain virus, it gets sent off to a university or other research center that specializes in the virus or viroid for DNA sequencing. For example, were a seed to test positive for Pepino mosaic virus, Village Farms would send the seed to Ling.
It’s worth the extra time and expense, says Bledsoe, especially with some of the rarer, more devastating viroids where greenhouse finds trigger a red alert. “We will take that infected plant out and all the other plants around it out,” he says. “We treat it like the plague.”