A new study led by Texas A&M AgriLife researchers has revealed some resistance to zebra chip disease among some wild potato varieties.
The study of 52 wild potato varieties – one resistant to the disease and three resistant to the disease – was carried out as part of an effort to identify new genetic resistance to diseases affecting potato production worldwide.
A study titled “Identification and characterization of potato zebra chip resistance among wild wilt species” was recently published in a scientific journal. Frontiers in Microbiology.
The study’s principal investigator, a Texas A&M AgriLife Research Scientist at the Texas A&M AgriLife Research and Extension Center in Weslaco and an assistant professor in Texas A&M’s Department of Plant Pathology and Microbiology, Ph.D. Kranthi was Mandadi.
Co-investigators on the study include Isabel Vales, Ph.D., associate professor of AgriLife Research and potato breeder, Bryan-College Station, and Carlos Avila, Ph.D., associate professor of AgriLife Research and vegetable breeder, Weslaco. Horticultural Sciences; and Freddy Ibanez, Ph.D., AgriLife Research Scientist at the center and assistant professor in the Texas A&M Department of Entomology.
Others involved in the study were Texas A&M AgriLife Research scientists Victoria Mora, MS, Manikandan Ramasamy, Ph.D., Mona Damaj, Ph.D. and Sonia Irigoyen, Ph.D., at the Weslaco center, as well as Veronica. Ancona, Ph.D., is a plant pathologist and associate professor at Texas A&M University-Kingsville.
Research funding was provided through Texas A&M AgriLife’s Insect Vector Disease Seed Grant Program.
“This kind of outcome is exactly what AgriLife Research envisioned when we decided to fund the Insect Vector Disease Seed Grants,” said Henry Fadamiro, senior scientist and associate director of AgriLife Research and associate dean of Texas A&M College. Agriculture and Life Sciences. “We would like to thank the Texas Legislature for funding AgriLife Research’s IVD Emergency Item Request, which made these seed grants possible. Their continued support is invaluable.”
What is zebra chip disease?
Zebra chip is a complex disease due to its association with the uncultured bacterium Candidatus Liberibacter solanacearum and transmission by its insect vector, the potato psyllid. First reported in Saltillo, Mexico and later in South Texas, the disease has been found in many other states and commercial potato growing regions around the world. If left unchecked, it can result in potato yield losses of up to 94%.
Above-ground symptoms of plants affected by zebra chip include purple discoloration of young leaves, upward rolling of upper leaves, presence of aerial tubers, wilting, stunted growth, and plant death.
“The tubers affected by zebra chip are of poor quality, showing darkening of the vascular ring and brown spots,” Mandadi said. “These chips also have a bitter taste and a dark brown striped, zebra-like pattern when fried.”
According to him, the disease ultimately reduces productivity and the tuber is of poor quality.
“If not controlled, the disease can seriously damage potato production.”
Potatoes are grown in more than 160 countries and are considered the fourth most important staple food after wheat, corn and rice. It is a rich source of carbohydrates and provides other important nutrients such as dietary fiber, vitamins, minerals, proteins and antioxidants.
“Potatoes are an important food crop around the world,” Mandadi said. “As global demand for fresh and processed potato products increases, there is a need to manage and control emerging diseases such as zebra chip.”
In Texas, potatoes are grown in all regions with significant commercial vegetable production. Commercial areas for potato production are located in the Southern Plains, Panhandle, and Rolling Plains, as well as the Winter Garden and Rio Grande Valley areas.
“In Texas, we’ve been doing zebra chips for over 20 years,” Vales said. “During that time, the disease spread widely, and not only in this state, but in other potato-producing states as well.”
The bacteria and insect vector associated with zebra chip disease can also affect other vegetable crops and crops, including tomatoes, peppers and carrots.
Vales said current strategies for managing zebra ticks primarily revolve around controlling the psyllid vector with insecticides or changing cultural practices such as planting dates to delay exposure to the psyllid population.
“However, both of these have only marginal benefits, and while the use of chemical measures can help control psyllid populations, this approach is associated with high costs and the potential for increased insecticide resistance,” he said. “Therefore, identifying and breeding new genetic resistance and tolerance to zebra finch is another important way to achieve integrated pest management.”
Previous studies have shown variation in the psyllid’s preference for wild potato species and their breeder clones, Vales said.
Results of the study
“For the past four years, our team has been studying approaches to control zebra tick disease thanks to seed funding from projects associated with the Insect Vector Disease Grant Program,” Mandadi said.
Plant material of 52 wild potato accessions belonging to Solanum sect. The study used a panel of Petota varieties grown from true potato seeds obtained from the National Plant Germplasm System in Wisconsin, USA.
“New sources of zebra chip resistance were identified among the wild collection of tuber-bearing Solanum species present in the Petota panel,” Mandadi said. “This wild potato panel is a taxonomically well-characterized and diverse collection that can be mined for valuable potato traits.”
Of the 52 accessions, several were susceptible and moderately susceptible, showing upward rolling of leaves, chlorosis and stunted plant growth, Mandadi said.
“However, after screening, phenotypic assessments, and quantification of bacteria in accessions infected with psyllids carrying the bacteria, we identified one zebra chip-resistant accession, Solanum berthaultii, and three other accessions moderately tolerant to zebra chip.”
The three accessions found to be moderately tolerant to zebra chip in the study were S. kurtzianum, S. okadae, and S. raphanifolium.
Mandadi’s team also found that S. berthaultii has densely glandular leaf trichomes, and this leaf structural modification may be one of the factors responsible for much of the observed zebra chip resistance.
“When the leaf part comes into contact with the psyllid, it produces a sticky substance that binds it to the plant,” Mandadi explained. “As a result, many psyllids die before they reproduce, thus reducing the transmission of the bacterium to plants.”
He noted that the wild potato accession S. berthautii originated in Bolivia, adjacent to Peru, historically identified as the “homeland” of the cultivated potato’s ancestors.
According to him, S. berthaultii is a promising source of zebra chip psyllid resistance that can be further studied to understand insect resistance mechanisms and incorporated into potato production system.
“It can be used in breeding new potato varieties or even as a ‘trap crop’ that can be planted alongside more traditional potato varieties to help eliminate psyllids,” he said.
He also noted that similar approaches to identifying new genetic resistance and tolerance in wild plant species could help control other devastating crop diseases such as potato late blight, citrus greening, Pierce’s disease of grape and banana wilt.