Rio Grande Valley citrus growers were told about a new strain of citrus disease discovered in South Texas during the semi-annual meeting of Texas Citrus Mutual (TCM) last week, but the potentially bad news was buffered by encouraging reports of new defense systems being developed to fight the spread of Huanglongbing (HLB), or Citrus Greening Disease.

TCM members gathered in Weslaco to hear updates about the disease first discovered in citrus groves in the Valley in January last year, one of many topics covered at the meeting. The disease, first discovered in a citrus grove near San Juan, caused Texas Agriculture Department and USDA officials to declare a quarantine of a five mile area last year limiting movement of citrus nursery stock and fruit containing leafy material. HLB is the disease that caused widespread destruction of citrus groves in Florida in the 1990s that resulted in multi-billion dollars losses to the industry.

Dr. John da Graca, Director of Texas A&M Citrus Center in Kingsville, told the assembly about the new strain of the disease found in the Valley last month.

“There are now three known species of the Liberibacter genus, the Liberibacter africanus, Liberibacter asiaticus, and the newly discovered one, Liberibacter americanus, which we discovered about two weeks ago in the Texas Valley,” da Graca reported.

He said the African and Asian strains are very similar, but africanus prefers higher, cooler elevations. It was the more common Asian strain found in Texas last year and previously in Florida and several other states in North America that infected a citrus tree in the Valley last year. California detected its first case of Liberibacter asiaticus this year. But until recently, the new strain, Liberibacter americanus, has never been reported in North America.

“This is cause for concern, but we are early in our evaluation of this new strain, so we don’t know a lot about what this means to citrus growers in Texas. But we have confirmation now from multiple labs that a solitary case of the new strain was found in the Texas Valley,” he told TCM members.


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Dr. da Graca has been working on citrus research from the Kingsville citrus center in recent years. He received his Ph.D. from University of Natal (South Africa) and was appointed to faculty of Texas A&M University-Kingsville Citrus Center in 1999. He currently holds the rank of Professor and Center Director in the Department of Agronomy and Resource Sciences and the Citrus Center, respectively.