2007 Annual Report
1a.Objectives (from AD-416)
The objective of this cooperative research is to understand the population genetics of the invasive weed Arundo donax (giant reed) and its insect herbivores using molecular approaches.
1b.Approach (from AD-416)
Populations of A. donax collected from its native range in Europe and Asia will be compared with invasive populations in North America, in particular the Rio Grande Basin, to determine their origin and invasion history. Custom microsatellite DNA probes will be developed for A. donax and the key insect herbivore species to investigate the population level co-evolution of the plant-herbivore interaction. This information will be used to select the candidate biological control agents that are best adapted to the invasive Rio Grande Basin genotype of A. donax.
This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Texas A&M University, Dept. of Biology. This research is integrated with objectives in the parent CRIS 6204-22000-019-00D, Biologically Based Management of Field and Greenhouse Crops.
Invasive exotic plant species and other noxious weeds pose a huge and increasing threat to agriculture and native ecosystems throughout North America. In our region, which includes the Rio Grande River Basin (RGB), invasive weeds degrade the riparian environment and consume water resources in an arid region impacted by recurrent drought. Arundo donax L. is one of the most serious and widespread invasive weeds in the watershed, and a biological control program is needed because available chemical and mechanical control methods are not applicable over such a large area. The introduction of natural enemies from the origin of the A. donax (Mediterranean Europe) could be an effective solution, but these agents must be rigorously evaluated for both safety and efficacy. This project was initiated in FY 2007 to determine the origin of the invasive RGB genotype of A. donax. Preliminary molecular data narrowed the origin to the Iberian Peninsula of Europe. Custom microsatellites were developed for A. donax to give finer scale geographic resolution of the genotypes found in this region. Six unique microsatellites were sequenced from more than 100 samples from the RGB, California, and New Mexico and then compared to 150 samples from the Iberian peninsula, and other parts of Mediterranean Europe. The samples from North America formed a distinct grouping which included two dominant genotypes in the RGB. All of the samples above Laredo, TX, on the Rio Grande River were determined to be the same genotype. The Laredo genotype matched most closely with populations from Valencia and Huelva, Spain. Candidate biological control agents from these locations have been collected and shipped to quarantine facilities for testing. Agents from the matching genotype of the A. donax are likely to be more effective in the field.
Development of custom microsatellites for the 3 candidate agents, Tetramesa romana, Rhizaspidotus donacis, and Cryptonevra sp., is underway. We will use this genetic information to determine if the populations of these three species are associated with specific genotypes of A. donax in the native range. Some or all of the species may be genotype-specific specialists that can be exploited to improve the efficacy of the biological control program targeted at the ‘Laredo’ invasive genotype of A. donax. The ADODR and cooperator are in contact via email and phone on a biweekly basis.