From genomic analysis of the rapid colonization of the exotic Sahara mustard (Brassica tournefortii Gouan 1773) in the United States to the search of its natural enemies

Authors: WINKLER, DANIEL - University Of California; BON, MARIE-CLAUDE - European Biological Control Laboratory (EBCL); CRISTOFARO, MASSIMO - Enea Casaccia Research Center; SFORZA, RENE - European Biological Control Laboratory (EBCL); MARINI, F - Bbca-Onlus, Italy; AUGE, M - Bbca-Onlus, Italy; KASHEFI, JAVID - European Biological Control Laboratory (EBCL); Smith, Lincoln

Submitted to: International Symposium on Biological Control of Weeds
Publication Type: Proceedings
Publication Acceptance Date: 6/12/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Sahara mustard (SM) (Brassica tournefortii) is a winter annual plant that is believed to have been introduced in California in the 1920s. Since then, it has rapidly invaded the southwestern United States and northern Mexico, displacing natives and altering these water-limited landscapes. We sequenced genome-wide single nucleotide polymorphisms to identify the population structure and spatial geography of Sahara mustard using 760 individuals from 52 sites across its invaded range. Herbaria records were also used to model the species’ expansion rate since its presumed introduction. Overall, results showed that SM has spread at a relative constant rate since its introduction. There are three genetically distinct populations in the U.S, which have low levels of diversity likely the result of self-fertilization. The origins of these populations was unknown but was hypothesized to be linked to the importation of date palms from northern Africa and/or east Asia. We sampled populations of SM across Western Europe, Northern Africa and the Middle East in order to determine the origin of the U.S. populations. We identified as many as 9 genetically distinct populations in SM’s native range. Ancestry analyses suggest that populations from one site in Morocco and two sites in Jordan are the putative origin(s) of Sahara mustard in the U.S. Little is known about natural enemies of Sahara mustard in the native range, providing a high potential for new discoveries. Several natural enemies were collected during our surveys, most of which were Coleoptera, mainly root galling weevils. We also observed one flea beetle, two galling midges, and a stem mining moth. Knowing the genetic diversity, probable regions of origin, and preliminary knowledge on prospective agents provides a strong foundation for developing a classical biological control program to help manage this weed.