Summary: Crop diversity underpins the productivity, resilience and adaptive capacity of agriculture. Loss of this diversity, termed crop genetic erosion, is therefore concerning. While alarms regarding evident declines in crop diversity have been raised for over a century, the magnitude, trajectory, drivers and significance of these losses remain insufficiently understood. We outline the various definitions, measurements, scales and sources of information on crop genetic erosion. We then provide a synthesis of evidence regarding changes in the diversity of traditional crop landraces on farms, modern crop cultivars in agriculture, crop wild relatives in their natural habitats and crop genetic resources held in conservation repositories. This evidence indicates that marked losses, but also maintenance and increases in diversity, have occurred in all these contexts, the extent depending on species, taxonomic and geographic scale, and region, as well as analytical approach. We discuss steps needed to further advance knowledge around the agricultural and societal significance, as well as conservation implications, of crop genetic erosion. Finally, we propose actions to mitigate, stem and reverse further losses of crop diversity.

Recent studies have shown that the genus Acacia Mill. s.l. is polyphyletic, consisting of at least seven distinct groups of species. One of these groups, the proposed genus Parasenegalia Seigler & Ebinger, consists of seven species. We describe a new species, Parasenegalia lundellii Seigler & Ebinger, and make the following new combinations: Parasenegalia muricata (L.) Seigler & Ebinger, Parasenegalia rurrenabaqueana (Rusby) Seigler & Ebinger, Parasenegalia santosii (G. P. Lewis) Seigler & Ebinger, Parasenegalia skleroxyla (Tussac) Seigler & Ebinger, Parasenegalia visco (Lorentz ex Griseb.) Seigler & Ebinger, and Parasenegalia vogeliana (Steud.) Seigler & Ebinger. A second proposed genus, Pseudosenegalia Seigler & Ebinger, consists of two species: Pseudosenegalia feddeana (Harms) Seigler & Ebinger and Pseudosenegalia riograndensis (Atahuachi & L. Rico) Seigler & Ebinger. The species of Parasenegalia are widespread in the tropical areas of the Caribbean and scattered in Central and South America....

— Studies have shown that the genus Acacia Miller s. l. is polyphyletic, consisting of at least seven distinct groups of species. One of these major groups, Senegalia s. l., was also determined to be non-monophyletic. This has resulted in the recent recognition of two new genera, Parasenegalia Seigler and Ebinger, consisting of seven species, and Pseudosenegalia Seigler and Ebinger, consisting of two species. A molecular phylogenetic analysis of these genera and sister taxa, especially Mariosousa Seigler and Ebinger, determined that each is monophyletic, although Parasenegalia visco (Lorentz and Grisebach) Seigler and Ebinger is weakly supported as sister to the rest of Parasenegalia. Pseudosenegalia is sister to the rest of the ingroup, however the node containing Parasenegalia, Mariosousa, and the remaining ingroup grade of Ingeae and Acacia s. s. is poorly supported. These results provide a phylogenetic resolution for the major genera of the American species of Acacia s. l., but full phylogenetic resolution requires a subfamily-based investigation. Simple synapomorphies do not correlate with all genera and these traits are discussed in the context of the phylogeny. A key to the four genera is presented.

Previous research reported the first case of resistance to mesotrione and other 4-hydroxyphenylpyruvate dioxygenase (HPPD) herbicides in a waterhemp (Amaranthus tuberculatus) population designated MCR (for McLean County mesotrione- and atrazine-resistant). Herein, experiments were conducted to determine if target site or nontarget site mechanisms confer mesotrione resistance in MCR. Additionally, the basis for atrazine resistance was investigated in MCR and an atrazine-resistant but mesotrione-sensitive population (ACR for Adams County mesotrione-sensitive but atrazine-resistant). A standard sensitive population (WCS for Wayne County herbicide-sensitive) was also used for comparison. Mesotrione resistance was not due to an alteration in HPPD sequence, HPPD expression, or reduced herbicide absorption. Metabolism studies using whole plants and excised leaves revealed that the time for 50% of absorbed mesotrione to degrade in MCR was significantly shorter than in ACR and WCS, which correlated with previous phenotypic responses to mesotrione and the quantity of the metabolite 4-hydroxy-mesotrione in excised leaves. The cytochrome P450 monooxygenase inhibitors malathion and tetcyclacis significantly reduced mesotrione metabolism in MCR and corn (Zea mays) excised leaves but not in ACR. Furthermore, malathion increased mesotrione activity in MCR seedlings in greenhouse studies. These results indicate that enhanced oxidative metabolism contributes significantly to mesotrione resistance in MCR. Sequence analysis of atrazine-resistant (MCR and ACR) and atrazine-sensitive (WCS) waterhemp populations detected no differences in the psbA gene. The times for 50% of absorbed atrazine to degrade in corn, MCR, and ACR leaves were shorter than in WCS, and a polar metabolite of atrazine was detected in corn, MCR, and ACR that cochromatographed with a synthetic atrazine-glutathione conjugate. Thus, elevated rates of metabolism via distinct detoxification mechanisms contribute to mesotrione and atrazine resistance within the MCR population.