Managing Onion Thrips can Limit Bacterial Stalk and Leaf Necrosis in Michigan Onion Fields

Biological Control and Habitat Management for the Control of Onion Thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), in Onion Production in Quebec, Canada

Onion thrips (Thrips tabaci) can pose a significant threat to onion crops, causing leaf damage, reduced bulb size and quality, and yield loss during severe infestations. Conventional insecticide use has been the primary method for managing this pest species, but the efficacy of this approach is inconsistent. Furthermore, emerging pest resistance is a growing concern in some regions. This two-year field study aimed to assess the effectiveness of several pest management strategies in controlling onion thrips populations and limiting their impact on onion yields. The strategies tested consisted of habitat manipulations (including flower strips and straw mulch), biological control agents (Stratiolaelaps scimitus, Neoseiulus cucumeris, Amblyseius swirskii, and Beauveria bassiana), as well as physical barrier control methods (exclusion nets, kaolin, and mineral oil). Habitat manipulation techniques, particularly the use of flower strips, reduced thrips populations by up to 50% and increased onion yields by 25%. In contrast, exclusion nets had a detrimental effect on onion yields, and the other alternative control methods produced results comparable to those obtained for untreated controls. When used alone, biological control agents were not effective at maintaining thrips populations below economically damaging levels. This study offers valuable insights into effective and sustainable pest management practices for the onion industry.

Unravelling the synergistic interaction of Thrips tabaci and newly recorded, Thrips parvispinus with Alternaria porri (Ellis.) Cif., inciting onion purple blotch

Onion purple blotch is the most indispensable foliar disease of crop and has become a major concern for farmers and research fraternity. An attempt to investigate the role of injury in parasitism by Alternaria porri indicated that disease incidence and severity enhance considerably with injury. Thrips injured plants inoculated with A. porri presented 100% incidence and 52-72% severity while mechanically injured plants inoculated with A. porri showed 60-70% incidence and 28-34% severity. The uninjured plants showed considerably less disease incidence (30-40%) and severity (10-16%). Injured inoculated plants presented reduced leaf length and leaf area while the leaf diameter remained unaffected. The lesion number, lesion length and size was substantially enhanced with concomitant infestation of pest and pathogen. Thrips tabaci injury led to more pronounced symptoms of purple blotch compared to Thrips parvispinus injury. There was substantial decrease in photosynthetic rate and chlorophyll content with stress imposed on plant whilst the relative stress injury was enhanced. The induction of injury and inoculation of A. porri had an impact on the concentration of total phenolics, total soluble sugars, total proteins and hydrogen peroxide in onion leaves. A. porri combined with injury caused a more pronounced decrease in total soluble sugars and total protein content while enhancement in total phenolics and hydrogen peroxide content compared to uninjured plants. The dynamic nature of morpho-physiological and biochemical changes owing to stress conditions imposed on onion plant adds an extra layer of complexity in understanding the onion plant physiology and their ability to work out in response to challenging environment conditions.

Isolation and Characterization of Bacteria Associated with Onion and First Report of Onion Diseases Caused by Five Bacterial Pathogens in Texas, U.S.A

Bacterial diseases pose a severe challenge to growers and cause significant loss to the billion-dollar onion industry in the United States. Texas is the sixth largest onion producing state, yet the bacterial communities associated with short-day onion crops grown in Texas have not been studied. This study was conducted to identify, characterize, and understand the diversity of bacteria associated with onion production in Texas. In 2020, 190 foliar and 210 bulb samples were collected from onion crops in the Rio Grande Valley and Winter Garden regions of Texas. Sequencing of the 16s rRNA gene was used to identify each bacterial strains to a genus. The pathogenicity to onion of each bacterial strain was tested using three assays: a red onion scale assay, a yellow onion bulb assay, and a foliar assay. Whole genome sequencing was done to identify the onion-pathogenic strains to species. Collectively, isolates of 24 genera belonging to three phyla were detected, including 19 genera from foliar samples and nine genera from bulb samples. Isolates in the Phylum Proteobacteria, including 15 genera of Gram-negative bacteria, were the most abundant of the taxa, comprising 90.0% of the strains isolated. The diversity of foliar isolates was evenly distributed between Gram-positive and Gram-negative bacteria, while Gram-negative bacteria dominated the isolates from bulb samples. In total, 83.9% of the bacterial isolates were not pathogenic on onion, with only isolates of Pantoea, Pseudomonas, Burkholderia, Erwinia, Enterobacter, and Curtobacterium proving pathogenic. Strains of Burkholderia gladioli, Pseudomonas alliivorans, Pantoea agglomerans, P. ananatis, and P. allii are the first documented cases of these pathogens of onion in Texas. Identifying and characterizing the nature of onion microflora, including pathogens of onion, is vital to developing rapid disease detection techniques via pathogenomics and minimizing losses through the application of effective disease management measures.

Onion Thrips (Thysanoptera: Thripidae) Host Plant Preference and Performance are Mediated by a Facultative Plant Pathogen of Onion

Insect vector and phytopathogen interactions are mediated by host plants. Insects interact with pathogens directly or indirectly and they may prefer host plants based on infection status. Performance on infected hosts varies depending on the type of pathogen involved. Species specific studies of economically important insects and phytopathogens are needed to understand how these interactions impact crop yields. Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is an economically devastating insect pest of onions (Allium cepa L., Asparagales: Amaryllidaceae) worldwide and it co-occurs simultaneously with many different pathogens. Colletotrichum coccodes (Wallr) (Glomerellales: Glomerellaceae) is a generalist fungal pathogen that attacks onion foliage, causing tan lesions and decreasing yield. Onion thrips and C. coccodes represent two important pests of onions, but the relationship between onion thrips and C. coccodes infected onions has not been studied, and it is unclear if onion thrips contribute to the spread of C. coccodes in onion fields. A four-choice test with control, artificially injured, artificially injured + symptomatic, and inoculated-symptomatic onion suggests that onion thrips distinguish between hosts based on health status. Furthermore, a two-choice test with control, inoculated-asymptomatic, and inoculated-symptomatic onion pairings revealed that onion thrips distinguish between hosts based on infection status and prefer inoculated-symptomatic hosts. In a no-choice test, onion thrips numbers increased on inoculated-symptomatic plants compared to control or inoculated-asymptomatic plants. Overall, we found that onion thrips preferred and performed best on C. coccodes infected plants.

The Changing Face of the Family Enterobacteriaceae (Order: "Enterobacterales"): New Members, Taxonomic Issues, Geographic Expansion, and New Diseases and Disease Syndromes

The family Enterobacteriaceae has undergone significant morphogenetic changes in its more than 85-year history, particularly during the past 2 decades (2000 to 2020). The development and introduction of new and novel molecular methods coupled with innovative laboratory techniques have led to many advances. We now know that the global range of enterobacteria is much more expansive than previously recognized, as they play important roles in the environment in vegetative processes and through widespread environmental distribution through insect vectors. In humans, many new species have been described, some associated with specific disease processes. Some established species are now observed in new infectious disease settings and syndromes. The results of molecular taxonomic and phylogenetics studies suggest that the current family Enterobacteriaceae should possibly be divided into seven or more separate families. The logarithmic explosion in the number of enterobacterial species described brings into question the relevancy, need, and mechanisms to potentially identify these taxa. This review covers the progression, transformation, and morphogenesis of the family from the seminal Centers for Disease Control and Prevention publication (J. J. Farmer III, B. R. Davis, F. W. Hickman-Brenner, A. McWhorter, et al., J Clin Microbiol 21:46-76, 1985, https://doi.org/10.1128/JCM.21.1.46-76.1985) to the present.

Foliar Chemical Protection Against Pantoea ananatis in Onion Is Negated by Thrips Feeding

Center rot of onion, caused by Pantoea ananatis, is an economically important disease in onion production in Georgia and elsewhere in the United States. Growers rely on frequent foliar applications of bactericides and, in some cases, plant defense inducers to manage this disease. However, regular prophylactic application of these chemicals is not cost-effective and may not be environmentally friendly. Thrips (Thrips tabaci and Frankliniella fusca) are vectors of P. ananatis, and their feeding may compromise the effectiveness of foliar applications against P. ananatis. In this study, foliar treatments with acibenzolar-S-methyl (Actigard 50WG), cupric hydroxide (Kocide 3000), and Actigard plus Kocide were evaluated for their effectiveness in the presence and absence of thrips infestation at two critical onion growth stages: bulb initiation and bulb swelling. Onion growth stage had no impact on the effectiveness of either Kocide or Actigard. In the absence of thrips, Kocide application resulted in reduced center rot incidence compared with Actigard, regardless of the growth stage. However, when thrips were present, the efficacy of both Kocide and Actigard was reduced, with bulb incidence not significantly different from the nontreated control. In independent greenhouse studies in the presence or absence of thrips, it was observed that use of protective chemicals (Kocide, Actigard, and their combinations) at different rates also affected pathogen progression into internal neck tissue and incidence of bulb rot. These results suggest that thrips infestation can reduce the efficacy of protective chemical treatments against P. ananatis. Thrips feeding on onion foliage and resulting feeding scars could facilitate P. ananatis entry and subsequently compromise the efficacy of protective chemical treatments. Therefore, an effective center rot management strategy should likely include thrips management in addition to bactericides at susceptible growth stages of onion.