Incidence of bacterial diseases associated with irrigation methods on onions (Allium cepa)

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.

Cytogenetic toxicity from pesticide and trace element mixtures in soils used for conventional and organic crops of Allium cepa L

Pesticides and trace elements occur in complex mixtures in agroecosystems, affecting soil health and food security. Hence, it is necessary to determine their toxicity in field conditions and to develop monitoring approaches to assess conventional and organic agriculture. The aim of this research was to evaluate the associations between Allium cepa L. cytogenetic biomarkers and the realistic mixture of pesticides and trace elements found in soils of conventional, conversion, and organic crops in an intensive agricultural region in Colombia. Pesticide screening was conducted using GC-MS/MS and LC-MS/MS methods. Arsenic, cadmium, lead, and zinc were analyzed by ICP-MS; chromium, copper, nickel, and selenium by ICP-OES; and mercury by a direct analyzer. The meristematic cells in roots of Allium cepa L. were analyzed through microscopic observations to quantify cytogenetic effects. In conventional crops, 26 pesticides were detected in the soil samples, and those were below the limit of quantification in organic crops. The mean levels of As, Cd, Cr, Ni, Pb, and Se were also greater in soils of conventional crops compared to the organics. In addition, the biomarkers of cytotoxicity and genotoxicity appeared augmented in conventional samples, and those were correlated with pesticide and trace element concentrations, pollution indices, and hazard quotients. Subsequently, a discriminant function based on the mitotic index, chromosomal aberrations, and nuclear abnormalities was suitable to classify the samples by crop type. These results demonstrate the sensitivity of Allium cepa L. to the toxicity of complex mixtures in field crops and its potential as an in-situ approach for soil health monitoring in organic and conventional crop systems.

Managing Crop Diseases Under Water Scarcity

The significance of water scarcity to crop production and food security has been globally recognized as a pivotal sustainability challenge in the UN Sustainable Development Goals (86). The critical link between water scarcity and sustainability is adaptation. Various changes in water use practices have been employed to alleviate production constraints. However, the potential for these changes to influence crop diseases has received relatively little attention, despite the circumglobal importance of diseases to agricultural sustainability. This article reviews what is known about the realized effects of scarcity-driven alterations in water use practices on diseases in the field in order to raise awareness of the potential for both increased disease risk and possible beneficial effects on crop disease management. This is followed by consideration of the primary mechanistic drivers underlying disease outcomes under various water use adaptation scenarios, concluding with a vision for disease-water co-management options and future research needs.