Significance and Impact of the Study: Transposon mutagenesis remains a powerful and inexpensive tool in bacterial functional genomics. We developed a transposon with multiple combined features that allow selection of inducible or expressed genes, real-time quantification of gene expression levels using promoter-less GFP and rapid cloning and identification of the inactivated gene. Our Tn5-derived transposon worked in mutagenizing bacteria in the Enterobacteriaceae, Pectobacteriaceae and Pseudomonaceae families, indicating a broad range application. Using the transposon, we generated a high-quality and saturated mutant library of Pectobacterium versatile. Our high efficiency transposon is customizable and has different options for delivery and antibiotic selection, which make it a promising tool for molecular studies.

Bacterial wilt (BW) caused by the Gram-negative bacterium, Erwinia tracheiphila (Et.), is an important disease in melon (Cucumis melo L.). BW-resistant commercial melon varieties are not widely available. There are also no effective pathogen-based disease management strategies as BW-infected plants ultimately die. The purpose of this study is to identify BW-resistant melon accessions in the United States Department of Agriculture (USDA) collection. We tested 118 melon accessions in two inoculation trials under controlled environments. Four-week-old seedlings of test materials were mechanically inoculated with the fluorescently (GFP) labeled or unlabeled E. tracheiphila strain, Hca1-5N. We recorded the number of days to wilting of inoculated leaf (DWIL), days to wilting of whole plant (DWWP) and days to death of the plant (DDP). We identified four melon lines with high resistance to BW inoculation based on all three parameters. Fluorescent microscopy was used to visualize the host colonization dynamics of labeled bacteria from the point of inoculation into petioles, stem and roots in resistant and susceptible melon accessions, which provides an insight into possible mechanisms of BW resistance in melon. The resistant melon lines identified from this study could be valuable resistance sources for breeding of BW resistance as well as the study of cucurbit—E. tracheiphila interactions.