Characterization of a Pantoea stewartii mutant affecting persistence in its flea beetle vector

Stewart’s wilt, a disease of corn characterized by wilting and leaf blight symptoms, is caused by Pantoea stewartii, a Gram-negative bacterium that is transmitted by the corn flea beetle, Chaetocnema pulicaria. Little is known about the molecular basis of the interactions of P. stewartii with its flea beetle vector, including the mechanism (s) by which P. stewartii is transmitted. Recent work indicated that P. stewartii carries gene clusters for two type III secretion systems (TTSS). These TTSS gene clusters encode pili-like structures that enable these bacteria to inject virulence proteins into host cells. It has already been shown that one TTSS gene cluster is required for plant infection, whereas the other cluster is not (Coplin, et al. 1992, Frederick, et al. 2001). We hypothesize that the second TTSS is important for the transmission of P. stewartii by flea beetles. To detect P. stewartii in the beetles, two methods were used. The first method involved the detection of transformed P. stewartii that express gfp from a plasmid and in the second method P. stewartii was detected with specific antibodies linked to Alexa-fluor. The localization of the bacteria was visualized in dissected beetle guts with confocal laser scanning microscopy (CLSM). These experiments showed that the bacteria were mainly found in the lumen of the hindgut at up to 10 days after acquisition of the bacteria from corn plants. The localization of two P. stewartii mutants was also investigated. One mutant carried a mutation in the ysaN gene that is part of the second TTSS, and the other had a mutation in the sapD gene, which is part of an antibacterial peptide resistance ABC transporter. The results of colony-forming unit (CFU) counts and CLSM revealed that the ysaN mutants did not persist in the beetles, whereas wild type bacteria and the sapD mutant did. These results suggest that the second TTSS is involved in persistence of P. stewartii in the flea beetle vector.OARDC Research Competitive Grants Program USDA Cooperative State Research, Education & Extension Servic

Nematodes Affecting Soybean and Sustainable Practices for Their Management

Plant‐parasitic nematodes are one of the limiting factors for soybean production worldwide. Overall, plant‐parasitic nematodes alone cause an estimated annual crop loss of $78 billion worldwide and an average crop yield loss of 10–15%. This imposes a challenge to sustainable production of food worldwide, since there has been increasing demand for food supply and food security. Unsustainable cropping production systems with monocultures, intensive use of soils and expansion of crops to newly opened areas have intensified problems associated with new pests and diseases. Thus, finding and applying sustainable methods to control diseases associated with soybean are in current need. Over hundred nematode species, comprising fifty genera, have been reported in association with soybean. Of these, the root‐knot nematode Meloidogyne spp., cyst nematode Heterodera glycines, lesion nematode Pratylenchus brachyurus and the reniform nematode Rotylenchulus reniformis are major nematode species limiting soybean production. Here, we report an up‐to‐date literature review on the biology, symptoms, damage and control methods used for these nematodes species. Additionally, unusual and emergent nematode species affecting soybean are discussed

Nematodes Affecting Potato and Sustainable Practices for Their Management

Plant-parasitic nematodes are a significant factor limiting potato production and tuber quality in several regions where potato is produced. Overall, parasitic nematodes alone cause an estimated annual crop loss of $ 78 billion worldwide and an average crop yield loss of 10–15%. As a result, sustainable food production and food security are directly impacted by pests and diseases. Degrading land use with monocultures and unsustainable cropping practices have intensified problems associated with plant pathogens. Proper identification of nematode species and isolates is crucial to choose effective and sustainable management strategies for nematode infection. Several nematode species have been reported associated with potato. Among those, the potato cyst nematodes Globodera rostochiensis and G. pallida, the root-knot nematode Meloidogyne spp., the root lesion nematode Pratylenchus spp., the potato rot nematode Ditylenchus destructor and the false root-knot nematode Nacobbus aberrans are major species limiting potato yield and leading to poor tuber quality. Here, we report a literature review on the biology, symptoms, damage and control methods used for these nematode species

Genetic diversity of Meloidogyne spp. parasitising potato in Brazil and aggressiveness of M. javanica populations on susceptible cultivars

Root-knot nematodes (Meloidogyne spp.) significantly impact potato production worldwide and in Brazil they are considered one of the most important group of nematodes affecting potatoes. The objectives of this study were to survey Meloidogyne spp. associated with potatoes in Brazil, determine their genetic diversity and assess the aggressiveness of M. javanica on two susceptible potato cultivars. Fifty-seven root-knot nematode populations were identified using esterase phenotyping, including Meloidogyne javanica, M. incognita, M. arenaria and M. ethiopica. Overall, root-knot nematodes were present in ca 43% of sampled sites, in which M. javanica was the most prevalent species, and the phenotypes Est J3, J2a and J2 occurred in 91.2, 6.7 and 2.1% of the positive samples, respectively. Other species, such as M. incognita, M. arenaria and M. ethiopica, were found less frequently and occurred at rates of 6.4, 4.3 and 2.1% of the samples, respectively. Sometimes, M. javanica was found in mixtures with other root-knot nematodes in ca 10.6% of sites containing Meloidogyne. After confirming the identification of 17 isolates of M. javanica and one isolate each of M. incognita, M. arenaria and M. ethiopica by SCAR markers, the populations were used to infer their genetic diversity using RAPD markers. Results revealed low intraspecifc genetic diversity among isolates (13.9%) for M. javanica. Similarly, M. javanica sub-populations (J2a) clustered together (81% of bootstrap), indicating subtle variation from typical J3 populations. The aggressiveness of four populations of M. javanica from different Brazilian states on two susceptible potato cultivars was tested under glasshouse conditions. Results indicated differences in aggressiveness among these populations and showed that potato disease was proportional to nematode reproduction factor