Bioactive and Structural Metabolites of Pseudomonas and Burkholderia Species Causal Agents of Cultivated Mushrooms Diseases1

Pseudomonas tolaasii, P. reactans and Burkholderia gladioli pv. agaricicola, are responsible of diseases on some species of cultivated mushrooms. The main bioactive metabolites produced by both Pseudomonas strains are the lipodepsipeptides (LDPs) tolaasin I and II and the so called White Line Inducing Principle (WLIP), respectively, LDPs which have been extensively studied for their role in the disease process and for their biological properties. In particular, their antimicrobial activity and the alteration of biological and model membranes (red blood cell and liposomes) was established. In the case of tolaasin I interaction with membranes was also related to the tridimensional structure in solution as determined by NMR combined with molecular dynamic calculation techniques. Recently, five news minor tolaasins, tolaasins A–E, were isolated from the culture filtrates of P. tolaasii and their chemical structure was determined by extensive use of NMR and MS spectroscopy. Furthermore, their antimicrobial activity was evaluated on target micro-organisms (fungi—including the cultivated mushrooms Agaricus bisporus, Lentinus edodes, and Pleurotus spp.—chromista, yeast and bacteria). The Gram positive bacteria resulted the most sensible and a significant structure-activity relationships was apparent. The isolation and structure determination of bioactive metabolites produced by B. gladioli pv. agaricicola are still in progress but preliminary results indicate their peptide nature. Furthermore, the exopolysaccharide (EPS) from the culture filtrates of B. gladioli pv. agaricicola, as well as the O-chain and lipid A, from the lipopolysaccharide (LPS) of the three bacteria, were isolated and the structures determined

Response of traditional cultivars of Fagioli di Sarconi beans to artificial inoculation with common bacterial blight agents

Cultivars of the Fagioli di Sarconi are a pool of high value common bean (Phaseolus vulgaris L.) traditional cultivars selected from various landraces. These cultivars are protected by the European Union (Reg. CEE n° 1263/96) with the mark PGI (Protected Geographical Indication) and are cultivated in Basilicata (southern Italy) for the production of dry seeds. Fagioli di Sarconi cultivars are susceptible to common bacterial blight (CBB), a disease caused by the varieties fuscans and non-fuscans of Xanthomonas axonopodis pv. phaseoli. Five Fagioli di Sarconi cultivars (Tondino bianco, Verdolino, Cannellino, Tabacchino and Ciuoto) were artificially inoculated with two virulent strains of this bacterium, representative of 59 recently characterized strains of both the fuscans and non-fuscans varieties, with the aim to evaluate the susceptibility of these cultivars to the pathogens. Four CBB–resistant breeding–lines were used for comparison. Suspensions of the bacterium were injected into the first trifoliate leaflets of bean plants and produced typical CBB symptoms on the Fagioli di Sarconi cultivars, and hypersensitive necrotic lesions on the CBB–resistant breeding–lines. When cultivars were inoculated with the strain of the variety fuscans, Tondino bianco, Verdolino and Cannellino were more susceptible than Tabacchino and Ciuoto, whereas when they were inoculated with the non–fuscans strains, Tondino bianco, Tabacchino and Verdolino were more susceptible than Ciuoto and Cannellino. The tolerant cultivars appeared good candidates for the introgression of CBB–resistance characters in a breeding programme. The varying response of the traditional Fagioli di Sarconi bean cultivars to artificial inoculation suggests that several plant and pathogen factors are involved in the interaction between X. a. pv. phaseoli varieties and the bean cultivars

Genetic diversity and population structure of Pseudomonas savastanoi, an endemic pathogen of the Mediterranean area, revealed up to strain level by the MLVA assay

© 2020, Società Italiana di Patologia Vegetale (S.I.Pa.V.). Pseudomonas savastanoi is a bacterial species included in the Pseudomonas syringae complex. It is further sub-typed in pathovars which are the causal agents of a group of diseases of woody plants, such as the “knot disease” on olive and oleander and the bacterial canker on ash. Given its long-established presence in the Mediterranean area, the pathogen causing the afore-mentioned diseases can be considered endemic. Here, an MLVA approach was developed to assess the genetic relationships among and within those pathovars, with a specific focus on P. savastanoi pv. savastanoi. By analyzing the genome of the P.savastanoi pv. savastanoi strain NCPPB 3335 (accession n° CP008742), 14 Tandem Repeat (TR) loci were identified and the corresponding primers were designed and used for the amplification of genomic DNAs from 84 strains belonging to Pseudomonas savastanoi pathovars. Data were analyzed using different approaches, such as hierarchical clustering, STRUCTURE, and k-means clustering with DAPC to evaluate the effectiveness of the assay in describing pathovars and population structure of the pathogen. Results reveal a very complex articulation of genetic relationships, as expected from a long-time evolving pathogen, while providing the possibility to discriminate the pathovars between each other. At intra-pathovar level, the MLVA assay clusters isolates mainly according to their hosts and geographic origin. This resulted particularly useful in the identification and tracking of P. savastanoi populations at local level.11n