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Now published in Microbiology Resource Announcements, 9:e00293-20. Phytopathogenic isolates ofRhodococcusspp. are known to cause disease on herbaceous and woody species (Putnam and Miller, 2007; Miller and Putnam 2010). In 2011, two distinctRhodococcusspecies designated as PBTS1 and PBTS2 caused serious losses to the pistachio industry in California and Arizona (Stamler et al, 2015a, b, 2016). On ornamental plants, major disease symptoms caused byR. fascianswere described as leafy galls and stems fasciations (Stes et al. 2013), while on woody trees the symptoms included stunted growth and proliferation of misshapen shoots known as witches’s brooms (Stamler et al, 2015a, b). The virulence strategy employed by the renownedR. fasciansD188 consists of the disruption of plant hormone balance through the production and modulation of cytokinins and auxins (Pertry et al, 2009, 2010). The genes that are essential for cytokinin biosynthesis and modification are encoded by three virulence loci clustered on thefasoperon which is located on a linear plasmid ofR. fascians(Crespi et al, 1992; Francis et al, 2012). Complete genome and plasmid sequences forR. fasciansD188 were previously reported (Francis et al, 2012; Creason et al, 2014) as well as the two pistachioRhodococcusPBTS 1 and PBTS 2 isolates (Stamler et al, 2016). Four distinctRhodococcusspecies isolates from symptomatic almond rootstocks, pistachio tree and ornamental plants in Tunisia were used in this study.The ornamentalRhodococcusisolate B10 was shown to cause stunting and shoot proliferation onIresine herbestiiplants in pathogenicity assays (Dhaouadi et al, 2019). The two almondRhodococcusisolates GS6 and SB10 and the pistachioRhodococcusisolate K5 developed shoot proliferation and stunting on both the host of origin and the pea seedlings bioassays (Unpublished data). It is well known that the population structure ofR. fascianstends to be diverse from one host to another and from a region to another (Creason et al, 2014). Here, we provide a first insight into the genetic diversity of phytopathogenicRhodococcusin Tunisia through the genome sequencing and assemblies of four isolates collected from pistachio, almond and the ornamental plantIresine herbestii.&nbsp

In this study, three local isolates of Trichoderma (Tr1: T. viride, Tr2: T. harzianum and Tr3: T. asperellum) were isolated and evaluated for their biocontrol effectiveness under in vitro conditions and in greenhouse. In vitro bioassay revealed a biopotential control against Fusarium oxysporum f. sp. radicis lycopersici and Meloidogyne javanica (RKN) separately. All species of Trichoderma exhibited biocontrol performance and (Tr1) Trichoderma viride was the most efficient. In fact, growth rate inhibition of Fusarium oxysporum f. sp. radicis lycopersici (FORL) was reached 75.5% with Tr1. Parasitism rate of root-knot nematode was 60% for juveniles and 75% for eggs with the same one. Pots experiment results showed that Tr1 and Tr2, compared to chemical treatment, enhanced the plant growth and exhibited better antagonism against root-knot nematode and root-rot fungi separated or combined. All Trichoderma isolates revealed a bioprotection potential against Fusarium oxysporum f. sp. radicis lycopersici. When pathogen fungi inoculated alone, Fusarium wilt index and browning vascular rate were reduced significantly with Tr1 (0.91, 2.38%) and Tr2 (1.5, 5.5%), respectively. In the case of combined infection with Fusarium and nematode, the same isolate of Trichoderma Tr1 and Tr2 decreased Fusarium wilt index at 1.1 and 0.83 and reduced the browning vascular rate at 6.5% and 6%, respectively. Similarly, the isolate Tr1 and Tr2 caused maximum inhibition of nematode multiplication. Multiplication rate was declined at 4% with both isolates either tomato infected by nematode separately or concomitantly with Fusarium. The chemical treatment was moderate in activity against Meloidogyne javanica and Fusarium oxysporum f. sp. radicis lycopersici alone and combined., {"references":["Chindo, P. S., Khan, E. A. and Frink, I. D. (1991). Reaction of three tomato cultivars against two vascular diseases in the presence of root knot nematode Meloidogyne incognita race-1. Crop Prot., 10: 62-64.","Fattah F, Webster JM. (1983). Ultrastructural changes caused by Fusarium oxysporum f.sp. lycopersici in Meloidogyne javanica-induced giant cells in Fusarium resistant and susceptible tomato cultivars. Journal of Nematology 15, 128–35.","Suleman P, Sardanelli S, Krusberg LR, Straney DC. (1997). Variability among Fusarium oxysporum f. sp. lycopersici isolates in their ability to interact with Meloidogyne incognita race 1. Kuwait Journal of Science and Engineering 24, 299–307.","Lewis, W. J., Stapel, J. O., Cortesero, A. M., and Takasu, K. (1998). Understanding how parasitoids balance food and host needs: Importance to biological control. Biol. Contr. 11, 175–183.","Wong, P.T.W., J.A. Mead and M.C. Croft. (2002). 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J. & Fragkiadakis G. A. (1999). Genetic diversity of Fusarium oxysporum isolates from cucumber: differentiation by pathogenicity, vegetative compatibility and RAPD fingerprinting. Phytopathology, 89, 161-168.\n[21]\tSong W., Zhou L., Yang C., Cao X., Zhang L. & Liu X. (2004). Tomato Fusarium wilt and its chemical control strategies in a hydroponic system. Crop Protection, 23, 243-247.\n[22]\tKatasantonis D, Hillocks RJ and Gowen S. (2003). Comparative Effect of Root-knot Nematode on Severity of Verticillium and Fusarium Wilt in Cotton. Phytoparasitica 31 (2).\n[23]\tSteel R.G.D. & J.H. Torrie. (1980). Principles and Procedures of Statistics: A Biometrical Approach. New York, USA: McGraw-Hill.\n[24]\tSaifullah and B.J. Thomas. (1996). Studies on the parasitism of Globodera rostochiensis by Trichoderma harzianum using low temperature scanning electron microscopy. Afro-Asian J. Nematol., 6: 117-122. \n[25]\tDos Santos MA, Ferraz S, Muchovez JJ. (1992). Evaluation of 20 species of fungi from Brazil for biocontrol of Meloidogyne incognita race-3. Nematropica. 22: 183-192.\n[26]\tMeyer SLF, Roberts DP, Chitwood DJ, Carta L.K, Lumsden RD, Mao W. (2001). Application of Burkholderia cepacia and Trichoderma virens, alone and in combinations, against Meloidogyne incognita on bell pepper, Nematropica, 31: 75-86.\n[27]\tWindham, G.L., M.T. Windham and P.W. Williams. (1989). Effects of Trichoderma spp. on maize growth and Meloidogyne arenaria reproduction. J. Plant Dis., 73: 493-495.\n[28]\tWindham M.T., Elad Y. & Baker R. (1986). A mechanism for increased plant growth induced by Trichoderma spp. Phytopathology, 76, 518- 521.\n[29]\tYedidia I., Benhamou N. & Chet I. (1999). Induction of defence responses in cucumber plants (Cucumis sativus L.) by biocontrol agent Trichoderma harzianum. Applied and Environmental Microbiology, 65, 1061-1070.\n[30]\tAl-Fattah A, Dababat A, Sikora A. (2007). 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The effects of different CdCl2 concentrations on the growth and on certain biochemical parameters of almond seedlings (Prunus dulcis) were studied under controlled conditions in the nutrient solutions containing increasing CdCl2 concentrations ranging from 0 to 150 μM CdCl2. Under Cd stress conditions, damage was variable. Cadmium reduced dry matter production in leaves and roots. While chlorophyll content was severely decreased, that of leaf sugars appeared to be increased. Furthermore, leaf nutritional status seemed to be more altered than that of roots. Both in roots and leaves, there was an increase in MDA content as metal concentration increased. It may be suggested from the present study that toxic concentrations of Cd cause oxidative damage as shown by the increase of lipid peroxidation.

International audience; The analysis of housekeeping recA gene sequences from 138 strains from 13 species or genomic species of Agrobacterium, nine being biovar 1 genomospecies, and the others Agrobacterium larrymoorei, Agrobacterium rubi, Agrobacterium sp. NCPPB 1650, and Agrobacterium vitis and one “former” Agrobacterium species, Rhizobium rhizogenes, led to the identification of 50 different recA alleles and to a clear delineation of the 14 species or genomospecies entirely consistent with that obtained by amplified fragment length polymorphism (AFLP) analysis. The relevance of a recA sequencing approach for epidemiological analyses was next assessed on agrobacterial Tunisian isolates. All Tunisian isolates were found to belong to the Agrobacterium tumefaciens/ biovar 1 species complex by both biochemical tests and rrs sequencing. recA sequence analysis further permitted their unambiguous assignment to A. tumefaciens genomospecies G4, G6, G7, and G8 in total agreement with the results of an AFLP-based analysis. At subspecific level, several Tunisian recA alleles were novel, indicating the power and accuracy of recA-based typing for studies of Agrobacterium spp.

National audience

National audience

National audience

Olive trees (cv. Chemlali) showing typical symptoms of wilt and dieback were collected from several areas in Tunisia. Visual diagnostic, isolation and microscopic observations identified the causal pathogen as Verticillium dahliae. The pathotype was determined using specific primers pairs for D (defoliating) and ND (non-defolitating) . Artificial inoculation of olive plants resulted in typical wilting with defoliation, proving that the isolate tested was pathogenic on olive, and this isolate belongs to the D pathotype. This is the first report of the defoliating pathotype causing wilting disease on olive in Tunisia.