Enhancement of plant growth, acclimatization, salt stress tolerance and verticillium wilt disease resistance using plant growth-promoting rhizobacteria (PGPR) associated with plum trees (Prunus domestica)

Plants interact with a great variety of microorganisms that inhabit the rhizosphere playing critical roles in several aspects of plant growth and protection against abiotic and biotic diseases. In this study, we performed a screening of bacteria associated with the rhizosphere of Prunus domestica trees to identify bacterial strains with plant growth-promoting activity. Ten strains isolated from the rhizosphere of P. domestica showed multiple in vitro plant growth promoting rhizobacteria (PGPR) activity such as the production of indole acetic acid, hydrogen cyanide, ammonia, solubilization of phosphates and antifungal activity against Verticillium dalhiae and Fusarium oxysporum f.sp. melonis. In planta, they significantly increased the growth (stem length, number of leaflets, leaf area and root weight) and biochemical (nitrate reductase activity, proline and chlorophyll content) parameters of tomato, as well as the rate of seed germination. Two selected strains (Pr7 and Pr8) with higher antagonistic activity against V. dalhiae and F. oxysporum f.sp. melonis protected tomato plants against Verticillium wilt and salt stress. In addition, they enhanced acclimatization of Vitis vinifera cv. Pinot noir and the peach root stock GF305 from in vitro to the greenhouse. 16S rRNA sequencing identified strains Pr7 and Pr8 as Pseudomonas stutzeri and Bacillus toyonensis, respectively. Since these two PGPR inoculants exhibited multiple traits beneficial to the examined host plants, they may be applied in the development of safe, and effective seed treatments as an alternative to chemical fungicides and fertilization but also for successful acclimatization of micropropagated plants.Mohamed Faize was supported by funding from the ‘Ministère de l'Enseignement Supérieur, de la Recherche Scientifique de la Formation des Cadres’ (MERSFC, Morocco) within the framework of ARIMNet2 Projec

Annual variations of alpha-amylase and invertases activities in buds and internodes of grapevines and their relation with carbohydrates and abscisic acid contents

The concentration of starch, soluble carbohydrates, free abscisic acid (ABA) and activities of α-amylases and invertases (the acid and the alkaline form) were investigated in buds and internodes of Vitis vinifera L. cv. Merlot during annual cycle. The levels of starch increased in the two organs from middle august to middle of November and the decreased until middle February. These variations seem to be controlled by α-amylase which activity was low during periods of starch accumulation and high when starch contents decreased. As the bud burst draws near (since the middle of February), starch accumulated in internodes and buds. However at the same time of the activity of α-amylase which activity also increased. Starch contents could be controlled by ABA which is known to reduce α-amylase activity. Indeed in internodes ABA content was high when α-amylase activity was low. This was also the case in the buds but after break dormancy phase. This difference of comportment of α-amylase towards ABA in the buds during the annual cycle could be in relation with the change of the physiological state of buds induced by the winter chilling. The invertases activities in buds and internodes changed inversely to the sucrose and raffinose contents during all the annual cycle suggesting that the levels of these sugars were controlled by invertases, highly by the acid form and slightly by the alkaline form. Nevertheless, in the buds, when alkaline activity of invertase was high, sucrose content was maximal. These invertases seem also implicated, with α-amylase, in the development of starch content particularly when starch was accumulated by glucose providing. In the case of buds, invertases activities appeared to change in the same sense of ABA content but not during all the cycle. This suggested that this growth regulator may not be crucial for the control of invertases activities

Variations of abscisic acid contents in various organs of grapevine infected by the eutypa dieback fungus, <em>Eutypa Lata</em>

In grapevine, eutypa dieback is a disease induced by ascomyceta fungus, Eutypa lata. At present, eutypa dieback is considered as the most serious deterioration disease of grapevine. The external symptoms of this disease are most conspicuous during the first months of the annual growth cycle and include dwarfed shoots with smaller and necrotic leaves and unfavourable development of grapes. All these symptoms were still suggested an hormonal perturbation in grapevine organs. The aim of this work was to determine the effects of eutypa dieback on abscisic acid contents in flower buds, flowers, young berries, leaves and internodes of grapevine. This study was also performed to determine the relationship between this growth regulator and disease development. The study was performed using organs (1) from healthy vines, (2) healthy appearing organs from vines with one symptomless arm and one diseased arm, and (3) moderately and (4) strongly diseased organs. From flowers buds separated to bunch of grapes closed stages, free abscisic acid (ABA) and the glucose esters of this acid (ABA-GE) were analysed in Vitis vinifera L. cv. Cabernet Sauvignon which is sensitive to E. lata. In the healthy appearing organs, growth and development as well as water and ABA contents were not changed by eutypa dieback fungi. Whereas eutypa dieback induced a decrease of water content and the rate of growth increase in diseased organs. During all the period studied in leaves and since fruit set stage in the internodes, the ABA and ABA-GE contents were increased by eutypa dieback proportionally to symptoms. The ABA levels increase in leaves and internodes were not seem to be produced by ABA-GE hydrolysis since increase in ABA-GE levels were also observed in response to eutypa dieback. The maximum of ABA characterising grapevine flowers was delayed by eutypa dieback and their level was reduced with increasing symptoms severity. In flower buds, flowers and young berries, this disease induced a decrease of ABA-GE contents during all period studied proportionally to symptoms severity. The mycelium of two E. lata isolates cultured in Errikson and Petersson medium culture can synthesize ABA. A part of this growth regulator was diffused in medium culture. It was suggested that increase of ABA levels in diseased organs must have many origins: perturbation of (1) ABA-GE translation, (2) synthesis of ABA by grapevine caused by water stress and (3) synthesis of ABA by the fungi. The possible relationship between increased ABA content in the diseased organs and expression of eutypa dieback symptoms is discussed

Effects of eutypiosis on free and conjugated polyamines content in internodes of grapevine (<em>Vitis vinifera</em> l. cv. Cabernet Sauvignon) during their active phase of growth

Development of polyamines levels [Putrescine (Put), Spermidine (Spd), and Spermine (Spm)] was investigated in internodes of grapevine infected by eutypiosis fungus, Eutypa lata. The study was performed using (1) internodes from healthy vines, (2) apparently healthy internodes from vines with one arm symptomless and one diseased arm and (3) diseased internodes. Free polyamines (PAs: hydrochloric acid soluble fraction), conjugated polyamines (PAs-fpm: PAs covalently linked to molecules with low molecular weight like hydroxycinnamic acids) and bound polyamines (PAs-mm: covalently linked to macromolecules) were analysed in Vitis vinifera L. cv. Cabernet sauvignon, which is sensitive to eutypiosis. The internodes stunting induced by eutypiosis was accompanied by a decrease of free Put and free Spm contents between flower buds separated and fruit set stages. The same results were observed for PAs-mm but more slightly than free PAs. The Put-fpm and Spd-fpm levels increased in the apparently healthy internodes and decreased in diseased organs by Eutypa lata effect. The relationship between free PAs contents in the diseased internodes and their growth reduction, as well as the involvement of PAs-fpm on the grapevine response to Eutypa lata infection are discussed

Protective effect of symmetrical N‐heterocyclic 1,3,4‐oxadiazole and 1,3,4‐thiadiazole derivatives against Pepino mosaic virus of tomato

International audienceAbstract Pepino mosaic virus (PepMV) is a highly infectious potexvirus, which has presently become a major pathogen for tomato crops worldwide. Since there is no effective method control for PepMV, strict preventive hygienic measures and cross‐protection have been established. However, the use of mild isolates to protect against aggressive isolates provides opportunities for interaction with other microorganisms, which under certain conditions may worsen disease symptoms. Thus, alternative control methods are needed. In this study we aimed at the development of chemical control against PepMV based on the use of heterocyclic compounds including symmetrical 2,5‐disubstituted 1,3,4‐oxadiazoles, symmetrical 2,5‐disubstituted 1,3,4‐thiadiazole and dihydrotetrazine derivatives. Results showed that spray application of three 1,3,4‐oxadiazole derivatives (OH‐Oxa, CH 3 ‐Oxa, NO 2 ‐Oxa) and of the derivative of 1,3,4‐thiadiazole (OH‐Thia) resulted in reducing the main symptoms of PepMV in tomato leaves, conversely to the dihydrotetrazine carboxylic acid. Double‐antibody sandwich enzyme‐linked immunosorbent assay (DAS‐ELISA) revealed that PepMV was not detected from tomato plants pre‐treated with the derivatives conferring elevated protection. Moreover, the protective ability of OH‐Oxa, CH 3 ‐Oxa, NO 2 ‐Oxa and OH‐Thia was closely related to the enhancement of the activity of antioxidant enzymes upon infection with PepMV

Protection of Solanum lycopesicum induced by chitosan and chitosan nano-hydroxyapatite against Pepino mosaic virus and Verticillium dahliae

International audienceThe main of the present study was to prepare chitosan (Chit) and chitosan hydroxyapatite nanoparticle (Chit-nHap) to assess their activities against two major diseases affecting tomato crop: pepino mosaic virus (PepMV) and verticillium wilt caused by the fungus Verticillium dahliae. The synthesized compounds were characterized using X-rays diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electronic microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). In vitro, the application of various concentrations of Chit and Chit-nHap showed significant inhibition of radial mycelial growth against V. dahliae. However, Chit-nHap was found to be more effective than Chit. In greenhouse trials, the disease severity was significantly reduced when Chit and Chit-nHap were sprayed to the leaves at 150 and 250 mu g mL- 1. The highest concentration of Chit and Chit-nHap reduced leaf alteration index by more than 81% and browning index by 96%. Both compounds also reduced PepMV disease severity and virus accumulation. Protection afforded against PepMV was associated with differential accumulation of H2O2 and with potentiation of the activity of antioxidant enzymes such as catalase, ascorbate peroxidase, guaiacol peroxidase and polyphenol oxidase