Durum wheat stress tolerance induced by endophyte <i>pantoea agglomerans</i> with genes contributing to plant functions and secondary metabolite arsenal

In the arid region Bou-Sa&acirc;da at the South of Algeria, durum wheat Triticum durum L. cv Waha production is severely threatened by abiotic stresses, mainly drought and salinity. Plant growth-promoting rhizobacteria (PGPR) hold promising prospects towards sustainable and environmentally-friendly agriculture. Using habitat-adapted symbiosis strategy, the PGPR Pantoea agglomerans strain Pa was recovered from wheat roots sampled in Bou-Sa&acirc;da, conferred alleviation of salt stress in durum wheat plants and allowed considerable growth in this unhostile environment. Strain Pa showed growth up to 35 &deg;C temperature, 5&ndash;10 pH range, and up to 30% polyethylene glycol (PEG), as well as 1 M salt concentration tolerance. Pa strain displayed pertinent plant growth promotion (PGP) features (direct and indirect) such as hormone auxin biosynthesis, production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and ammonia and phosphate solubilization. PGPR features were stable over wide salt concentrations (0&ndash;400 mM). Pa strain was also able to survive in seeds, in the non-sterile and sterile wheat rhizosphere, and was shown to have an endophytic life style. Phylogenomic analysis of strain Pa indicated that Pantoea genus suffers taxonomic imprecision which blurs species delimitation and may have impacted their practical use as biofertilizers. When applied to plants, strain Pa promoted considerable growth of wheat seedlings, high chlorophyll content, lower accumulation of proline, and favored K+ accumulation in the inoculated plants when compared to Na+ in control non-inoculated plants. Metabolomic profiling of strain Pa under one strain many compounds (OSMAC) conditions revealed a wide diversity of secondary metabolites (SM) with interesting salt stress alleviation and PGP activities. All these findings strongly promote the implementation of Pantoea agglomerans strain Pa as an efficient biofertilizer in wheat plants culture in arid and salinity-impacted regions

Critical Evaluation of Biocontrol Ability of Bayoud Infected Date Palm Phyllospheric Bacillus spp. Suggests That In Vitro Selection Does Not Guarantee Success in Planta

The vascular wilt of date palm (Phoenix dactylifera L.), also known as Bayoud and caused by Fusarium oxysporum f.sp. albedinis (FOA), is the most destructive disease in North Africa. The disease has resulted in huge economic losses due to declining crop yield and quality. The use of potential biocontrol agents is a sustainable and environmentally friendly strategy compared to synthetic fungicides. The use of date palm-associated microflora for the screening of native antagonistic bacteria with potential applications is the most promising way to control this disease. Thus, the epidemic palm groves (in the valley of M&rsquo;zab-Ghardaia-Algeria) were chosen for the isolation of rhizospheric bacteria and endophytes from the soil and roots of healthy or infected plants. A total of 8 bacterial isolates (83, 84, 300, 333, 322, 260, 249, and 227) selected from 75 FOA-active strains, showed strong activity against several strains of FOA and other major plant pathogens. Their phylogenetic identification proved they belong to the genus Bacillus (Bacillus sp., B. subtilis, B.&nbsp;atrophaeus, B.&nbsp;halotolerans, B.&nbsp;amyloliquefasiens, and B.&nbsp;paralicheformis). Bacterial cultures and a cell-free culture supernatant tested alone or in co-culture showed FOA inhibitory activity. However, the effect of the co-culture did not show any synergy in both cases. Unlike diffusible compounds, volatile organic compounds did not show a significant antifungal ability. The concept of selecting biocontrol agents in vitro does not always guarantee in vivo performance. In addition to antibiosis, other strategies such as competition and resistance induction are required for biocontrol agent efficacy. To evaluate the biocontrol effect in vivo, germinated seeds of date palm were treated with bacteria, infected with the pathogen, and then incubated for 45 days at room temperature in the dark. The majority of the strains (84, 300, and 333) tested showed moderate fungistatic effects and the protection rate reached an average of 60%. In particular, promising results were obtained with B. paralicheniformis strain 260 which significantly protected palm seeds up to 85%, compared to its in vitro test where a low inhibition rate (27.77%) was recorded. Screening methods should be equipped with multifactorial or plant-mediated control mechanisms. Furthermore, these bacteria have shown other potentialities to improve plant growth and resist stressful conditions. Thus, an effective biocontrol agent must combine several beneficial characteristics to be used successfully in situ. In this respect, Bacillus remains the best candidate for biological control

Semi-Arid-Habitat-Adapted Plant-Growth-Promoting Rhizobacteria Allows Efficient Wheat Growth Promotion

Plant-growth-promoting rhizobacteria (PGPR) introduced into agricultural ecosystems positively affect agricultural production and constitute an ecological method for sustainable agriculture. The present study demonstrated the effects of two PGPR, Pantoea agglomerans strain Pa and Bacillus thuringiensis strain B25, on seed germination, on the plant growth of two durum wheat varieties, Bousselam and Boutaleb, and on the frequency of the cultivable beneficial bacterial community. The bacterial strains were used as seed primers (individually or in consortia) by coating them with carboxymethyl cellulose (CMC 1%). The effect of PGPR was negligible on germinative ability but improved seed vigor in the Boutaleb variety after inoculation with the Pa strain alone or in combination with the B25 strain. The results showed that the germination capacity depends on the wheat variety. It seemed to be better in the Bousselam variety. Analysis of the results of morphological plant parameters in sterile compost after 75 days under controlled conditions (16 h light, 26/16 °C day/night) showed a significant improvement in plant growth in both wheat varieties with the Pa strain alone or in combination. Chlorophyll (a, and total), carotenoid, and total soluble sugars were significantly increased, while proline and MDA were strongly reduced by inoculation of the Bousselam variety. Bacterial survival of the Pa and B25 strains in the rhizosphere of sterile compost was appreciable (105–107 CFU/g) for both the Pa and B25 strains. Only the Pa strain was endophytic and able to colonize roots. Contrary to sterile compost, the different inoculation treatments in natural soil (after 114 days) significantly improved all morphological parameters and chlorophyll pigments in both wheat varieties. The reduction of proline contents at the leaf level was observed with Pa, mainly in Bousselam. Bacterial densities of the rhizosphere and endophyte cultivable communities did not differ significantly. However, the number of cultivable beneficial bacteria isolated from roots and rhizosphere with multiple PGP traits was significantly increased. Bacterial survival of CMC-coated seed inoculum was appreciable and remained constant, especially for the Pa strain, during 21 months at room temperature. Based on these results, the PGPR used after seed priming would be a feasible and sustainable strategy to improve soil fertility and promote growth of durum wheat in stressful and non-stressful environments

Semi-Arid-Habitat-Adapted Plant-Growth-Promoting Rhizobacteria Allows Efficient Wheat Growth Promotion

Plant-growth-promoting rhizobacteria (PGPR) introduced into agricultural ecosystems positively affect agricultural production and constitute an ecological method for sustainable agriculture. The present study demonstrated the effects of two PGPR, Pantoea agglomerans strain Pa and Bacillus thuringiensis strain B25, on seed germination, on the plant growth of two durum wheat varieties, Bousselam and Boutaleb, and on the frequency of the cultivable beneficial bacterial community. The bacterial strains were used as seed primers (individually or in consortia) by coating them with carboxymethyl cellulose (CMC 1%). The effect of PGPR was negligible on germinative ability but improved seed vigor in the Boutaleb variety after inoculation with the Pa strain alone or in combination with the B25 strain. The results showed that the germination capacity depends on the wheat variety. It seemed to be better in the Bousselam variety. Analysis of the results of morphological plant parameters in sterile compost after 75 days under controlled conditions (16 h light, 26/16 &deg;C day/night) showed a significant improvement in plant growth in both wheat varieties with the Pa strain alone or in combination. Chlorophyll (a, and total), carotenoid, and total soluble sugars were significantly increased, while proline and MDA were strongly reduced by inoculation of the Bousselam variety. Bacterial survival of the Pa and B25 strains in the rhizosphere of sterile compost was appreciable (105&ndash;107 CFU/g) for both the Pa and B25 strains. Only the Pa strain was endophytic and able to colonize roots. Contrary to sterile compost, the different inoculation treatments in natural soil (after 114 days) significantly improved all morphological parameters and chlorophyll pigments in both wheat varieties. The reduction of proline contents at the leaf level was observed with Pa, mainly in Bousselam. Bacterial densities of the rhizosphere and endophyte cultivable communities did not differ significantly. However, the number of cultivable beneficial bacteria isolated from roots and rhizosphere with multiple PGP traits was significantly increased. Bacterial survival of CMC-coated seed inoculum was appreciable and remained constant, especially for the Pa strain, during 21 months at room temperature. Based on these results, the PGPR used after seed priming would be a feasible and sustainable strategy to improve soil fertility and promote growth of durum wheat in stressful and non-stressful environments