No abstract

Two novel Algerian field-collected isolates were selected for their antifungal activity against Zymoseptoria tritici (teleomorph Mycosphaerella graminicola). The novel strains, termed Alg.24B1 and Alg.24B2, were identified as Bacillus subtilis and Bacillus simplex since their respective nucleotide sequences of the 16S rRNA gene were 100% and 99.93% identical to those of B. subtilis and B. simplex, respectively. The antifungal activities of Alg.24B1 and Alg.24B2 were evaluated by the well diffusion method and compared to those of other Bacillus species. The maximum activity was obtained after two days of confrontation of the bacterial strain supernatants with the fungus for Alg.24B1 and three days for Alg.24B2. Furthermore, the metabolites responsible for the antifungal activity of both strains were detected by the investigation of either gene presence (PCR) or molecule production (activity detection of lytic enzymes and HPLC detection of lipopeptides). Overall, this study showed that in addition to their ability to produce lytic enzymes (protease and β-glucanase), both strains coproduce three types of lipopeptides viz. surfactin, iturin, and fengycin. Thus, the biofungicide activity of both strains may be a result of a combination of different mechanisms. Therefore, they had a great potential to be used as biocontrol agents to effectively manage septoria tritici blotch of wheat (STB).

To assess the impact of heavy metals (cadmium, copper) on the germination, metabolism and growth of zucchini seedlings (Cucurbita pepo L.), a test was conducted 'in vitro' on the germination and growth of zucchini seedlings, subjected to two concentrations (100 and 200 μM) of CdCl2 and CuCl2. The germination parameters, as well as the biochemical and phytochemical properties of the embryonic axes of the seedlings, were studied. The obtained results showed that the seed vigor index (SVI) of zucchini seeds recorded a significant and remarkable decrease under the effect of Cd. A significant decrease was also noted in the length and the dry weight of the embryonic axes of the young seedlings, which differed according to the type of metal. No significant increases in malondialdehyde (MDA) and H2O2 content, or in catalase (CAT) activity were noted at the tested concentrations of the Cd and Cu salt, but very significant decreases in superoxide dismutase (SOD) activity of embryonic axis tissues were observed. Glutathione S-transferase (GST) activity exhibited a significant increase at 200 μM CdCl2 whereas the glutathione (GSH) content decreased with increasing metal concentrations (Cd, Cu) of the medium. An increase in total phenol content and antioxidant activity was recorded at 200 μM of CuCl2. Based on the obtained results, we can conclude that heavy metals (Cd, Cu) reduce the germination efficiency of zucchini seeds and cause metabolic alterations of embryonic tissue cells, and the response of zucchini seedlings to metal stress depends on the type of metal and its concentration.