Embryo growth alteration and oxidative stress responses in germinating Cucurbita pepo seeds exposed to cadmium and copper toxicity

This study investigated the influence of cadmium (Cd) and copper (Cu) heavy metals on germination, metabolism, and growth of zucchini seedlings (Cucurbita pepo L.). Zucchini seeds were subjected to two concentrations (100 and 200 μM) of CdCl2 and CuCl2. Germination parameters, biochemical and phytochemical attributes of embryonic axes were assessed. Results revealed that germination rate remained unaffected by heavy metals (Cd, Cu). However, seed vigor index (SVI) notably decreased under Cd and Cu exposure. Embryonic axis length and dry weight exhibited significant reductions, with variations depending on the type of metal used. Malondialdehyde and H2O2 content, as well as catalase activity, did not show a significant increase at the tested Cd and Cu concentrations. Superoxide dismutase activity decreased in embryonic axis tissues. Glutathione S-transferase activity significantly rose with 200 μM CdCl2, while glutathione content declined with increasing Cd and Cu concentrations. Total phenol content and antioxidant activity increased at 200 μM CuCl2. In conclusion, Cd and Cu heavy metals impede zucchini seed germination efficiency and trigger metabolic shifts in embryonic tissue cells. Response to metal stress is metal-specific and concentration-dependent. These findings contribute to understanding the intricate interactions between heavy metals and plant physiology, aiding strategies for mitigating their detrimental effects on plants.

Two Novel Bacillus Strains (subtilis and simplex Species) with Promising Potential for the Biocontrol of Zymoseptoria tritici, the Causal Agent of Septoria Tritici Blotch of Wheat

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).

GENETIC CHARACTERIZATION OF AN ALGERIAN POPULATION OF MYCOSPHAERELLA GRAMINICOLA WITH MICROSATELLITE MARKERS

Mycosphaerella graminicola (anamorph: Zymoseptoria tritici, formerly Septoria tritici), the responsible for Septoria tritici blotch, is the most frequently occurring disease on wheat crops worldwide. The populations of this pathogen were previously characterized in several areas around the world, but not in Algeria so far. The present study aims thus at investigating the genetic diversity and population structure of M. graminicola in this country. One hundred and twenty monoconidial isolates of this fungus (60 from bread wheat and 60 from durum wheat) were collected during the 2012 growing season from five distinct geographical locations in Algeria. They were then fingerprinted using eight microsatellite markers. The number of alleles per locus ranged from 2 to 11, with an average of 6.25 alleles per locus. We found out a moderate gene diversity, a high genotype diversity (72% of unique haplotypes) and a low population differentiation within the population. Further analyses using both UPGMA and Bayesian clustering methods confirmed the lack of genetic structuration irrespective of geographical locations and host species. These findings are likely due to the frequent occurrence of sexual reproduction in the field, leading to genetic diversification and allele homogenization via wind born ascospores within the population.

BOTH MAT1-1 AND MAT1-2 MATING TYPES OF MYCOSPHAERELLA GRAMINICOLA OCCUR AT EQUAL FREQUENCIES IN ALGERIA

Septoria tritici blotch caused by Mycosphaerella graminicola is currently the most devastating disease on wheat crops worldwide. Mycosphaerella graminicola sexual reproduction involves two mating type idiomorphs that were previously studied in several areas around the world, but not in Algeria so far. The objective of this study was thus to determine the frequencies and distribution of M. graminicola mating types in this country. One hundred and twenty monoconidial isolates of this fungus (60 from bread wheat and 60 from durum wheat) were collected during the 2012 growing season from five distinct geographical locations in Algeria. The mating type of each isolate was identified using a multiplex PCR that amplifies either MAT1-1 or MAT1-2 fragment from mating type loci. Both idiomorphs were found at equal frequencies according to the chi-square test at the whole country level (46% MAT1-1 and 54% MAT1-2) and in each of the sampled locations. The two mating types were also detected at equal frequencies on both host species (47% MAT1-1 vs 53% MAT1-2 on bread wheat and 45% MAT1-1 vs 55% MAT1-2 on durum wheat). Our study showed that the two mating types of M. graminicola occur at equal proportions in Algeria and suggests a strong potential for sexual reproduction of the pathogen in this country that may eventually lead to either adaptation to local conditions, plant resistance overcoming or the emergence of resistance to fungicides.

Assessment of the cytochrome B substitution G143A in the Algerian population of Mycosphaerella graminicola

Mycosphoerella graminicola (anamorph: Zymoseptoria tritici), causal agent of Septoria tritici blotch, is currently one of the most damaging diseases on both bread and durum wheat crops worldwide. Since wheat resistance against this pathogen is always partial at various extents in most cultivars, disease control relies mainly on the use of fungicides. However, management of fungicide applications is necessary in order to avoid the emergence and widespread of fungicide resistant genotypes within populations of the pathogen. In the present study, we investigated for the first time the resistance of M. graminicola toward strobilurin fungicides in Algeria. This was performed by identifying the G143A substitution of the cytochrome b encoding sequence (which confers resistance to strobilurins) in a collection of 120 single-conidial isolates. These isolates have been sampled during the 2012 growing season from five distinct geographical locations (Guelma, Annaba, Constantine, Skikda and Oran). We used a PCR-based mismatch mutation assay allowing the amplification of either G143 (sensitive) or A143 (resistant) allele in each isolate. This study should give valuable information regarding the management of strobilurin use in order to control in a durable manner M. graminicola epidemics in Algeria.