Molecular heterogeneity in the 18s DNA gene of Alternaria sp. and Fusarium sp. producing mycotoxins in rice and maize grains

Background: Food contaminated with fungi and their toxins is a problem that threatens many developing countries. Kingdom of Saudi Arabia depends on the exported grain and legume seeds. Materials and methods: The study involved examination of 160 samples of rice and maize seeds collected from different locations in the Kingdom of Saudi Arabia. Heterogeneity in the 18s rRNA gene of toxigenic Alternaria sp. and Fusarium sp. was unraveled. The seeds were disinfected and cultured on Potato Dextrose Agar (PDA), Yeast Extract Sucrose (YES) media and incubated at 25 °C/7 days. The isolated fungi were subjected to 18s rRNA gene sequencing. Five toxins were extracted from maize and rice grains infected with isolated fungi. Results: The isolated fungi were identified based on morphological and spores characters as Fusarium sp. and Alternaria sp. Molecular identification based on18s rDNA barcode' was performed due to its high degree of inter specific variability, conserved primer sites and multi-copy nature in the genome. Fusarium sp. produced the highest detected (2070 μg/kg) fumonisin especially in cereal production season 2011. The collected grain from Dammam recorded the highest percentage (5485.2 g/kg) of toxins. Conclusion: This work highlights that 50% of samples were found contaminated with toxins in various concentrations which impose a threat for public health and necessitate rapid identification methods for toxigenic fungi such as 18s rDNA sequencing. Keywords: Alternaria sp., Fusarium sp., Mycotoxins, PCR, 18s rDN

Avicennia marina endophytic fungi shows antagonism against tomato pathogenic fungi

Mangrove endophytes have been widely studied for several years and Avicennia marina endophytic fungi is known for its remarkable activity against many plant pathogens. Tomato is an important food crop in Saudi Arabia but it is susceptible to fungal diseases.The control of these phytopathogens through fungicides and pesticides is temporary. Thus, this study is aimed to isolate mangrove plant i.e. Avicennia marina endophytic fungal antagonists, characterize their phylogenetic positions and determine their antagonistic activities against tomato fungal pathogens. This study isintended to find a suitable alternative method to control or limit the spread of tomato diseases by using endogenous fungi of mangroves. Ninety fungal pathogens were isolated from three tomato farms in different regions of Riyadh city, Saudi Arabia. In addition, 40 endophytic mangrove i.e. Avicennia marina fungi were isolated from the eastern and western mangrove stands of the Kingdom of Saudi Arabia using potato dextrose agar, Czapek dox broth and malt extract broth media. These fungal strains were phylogenetically classified into at least sixteen genera based on 18S rRNA gene sequencing analysis. The antagonistic strains were screened via a Dual Culture Plate Assay and filter paper disc method. This study showed that endophytic fungal isolates have an antagonistic effect on most tomato pathogenic fungi. Cladosporium sphaerospermum had the highest inhibition while Trichoderma asperellum showed least antagonism against Avicennia marina endophytic fungi. This study proved that endophytic fungi present in Avicennia marina can control many tomato pathogens and their respective diseases. This work also cleared many aspects regarding the use of Avicennia marina endophytic fungal strains as potential biocontrol agents. Also, the diversity observed by these endophytic fungal strains from different areas of Saudi Arabia opened many doors for future research in the control of fungal pathogens

Evaluation of Silicon and Proline Application on the Oxidative Machinery in Drought-Stressed Sugar Beet

Drought stress deleteriously affects growth, development and productivity in plants. So, we examined the silicon effect (2 mmol) and proline (10 mmol) individually or the combination (Si + proline) in alleviating the harmful effect of drought on total phenolic compounds, reactive oxygen species (ROS), chlorophyll concentration and antioxidant enzymes as well as yield parameters of drought-stressed sugar beet plants during 2018/2019 and 2019/2020 seasons. Our findings indicated that the root diameter and length (cm), root and shoot fresh weights (g plant−1) as well as root and sugar yield significantly decreased in sugar beet plants under drought. Relative water content (RWC), nitrogen (N), phosphorus (P) and potassium (K) contents and chlorophyll (Chl) concentration considerably reduced in stressed sugar beet plants that compared with control in both seasons. Nonetheless, lipid peroxidation (MDA), electrolyte leakage (EL), hydrogen peroxide (H2O2) and superoxide (O2●−) considerably elevated as signals of drought. Drought-stressed sugar beet plants showed an increase in proline accumulation, total phenolic compounds and up-regulation of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) activity to mitigate drought effects. Si and proline individually or the combination Si + proline considerably increased root and sugar yield, sucrose%, Chl concentration and RWC, MDA and EL were remarkably reduced. The treatments led to adjust proline and total phenolic compounds as well as CAT and SOD activity in stressed sugar beet plants. We concluded that application of Si + proline under drought stress led to improve the resistance of sugar beet by regulating of proline, antioxidant enzymes, phenolic compounds and improving RWC, Chl concentration and Nitrogen, Phosphorus and Potassium (NPK) contents as well as yield parameters