Potato dextrose agar (pda)

The F. verticillioides (Sacc. Nirenberg) strain, MRC 826, used in this study, was provided by Pannar Seed (Pty) Ltd. (Greytown, South Africa). The fungus was maintained at 30 °C and sub-cultured weekly on Potato Dextrose Agar (PDA) (Lab M Limited, Ayr, UK) or stored in 20% glycerol at −70 °C.

The fungus, T. punctulata (DSM-102798), was previously identified by Saeed et al. (2016) (link) as the causal agent of the date palm scorch disease in the UAE. T. punctulata was cultured on potato dextrose agar (PDA; Lab M Limited, Lancashire, United Kingdom) plates (pH 6.0); supplemented with ampicillin (Sigma–Aldrich Chemie GmbH, Taufkirchen, Germany) used at a rate of 25 mg l^-1 of agar medium, to inhibit the bacterial contaminants. The pathogen was subcultured on fresh PDA plates every 10 days and incubated at 28°C.
For disease assays, leaf bases of 8-month-old date palm (cv. Chichi) seedlings, obtained from the Date Palm Development Research Unit (DPDRU), United Arab Emirates University, Al-Ain, UAE, were surface-sterilized with 70% ethanol, and mechanical wounding was performed with sterilized scalpels prior to inoculation. These date palm seedlings were inoculated with agar plugs (8-mm in diameter) colonized by fungal mycelium from 10-days old T. punctulata cultures at the leaf base region, and the area of inoculation was wrapped with parafilm (Sigma–Aldrich) (Saeed et al., 2016 (link)). Inoculated seedlings were maintained in a greenhouse at 28°C, and examined for disease development.

The pathogen, L. theobromae (DSM 105134), was previously reported as the cause of mango dieback disease in the UAE (Saeed et al., 2017a (link)). Strain DSM 105134 was isolated from tissues sampled from diseased mango trees affected by L. theobromae, and identified using combined ITS sequences (GenBank accession number: MF114110). The pathogen was cultured on potato dextrose agar (PDA, pH 6.0; Lab M Limited, Lancashire, United Kingdom) plates, supplemented with 25 mg l⁻¹ ampicillin (Sigma–Aldrich Chemie GmbH, Taufkirchen, Germany) to suppress bacterial contaminants. The fungus was sub-cultured every 10 days on PDA plates at 28°C.

The Bs MBI600 strain used in the study was isolated from a commercial formulation of the product (Serifel 9.9 WP, BASF Hellas), following a procedure described previously [25 (link)]. The isolated strain was maintained at −80 °C in tryptone soy broth (TSB, LabM, Hungary) supplemented with 40% glycerol. Before use, the bacterial culture was grown on tryptone soy agar (TSA) medium and incubated at 37 °C for 24 h.
Fusarium oxysporum f.sp. radicis-lycopersici (Forl), Rhizoctonia solani, and Pythium ultimum isolates used in the study belonged to the fungal isolates collection from the Lab of Plant Pathology, AUTH. All pathogens had been isolated from diseased tomato plants. The fungal isolates were grown and maintained on potato dextrose agar (PDA, LabM, Hungary) slants at 4 °C until use.

Moulds in all the food samples were recovered by dilution plating according to Samson et al. (1995 ). Briefly, 10 g of each sample was diluted in 90 mL of sterile distilled water and homogenized for 2 min. Aliquots of 0.1 mL from the homogenized samples were spread-plated in duplicates on freshly prepared potato dextrose agar (PDA; Lab M, UK) supplemented with 30 mg/L chloramphenicol. The inoculated plates were incubated for 3 days at 30 °C in order to mimic the optimum temperature in the region. Thereafter, distinct fungal colonies with different colony ornamentations were purified on freshly prepared ¼ strength PDA plates (9.75 g; 2% agar/L of distilled water). Purified colonies were maintained at 4 °C as malt extract agar (MEA) slants in 4 mL vials.

The fungal pathogen, F. solani (DSM-106836), was previously identified as the causal agent of the SDS on date palm in the UAE [30 (link)]. F. solani was cultivated at 28 °C on potato dextrose agar (PDA; Lab M Limited, Lancashire, UK) plates (Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany).