Biocontrol Potential of an Endophytic <i>Streptomyces</i> sp. Strain MBCN152-1 against <i>Alternaria brassicicola</i> on Cabbage Plug Seedlings

Abstract

In the present study, 77 strains of endophytic actinomycetes isolated from cabbage were screened in order to assess their biocontrol potential against Alternaria brassicicola on cabbage seedlings. In the first and second screening trials, cabbage seedlings pretreated with mycelial suspensions of each isolate were spray-inoculated with A. brassicicola. Strain MBCN152-1, which exhibited the best protection in screening trials and had no adverse effects on seedling growth, was selected for the greenhouse trial. In the greenhouse trial, cabbage seedlings, which had been grown in plug trays filled with soil mix containing spores of MBCN152-1 (1×10 8 spores g -1 of soil mix), were spray-inoculated with A. brassicicola and grown in greenhouse conditions. MBCN152-1 reduced disease incidence and significantly increased the number of viable seedlings. The efficacy of MBCN152-1 against damping-off caused by seed-borne A. brassicicola was then evaluated. Cabbage seeds, artificially infested with A. brassicicola, were sown in soil mix containing MBCN152-1 spores. The disease was completely suppressed when infested seeds were sown in a soil mix blended with MBCN152-1 at 1.5×10 7 spores g -1 of soil mix. These results strongly suggest that MBCN152-1 has the potential to control A. brassicicola on cabbage plug seedlings. MBCN152-1 was identified as a Streptomyces humidus-related species based on 16S rDNA sequencing. Scanning electron microscopy showed that the hyphae of MBCN152-1 multiplied on the surface of the seedlings and penetrated their epidermal cells. In conclusion, strain MBCN152-1 is a promising biocontrol agent against A. brassicicola on cabbage plug seedlings.

Bioprocessing strategies for cost-effective large-scale biogenic synthesis of nano-MgO from endophytic Streptomyces coelicolor strain E72 as an anti-multidrug-resistant pathogens agent

“…The ethanol sterilized leaves were dried on sterilized filter paper for 10 min and then were treated with 6% sodium hypochlorite with Tween 20 (0.1%) for 2 min to remove epiphytic microorganisms. The leaves were soaked in 10% NaHCO 3 for 20 min to disrupt the growth of the fungi 29 , 31 . At last leaves rinsed with sterilized distilled water for many times and sterility checked (the final rinsing water was spread on starch casein agar as the control plates) 23 – 25 .…”

“…The surface sterilized leaves were cut with sterile scalpel blade and crushed in sterilized distilled water by using sterile pestle and mortar. By using serial dilution method 100 μl of the diluted extract was spread on starch casein agar (0.1% sodium caseinate, 1% soluble starch, 0.03% K 2 HPO 4 , 1.8% agar, pH 6.8–7.0) supplemented with 25 µg/ml cycloheximide, 50 μg/ml nalidixic acid and 50 μg/ml nystatin to suppress fungal growth and incubated at 30 °C for three weeks 29 , 31 . Actinomycetes growing on the media were isolated and purified.…”

“…Also, the total carbohydrate contents of both cell fractionations were determined by using the total carbohydrate colorimetric assay kit (Milpitas, CA 95035 USA). The nitrate reductase enzyme in both cell fractionations was checked and assayed according to 29 , 31 , 52 . Cell fractionations were mixed with 10 ml of assay medium (30 mM KNO 3 and 5% isopropanol in 0.1 M phosphate buffer of pH 7.5) and incubated at 30 °C for 1 hr in the dark condition.…”

“…It is important to note that these treasure troves of natural drugs are most effective with negligible side effects and investment costless available 26 – 28 . Endophyte is a microbe that colonizes in the intracellular or intercellular tissues of healthy plant and explored as an important part of micro-ecosystem 29 – 31 . Endophytic microbe’s flora that isolated from these medicinal plants has the same and/or similar bioactive metabolites, thus making them a proficient and unique source of novel safe natural compounds for medicinal applications 32 – 35 .…”

“…In recent years, secondary metabolites of isolated endophytes used as antitumor, antimicrobial, antioxidant, and other functions that have a potential application prospect in pharmacy 28 , 31 , 36 – 38 . Until now, very few researchers have reported endophytic actinomycetes as nanoparticles biosynthesizer by using nanobiotechnological strategies 29 , 30 . So, endophytic actinomycetes have attracted attention in the search for an increasingly important source of promising potential new bioactive compounds that used as novel nanoparticles-synthesizers 26 – 28 , 34 , 35 .…”