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Introduction: Phytophthora nicotianae is a destructive plant pathogen with a worldwide distribution that causes root, fruit, leaf, and crown rot. Phytophthora species are the main reason for various diseases in a wide range of plant species including vegetables. Symptoms include fruit, stem, crown, and root rot. They lead to plant host death and in most cases, the economic losses caused by P. nicotianae are very high due to the diversity of the host range and its damage, therefore, controlling this pathogen is a constant challenge. Materials and methods: In order to biologically control the disease, three Streptomyces isolates including M6, M8, and M215 were selected from a large number of soil-inhabitant actinomycetes isolated from Kerman province, which showed effective anti-Oomycete activity against P. nicotianae. To better understand the inhibitory mechanism of these isolates, in vitro dual-culture assay, plant growth promotion, and pathogen control effects were investigated through the application of antagonists under laboratory and greenhouse conditions. Molecular identification of the most promising isolate was also achieved. Results: The antagonistic activity of three isolates including M8, M6, and M215 against P. nicotianae in tomato plants (super chef variety) was evaluated. Among all, based on the statistical analysis under both laboratory and glasshouse conditions, the M8 isolate had an inhibitory effect on the crown and root rot of tomato. The comparison of the effects of antagonists on the tomato plant yield indices revealed that M8 isolate had the greatest effect on increasing the growth indices of the tomato plant (super chef cultivar) including plant height, the number of flowers, shoot, and root dry weight. The M8 isolate was identified by the sequence analysis of a small ribosomal RNA subunit (16S rRNA). Based on the results of the present study, Streptomyces venetus CMU-AB225T strain had the highest similarity (96.08%) with the M8 isolate. Discussion and conclusion: The results showed that M8 isolate can be considered as a beneficial microorganism to produce some useful biofertilizers and bioactive materials to control tomato crown and root rot biologically. Some biocontrol agents such as T. harzianum and T. asperellum within composts can be effective in reducing the symptoms of Ph. nicotianae in pepper seedlings. The production of any product based on the S. venetus (M8) requires fulfilling further research steps such as the interaction of the bacterium with other beneficial soil microorganisms and its impact on the population of beneficial soil microbes, evaluation of the antimicrobial activity of M8 against other plant pathogenic fungi, fungal-like microorganisms and bacteria. Moreover, biosafety considerations and measures have to be investigated.

Endophytic bacteria are one of the most powerful tools in bio-controlling plant pathogens and protecting plants from damage. The evaluation of inhibitory effect of endophytic bacteria isolated from Mandarin orchards in Hormozgan province against crown and root rot caused by fungal-like Phytophthora nicotianae and Phytophthora citrophthora in laboratory (completely randomized design) and greenhouse (factorial experiment in completely randomized design) was performed with three replications. Also, the biomass parameter of fresh and dry weight of the stem, root and their corresponding lengths were investigated. In this experiment, 17 isolates of endophytic bacteria were identified using 16S rDNA gene. In the laboratory experiment was found that out of 17 endophytic bacteria, 3 isolates had significant inhibitory effect at the 5 percentage probability level; So that in the greenhouse conditions they reduced the disease severity of P. nicotianae and P. citrophthora isolates by 75.5 percentage compared to the control. The sequence of these three isolates was 99 percentage similar to the sequence of Paracrauroccus sp., Kytococcus schroeteri and Psychrobacillus psychrodurance species. In the greenhouse experiment, the comparison of the means showed that the fresh weight of stem, root and stem length treated with endophytic bacteria increased compared to the control. In general, the endophytic bacteria Paracrauroccus sp.,Kytococcus schroeteri and Psychrobacillus psychrodurance separately and in combination can be suggested as an effective tool for biological control of the cause of crown and root rot at the Bakraii rootstock. [ABSTRACT FROM AUTHOR]