Identification of biological agents which is thermo- tolerance is a key success for biological control in the arid regions such as Arabian Peninsula. Date palm is one of the indigenous plants in this region. It can tolerate high temperature and survive the drought. It is expected that microbial communities associated with date palms would have similar characters. It would be reasonable to search for bio-agents from such microbial communities. This study is a apart of a project to identify microbial communities living in the phyllosphere and rhizosphere of date palms. Bacterial colonies were isolated from date palm leaflets and soil samples containing date palm roots. Samples were collected from the date palm experimental field at the Agricultural Research Farm, Rwdet Al-Faras, Qatar. Isolation of bacteria were conducted on nutrient agar media using the standard techniques. Hundred eighty five bacterial isolates were obtained. They were evaluated for their antagonism potentiality against Alternaria alternate as a causal agent for leaf spot diseases in date palm and Fusarium solani and Macrophomina phaseolina as causal agents for root rot in Phaseolus vulgaris crops. Suppression of mycelial growth of the pathogens were recorded as the result of the interaction between the pathogen and different bacteria. Two modes of action were observed. Eleven isolates grew on the area of inoculation but they suppressed the pathogen by their extracellular antifungal metabolites while the growth of 18 isolates spread all over the plate and prevented pathogens from growing either by their growth or by both the growth and the extracellular antifungal metabolites. Screening for thermos-tolerance were carried out by picking up a single colony from each bacterial isolate, inoculating it in 1 ml of LB liquid media and incubating the culture at 90 °C for 24 hours. Then they were cultured on nutrient agar media plates, incubated at 30 °C for 24 hours. The two separate evaluations of antagonism and thermos-tolerance of the bacterial isolates showed that only 18 isolates had both characters. These 18 isolates were exposed to high temperature then evaluated for their antagonism. Only 7 isolates kept their potential to suppress the growth of pathogens. This test demonstrated the possibility of losing the antagonism effect as a result of high temperature. In this test 90 °C/24 hours was used. Molecular identification was carried out to on the seven bacterial isolates. They were identified based on 16s rDNA sequencing using universal primers and standard procedures. They were Pseudomonas putida (3 isolates), Bacillus subtilis (2 isolates) and Bacillus megaterium (2 isolates). These species were reported to have a potential as a bioagents and some of their isolates were developed and being used commercially as biopesticide. We do not recommend using Pseudomonas putida as biopesticide because they might have a potential risk for human. They can cause infections in cases of immunocompromised patients It can be concluded that both thermos-tolerance and antagonism are important to have a successful bio pesticide in the arid region. Losing the antagonism after exposing to high temperature showed the importance of evaluating each bio-agent for this character. So far we did not elucidate the mechanism of losing the antagonism. In this experiment, a very high temperature for long time was used however using lower temperatures for shorter periods can reveal different results.


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