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Abstract
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Damping-off disease caused by Phytophthora drechsleri is one of the most devastating diseases of Cucurbitaceae family, especially cucumber in Iran. Fluorescent pseudomonads are able to control plant pathogens through producing different different metabolites including antibiotics, siderophore, hydrogen cyanide and extracellular enzymes. Pyoluteorin is one of the important antibiotics produced by these bacteria which is effective against Oomycetes . In this study, 80 strains of Pseudomonas spp. were isolated from the rhizosphere of cucumber, barley and wheat in different regions in Bushehr province. Polymerase chain reaction (PCR) using PLTBr/PLTBf primers were performed in order to monitor strains harboring pltB gene, the key gene involved in biosynthesis of Pyoverdine antibiotic. Results revealed that among strains tested, 16 strains including BD8, GN2-5, BD10, Gbco2, RN3-4, RN1-8, M2-15, Wh-DN2, WT1-21, WKZ1-87, T26, B1-10, B1-3, B2-14, B4-6 and BT9 had the target gene. Superior strains were selected based on preventing hyphl growth of Ph. drechsleri u through dual culture method on KB and PDA media cultures. Among them three strains M2-15, RN1-8, B2-14 of Bushehr province and three strains CHA0, UTPF101 and UTPF68 had the highest inhibitory effect on pathogen growth. The ability to produce antimicrobial metabolites (volatile compounds, protease and hydrogen cyanide) and plant growth promoting traits (inorganic phosphate solubilization and siderophore production) was measured under in vitro conditions. Then, toain to evaluate the cultivar resistance to the pathogen, the reaction of eight cucumber cultivars including Barracuda, Kashmir, PS 547, Number one, Storom, Phenomeno, Aseel and Sultan was measured againstof disease Ph.drechsleri in invitro condition; Thereafter, the ability of the selected strains on two semi-sensitive cultivars was evaluated in the greenhouse. The results showed that UTPF101 produced the most volatile compounds but the greatest amount of hy
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