Characterization of an endophytic bacterium (Pseudomonas aeruginosa), originating from tomato (Solanum lycopersicum L.), and its ability to inhabit the parasitic weed Phelipanche aegyptiaca.

PHELIPANCHE AEGYPTIACA: is an obligate holo-parasitic weedlacking a functional photosynthetic system, which subsists on roots of a wide range of host crops, causing severe losses in yield quality and quantity. The parasite and its host are connected through their vascular system, forming a unique ecological system that enables the exchange of various substances. In a previous study, it was suggested that endophytic bacteria, which naturally inhabit the internal tissues of plants, can also be transmitted from the parasitic weed to its host and vice versa. In the current study, we investigate the characteristics of a previously isolated Pseudomonas sp. PhelS10 strain using both biochemical and molecular methods. This isolate was obtained from tomato plant tissue and was able to reduce P. aegyptiaca parasitism, and thus it may serve as a biocontrol agent. Our results revealed that production of Pseudomonas aeruginosa quinolone signal (PQS) was 2.1 times higher than that of the standard Pseudomonas aeruginosa strain (PAO1), which contributed to a 22% higher biofilm formation capability. PhelS10 strain was detected in the xylem of tomato plants using FISH analysis. In addition, PhelS10 strain was found in the parasitic weed's inner tissues, confirming the hypothesis that endophytic bacteria traffic between the host plant and its parasitic weed.

Host-Parasite-Bacteria Triangle: The Microbiome of the Parasitic Weed Phelipanche aegyptiaca and Tomato-Solanum lycopersicum (Mill.) as a Host.

Broomrapes (Phelipanche/Orobanche spp.) are holoparasitic plants that subsist on the roots of a variety of agricultural crops, establishing direct connections with the host vascular system. This connection allows for the exchange of various substances and a possible exchange of endophytic microorganisms that inhabit the internal tissues of both plants. To shed some light on bacterial interactions occurring between the parasitic Phelipanche aegyptiaca and its host tomato, we characterized the endophytic composition in the parasite during the parasitization process and ascertained if these changes were accompanied by changes to endophytes in the host root. Endophyte communities of the parasitic weed were significantly different from that of the non-parasitized tomato root but no significant differences were observed between the parasite and its host after parasitization, suggesting the occurrence of bacterial exchange between these two plants. Moreover, the P. aegyptiaca endophytic community composition showed a clear shift from gram negative to gram-positive bacteria at different developmental stages of the parasite life cycle. To examine possible functions of the endophytic bacteria in both the host and the parasite plants, a number of unique bacterial candidates were isolated and characterized. Results showed that a Pseudomonas strain PhelS10, originating from the tomato roots, suppressed approximately 80% of P. aegyptiaca seed germination and significantly reduced P. aegyptiaca parasitism. The information gleaned in the present study regarding the endophytic microbial communities in this unique ecological system of two plants connected by their vascular system, highlights the potential of exploiting alternative environmentally friendly approaches for parasitic weed control.