Food attraction and population growth of fungivorous nematodes with different fungi

Food attraction of the fungivorous nematodes Aphelenchus avenae and Aphelenchoides spp. to seven fungal species (Pyrenochaeta lycopersici, Botrytis cinerea, Rhizoctonia solani strains AG 3 and AG 2‐1, Verticillium dahliae, Pochonia bulbillosa, Mortierella hyalina and Trichoderma harzianum) was determined on agar plates by counting the number of test nematodes present on the mycelium of each fungus 24 h after inoculation. Population growth of A. avenae and Aphelenchoides spp. on five of the seven fungi included in the attraction test (P. lycopersici, R. solani strain AG 3, V. dahliae, P. bulbillosa and T. harzianum) was also determined on agar plates by counting nematode numbers every week during a 6‐week period. A. avenae and Aphelenchoides spp. were attracted to all the fungi tested. A. avenae was preferentially attracted to V. dahliae (P < 0.0001), and Aphelenchoides spp. did not show any preference except for low attraction to R. solani. A. avenae and Aphelenchoides spp. reproduced on all fungal species tested. After 6 weeks of incubation, the highest number of nematodes was found on P. lycopersici and P. bulbillosa, while the lowest number occurred on R. solani for A. avenae and on T. harzianum for Aphelenchoides spp. The suitability of a fungus as a host was not clearly related to the attraction to that fungus.     

Root bacteria from nematicidal plants and their biocontrol potential against trichodorid nematodes in potato

Trichodorid nematodes (Nematoda: Trichodoridae) are vectors of tobacco rattle virus (TRV), one of the causal agents of spraing disease in potato. Root bacteria from nematicidal plants and their control potential against Trichodoridae were the focus of this study. Bacteria isolated from the roots of 12 nematicidal plants and potato were characterized for their production of hydrolytic enzymes, hydrogen cyanide, phenol oxidation ability and antifungal activity towards the potato pathogen Rhizoctonia solani. Based on these functional traits, bacteria isolates were selected and tested in greenhouse conditions on potato (cv. Saturna) for their effect on plant growth, and screened for nematicidal activity against Paratrichodorus pachydermus and Trichodorus primitivus in naturally infested soil. Sixteen bacteria isolates out of 44 reduced nematode densities by 50–100%. Nine selected isolated were further tested by bacterizing potato tubers (cv. King Edward) which were planted in a trichodorid and TRV-infested soil. Four bacterial isolates consistently reduced nematode densities (by 56.7–74.4%) with no visual negative effect on plant growth. These isolates were tentatively identified, partly by fatty acid methyl ester (FAME) analysis as: Stenotrophomonas maltophilia, Bacillus mycoides, Pseudomonas sp., and one unidentified bacterium. The isolates originated from potato, Plantago major, Thymus vulgaris and Asparagus officinalis, respectively. Two Pseudomonas isolates obtained from Zinnia elegans and selected for their strong nematicidal activity in soil screening tests, did not reduce the nematode population when tested on potato. It is concluded that plants releasing nematicidal compounds may harbour nematode-antagonistic bacteria as well.