Biological products promote tomato growth and induce changes in microbial communities to reduce root-knot nematode infestation

Onyemaechi Henry  Obiazikwor

doi:10.60867/00000089

Tomatoes are the most-grown vegetable globally. Tomato crops are vulnerable to soilborne pathogens, including root-knot nematodes, which can result in complete crop failure. Biological products are promising alternatives to synthetic fertilisers and can induce changes in rhizosphere microbial communities, offering protection against soilborne biotic stressors. This thesis investigated three commercial biological products Popul8 (microbial), Eco-Humate (organic-acid) and Eco-Vital® (fish+seaweed) for their ability to increase tomato crop growth and yield and to reduce root-knot nematode infestation by inducing changes in microbial communities. Field trials were conducted at two farms during the 2022/2023 and 2023/2024 summer tomato cropping seasons in Western Australia. Biological products were applied to tomatoes concurrently with synthetic fertiliser at Farm A (conventional), while Farm B (non-conventional) had only the products applied. Crop biomass, yield, and soil physicochemical properties were measured. DNA from rhizosphere and bulk soil samples was sequenced to assess bacterial and fungal communities at the end of the growing seasons. Crop biomass and yield were higher in biological product-treated plots at both farms. Biological products did not change microbial community composition in any trial; however, relative abundances of beneficial microbes, such as Mortierella and Rhodotorula, were increased. In a second field trial in 2023/24, rhizosphere samples were collected approximately every 4 weeks from seedling to crop senescence, and bacterial and fungal communities assessed by amplicon sequencing. Microbial communities changed across tomato growth stages, particularly at Farm A, and growth stage had a stronger influence on the communities than biological products. However, product application induced changes in abundances of some taxa in a growth stage-dependent manner, including increases in known beneficial bacteria and fungi. The ability of biological products to reduce root-knot nematode (Meloidogyne javanica; RKN) symptoms on tomato crops was tested in a greenhouse trial using soil from the Farm B 2023/24 field trial. Three-week-old tomato ‘Moneymaker’ seedlings were inoculated with M. javanica eggs (~10000/pot) and grown for eleven weeks. Roots were scored for RKN induced galling, RKN eggs were counted from infested roots, and rhizosphere and root samples were sequenced for bacterial communities. Tomato plants grown in preconditioned field soil had significant reductions in galling level, possibly due to higher abundances of bacterial antagonists, such as Streptomyces and Lysobacter. The findings in this thesis have significant practical implications for field-grown tomatoes. The biological products investigated are potential tools worthy of future investigation for integrated management of root-knot nematodes and could serve as an alternative/supplement to synthetic fertilisers for sustainable tomato crop production.

Biological products promote tomato growth and induce changes in microbial communities to reduce root-knot nematode infestation

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