Trichoderma biocontrol against Fusarium basal rot in onion

Published: 8 August 2018| Version 2 | DOI: 10.17632/d8cdzdz83j.2
Contributor:
Adele Bunbury-Blanchette

Description

*In all data T.viridescens was misID'd and should be Trichoderma koningiopsis. 7 Trichoderma species were identified from agricultural soil of the Annapolis Valley, NS, and were evaluated for biocontrol potential of Fusarium oxysporum f. sp. cepae (FOC), the cause of Fusarium basal rot in onion. Dual culture growth measurement data: Plates of each combination (FOC + Trichoderma sp.) were 1. simultaneously inoculated with both fungi, 2. Trichoderma was added after 72 h, and 3. single-fungus control plates for each species. Radial colony growth of species along the center diameter was measured daily for 7 days, as well as widest diameter, and then every other day until 14 days. Measurements are provided individually for each species in each condition. "Trial" in 'FOC axenic growth.xlsx' refers to the Trichoderma species being tested in a concurrent dual culture trial; axenic FOC plates were prepared alongside each separate batch of dual culture plates. "Tghh" reflects dual culture plates with each of T. gamsii, T. hamatum, and T. harzianum prepared concurrently. FOC virulence bioassays data: FOC was used to inoculate soil distributed into pots. Eight treatments were prepared as concentrations of FOC spores per gram of soil (s/g): 0 s/g (control), 5 s/g, 10 s/g, 50 s/g, 1000 s/g, 5000 s/g, 10 000 s/g, and 100 000 s/g. 25 Mountaineer onion seeds were planted per pot. All treatments did not occur concurrently (described by "trial"). Pots were monitored daily for 2 weeks then weekly for 2 weeks. Number of emerged onion seedlings was recorded, disease symptoms of resulting seedlings were evaluated, and dead seedlings noted. For analysis, each seedling was rated as ‘asymptomatic’, ‘infected’, or ‘un-emerged/dead’. This count was totaled and pooled to create a variable of onion health per pot. Trichoderma treatment bioassays data: Two assays were completed testing the effect of addition of Trichoderma species on FBR symptoms on onions. Methods were as in FOC virulence bioassays using 1000 s/g, except Trichoderma treatments were added. In dual culture, percent inhibition of radial growth (PIRG) was calculated after seven days growth: PIRG=(R1-R2)⁄R1 x 100. R1 = radial growth of FOC in axenic culture, R2 = radial growth of FOC in dual culture. Median toxicity of FOC on onion in virulence bioassay was estimated as well as toxicity of the 1000 s/g treatment. Symptoms were considered as proportion of seedlings with symptoms per pot on the final day of observations (day 28) for models. Treatment conditions were compared to the 0 s/g FOC condition (virulence bioassay) or the FOC-only condition (Trichoderma treatment bioassays). General linear models were fit. T. gamsii most inhibited FOC growth in dual culture. Soil inoculated with 1000 s/g FOC produced approximately 65% toxicity in onion seedlings; application of T. atroviride and T. harzianum significantly reduced FBR symptoms in greenhouse grown onions in FOC inoculated soil.

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