|SHARMA-POUDYAL, DIPAK - Oregon Department Of Agriculture|
|LINDERMAN, ROBERT - Oregon State University|
|DU TOIT, LINDSEY - Washington State University|
Submitted to: Plant Disease Management Reports
Publication Type: Other
Publication Acceptance Date: 7/7/2014
Publication Date: N/A
Interpretive Summary: A greenhouse experiment was conducted to determine the ability of Arbuscular Mycorrhizal Fungi (AMF) to reduce onion stunting caused by Rhizoctonia solani AG-8. Commercial AMF inoculum (BioTerra Plus) was tested. Inoculation of soil with R. solani AG 8 reduced onion plant height, shoot, root, and total dry weights. Soil treated with BioTerra Plus had significantly taller onion plants compared to plants in non-inoculated soiland plants in soil inoculated with R. solani AG 8. However, onion seedlings were taller in soil amended with BioTerraPlus alone and BioTerraPlus + R. solani AG 8, respectively, compared with plants growing in soil amended with R. solani AG 8 alone. Therefore, inoculation of soil with AMF increased onion height not only in the absence of the onion stunting pathogen, but also in the presence of this pathogen. Research is needed to assess the potential use of AMF.
Technical Abstract: A preliminary study was conducted in a greenhouse (15 ± 1oC, with supplemental lights for 12 h/day) to determine the role of AMF on onion growth and for reducing the severity of onion stunting, using a commercial AMF inoculant, BioTerra Plus, that contains 104 propagules/g (ppg) of Glomus intraradices and 9 ppg of each of G. mosseae, G. aggregatum, G. clarum, G. etunicatum, G. claroidium, and Gigaspora albida (Plant Health LLC, Corvallis, OR). Four soil treatments were compared: BioTerraPlus, R. solani AG 8, BioTerraPlus + R. solani AG 8, and non-inoculated control soil. Pasteurized soil with a low P concentration (29 ppm) was used in plastic cone-tainers (4 cm x 21 cm, Steuwe & Sons, Corvallis, OR). A two cm thick layer (16 g) of BioTerra Plus was placed on top of 110 g of soil (13 cm deep) in each replicate cone-tainer for the AMF treatment. Sterilized oat grains colonized with R. solani AG 8 were ground just prior to inoculation, and mixed into pasteurized soil (1% w/w for a total soil weight of 130 g = 15 cm deep in the cone-tainer) for the R. solani AG 8 treatment. For co-inoculation of AMF and R. solani AG 8, the same amount of BioTerraPlus as in the first treatment was top-dressed above 110 g soil (13 cm deep) inoculated with R. solani AG 8 (1% w/w). The non-inoculated control soil consisted of 130 g pasteurized soil in each cone-tainer. The soil in each cone-tainer was moistened with 50 ml water just prior to seeding. Four seeds of the onion cv. Talon were planted in each cone-tainer, and covered with 0.5 cm of soil. Treatments were replicated five times and arranged in a completely randomized block design. Onion seedling height, root length, and root and shoot dry weights were measured 60 days after seeding. Analysis of variance and means comparisons were computed with JMP Version 11 Pro (SAS Institute Inc., Cary, NC). Inoculation of soil with R. solani AG 8 reduced onion plant height by 56%, and onion shoot, root, and total dry weights by 73, 70, and 72%, respectively, compared to plants growing in non-inoculated control soil. Soil treated with BioTerra Plus had significantly taller onion plants (average 20.0 cm) compared to plants in non-inoculated soil (15.8 cm) and plants in soil inoculated with R. solani AG 8 (7.0 cm). However, BioTerra Plus alone did not affect onion root length or shoot, root, or total dry weights significantly compared to the control soil, and neither did co-inoculation of the soil with BioTerra Plus + R. solani AG 8. However, onion seedlings were 2.9 and 2.6 times taller in soil amended with BioTerraPlus alone and BioTerraPlus + R. solani AG 8, respectively, compared with plants growing in soil amended with R. solani AG 8 alone. Similarly, soil treated with BioTerraPlus only and BioTerraPlus + R. solani AG 8 produced seedlings 1.3 and 1.2 times taller, respectively, than plants in the control soil. Therefore, inoculation of soil with AMF increased onion height not only in the absence of the onion stunting pathogen, but also in the presence of this pathogen. Research is needed to assess the potential use of AMF for enhancing onion yield in growers’ fields in the Columbia Basin of central Washington and north-central Oregon, particularly in fields with a high risk of onion stunting caused by R. solani.