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Title: Mid-infared (MidIR) and near-infared (NIR) dection of rhizoctonia solani AG 2-2 IIIB on barley based artificial inoculum

item Webb, Kimberly
item Calderon, Francisco

Submitted to: Applied Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2015
Publication Date: 10/1/2015
Citation: Webb, K.M., Calderon, F.J. 2015. Mid-infared (MidIR) and near-infared (NIR) dection of rhizoctonia solani AG 2-2 IIIB on barley based artificial inoculum. Applied Spectroscopy. 69:1129-1136.

Interpretive Summary: In this work, we document the value of using infrared spectroscopy to differentiate between barley grain infected with crown rot fungi from clean barley grain. Fungal inoculants are used to test for disease susceptibility of sugarbeet cultivars, and it is challenging to produce inocula of consistent quality year to year. Our findings are important because spectroscopy is a relatively quick and easy procedure that will facilitate the production of infected barley inoculum for field trials.

Technical Abstract: The amount of Rhizoctonia solani in the soil and how much is needed to cause disease in sugar beet (Beta vulgaris L.) is relatively unknown. This is mostly because of the usually low inoculum densities natually found in soil, and the low sensitivity of traditional serial dilution assays. We investigated the usefulness of using Fourier-transform mid-infared (MidIR) and near-infared (NIR) spectroscopic properties to identify the artificial colonization of barley grains with R. solani AG 2-2 IIIB to detect R. solani in plant tissues and inoculants. The objectives of this study were to compare the ability of traditional plating assays to NIR and/or MidIR to identify R. solani from different sized fractions of colonized ground barley that is being used as an artifical inoculum from un-inoculated barley. NIR and MidIR were sensitive in resolving different barley particle sizes, with the <0.25 mm and 0.25-0.5 mm particles having different spectral properties relative to the more coarse particles. We found that barley colonized with R. solani had diffent MidIR spectral properties than un-inoculated samples in the larger fractions (0.5-1.0 mm, 1.0-2.0 mm and >2.0 mm) of the ground barley. This colonization was confirmed by traditional plating assays. Comparison with the spectra from pure fungal cultures and un-inoculated barley suggests that the colonized barley MidIR is different because of consumption of grain C substrates by the fungus, rather than by the presence of fungal bands in the colonized samples. MidIR was better than NIR in resolving colonized from control samples.