Effect of soil physical conditions on emission of allyl isothiocyanate and subsequent microbial inhibition in response to Brassicaceae seed meal amendment

Authors: WANG, LIKUN - Washington State University; Mazzola, Mark

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2018
Publication Date: 3/11/2019
Citation: Wang, L., Mazzola, M. 2019. Effect of soil physical conditions on emission of allyl isothiocyanate and subsequent microbial inhibition in response to Brassicaceae seed meal amendment. Plant Disease. 103:846-852. https://doi.org/10.1094/PDIS-08-18-1389-RE.
DOI: https://doi.org/10.1094/PDIS-08-18-1389-RE

Interpretive Summary: Apple replant disease is incited by a pathogen complex composed of multiple fungal, oomycete and nematode species. Brassicaceae seed meal amendments can provide control of numerous plant pests, including a number of the agents contributing to apple replant disease. Pest control in response to brassicaceae seed meal amendments may result in response to the generation of biologically active chemistries, such as the generation of allyl isothiocyanate (AITC), or indirectly through transformation and activity of the resident soil biology. Studies were conducted to examine the effect of soil physical conditions on the generation of AITC in response to soil amendment with a one-to-one formulation of Brassica juncea and Sinapis alba seed meals. Soil water potential and temperature both influenced the production of AITC in seed meal amended soil. AITC generation was highest in moist soils and was severely limited when seed meal was applied to excessively dry or wet soils. Differences in AITC production were also observed among the different orchard soils, with the highest levels observed in a Burch loam soil and lowest level observed in a high organic matter gravelly sandy loam soil. Various fungal and oomycete plant pathogens demonstrated differences in sensitivity to AITC with Pythium spp. being highly sensitive to this chemistry. Overall, findings indicate that managing the soil conditions through either irrigation or seasonality of seed meal amendment to correspond with elevated soil temperatures can be used to maximize production of AITC and associated soil-borne disease control.

Technical Abstract: Generation of allyl isothiocyanate (AITC) in soil treated with residues of specific Brassica species yields direct and indirect suppression of soil-borne plant pathogens. Soil physical conditions demonstrably affected quantity of AITC generated in response to soil incorporation of a Brassica juncea:Sinapis alba seed meal (SM) formulation. Concentration of AITC generated in SM-amended soil increased with an increase in temperature from 10 to 30°C. Production of AITC was also elevated with an increase in soil moisture from 'T -1000 kPa through 'T -40 kPa; however, a significant decrease in AITC generation was observed in a saturated soil environment (0 kPa). Peak AITC emission from soil was obtained 2 to 3 h post-SM amendment under optimal conditions but the peak was delayed in soils incubated at low temperature or extreme moisture environments. At the same soil moisture and temperature, AITC production varied significantly across different orchard soils. When SM was applied at 2.2 t ha-1, maximum AITC production was observed in a Burch loam soil incubated at 30°C and 'T -40 kPa. AITC-induced inhibition of fungi/oomycete mycelial growth was affected by both concentration and duration of the exposure period. Pythium ultimum exhibited sensitivity to AITC, with growth restricted at concentrations ranging from 0.01 to 0.22 µg g-1 soil while Hypocrea lixii was insensitive to AITC with no restriction of hyphal growth observed after 96 h incubation. Exposure to AITC at a concentration of 0.22 µg g-1 soil for a period of 2 h, restricted hyphal growth of Rhizoctonia solani AG-5, Ilyonectria destructans, and Mortierella alpina. Rhizoctonia solani AG-5 exhibited significant growth inhibition when incubated in the presence of AITC at concentrations 0.008 to 0.011 µg g-1 soil for as long as 8 h. These findings provide information that will be useful in monitoring and management of appropriate soil variables to obtain optimal soil-borne disease control efficacy in response to SM soil amendments.