Detection and Quantification of <i>Rhizoctonia solani</i> and <i>Rhizoctonia solani</i> AG1-IB Causing the Bottom Rot of Lettuce in Tissues and Soils by Multiplex qPCR

• Main Authors: Thérèse Wallon, Andréanne Sauvageau, Hervé Van der Heyden
• Format: Article
• Language: English
• Published: MDPI AG 2021-12-01
• Series: Plants
• Subjects: bottom rot of lettuce; <i>Rhizoctonia solani</i>; AG 1-IB; AG-BI; multiplex qPCR; plant detection
• Online Access: https://www.mdpi.com/2223-7747/10/1/57

In the muck soil region of southwestern Quebec, vegetable growers are threatened by several soilborne diseases, particularly the bottom rot of lettuce caused by the fungus <i>Rhizoctonia solani</i>. The particularly warm temperature of the few last seasons was marked by an increase in disease severity, and the associated yield losses were significant for Quebec lettuce growers. In the absence of registered fungicides and resistant cultivars, the management of <i>Rhizoctonia solani</i>-induced diseases in lettuce is based on good agricultural practices, which require detailed knowledge of the pathogen. In this study, <i>Rhizoctonia solani</i> fungal strains were isolated from infected field-grown lettuce plants presenting bottom rot symptoms to determine the anastomotic groups (AGs) of these isolates by internal transcribed spacer region (ITS) sequencing. <i>Rhizoctonia solani</i> AG 1-IB was identified as the main anastomotic group causing bottom rot lettuce in field-grown lettuce in organic soils in the Montérégie region. Two specific and sensitive quantitative PCR assays were then developed for <i>R. solani</i> AG1-IB and <i>R. solani</i>. The AG 1-IB qPCR assay amplified all strains of <i>R. solani</i> AG 1-IB tested, and no PCR product was obtained for any non-target strains. The <i>R. solani</i> qPCR assay amplified all strains of <i>R. solani</i> and did not amplify non-target strains, except for two strains of binucleate <i>Rhizoctonia</i> AG-E. In artificially inoculated soils, the sensitivity of both qPCR assays was set to 1 μg of sclerotia g⁻¹ of dry soil. In the growth chamber experiment, a minimum concentration between 14 and 42 μg sclerotia g⁻¹ of dry soil was required to induce the development of symptoms on the lettuce. Indeed, the AG 1-IB qPCR assay was sensitive enough to detect the lowest soil concentration of AG1-IB capable of inducing symptoms in head lettuce. In addition, the qPCR assays successfully detected <i>R. solani</i> and <i>R. solani</i> AG 1-IB from infected plant tissue samples and soil samples from lettuce fields. The qPCR assays developed in this study will be useful tools in lettuce bottom rot management.