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

Thérèse Wallon,Hervé Van Der Heyden,Andréanne Sauvageau

doi:10.3390/plants10010057

Abstract

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 Rhizoctonia solani. 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 Rhizoctonia solani-induced diseases in lettuce is based on good agricultural practices, which require detailed knowledge of the pathogen. In this study, Rhizoctonia solani 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. Rhizoctonia solani 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 R. solani AG1-IB and R. solani. The AG 1-IB qPCR assay amplified all strains of R. solani AG 1-IB tested, and no PCR product was obtained for any non-target strains. The R. solani qPCR assay amplified all strains of R. solani and did not amplify non-target strains, except for two strains of binucleate Rhizoctonia 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 R. solani and R. solani 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.

Highlights

In southwestern Québec (Canada), lettuce is an important crop with an annual production of about 3500 metric tons, representing 62% of Canada’s production [1]
Sequencing of the internal transcribed spacer region (ITS) conducted on 60 R. solani isolates collected from infected lettuce showed that 95% of the isolates belonged to anastomotic groups (AGs) 1-IB, 3.3% to AG-BI, and 1.7% to AG 1-1C (Figure S1)
The closest sequences to our AG-BI isolates came from pathogenic AG-BI strains isolated from lettuce in Belgian greenhouses [16]

Summary

Introduction

In southwestern Québec (Canada), lettuce is an important crop with an annual production of about 3500 metric tons, representing 62% of Canada’s production [1]. In this area, lettuce is mainly grown in muck soils from late April to early October, predominantly through the use of transplants. Lettuce is mainly grown in muck soils from late April to early October, predominantly through the use of transplants This production is threatened by several soilborne diseases. Rhizoctonia solani (Kühn) is a ubiquitous soilborne plant pathogen capable of infecting the seedlings, roots, leaves, and stems of a multitude of vegetable plants, causing a variety of diseases [3]. The first symptoms often occur as golden-brown lesions on leaf

Objectives

Methods

Conclusion