Control of Rhizoctonia solani in Sugar Beet and Effect of Fungicide Application and Plant Cultivar on Inoculum Potential in the Soil

Abstract

Rhizoctonia solani (AG 2-2 IIIB) is the causal agent of Rhizoctonia root and crown rot, a disease that causes severe economic problems in sugar beet growing areas worldwide. In the United States, azoxystrobin is the most important active ingredient for fungicidal control of R. solani in sugar beet, showing efficacy superior to other substances. First reports on resistance development in R. solani, however, underline the importance of a careful fungicide resistance management. For this reason, the efficacy of a new fungicide mixture of azoxystrobin and difenoconazole was compared with a fungicide containing only azoxystrobin. Field trials were carried out under natural infection conditions as well as with inoculation in the years 2012, 2013, and 2014. Evaluation of the disease severity and the obtained white sugar yield of different sugar beet cultivars demonstrated that both fungicide treatments possess a similar efficacy, reducing the diseased beet surface by up to 78% and preventing yield losses. Additionally, a real-time PCR assay, based on DNA extracts from representative soil samples (250 g), was used to directly determine the effect of chemical treatment and plant cultivar on the soil-borne inoculum. Fungicide application significantly reduced the concentration of soil-borne inoculum by up to 97%. Furthermore, the results demonstrated that the cultivation of a susceptible cultivar significantly increases the concentration of R. solani in the soil by a factor of 200. In conclusion, the study implies that only a combination of resistant cultivar and fungicide application can prevent an accumulation of R. solani inoculum under conducive conditions in infested fields.

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

“…In the specific case of Rhizoctonia-induced diseases, quantification of the soil inoculum was found to be useful in different contexts. For example, it was used to assess rice cultivar susceptibility to R. solani AG 1-IA [26] to assess the impact of different crop rotations on the inoculum levels of a specific AG and its main host plant [27,28], and to map the inoculum level at the field scale to make site-specific fungicide applications to limit the local transmission of the pathogen [29]. A positive correlation between R. solani soilborne inoculum and disease incidence or severity was found for several R. solani AGs and their host plants under controlled experiments [19,30], but fewer studies confirmed this relationship in field experiments [31].…”

Identification, pathogenicity, fungicide sensitivity and biological control of Rhizoctonia solani associated with damping-off disease of sugar beet in Morocco

“…Indeed, for a long time, the application of fungicides with different modes of action has been generally accepted to improve diseases protections synergistically, as well as to minimize the emergence of fungicide resistant strains in the elds (Gisi 1996). Azoxystrobin and difenoconazole synergism was well con rmed during the management of R. solani damping-off and root rot in sugar beet (Bartholomäus et al 2017).…”

Selection Pressure Pathways and Mechanisms of Resistance to the Demethylation Inhibitor-Difenoconazole in Penicillium expansum

“…High control efficacy of DIF has been reported in several ascomycetes such as Phacidiopycnis spp., Venturia inaequalis, Colletotrichum spp., Marssonina coronaria, Alternaria spp., and Fusarium spp. ( Munkvold and O’Mara, 2002 ; Villani et al, 2015 ; Fonseka and Gudmestad, 2016 ; Cao et al, 2017 ; Dang et al, 2017 ; Ali et al, 2018 ) and the basidiomycete Rhizoctonia solani ( Bartholomäus et al, 2017 ). Given the widespread occurrence of resistance to two of the three current postharvest fungicides and the stringent limitations to new postharvest fungicides registration, DIF could be a valuable additional tool to manage blue mold of pome fruit in the years to come if used appropriately and if its efficacy against other major postharvest diseases is proven.…”

“…It is pre-mixed with FDL and commercially available as Academy™ (Syngenta Crop Protection). Difenoconazole (DIF) has a systemic activity and broad-spectrum antifungal potency as shown recently ( Hof, 2001 ; Fonseka and Gudmestad, 2016 ; Bartholomäus et al, 2017 ; Dang et al, 2017 ; Jurick et al, 2017 ; Koehler and Shew, 2018 ; Ali et al, 2018 ). DMIs, such as DIF, target the sterol 14α-Demethylase Cytochrome P450 ( CYP51 ), an essential component of fungal membrane sterols required for a proper membrane functioning ( Rodriguez et al, 1985 ; Joseph-Horne and Hollomon, 1997 ).…”