Rhizoctonia solani represents an important plant pathogenic Basidiomycota species complex and the host of many different mycoviruses, as indicated by frequent detection of dsRNA elements in natural populations of the fungus. To date, eight different mycoviruses have been characterized in Rhizoctonia and some of them have been reported to modulate its virulence. DsRNA extracts of the avirulent R. solani isolate DC17 (AG2-2-IV) displayed a diverse pattern, indicating multiple infections with mycoviruses. Deep sequencing analysis of the dsRNA extract, converted to cDNA, revealed that this isolate harbors at least 17 different mycovirus species. Based on the alignment of the conserved RNA-dependent RNA-polymerase (RdRp) domain, this viral community included putative members of the families Narnaviridae, Endornaviridae, Partitiviridae and Megabirnaviridae as well as of the order Tymovirales. Furthermore, viruses, which could not be assigned to any existing family or order, but showed similarities to so far unassigned species like Sclerotinia sclerotiorum RNA virus L, Rhizoctonia solani dsRNA virus 1, Aspergillus foetidus slow virus 2 or Rhizoctonia fumigata virus 1, were identified. This is the first report of a fungal isolate infected by 17 different viral species and a valuable study case to explore the diversity of mycoviruses infecting R. solani.
The complete genome of a novel mycovirus, named Rhizoctonia solani flexivirus 1 (RsFV-1), which infects an avirulent strain of Rhizoctonia solani AG 2-2 IV, was sequenced and analyzed. Its RNA genome consists of 10,621 nucleotides, excluding the poly-A tail, and encodes a single protein of 3477 amino acids. The identification of conserved motifs of methyltransferase, helicase and RNA-dependent RNA polymerase revealed its relatedness to members of the alphavirus-like superfamily of positive-strand RNA viruses. Phylogenetic analysis of these fused domains suggested that this virus should be assigned to the order Tymovirales. The recently described Fusarium graminearum deltaflexivirus 1 was found to be its closest relative. However, the whole genome, as well as the encoded protein of RsFV-1, is larger than that of other known members of the order Tymovirales, and unlike all other viruses belonging to this order, its methyltransferase domain is not located at the N-terminus of the replicase. Although genome diversity, as a result of recombination and gene loss, is a well-documented trait in members of the order Tymovirales, no related virus with a comparable genome alteration has been reported before. For these reasons, RsFV-1 broadens our perception about genome plasticity and diversity within the order Tymovirales.
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.
Rhizoctonia solani AG2-2IIIB ist ein bodenbürtiger Pilz, der in Zuckerrüben regelmäßig große Schäden in Form von „Damping-off“ und Später Rübenfäule verursacht. Aufgrund der Biologie des Pathogens ist die Bekämpfung mit pflanzenbaulichen Maßnahmen limitiert und Sorten mit quantitativen Resistenzeigenschaften zeigen einen deutlichen Minderertrag unter Nicht-Befallsbedingungen im Vergleich zu anfälligen Sorten. In den USA stellt eine Fungizidapplikation im Band in BBCH14 die Hauptbekämpfungsstrategie gegen die Späte Rübenfäule dar. Die hervorragende Wirksamkeit dieser Maßnahme ist dort durch zahlreiche Studien dokumentiert. In Deutschland sind bisher keine Mittel zur Bekämpfung von Rhizoctonia solani in Zuckerrüben zugelassen und es liegen auch keine veröffentlichten Untersuchungen zum potenziellen Einsatz von Fungiziden zur Kontrolle der Späten Rübenfäule in europäischen Rübenanbaugebieten vor. Aus diesem Grund wurde die Wirksamkeit eines neuen Fungizides mit einer Wirkstoffkombination aus Strobilurine und Azole unter mitteleuropäischen Anbaubedingungen in einem Versuch mit natürlichem Befall sowie mit künstlicher Inokulation untersucht. Die Effizienz einer Bandapplikation wurde dabei mit einer flächigen Applikation, als Einzel- und Doppelbehandlung, zu unterschiedlichen Zeitpunkten ver- glichen. Genutzt wurden in diesem Versuch zwei zugelassene Sorten mit unterschiedlicher Anfälligkeit gegenüber Rhizoctonia. Die Inokulation führte in der anfälligen Sorte zu einem starken Befall, der deutliche Ertragseinbußen zur Folge hatte. Dagegen konnte in der resistenten Sorte unter den gleichen Bedingungen nur ein geringes Auftreten von Symptomen beobachtet werden, die keine signifikanten Auswirkungen auf den Ertrag hatten. Eine Fungizidbehandlung reduzierte den Befall allerdings um 75%, was aufgrund der höheren Leistung dieser Sorte zu einem signifikant höheren Bereinigten Zuckerertrag führte als in der resistenten Sorte. Eine Bandbehandlung der Fungizide erreichte bei allen getesteten Applikationszeitpunkten eine vergleichbare Kontrolle der Späten Rübenfäule wie eine Flächenbehandlung und könnte damit eine geeignete Maßnahme zur Aufwandmengenreduktion darstellen. Der Versuch verdeutlicht, dass sowohl mit einer direkten chemischen Bekämpfungsmaßnahme als auch durch die Auswahl resistenter Sorten selbst bei starkem Befall stabile Erträge erzielt werden können.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.