Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: ENHANCING PATHOGEN DETECTION AND CROP PROTECTION IN SUGARBEET USING MOLECULAR TECHNOLOGIES

Location: Sugarbeet and Potato Research

Title: Temperature, Moisture, and Fungicide Effects in Managing Rhizoctonia Root and Crown Rot of Sugar Beet

Authors
item Bolton, Melvin
item Panella, Leonard
item Campbell, Larry
item Khan, Mohmamed -

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 31, 2010
Publication Date: June 1, 2010
Repository URL: http://hdl.handle.net/10113/43487
Citation: Bolton, M.D., Panella, L.W., Campbell, L.G., Khan, M.F. 2010. Temperature, Moisture, and Fungicide Effects in Managing Rhizoctonia Root and Crown Rot of Sugar Beet. Phytopathology. 100(7):689-697.

Interpretive Summary: Rhizoctonia solani causes Rhizoctonia root and crown rot disease in sugar beet. This fungus is divided into groups called anastomosis groups (AGs) which can be further divided into subgroups. We tested 15 AGs and subgroups for their ability to cause disease on a resistant (FC708 CMS) and susceptible (Monohikari) seedlings and 10-week old plants. Several AGs and subgroups were pathogenic on seedlings regardless of whether the sugar beet was resistant, but only AG-2-2 IIIB and AG-2-2 IV caused significant disease on 10-week old plants. To assess how temperature affects Rhizoctonia root and crown rot, the disease was evaluated in climate controlled settings of 7 to 22 growing degree days (GDDs) per day. The results showed that disease increased as the temperature increased and that maximum disease symptoms occurred at 22 GDDs per day. However, there was no disease when plants were grown at 11 GDDs per day. To assess how ground moisture affects Rhizoctonia root and crown rot, the disease was evaluated at 25, 50, 75, and 100% moisture holding capacity (MHC), a technique that measures the amount of water soil can hold, regardless of the soil type used. Disease was highest in wet soils, but disease still occurred in dry soils. The fungus was also tested for the ability to cause disease at 1, 4 and 8 cm from the plant hypocotyl. Only AG-2-2 IIIB was able to cause disease symptoms at 8 cm during the evaluation period. In all experiments, isolates of AG-2-2 IIIB were found to be more aggressive than AG-2-2 IV. Using environmental parameters we identified as the most conducive to disease development, the fungicides azoxystrobin, prothioconazole, pyraclostrobin, difenoconazole/propiconazole, flutolanil, polyoxin D, and a water control were evaluated for their ability to suppress disease development by AG-2-2 IIIB and AG-2-2 IV 17 days after planting. Flutolanil, polyoxin-D, and azoxystrobin provided the highest level of disease suppression. Since R. solani AG-2-2 IIIB and AG-2-2 IV are affected by temperature and moisture, growers may be able to evaluate environmental parameters for optimization of fungicide application.

Technical Abstract: Rhizoctonia solani AG-2-2 is the causal agent of Rhizoctonia root and crown rot in sugar beet. To assess the capacity at which other anastomosis groups (AGs) are able to infect sugar beet, 15 AGs and subgroups were tested for pathogenicity on resistant (FC708 CMS) and susceptible (Monohikari) seedlings and 10-week old plants. Several AGs and subgroups were pathogenic on seedlings regardless of host resistance, but only AG-2-2 IIIB and AG-2-2 IV caused significant disease on 10-week old plants. Root and leaf disease indices were used to evaluate disease progression of AG-2-2 IIIB- and AG-2-2 IV-inoculated plants in controlled climate conditions from 7 to 22 growing degree days (GDDs) per day. Root disease ratings were positively correlated with increasing temperature of both ISGs, with maximum disease symptoms occurring at 22 GDDs per day. No disease symptoms were evident from either ISG at 10 GDDs per day, but disease symptoms did occur in plants grown in growth chambers set to 11 GDDs per day. Using growth chambers adjusted to 22 GDDs per day, disease was evaluated at 25, 50, 75, and 100% moisture holding capacity (MHC). Disease symptoms for each ISG were highest in soils with 75 and 100% MHC. Isolates were tested for their ability to cause disease at 1, 4 and 8 cm from the plant hypocotyl. Only AG-2-2 IIIB was able to cause disease symptoms at 8 cm during the evaluation period. In all experiments, isolates of AG-2-2 IIIB were found to be more aggressive than AG-2-2 IV. Using environmental parameters we identified as the most conducive to disease development, azoxystrobin, prothioconazole, pyraclostrobin, difenoconazole/propiconazole, flutolanil, polyoxin D, and a water control were evaluated for their ability to suppress disease development by AG-2-2 IIIB and AG-2-2 IV 17 days after planting. Flutolanil, polyoxin-D, and azoxystrobin provided the highest level of disease suppression. Since R. solani AG-2-2 IIIB and AG-2-2 IV are affected by temperature and moisture, growers may be able to evaluate environmental parameters for optimization of fungicide application.

Last Modified: 9/10/2014
Footer Content Back to Top of Page