RHIZOCTONIA FORUM: EPIDEMIOLOGY AND ROTATION CROPS Carol Windels University of Minnesota NW Research & Outreach Center Crookston, Minnesota Moderator: Gary Franc
Why is Rhizoctonia increasing? Favorable weather Susceptible crops sown in rotations - Crops affect populations of R. solani in soil Management Rhizoctonia on sugarbeet - Rotation crops & other cultural practices - Plant resistance - Fungicides
Background: : Rhizoctonia solani Common soil fungus worldwide Infects wide range of plants Field crops, weeds, vegetables, ornamentals Temperature: 55-95 0 F; ideal = 70-85 0 F Soil moisture: variable; ideal = moist - wet
Background: : Rhizoctonia solani Common soil fungus worldwide Infects wide range of plants Field crops, weeds, vegetables, ornamentals Temperature: 55-95 0 F; ideal = 70-85 0 F Soil moisture: variable; ideal = moist - wet Survives In diseased plants (mycelium & sclerotia) Colonizes plant debris Primarily in 0- to 6-inch depth
R. solani a complex species Composed of different populations Anastomosis Groups = AG Sugarbeet seed rot and damping-off: AG: 2-1, 2-2, 2, 4, 5 Rhizoctonia i crown & root rot (RCRR) AG-4 AG-2-2 2IV&AG2 2-2 2 IIIB (intraspecific ifi groups) AG-2-2 2 IIIB grows @ 95 0 F, AG 2-22 IV does not
Rhizoctonia solani AG 2-2 2 ISGs known to attack crops grown in MN & ND Crop R. solani R. solani AG 2-2 IV AG 2-2 IIIB Sugarbeet ++ +++ Soybean ++ +++ Edible beans ++ +++ Corn - + Spring wheat - - - = nonhost ++ = moderately aggressive + = slightly aggressive +++ = severely aggressive
Red River Valley acres sown: 1995 to 2007 FROM: USDA Agricultural Statistics Service
Crops grown before 2007 sugarbeet in SMBSC Corn S. corn Soybean Mix Peas Less than 1% each of: alfalfa, navy bean, potato, set aside, small grain
Prevalence of R. solani AG 2-2 ISGs in RRV & So. MN ~ 970 isolates of R. solani AG 2-2 collected from infected sugarbeet: Red River Valley (465) Traditional small grain rotation Shift to corn/soybean last 10 yr So. Minnesota (504) Sugar beet rotated with corn/soybean since 1975 27% 7% AG 2-2 IV AG 2-2 IIIB Intermediate 66%
Prevalence of ISG in the RRV by previous crop 6% 7% 17% 39% Wheat (227) 77% 54% AG 2-2 IV Edible bean (76) AG 2-2 IIIB Corn? (6) Intermediate 6% 13% Soybean (49) Potato (16) 81%
Prevalence of ISG in So. MN by previous crop AG 2-2 IV AG 2-2 IIIB 6% Intermediate t 25% Corn (301) Soybean (36) Wheat? 69% Edible bean (16) Unknown (133)
Crops rotated with sugarbeet in various regions of USA Michigan (Steve Poindexter): Soybean, dry bean, corn Wyoming (Gary Franc): Dry bean, barley Montana (Gary Franc): Dry bean, barley, spring wheat, corn Idaho (Carl (Carl Strausbaugh): Winter wheat,,p potato, corn, hay, alfalfa
Reasons for variable Rhizoctonia disease Rhizoctonia ISG present Population density Environment Temperature Moisture Soil type Plants Sugarbeet Wheat Corn Beans Weeds
Rhizoctonia control strategies Correct diagnosis of root rot problem Symptoms May require lab analysis
Rhizoctonia
Non-typical Rhizoctonia Aphanomyces
R. solani AG 2-2 2 ISGs effects on: Rotation crops Sugarbeet
Soil inoculated R. solani AG 2-2 IV, IIIB & control Planted to rotation crops followed by sugarbeet
R. solani AG 2-2 2 ISGs & rotation crops Spring wheat No increase on roots No effect on yield Historically, RSA of sugarbeet following wheat (barley) very good on wide range of soil types Soybean Symptoms may/may not be observed Increase populations in both ISGs (IV and IIIB)
Susceptibility of corn to AG 2-2 2ISGs Corn: susceptible to 2-2IIIB 2IIIB No above-ground symptoms No effects on yield Lesions on roots Build-up up ponroots 4/5 field trials
Spring wheat Soybean Corn Not inoculated
Spring wheat Corn Soybean R. solani AG 2-2 IV
Soybean Corn Spring wheat R. solani AG 2-2 IIIB
Corn variety & R. solani AG 2-2 2ISGs Inoculated soil Grew full-season crop of several transgenic corn varieties Planted sugarbeet following year (2 sites)
Non inoculated control following corn
R. solani AG 2 2 IV following corn
R. solani AG 2 2 IIIB following corn
RCRR on sugarbeet also can affect soybean Carry-over roots/root parts of infected sugarbeet are focal points for basal stem & root rot of soybean
Sugarbeet 2007, Soybean 2008
Sugarbeet 2007, Soybean 2008
Sugarbeet 2007, Soybean 2008
Some follow-up questions Ideal rotation of crops to prevent build-up? up? Ideal rotation of crops to reduce R. solani population p in infested fields? Minimum threshold level of R. solani population for disease management? Role of soil moisture & temperature & R. solani population on time of infection, disease development & symptoms? Models to predict conditions favorable for Rhizoctonia diseases?