Location: Crop Genetics Research Unit
2013 Annual Report
All of the entries in the 2012 Mississippi State Variety trials were evaluated for stem canker resistance. The results were published in Plant Disease Management Reports. The 2012 growing season was abnormally hot throughout the season. Therefore, stem canker may not have had time to develop in the Maturity Group IV entries. There are still several entries in the trials which are susceptible to stem canker. Any entry rated above a 2.0 has the potential to have several yield losses due to stem canker.
All of the entries in the 2012 trials have been evaluated for frogeye leaf spot in greenhouse and field studies. The results were published in Plant Disease Management Reports. Entries from every maturity group were susceptible to frogeye leaf spot. Even though a large number of frogeye susceptible varieties are planted, losses to frogeye leaf spot have been minimal in recent years. This is probably because of the widespread use of foliar applied strobulurin fungicides. With the emergence of strobulurin resistant frogeye cultures, the incidence of this disease is sure to increase.
The entries in the 2012 trials were inoculated with the purple leaf stain fungus at the R5 growth stage. The results were published in Plant Disease Management Reports. Many entries were susceptible to this disease. This is usually the foliar disease which causes the largest yield losses in Mississippi. Foliar applied fungicides are erratic in the control of this disease.
Black root rot is becoming a problem in areas where soybeans are grown in soil with a history of being cropped to cotton. This fungus also causes black root rot of cotton. Cool wet conditions are needed early in the growing season for this disease to become a problem. The entries in the 2012 trials were inoculated with the black root rot fungus in the field. The disease failed to develop, therefore, we are in the process of evaluating the entries in growth chamber studies. We should finish our evaluations this summer.
A trial was planted late in 2012 to evaluate soybean rust resistance. However, no rust developed in the trials.
Seed were collected from a foliar fungicide trials and plated out to determine the incidence of purple leaf stain and Phomophsis on the seed. There were significant differences in incidence of both purple leaf stain and Phomophsis in some of the trials.
Seed treatments were evaluated in plots inoculated with Rhizoctonia solani or Pythium species for percent seedling survival and soybean yield. Several of the seed treatments significantly increase yields over the untreated seed.
Purple pod rot and Phomophsis seed decay diseases were evaluated by collecting mature green soybean pods of each variety from the field, surface disinfecting them, and placing them in humidity chambers. The pods were inoculated with spores of Cercospora kikuchii (purple pod rot) or Phomophsis longicola (Phomopsis seed decay) and incubated for two weeks. There were significant differences in purple pod rot ratings. We have isolated several cultures of this fungus and are testing them for virulence. Phomophsis seed decay incidence was high. Most of the varieties were susceptible to this disease. However, there was a range of reactions to this disease and some entries had more resistance than others.
The black root rot trials conducted in the growth chamber are ongoing. Most of the entries were susceptible to black root rot. This disease may become a major problem as more soybeans are grown on land previously cropped to cotton.