SPURIOUS SYMPTOMS CAUSED BY INOCULUM CARRIERS USED IN PLANT DISEASE RESISTANCE EVALUATION

Abstract

Symptom development resulting from inoculation and infection with plant pathogens is necessary in order to evaluate plants for disease resistance. The standard technique for infecting soybean (Glycine max) with Fusarium solani, a root rot pathogen, involves inoculation of growth media with infested seed as an inoculum substrate carrying the pathogen. It has been reported that some uninfested substrates can have adverse effects upon shoot growth and root development. These effects also include lesion-like necrosis similar to that caused by soybean root rot pathogens. The objective of our research is to determine if uninfested inoculum substrate affects soybean shoot or root growth and root symptom development. Soybean seeds were planted in media inoculated with seed of red sorghum, white sorghum, or sudan grass that had been infested with Fusarium solani or remained uninfested. After 14 days of growth, foliar and root necrosis scores, shoot and root dry weights, and stand counts were evaluated. When the effect of uninfested seed was compared with that of infested seed, the uninfested treatment caused more severe root rot symptoms and decreased shoot and root biomass by 20% and 15% respectively. Our results indicate that the uninfested inoculum substrate can cause both spurious growth reduction and symptom development that may mislead the researcher conducting soybean variety evaluations for disease resistance.