Isolating Crown Rot Disease Organisms in a Nursery Production System

Major production plant losses up to 20% in ‘Big Blue’ liriope container production have been measured in nurseries. Crown rot was suspected of causing these losses due to plant mortality. The objective of this project was to isolate, culture, and confirm the causal organisms responsible for the crown rot symptoms of liriope. Initially, pathogens from diseased tissue of infected plants were cultured for research purposes. Phytophthora palmivora (PP) and Fusarium oxysporum (FO) (liriope leaf and crown rot) were isolated and cultured. A RCBD design with 6 blocks consisting and four disease treatments [no inoculation (control), PP, FO, and PP+FO] were established. Disease free ‘Big Blue’ liriope plants were grown in a covered greenhouse and established for 6 weeks prior to inoculation in 10.2cm plastic containers filled with a fertilized soilless medium. Within 6 weeks symptoms occurred within the PP and PP+FO treatments. A characteristic leaf yellowing and eventual browning of leaves followed by foliage being easily separated from the crown was observed. Also, sunken root lesions were observed in symptomatic and some asymptomatic plants. Fusarium oxysporum symptoms occurred later after 8 to 12 weeks of inoculation. These symptoms were characterized by a golden yellow color and stunted growth for both FO and PP+FO plants. Plant infection rates were slightly lower than some reported field infection levels, however PP and FO cultures were isolated and confirmed for both organisms using Koch’ postulates. Both pathogens were reisolated from the new host and shown to be the same as the originally inoculated pathogen.