Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2011
Publication Date: 4/2/2012
Citation: Vargas, M., Loyola, C., Zapata, N., Rivera, V., Secor, G., Bolton, M.D., France, A. 2012. First report of root rot of Chicory caused by Phytophthora cryptogea in Chile. Plant Disease. 96(4):591. Interpretive Summary: Chicory is grown for the production of inulin in Chile. Inulins are sugars extracted from chicory roots that are used in some processed foods. Recently, a severe rot of 1-3% of mature roots in the field and after harvest has been observed in most fields causing yield and quality losses. Typical symptoms include a brown discoloration and a soft, watery decay of the root. The pathogen was isolated from diseased tissue and based on culture characteristics and molecular data, the pathogen was identified as Phytophthora cryptogea. These isolates were used to re-infect chicory plants by incubating chicory roots together with P. cryptogea inoculum. After four days, symptoms similar to those observed in the field were present. To our knowledge, this is the first report of Phytophthora root rot of chicory caused by P. cryptogea in Chile.
Technical Abstract: Chicory (Cichorium intybus L. var sativum Bisch.), a relatively new high value crop in Chile, was introduced for commercial production of inulin. Inulins are polysaccharides extracted from chicory tap roots that are used in processed foods due to their beneficial gastrointestinal properties. Approximately 3000 ha of chicory are grown in the BioBio region near Chillan in south central Chile for local processing. Recently, a severe rot of 1-3% of mature roots in the field and after harvest has been observed in most fields causing yield and quality losses. Typical symptoms include a brown discoloration and a soft, watery decay of the root. Tissue pieces from symptomatic roots were placed on water agar and clarified V8 juice agar medium amended with antibiotics for isolation of the causal pathogen. A Phytopthora species had been consistently isolated from root lesions and axenic cultures using single-hypha transfers. The species was provisionally identified as P. cryptogea (Pethybridge and Lafferty, 1919) based on morphological and cultural characteristics (1). Mycelia grew between 5 and 30ºC, with optimal growth at 20-25ºC and no growth at 35ºC. All isolates produced nonpapillate, persistent, internally proliferating, and ovoid to obpyriform sporangia. The isolates were mating type A1 as they produced oospores only when paired with reference isolates of P. cinnamomi A2 on clarified V8 juice agar amended with thiamine, tryptophan, and ß–sitosterol (1) after 20 days at 20ºC in the dark. On the basis of morphological and sequence data from cytochrome c oxidase subunit 1 and 2, internal transcribed spacer 2, and ß-tubulin (GenBank Accession Nos. JQ037796-JQ037798, respectively), the pathogen was identified as Phytopthora cryptogea. Pathogenicity tests were conducted using three isolates of P. cryptogea by placing a 7-mm-diameter disk from a 1-week-old V8 agar culture on ten wounded and non-wounded healthy chicory roots. Control roots were inoculated with agar plugs free of P. cryptogea. The inoculated roots were incubated at 20ºC in a moist chamber. Root rot symptoms, typical of those observed in the field and storage, developed after 4-6 days only on inoculated wounded sites with the pathogen, and P. cryptogea was reisolated from these inoculated plants. Control root and non-wounded inoculated-pathogen roots remained healthy. This experiment was completed two times and the results were similar. To our knowledge, this is the first report of Phytophthora root rot of chicory caused by P. cryptogea in Chile.