Phytophthora species causing root and crown rot on castor bean (Ricinus communis) in Brazil

Castor bean (Ricinus communis) is a crop of great economic importance in Brazil. It is used for producing oil used in the manufacture of cosmetics and biodiesel. The genus Phytophthora contains pathogens with a wide range of host plants, including ornamentals, fruit and vegetable crops. Among the symptoms induced by Phytophthora species are collar and root rot. This study aimed to identify Phytophthora species causing collar and root rot in castor bean seedlings in the Federal District and test their pathogenicity. Samples of symptomatic plants were collected in four satellite cities in Distrito Federal, Brazil. Fourteen isolates were obtained, and they were initially identified through the morphology of reproductive structures. The isolates were subjected to molecular characterization using phylogeny of the sequences from the ITS region and the Cytochrome Oxidase II gene. Ten isolates of the pathogen were tested for pathogenicity on seedlings of two castor bean accessions and species known to be hosts of P. nicotianae. The isolates were identified as P. nicotianae (12 isolates) and P. palmivora (two isolates). In the pathogenicity test, all isolates were capable of causing disease in castor beans. The isolates of P. nicotianae and P. palmivora varied in pathogenicity to other plant species. This is the first report of P. nicotianae causing collar and root rot in castor bean in the Central-West Region of Brazil. It is also the first report of P. palmivora causing diseases in castor beans in South America.