Sugarcane chlorotic streak disease is caused by a new cercozoan species: Phytocercomonas venanatans
Chlorotic streak is a disease of sugarcane (Saccharum spp.), first observed in the 1930s on sugarcane crops in Australia, Java (Indonesia) and Hawaii (US), which was then observed in other sugarcane-growing areas of the world. The disease is characterized by yellow to creamy-white leaf streaks with irregular wavy margins. Necrotic areas within streaks and leaf tips can also be present, as well as reddening of the vascular bundles at the nodes within stalks. Affected sugarcane crops show reduced height and leaf number. The disease is spread by water and infected planting material. Although significant research has been done on sugarcane chlorotic streak disease, the identification of its causal agent remained unsuccessful for more than 90 years.
Recent studies using HTS techniques detected the presence of a new cercozoan species (in the order of Cercomonadida and belonging to a new genus) in diseased sugarcane plants, which was called Phytocercomonas venanatans. Pure cultures of P. venanatans could be established and inoculation studies confirmed that this new cercozoan species is the causal agent of sugarcane chlorotic streak disease (Koch’s postulates could be completed).
P. venanatans is a single-celled eukaryotic organism. Cells are round to ovoid (6 to 15 μm long), ventrally flattened, and with two flagella. Cercomonads are abundant in soil and freshwater habitats where they are important bacterivores. They are also known to predate other microbial eukaryotes and larger organisms such as nematodes. However, this is the first time that a cercomonad is associated with a disease of a higher plant.
Sources
Braithwaite KS, Ngo CN, Croft BJ (2018) Confirmation that the novel cercozoan Phytocercomonas venanatans, is the cause of the disease chlorotic streak in sugarcane. Phytopathology 108(4), 487-494.
Ngo CN, Braithwaite KS, Bass D, Young AJ, Croft BJ (2018) Phytocercomonas venanatans, a new species of cercozoa associated with chlorotic streak of sugarcane. Phytopathology 108(4), 479-486.