Phytomonas spp.

In vitro cultured trypanosomatid isolated from coconut affected by hartrot (Hart 1) in transmission electron microscopy. (Michel Dollet)

In humans and animals, two Trypanosomatidae genera, Trypanosoma and Leishmania (flagellate protozoa) cause severe diseases, including sleeping sickness, Chagas disease and kala-azar, while Phytomonas -an arbitrary genus- can be phytopathogenic or like symbiont.

First stage symptoms of hartrot on coconut palm - Cocos nucifera- in French Guiana: ascending yellowing, browning and drying up of the leaves. (Michel Dollet).

One group of plant trypanosomes (“Group H” or “Phloemicola”) associated with wilt of coconut palms (hartrot), oil palm (marchitez sorpresiva), coffee trees (Coffee phloem necrosis) and Zingiberaceae flowers (yellow wilt of Alpinia purpurata) in Latin America and in the Caribbean. They are specifically transmitted by heteropterous insects (pentatomid bugs) and multiply in the sap of the plants. They cause important economic damages, and they are responsible of frequent expensive and polluting insecticides treatments in the Amazonian basin. The isolate used in this project originates in coconut palm affected by hartrot in French Guiana: HART1.

Lincus lethifer (Pentatomidae) vector of trypanosomes associated with marchitez of oil palm in Ecuador. (Roch Desmier de Chenon)

Another group (“Group D” or “Old world latex group”) is a symbiont-like. They are also transmitted by heteropterous insects but live in the latex tubes. They don’t cause any disease. There are latex trypanosomes everywhere in several laticiferous plants, especially in euphorbia and asclepiads. For this project, we chose one isolate from Euphorbia pinea (E.M.1) from South of France.

Smear of latex trypanosomatids from an Ecuadorian euphorbia stained Giemsa. (Michel Dollet).

Both groups H and D are phylogenetically distant and there is an extremely different genomic organization between both groups. The chromosome number is 7 in the group H versus 21 in the group D. Because nobody could culture in vitro these trypanosomes before 1982, they are poorly known. Furthermore the world of plant trypanosomes is vast and limits between plant trypanosomes and insect trypanosomes are undetermined. For instance former “insect trypanosomes” (Herpetomonas, Leptomonas, Crithidia) can multiply in plants. Taxonomy of the former “lower trypanosomatids” needs a revision.

Schematic representation of the complete karyotypes of the Phytomonas isolate EM1 from Group D (latex, symbiont-like) isolated from Euphorbia pinea and phloem restricted Phytomonas – Group H - associated with hartrot of coconut: Hart 1 and Hart 4. Each box represents a chromosomal band. The scale is not directly proportional, but tries to represent the actual resolution seen on different pulse field gels. Molecular size markers from Leishmania spp chromosomes are indicated on the left. (Marin C., Dollet, M., Pagès,M., Bastien P. 2009. Infection, Genetics and Evolution. (9) 235-240