Characteristics
- The flagellates have a long, oval or spherical body with a thin, flexible covering membrane or it may be armoured.
- They have one or more slender flagella, which are used for both locomotion and food capture.
- Many species of the flagellates like Phytomonas have been reported from several plants belonging to the family Euphorbiaceae (P. davide on Euphorbia sp.), Asclepiadaceae (P. almassiani on milkweed), Moraceae (P. bancrofti on Ficus sp.), and Rubiaceae (P. leptovasorum on coffee).
- Some other unknown forms are parasitic on oil palm and coconut palm.
- These parasites seem to be insect- transmitted, though an insect vector has been reported only for P. almassiani.
- Since most of those associated with laticiferous plants do not produce any clear symptoms, there is a feeling that these are just parasites but not pathogens.
- The non-laticiferous plants like coffee, coconut palm and oil palm develop characteristic external symptoms, such as leaf yellowing, wilting and malformation of phloem tissue often leading to considerable damage to the plant and ultimately death.
Phloem necrosis of coffee
- It is caused by Phytomonas leptovasorum and occurs in Suriname, British Guyana, and probably Brazil and Columbia.
- It affects the tree of Coffea liberica and C. arabica. Infected trees show sparse yellowing and dropping of leaves, and, only the young top leaves remain on the otherwise bare branches, followed by death of the trees, sometimes within 3-6 weeks.
- The flagellates can be traced from the roots upward to trunk, where they seem to migrate vertically in the phloem and laterally through the sieve plates into healthy sieve tubes.
- This disease can be transmitted through root grafts but not through green branch or leaf grafts. Its insect vector is a pentatomid Lincus sp.
Hart rot of coconut palms
- Hart rot has been known in Suriname since 1906, sometimes under the more appropriate names of lethal yellowing or bronze-leaf wilt , Cedros wilt and unknown disease.
- Many of the symptoms of hart rot are similar to those caused by lethal yellowing disease of coconut palm in the Caribbean, West Africa, Florida, the cause of the two diseases seem to be unrelated.
- The hart rot symptoms include yellowing and browning of the tips of the older leaves which subsequently spread to the younger leaves.
- Recently opened inflorescences are black , and unripe nuts of the symptomatic trees fall off.
- Flagellates of the genus Phytomonas occur in mature sieve elements of young leaves and inflorescences of hart rot affected coconut palms.
- The number and spread of the flagellates in the sieve tubes increase proportionally with the development of the disease.
- They are also transmitted by the pentatomid insects of genera Lincus and Ochlerus.
Sudden wilt (Marchitez) of oil palm
- The symptoms begin as browning of the tips of the lower leaflets of the oil palms.
- The browning subsequently spreads to the upper leaves and eventually becomes ash grey.
- In the mean time, root tips also begin to die and the whole root system deteriorates.
- As a result, the plant growth slows down, fruit bunches discolour and rot or fall off; and within a few weeks, all leaves become ash grey and dry up and the whole tree dies out.
- Phytomonas flagellates occur widely in the phloem sieve elements of the roots, leaves and inflorescences of the infected plants.
- These flagellates are also transmitted by Pentatomid insects Lincus and Ochlerus.
Empty root of Cassava
- The empty root disease was observed affecting certain cultivars of cassava (Manihot esculenta) in the Espirito Santo state of Brazil.
- Affected plants show poor root development.
- They remain small and slender, and contain little or no starch.
- Above ground parts of the infected plants show chlorosis and decline.
- Diseased plants contain numerous Phytomonas like protozoa in the laticiferous ducts but not in phloem.
- The empty root disease can be transmitted by grafting.
- It also spreads rapidly in the field, probably by the above insect vectors.
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