• Conservation, sources d'inoculum
  

Rhizobium radiobacter (Agrobacterium tumefaciens) is able to live saprophytically in soil for at least 2 years . It can also stay on and in plant debris. Contaminated water and soil can be sources of contamination. This bacterium must be able to maintain itself in the substrates if they are not replaced. It affects many cultivated, fruit and ornamental plants, including apple, apricot, cherry, peach, grapevine, rose, aster, chrysanthemum. Several vegetables, in addition to tomatoes, have galls: beetroot, turnip… These plants, when grown near tomato plots or produced in the same greenhouse, can constitute sources of inoculum.

• Penetration and invasion

The plant is often penetrated by wounds forming on the roots or the stem near the surface of the soil or the substrate, following cultivation operations, damage linked to pests or due to frost, etc. Motile bacterial cells are chemotaxically attracted to the root as a result of the release of sugars and other compounds in the rhizosphere.

Once in place, it stimulates the rapid and anarchic division of the surrounding plant cells. Indeed, the insertion of part of its genome into that of the plant leads to the overproduction of growth regulators (cytokinins and auxins, which cause cell proliferation) and opins which will serve as nutrients for the bacteria. . Most of the genes involved are not on the chromosome R. radiobacter , but originate from a plasmid Ti tumor-inducing which is an extra-chromosomal DNA fragment. The tissues continue to grow locally and the tumors gradually enlarge, resulting in reduced transport of water and nutrients in the plant. The bacteria seem to multiply in intercellular spaces, at the periphery of tumors.

• Multiplication and dissemination

R. radiobacter can be transmitted by water and contaminated soil particles to other plants or crops. Workers in the course of their activities in crops, with agricultural machinery on wheels loaded with clods of earth, can ensure the dispersion of this bacterium. It is found in the substrates and nutrient solution of soilless crops. It is not impossible that it could be disseminated by the latter.

• Conditions favorable to its development

High temperatures favor its development.