Biology, epidemiology

• 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 melon, present galls: tomato, beetroot, turnip ... These plants, when cultivated near plots of melon or produced in the same greenhouse, can constitute sources inoculum.

• Penetration and invasion

Plant penetration often occurs through wounds forming on the roots or stems near the surface of the soil or substrate, as a result of cultivation operations, pest damage or frost? ?. 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 genes are on the chromosome of ' R. radiobacter , but come from a plasmid Ti inducing tumor that is a DNA fragment extra-chromosomal. 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.

• Sporulation and dissemination

R. radiobacter can be transmitted to other plants or crops by water and contaminated soil particles . 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.