Members of F. oxysporum are present throughout the world's soils. However, before global transportation, many of the different varieties of the pathogen were isolated. Now, global trade has spread F. oxysporum inoculum with the crop. A recent example of this is the spread of Fusarium oxysporum f.sp. cubense which may have originated in Asia and just recently has appeared in banana producing areas in the South Pacific.
Inoculum can originate from many sources. F. oxysporum conidia and chlamydospores can attach to the outside of seeds. Commercial seed companies must practice proper sanitation techniques, or the seed can carry its own inoculum to the grower's field. This has been demonstrated with the seeds of various legumes, tomatoes, sugarbeet, aster, oil palm, and more. Vegetative cuttings can also carry inoculum or the live pathogen. Importantly, plants used for cuttings carrying no outward symptoms of infection may still transmit the pathogen. This has become a problem in some greenhouse floral crops like Crysanthemum and Carnation. The pathogen's sporodochia and other inoculum sources may also be spread by soil movement and shipment of nonhost plants carried with infected soil.
Certain rare soils are said to be "Fusarium-suppressive," that is, given two soils with high populations of infective F. oxysporum in the soil and the proper hosts, one soil will have a lower incidence of Fusarium wilt. Study of these soils is ongoing, but the decreased disease rate is thought to be due to other soil flora.
Read more about this topic: Fusarium Wilt
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