Oxysporum, scientifically referred to as Fusarium oxysporum or F. oxysporum, is a plant pathogen. It has a number of specialized forms that include Fusarium oxysporum asparagi (the kind that causes disease in asparagus), F. oxysporum callistephi (the kind that causes disease on the plant China aster), and F. oxysporum cubense (the kind that causes wilting on bananas), according to Crop Knowledge Master.
F. oxysporum has a variety of hosts that include sugarcane, garden beans, cowpeas, potatoes, baby's breath and cultivated zinnia. The symptoms of the pathogen include yellowing of the plant, root rot, corn rot and vascular wilt, according to Crop Knowledge Master.
Vascular wilt is an important disease caused by the F. oxysporum because it affects the seedling stage of the plant. When plants are attacked at this stage, they often die. The symptoms of older plants attacked by F. oxysporum include vein clearing and leaf epinasty, which is then followed by stunting and yellowing, according to Crop Knowledge Master.
F. oxysporum produce three types of asexual spores. These include the macroconidia, microconidia, and chlamydospores. Macrconidia spores have between three and five cells that are curved at the ends. These spores are often found on the surface of the plants killed by F. oxysporum. Microconidia spores have between one or two cells. They are the type most often produced by the pathogen and are located within the actual vessel of infected plants, according to Crop Knowledge Master. Chlamydospores are round spores that have between one and two cells. They have thick walls that are created in either older mycelium (vegetative part of the fungus) or in macroconidida.
F. oxysporum enters the plant through the roots and spreads to its vascular system, throughout the plant. It can also invade the plant with its sporangial germ tube or the mycelium, according to Crop Knowledge Master. Once inside the plant, the mycelium grows within the cells, through the root cortex. When the mycelium reaches the xylem, it invades the vessels. It remains in the vessels and moves up toward the stem and the top of the plant. Then the mycelium branches and produces microcondidia, which is carried to the plant's sap stream. The mycelium can penetrate the upper wall of the xylem vessel when the microconidia germinates and produces the next vessel.
F. oxysporum is considered a warm-weather disease that is generally found in sandy and acidic soil. It can remain in the soil for up to 10 years, according to Mui-Yun Wong at North Carolina State University. The optimal soil and air temperature for the pathogen is about 28 degrees Celsius. If the air temperature is cooler but the soil temperature is optimal, F. oxysporum will extend into the lower sections of the plant's stem. This case is very dangerous because the plant will not exhibit any external symptoms. The pathogen's strength is also increased by certain micronutrients found in the soil, as well as ammonium nitrogen and phosphorus.