The Fusarium spp. are predominantly common soil fungi, found in almost all parts of the world as a not-detrimental colonizer of root surfaces or a weak invader of the root cortex of many plants. There are over 80 known strains only of F. oxysporum, which show specific pathogenicity to particular crops, causing the vascular wilt diseases. Mirza and Qureshi (1978) found that most of root infecting fungi including Fusarium spp. are known to attack many cultivated plants and parasitized 36 hosts in Pakistan. The cotton husks, used as cattle feed are identified as a potential source for spread of wilt causing fungus (F. oxysporum f. sp. vasinfectum).

In addition, both the pathogens (Fusarium and Verticillium spp.) are seed-borne, may carry over for long-distance, spread from year to year by sowing infected seed; also move from field to field, farm to farm and region to region, whenever very small quantities of infested soil is transported through boots, farm equipments, vehicles, in water (irrigation and overland flows), in flood irrigation and also in infected plant material, including seed etc. The diseased plant debris lying in the field or in the threshing area also helps both the fungi to remain alive. In case of banana, Fusarium wilt or Panama disease is considered the world’s worst disease and the greatest danger of its spread comes from moving infected suckers (planting material, look like healthy on the outside).

The wilts start appearance at seedling in case of early attack and/or may also occur at any plant growth stage. Symptoms include seed rot, seedling death and wilting, and death of adult plants. Initially, vein clearing and leaves show a distinct loss of turgor and yellowing occurs starting at the leaf margin between the main veins, sometimes referred as leaf epinasty, followed by stunting. The stunted plants may fruit early. The yellowing progresses inward and is followed by necrosis hence defoliation occurs starting at the bottom of the plant, and working towards the top, results progressive wilting of leaves and stem, defoliation and finally death of the plant (partially or wholly). The diseased plants are pulled out easily, due to the loss of rigidity. Brown, red or yellow rings of discolored tissue observed in case of cutting the stem in crossways, mostly close to the base. Fusarium wilt is a solid dark brown ring around the outer portion of the stem, in cross section in the area of the vascular bundles, and that the infected areas observed irregular in shape and size. The wilt diseases mostly spread in patches, but entire field may also be affected in severe conditions. Some formae speciales are not primarily vascular pathogens but Fusarium spp. may cause foot and root rot or bulb rot in cotton.

Preventive and curative control measures
Prevention is better than cure, because control of wilt diseases is very difficult, chemical control is very costly and even is impossible to recover heavily infected, shriveled and damaged plant. However, cultivation of resistant variety is only the most easy, economical and safe method. Growers are advised to plant improved immune or resistant varieties, because these are equal to the susceptible varieties in yield, adaptation and other cultural characteristics and field practices; since new races of the fungi may develop and attack on these. However, it is necessary that growers must keep in touch with the latest information on resistant varieties and control measures. The following preventive measures also help to minimize risk of damage.

• Avoid cultivation of susceptible varieties/cultivars in the diseased area at least for three years.
• Clean cultivation through deep and repeatedly tillage operations help to destroy infected plant parts from field.
• Good drainage improves soil conditions which help to minimize the disease incidence.
• Use of disease free seed or seed treatment with suitable seed dressing fungicides before sowing is also recommended.
• In some cases, late and deep sowing reduces disease incidence.
• Mixed cropping of with non host crops help to check the disease.
• Uprooting and burning of diseased plants minimize further spread of the problem.
• Avoid storage of plant waste material and even threshing in the field, otherwise sweeping the threshing floor and burning or burying all plant debris must be ensured.