WILT is the loss of rigidity and dropping of plant parts (partially or wholly). It is one of the most common and destructive disease of vegetables and fruits. It also attacks many species of wild plants and trees.

In our country 23 different crops, including cotton, rapeseed, mustard, groundnut, linseed, sunflower, gram, mung, moth, mash, lentil, pea, guar, potato, chilly, tomato, cucurbits (vine crops e.g. melons, cucumber etc.), citrus, fruits, banana and guava. are attacked by wilt. Symptoms similar to wilt disease also occur in wheat, maize, sugarcane, sesame, castor, soybean, pigeon pea, mango and papaya.

Wilt is a common feature in those fields which is infested by this disease once and where crops are sown without rotation. The disease causes immense loss to crops. In most cases the farmers are not aware of the problem.

The symptoms, preventive and curative measures are given here for the guidance of farmers as well as a reminder to research fellows and extension workers, so that they may try to find an easy and economical way to fight the disease. It is also expected to guide the breeders to develop and select wilt resistant varieties.

Wilt may be caused by fungi, viruses, nematodes, parasitic flowering plants and insects. These are usually confused with root and crown rots, stem cankers, insect injuries, drought or excess water, soil compaction, and other non-infectious problems.

Bacterial wilt, caused by Ralstonia solanacearum has now become very harmful after fungal wilts. According to Ahmed and Burney (second International Bacterial Wilt Symposium, 22-27 June, 1997), bacterial wilt was first reported in 1968 in potato growing areas of Punjab. The prevalence and incidence of this disease on other crops were lacking, but recent surveys of areas growing potato, tomato and chilli reveal that the pathogen is present in all the four provinces. The incidence of this disease was also reported in tomato and chilli. Isolated cases of wilt pathogen were also identified in peanut, beans and sunflower plants. However, the damage caused by bacterial wilt to the hosts has not been documented.

The most common and destructive diseases is caused by several species of Fusarium and Verticillium fungi, their common names are referred to causal fungus such as Fusarium or Verticillium wilt. Both the fungi differ from each other, but cause similar symptoms. The only reliable method for separating and identifying these diseases is taxonomy of causal fungi. Both can be readily isolated from the diseased plant portions and cultured. Both the fungal wilts thrive with high nitrogen fertiliser, excessive soil moisture, thin stands, and deep cultivation during growing season. Both the fungi survive for longer periods (for at least a decade) in soil on organic matter and even on non-host plant. However, some of the differential general characteristics between both the wilt fungi may also help in identification and control.

The Fusarium spp, predominantly common soil fungi, is found all over the world as a not-detrimental coloniser 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 parasitised 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 even small quantity of infested soil is transported through boots, farm equipment, vehicles, through water (irrigation and overland flows), in flood irrigation and also in infected plant material, including seed etc. Diseased plant debris lying in field or in threshing area also help 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 is from moving infected suckers.

Wilt starts its appearance at seedling in case of early attack and/or may also occur at any stage of plant growth. Symptoms include seed rot, seedling death and wilting, and death of adult plants. Initially, the leaf margin starts growing yellowish 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 starts occurring at the bottom of the plant, and working towards the top which results in progressive wilting of leaves and stem, defoliation and finally death of the plant. Brown, red or yellow rings of discoloured tissue are observed in case the stem is cut 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. Wilt disease mostly spreads 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 is impossible to recover heavily infected and damaged plant.

However, cultivation of resistant variety is 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 minimise 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 minimise 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 minimise 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.