![]() ![]() ![]() (iii) Crop rotation, late sowing, early thinning, good tillage, early irrigation, and adding potash to soil help reduce disease incidence. (ii) Since the bacteria contained in infected stalks buried in moist soil die after sometime, deep ploughing after harvest helps reducing disease incidence. (i) Diseased plant debris should be removed and burnt. However, primary infection is favoured by a temperature of 30☌ and secondary infection by 35☌ temperature. Severity of the disease ranges up if it rains accompanied with strong winds. High relative humidity and high moderate temperatures favour disease incidence. They are spread in the field mainly by wind supported rain splashes, enter inside the host, and result in disease development. Secondary infections are caused during the same growing season by bacteria that ooze out from primary infections. The pathogen inoculum occurring in infected seeds lying dormant in soil, in un-decomposed plant debris, or brought into soil by sowing infected seeds causes primary infection on cotton plants. It has been studied that the bacteria may remain viable upto 17 years in un-decomposed plant debris. They inhabit seeds either internally or externally as slimy mass on the fuzz. The pathogen perennates on or in the seeds, and on un-decomposed plant debris lying on the ground. It occurs singly or in pairs and does not develop endospores, Colonies developed on beef agar medium are circular, pale yellow, raised, smooth and shining. It is a rod-shaped, uniflagellate, aerobic. ![]() The pathogenic bacterium has been formerly named Xanthomonas malvacearum, Pseudomonas malvacearum, Bacterium malvacearum, Bacillus malvacearum, and Phytomonas malvacearum. For instance, black arm infection is most serious in Sudan, Egypt, and Uganda seedling blight commonly occurs in USA and, the angular leaf spot and ball-rot infections cause severe damage in India. The bacteria may invade and rot the balls and cause them to drop or to become distorted if predisposing conditions prevail in the field.Įither all type of symptoms appears on the same plant or anyone of them appears and causes severe damage. Stems and branches so infected are, sometimes, girdled and killed.Ĭotton balls or fruits also show water-soaked spots which turn dark-brown to black and become sunken. This has given the name “black arm” to the disease. Stem and fruiting branches of the plant show long, dark-brown to black, sunken lesions covering almost their whole circumference. The leaves so infected generally curl, die, and fall off. In later stages, the spots on leaves become angular (hence the name “angular leaf-spot”) brown to black, and may coalesce forming large lesions. Leaves also show small, water-soaked spots first on the undersurface and then on the upper surface. Later on, they increase in size, turn brown to black, form irregular patches distorting the shape of the cotyledons, drying and withering (i.e., blight) of the seedlings, and, finally, the death of the seedlings hence the name “seedling blight”. Small, round, water-soaked spots appear on the undersides of cotyledons. Symptoms are produced almost on all the aerial parts of the plants seedling cotyledons, leaves, stem and fruiting branches, and cotton bolls or fruits show different types of symptoms.Ĭotyledons of seedlings show the first symptoms. Since then the disease has been reported occurring time and again from states like Maharashtra, Andhra Pradesh, Gujarat, M.P., and U.P. In India, the disease was first reported from Tamil Nadu (then Madras State) in 1918. Bacterial blight disease occurs wherever cotton is grown in the world, and causes serious Joss. ![]()
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