Bacterial blight: Once a menacing disease of cotton in India, now tamed and fading from research spotlight

Abstract

Bacterial blight, incited by Xanthomonas citri pv. malvacearum (Xcm), is historically one of the most devastating diseases of cotton globally. In India, the initial documentation of the disease dates back to 1918 and it assumed a great magnitude after 1947, primarily triggered by cultivation of tetraploid cotton, as the earlier cultivated indigenous diploid cotton was naturally resistant to the pathogen, and became widespread during the 1970s. Among 20 races of bacterial blight pathogen documented at global level, Race 18 is the most virulent one and prominent in India. The pathogen inflicts damage at all crop stages, beginning with seedlings. The disease caused regular yield losses of 30%–35% in India and had become a formidable adversary to cotton cultivation in the country; however, over the years its appearance diminished. Much larger gains were apparently achieved when disease was managed with a combination of seed treatment, foliar sprays and bio‐agents. Furthermore, extensive breeding programmes led to development of resistant cultivars, which proved instrumental in managing the disease. The disease exhibited a sharp decline from the beginning of the 21st century and is now no longer a chronic problem in India. This comprehensive review attempts to provide insight into the dynamic nature of bacterial blight threatening cotton cultivation in India during the last century and the underpinning multifaceted research efforts that paved the way for countering the disease. An attempt is made to discuss the qualitative and quantitative studies on genetics of bacterial blight for facilitating the breeding programmes.