COIMBATORE: Naturally-coloured cotton has been around for thousands of years. But the crop yield is typically too low and the short fibre unsuitable for mass manufacture of cloth with machines. Researchers at the Tamil Nadu Agricultural University (TNAU) are developing naturally-coloured cotton that will not only eliminate the use of dyes, which are potential pollutants, but is also market-friendly.

The sixth round of trials of coloured cotton crop is set to start in two months on a patch of land on the TNAU campus.Though TNAU conducted trials in 2014 which helped scientists identify a few strains producing lengthy fibres that are strong enough to withstand mid-speed spinning, the cotton had certain flaws. The colour faded out too quickly. "We have been constantly working on the project to improvise the quality of the cotton," said TNAU cotton scientist Amala Balu.

Coloured cotton was found and has been in use since 2,500BC and was grown in parts of Asia and South America. The varieties come in hues of brown, red and green, and are eco-friendly and softer.

Presently , organic clothes brands ensure they use natural colouring agents instead of synthetic dyes. But naturally coloured cotton is a more natural fit in this niche market. In India, the Dharwad centre of the All India Coordinated Cotton Improvement Programme released the first naturally coloured cotton genotype in 2010. But it was more suited for farmers in that region.

Dharwad cotton has managed to overcome some of the challenges associated with coloured cotton and is aimed at producing long fibres that retain colours. TNAU is experimenting with versions which work better in Tamil Nadu soil and weather conditions, said TNAU scientist R Ravikesavan.

"We slowly tried improvising the existing cotton varieties through gene mutation and planted it on 2 to 3 acres of TNAU's land to test them," he said. "We managed to grow stronger fibres but they did not retain the dark dense colour of brown and green," he said.