Induced high yielding mutants in cotton (Gossypium hirsuthum L.)

Mutations are known to enhance the genetic variability of crop plants as the variability at species level has reached the ceiling due to high breeding intensity and rapid erosion of genetic resources. Since spontaneous mutations occur at very low frequency, induced mutations facilitate the development of improved varieties at a swifter rate. Besides the vital role in plant breeding programs, a new role of induced mutations in releasing of gene silencing in transgenic plants has been reported]. Cotton is an economically important crop plant and cultivated in many parts of the world and it is a leading fiber crop, the second best potential source of plant proteins and fifth best oil-producing crop. Cotton (white gold) enjoys a predominant position amongst all cash crops in India. Cotton is an important raw material for the Indian textile industry, constituting about 65% of its requirements. In addition to being the world's most important textile fiber crop, cotton is also an important source of edible oil and protein. By-products such as cotton seed cakes, hulls and cotton stalks are useful in generating several industrial goods. Among the different breeding methods used, mutation induction has been used as an important tool to supplement existing variability and to create additional variability for qualitatively as well as quantitatively inherited traits in cotton, especially various degrees of resistance to biotic and abiotic stress, number of bolls, seed yield and oil content. Well-developed, fresh, uniform and delinted seeds of two tetraploid varieties of cotton (Gossypium hirsutum L.) Var. MCU 5 and MCU 11, were obtained from the Cotton Breeding Centre, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India. After standardization for moisture content at 16% (with glycerol), seeds were irradiated with gamma rays (GR) from a 60Co at the Sugarcane Breeding Institute (ICAR), Coimbatore at doses of 100, 200, 300, 400 and 500 Gy. Another set of seeds were presoaked in distilled water for 8 h and were treated with various concentrations of ethyl methane sulphonate (EMS) and sodium azide (SA) which were prepared in a phosphate buffer solution of pH 6.0 and 3.0 respectively for 4 hours. The seeds treated with chemical mutagens were thoroughly washed in running tap water for 1 h and sown in the pre-irrigated field. The dry seeds without gamma irradiation and soaked in distilled water served as control. The treated seeds along with control were sown in the experimental field of randomized block design during August 1997 with three replications. For each treatment 5 rows of seeds were sown spaced at 75 cm between rows and 45 cm between seeds in a row, with two seeds per hole. In M1 generation, groups of plants (treatment wise) were harvested on a bulk basis. In M2 generation, the plants were analyzed thoroughly and selected based on yield characters with respect to control. The seeds from those plants were collected separately. The selected seeds from M2 generation were advanced to M3 generation and examined for yield characters in February 1998. Selected superior mutant progenies were evaluated in M4 during 1998-1999 and M5 during 1999-2000. Ten mutants were selected based on yield and plant type, by in vivo mutagenesis. Out of these 10 mutants, 6 belong to the variety MCU 5 and 4 belong to the variety MCU 11. The selected characters of each mutant show higher yield characters in each generation. These mutants are now being tested at Central Institute for Cotton Research (ICAR), Regional Station, Coimbatore, Tamil Nadu, for multilocation experiments