ABSTRACT
Cotton has received attention of geneticists since more than a century. Gossypium hirsutum, the predominantly cultivated cotton species worldwide, has a narrow genetic base. It is important to broaden its genetic base through introgression of novel alleles from related species. Here, we report the development and characterization of a backcross population derived from the hybridization of a ‘synthetic’ (derived by crossing and chromosomal doubling of nonprogenitor Gossypium species) and natural tetraploid upland cotton. ‘Synthetic’ was observed to be male-sterile and thus, was used as the female parent. A total of 7434 flowers were pollinated to obtain 1868 BC1F1 seeds by direct and reciprocal crosses. Characterization of the experimental plant material was conducted in the field for several morphological traits such as pubescence on the stem, leaf, petiole and bract, presence/absence of petal spot, petal margin colouration and stamen filament colouration. Genetic analysis revealed that petal margin colouration phenotype was governed by a single dominant gene, whereas the petal spot and filament colouration phenotypes manifested segregation distortion. None of the BC1F1 plants was devoid of trichomes thus demonstrating that presence of trichomes is dominant over their absence. Modern upland cotton cultivars are usually devoid of petal spot, petal margin colouration and stamen filament colouration. These floral anthocyanin pigmentation characteristics, if fixed in the cotton germplasm, may serve as diagnostic features for the identification of cultivars during DUS testing as well as in the maintenance breeding programmes
ABSTRACT
From the first test cross progenies of control (no larval transfers; no ethyl methanesulphonate), physical stress (two larval transfers; no ethyl methanesulphonate) and 0·75% ethyl methanesulphonate (two larval transfers; 0·75% ethyl methanesulphonate)- treated F1 (Oregon Κ + /dumpy black cinnabar, dp b cn) males of Drosophila melanogaster, respectively, 6,10 and 52 wild-looking first test cross males were again test crossed to obtain second generation. The overall percentages of male recombination detected in the second test cross progenies, in the three sets of experiments, were statistically the same as those in the first test cross progenies. Thus the enhanced male recombination caused by physical stress (with or without ethyl methanesulphonate) was transmitted to next generation. Non-reciprocal male recombination was observed in dp b but not in b cn region in both first and second test cross progenies. Three abnormalities, (i) production of wild-type flies in majority over dp b cn type, (ii) Non-Mendelian segregation at dp b and cn loci and (iii) sex-ratio differences for dp b cn and + b cn types observed in test cross progenies of F1 males of Drosophila melanogaster were transmitted to next generation when induced with 0·75 % ethyl methanesulphonate but not when these abnormalities were induced with physical stress. The data suggest possible association of non-reciprocal male recombination, segregation distortion and sex-ratio imbalance in Drosophila melanogaster. In fact these may be representing different aspects of the same phenomenon.