Abstract
The present research work was carried out for the development of hexaploid Brassica (AABBCC) through interspecific crossing within the U-triangle of Brassica followed by chromosome doubling during August 2002 to April 2005. The study included 23 genotypes comprising of six genotypes of B. rapa var. 'yellow sarson', one genotype, each of B. rapa var. 'toria', B. rapa ssp. chinensis, B. rapa ssp. pekinensis, B. carinata, B. oleracea var. 'botrytis', B. oleracea var. 'alboglabra' and B. nigra and five genotypes, each of B. juncea and B. napus. The cross combinations consisted of B. carinata (2n=34, BBCC) x B. rapa (2n=20, AA), B. juncea (2n=36, AABB) x B. oleracea (2n=18, CC) and B. napus (2n=38, AACC) × B. nigra (2n=16, BB) and all of their reciprocals. The results showed, on an average, 15.7% successful cross in B. carinata x B. rapa var. 'yellow sarson' and in contrast, 51.7% crosses were successful in their reciprocals. In the crosses of B. carinata x B. rapa var. 'toria', B. carinata x B. rapa ssp. pekinensis and B. carinata x B. rapa ssp. chinensis, the rate of success was found to be 37.5%, 25.1% and 28.1% while in their reciprocal crosses it was found to be lower, i. e., only 11.5%, 8.0% and 14.0%, respectively. In the crosses of B. juncea x B. oleracea, B. napus x B. nigra, and their reciprocals, only B. napus x B. nigra was merely successful (0.26%). The hybrids were intermediate for most of the morphological characters, but had higher vigour than their respective parents and showed 98%-100% pollen sterility and contained 27 somatic chromosomes. Of the two methods followed to induce chromosome doubling in the hybrids, the modified injection method was found to be more effective than the cotton plug method. On an average, achievement in chromosome doubling was 36.4%, 56.0% and 71.8% in the modified injection method and 27.4%, 38.0% and 39.1% in the cotton plug method using 0.10%, 0.15% and 0.20% colchicine, respectively. The chromosome doubled C, hexaploids produced fertile pollens and set siliquae and seeds. On an average, 59% C2 seeds were with 54 chromosomes as expected for hexaploids and; 41% C2 seeds were aneuploids and contained 45 to 57 chromosomes. The C2 hexaploid plants were found to be morphologically intermediate between the parents, but closer to the characters of B. carinata. The C2 plants exhibited a wider range with higher coefficients of variation for all the characters as compared to the parents. Mean pollen fertility and number of seeds per siliqua were lower than their respective parents in the C2 plants. The C2 plants of eight cross combinations had higher pollen fertility, siliqua setting and seeds per siliqua over C1. Mean seed yield per plant in all the C2 plants was found to be lower than their parents except moderate yield in one cross combination. It was also found that a few of the C2 plants of three cross combinations had higher seed yield than their parents. Flowering and maturity period was found to be intermediate between the parents.