Synthesis, morphology and cytogenetics of Raphanofortii (TTRR, 2n=38): a new amphidiploid of hybrid Brassica tournefortii (TT, 2n=20) x Raphanus caudatus (RR, 2n=18)

Amphidiploid Raphanofortii was synthesized by colchicinization of the F-1 h ybrid Brassica tournefortii (TT, 2n = 20)xRaphanus caudatus (RR, 2n = 18). The crossability between these two species, and the cytomorphology of the F , plants and the amphidiploids were investigated. Intergeneric hybrids betw een the species were obtained only when B. tournefortii was involved as fem ale parent. The hybrid plants were intermediate for most of the morphologic al attributes and showed very low pollen fertility compared to the parents. Although a majority of the pollen mother cells of the dihaploid hybrid (TR , 2n = 19) harboured univalents, a maximum of six bivalents were also obser ved. Of the 37 colchicine-treated F-1 plants analyzed cytologically, 21 wer e found to be true amphidiploids (2n = 38), whereas seven were mixoploids. Meiosis in the amphidiploids was characterized by the occurrence of 19 biva lents, though multivalents and univalents were also observed in a few cells . Most of the amphidiploid plants exhibited a fairly high pollen and seed f ertility, which was further enhanced with the advancement of generations. O ut of 69 plants investigated in the A(2) generation, 64 were euploids while the remaining five were aneuploids (2n = 36, 37, 39, 40 and 42). The newly synthesized Raphanofortii has great potential as a new commercial crop, as well as a bridge species for the transfer of economically important attrib utes of both the species to other Brassicas.