Studies on the Interspecific Hybrid between Cosmos sulphureus and C. caudatus with Special Reference to Flower Color and Pigments

Abstract

(1) Cosmos caudatus is a wild species indigenous to Burma. It bears a striking resemblance in the morphology of flowers, Ieaves ancl seeds to Cosmos sulphureus which is a popular cultivated species. The forrrrer species shows a bright pink flower color which lacks in the latter species. There is a possibility in breeding a new hybrid with pink colored flowers of sulphureu.s type, if the interspecific hybridization between the two species is successful. (2) Since 1966, the reciprocal crosses between these species have been made, and five F₁ plants were obtained (Table 1). Although four of them were corn.pletely sterile, one colchicine-treated plant produced 15 seeds on two fiower-heads of the lowest branch. From these seeds, offsprings with some fertility were obtained and now the F₇ plants are grown (Fig. 1). (3) The F₁ hybrids showed a reddish orange flower color. In. the F₅ generation, how ever, inclividuals with bright pink flower appeared and their offspring bred true as to this color. Though this hybrid is desirable in flower color, it is, at present, far from being used as a practical variety because of the too tall plant height, too late ffowering time and poor fertility (Fig.1, Table 2). Hunter's color chart of the parent species and their hybrids are represented in Fig.4.