Effect of abyssinian mustard cytoplasm on CC genome of Brassica.

Abstract

Abyssinian mustard (B. carinata, BC genomes, 2n = 34) was repeatedly backcrossed with the broccoli cv. Green Comet (F1 hybrid, B. oleracea var. italica, C genome, 2n = 18). In the process of cytoplasm-substitution, seed fertility increased exponentially as plant chromosome numbers approached 2n = 18. In the BC2 generation, plants with 2n = 18 chromosomes were obtained. Judging from their chromosome associations, they were assumed to be C genome plants with Abyssinian mustard cytoplasm. When these 2n = 18 plants were reciprocally crossed with normal-cytoplasm broccoli plants and some characters compared between the reciprocal F1 plants, alteration of flower shape and male sterility in cytoplasm-substituted plants was attributable to Abyssinian mustard cytoplasm. Photosynthetic rate and chlorophyll content were lower in alloplasmic plants than in normal plants. Alloplasmic plants were more severely damaged than normal cytoplasmic plants when exposed to overnight cold (-5 to -6 deg C for 8 h). Therefore cold tolerance, which is universal in C genome species of Brassica, may be influenced not only by nuclear genes but also by cytoplasmic factors.