Peduncle explants from 12 Brassica oleracea L. lines representing five varieties [broccoli (italica), cabbage (capitata), cauliflower (botrytis), Chinese broccoli (alboglabra), and rapid-cycling B. oleracea] readily regenerated shoots in vitro. Average regeneration rates of more than 75% were obtained for most lines, with up to 35 shoots per explant. Shoots were visible within 7 to 10 days. Initial regeneration was polarized, occurring mainly from the basal end of explants. Linsmaier-Skoog-based medium containing 1 mg BA/liter was suitable for shoot regeneration from all 12 lines tested. Plants were rooted on hormone-free medium and transferred to soil. Chemical name used: benzyladenine (BA).
Mary C. Christey and Elizabeth D. Earle
Peter T. Hyde, Elizabeth D. Earle and Martha A. Mutschler
Production of double haploid (DH) lines is a rapid method of obtaining completely homozygous inbred lines for numerous crops; however, practical trials testing the use of DH onion lines have been limited. DH onion lines were produced from diverse highly heterozygous material in development within the Cornell onion breeding program. These DH lines were evaluated in multiple replicated trials in onion fields in New York as lines and as parents of hybrids to assess the impact and commercial potential of DH onions. Twenty DH onion lines were compared with open-pollinated cultivars developed from the same source germplasm and with a commercial hybrid over two years. The vegetative vigor of the DH lines was comparable to that of related open-pollinated cultivars, showing minimal, if any, inbreeding depression. Two sets of hybrids were produced using the DH lines as males and two different females that are the female parents of the commercial hybrid controls. Therefore, hybrids in each set are half-sibs, and any performance differences are attributable to their DH male lines. In four replicated trials of these hybrids and controls, the experimental hybrids were either not significantly different or significantly better in measures of vegetative vigor compared with conventional half-sib hybrid controls. The vegetative vigor of DH lines, and their derived hybrids, might result from selection of plantlets without deleterious sublethal genes during gynogenesis. The shortened development time and equivalent quality of DH lines compared with the traditionally bred onion inbreds warrant their use. The increased vigor in hybrid combination could be an additional benefit for onion breeding strategies.
Douglas W. Heath, Elizabeth D. Earle and Michael H. Dickson
Cold-tolerant, Ogura male-sterile, somatic hybrid rapeseed (Brassica napus L.) lines were used as maternal parents in two independent introgression experiments. In one experiment, an atrazine-sensitive B. napus (aacc) somatic hybrid was crossed directly with a male-fertile pak choi (B. campestris Chinensis Group, aa) accession. Allotriploid (sac) progeny were then backcrossed to the recurrent pak choi parent. Forty-five percent of the progeny from the first backcross were determined to be diploids (aa). In the other experiment, an atrazine-resistant B. napus somatic hybrid was crossed first to a bridge line. Three additional backcross generations to Chinese cabbage (B. campestris Pekinensis Group) resulted in Chinese cabbage resistant to black rot (Xanthomonas campestris pv. campestris). These materials may be useful for production of B. campestris hybrid vegetable seed.