New generation hybrids of white cabbage (Brassica oleracea L. convar. capitata var. alba DC) based on doubled haploids

Presently, cabbage breeding is mainly focused on F1 hybrids necessitating constant parental lines to be obtained. Doubled haploid (DH) technology based on isolated microspore in vitro culture is widely used to produce pure lines of brassica crops. This method allows us to rapidly develop homozygous lines, in contrast to time-consuming traditional breeding for heterosis in cross-pollinating crops which takes 7 to 10 years for annuals and 14 to 20 years for biennial plants. One of the objectives of DH technology is to provide the all possible number of doubled haploid plants that allows more fully encompass the spectrum of genetic recombination, including the recessive locus. The aim of our study was to evaluate economically important traits in white cabbage ( Brassica oleracea L. convar. capitata var. alba DC) constant doubled haploid lines of late ripening and to improve the technology for producing DH based F1 hybrids. Eleven breeding lines of late ripening cabbage were used to obtain doubled haploid lines from microspore in vitro culture. Of the obtained lines, twelve doubled haploid genotypes were selected for further use based on evaluation of ploidy and combining ability. Seed progeny was reproduced by hybridization of regenerated plants in a climatic chamber (2014-2015). We used the schemes of creating self-incompatible lines and two-line-based hybrids. In the field trials (Moscow region, 2014-2015), the doubled haploids and their hybrid combinations were compared to the standard (Severyanka F1) for the main valuable characteristics (i.e. the content of dry matter, nitrates, and vitamin C). The field resistance to Fusarium wilt, alternariosis, and pest damage were determined at cabbagehead technical maturity. The resistance to clubroot was assessed under artificial infection. There was a direct relationship of the average number of chromosomes to the number of chloroplasts in the stomata guard cells and the length of guard cells. The frequency of spontaneous doubling of the chromosomes numbers varied from 50.0 % to 87.5 % in different geotypes. A total of 11 to 73 % produced lines were high self-incompatible. Their geitonogamic pollination in the topcrosses resulted in 42 hybrid combinations. The model of F1 hybrid most fully responding to consumer market demands was developed. Ten promising hybrid combinations which matched the model parameters in two-year field testing were recommended for variety testing. Hybrids were characterized by uniformity, high biochemical quality, the resistance to major diseases and pests and the yield of 104.60±8.27 t/ha. The dry matter content reached to 10.5 %, the sugar content was about 4.21-5.10 %, and ascorbic acid level ranged from 21.12 to 38.70 mg%. Both the highest level of ascorbic acid (92.0 mg%) and the smallest nitrate accumulation (33 mg/kg) were characteristic of one hybrid combination