Date Published: April 18, 2019
Publisher: Public Library of Science
Author(s): Laurencja Szała, Zygmunt Kaczmarek, Wiesława Popławska, Alina Liersch, Marek Wójtowicz, Marcin Matuszczak, Zdzisław R. Biliński, Katarzyna Sosnowska, Michał Stefanowicz, Teresa Cegielska-Taras, Maoteng Li.
Resynthesized (RS) Brassica napus can be used to increase the genetic diversity of this important crop plant and to develop the heterotic gene pool required for successful hybrid breeding programmes. The level of heterosis in F1 hybrids depends on the individual performance of the parents and on the degree of genetic difference between them. However, RS forms obtained from crosses of B. rapa ssp. with B. oleracea ssp. possess many undesirable agronomic traits, such as low quality of seeds, low yield and seed oil content, high erucic acid level in the oil and high glucosinolate content in seed meal. Therefore, RS oilseed rape needs to be improved by crossing with natural double-low oilseed rape, leading to selected double-low quality semi-RS lines that can be used for breeding. In this study, we evaluated the seed yield potential of F1 hybrids derived from crosses between Ogura cytoplasmic male-sterility (CMS) lines and doubled haploid (DH) semi-RS lines with restorer gene in three locations in Poland. The genotype by environment interaction (GE interaction) and general combining ability (GCA) of the restorer and CMS line effects, as well as the effects of heterosis, were also assessed. The results of the study provide the first insights into the use of semi-RS lines as components for the development of new hybrid cultivars. Even the introduction of 50% of the RS oilseed rape genotype to natural restorer lines resulted in a marked heterosis effect, with seed yield ranging from 4.56% to 90.17% more than that of the better parent. The yield of the best hybrid amounted to 108.6% of the seed yield of the open-pollinated cultivar Monolit and 94.4% of that of the hybrid cultivar Arsenal. The best DH semi-RS line S1, which had a significantly positive GCA for seed yield, can be recommended as a possible parent for inclusion in breeding programmes aimed at developing new hybrid cultivars.
Oilseed rape (Brassica napus L.) is considered a relatively young species. Although its origin is not yet fully explained, it is thought that B. napus was formed as a result of multiple spontaneous and independent hybridizations of B. rapa and B. oleracea on the coast of northern Europe, where both diploid parental species grow wild. Other researchers believe that oilseed rape originated in the Mediterranean region or in western or northern Europe . It is also possible that B. napus could have formed elsewhere from crosses between different forms of B. oleracea and B. rapa . Based on the sequencing of its polyploid genome, Chalhoub et al. have suggested that the hybridization that gave rise to B. napus occurred about 7500 years ago .
Analysis of the seed yield of fifteen F1 hybrids, three semi-RS DH lines with restorer gene, five Ogura CMS lines and two cultivars, Arsenal and Monolit, as controls was carried out on the results obtained from three locations. The mean values of seed yield and the degree of heterosis over mid-parent and the better parent are presented in Table 1. The highest mean yield for all genotypes was obtained in Wiatrowo. The mean seed yield over all locations was 20.06 dt·ha-1 and in individual genotypes (hybrids and their components) ranged from 14.03 to 27.46 dt·ha-1. The low yields in the season in question were a result of unfavorable weather conditions. For comparison, an year earlier (2014/2015) at COBORU (Research Center for Cultivar Testing) experimental stations located in south-western Poland, where Bąków is located, cv. Monolite and Arsenal yielded 39.3 and 47.1 dt·ha-1, respectively and two years earlier (2013/14)– 50.9 and 59.6 dt·ha-1, respectively. Whereas, at COBORU experimental stations located in the region of Poland, where Cerekwica and Wiatrowo are located, the Monolit and Arsenal cultivars yielded 39.3 and 43.8 dt·ha-1in the season 2014/15 and 49.4 and 50.9 dt·ha-1in the season 2013/2014, respectively .
Resynthesized B. napus has gained much interest for its high genetic diversity compared to natural oilseed rape cultivars: this diversity is especially beneficial to hybrid breeding programmes [23, 24, 25]. However, it is difficult to create a new gene pool based directly on RS lines because of their unfavorable agronomic traits, including low yield, poor seed quality [26–27] and self-incompatibility. Other reports have indicated that RS oilseed rape may be crossed with natural oilseed rape to produce semi-RS lines for developing male sterility lines or introgression of new genes for specific breeding procedures, thereby broadening the genetic diversity of this crop [28–29]. In vitro androgenesis from the F1 hybrids provides the possibility of obtaining large populations of homozygous semi-RS DH lines from which the desired genotypes can easily be selected. In our research, RS plants were used as pollinators in crosses with two double-low restorer lines of winter oilseed rape. From two F1 hybrids, 801 semi-RS DH lines were obtained, from which the S1, S3 and S4 lines were selected for the presence of the Rfo gene, self-compatibility, low glucosinolate content and the absence of erucic acid .
This study represents the first insights into the application of semi-RS DH lines as paternal components for the development of new hybrid varieties. The introduction of 50% of a resynthesized oilseed rape genotype to natural restorer lines is sufficient to deliver a high heterosis effect. The semi-RS DH line S1, which has a significant GCA for seed yield, can be recommended as a potential parent for inclusion in breeding programmes aimed at developing new hybrid varieties.