Rapeseed breeding programs are focused mainly on improving plant potential and seed yield. One of the ways to improve seed yield in oilseed rape is heterosis, which is hybrid vigor that results in a greater biomass, increased seed yield, and faster development. The purpose of this study was to estimate yield-related trait heterosis for single cross and three-way cross hybrids of winter oilseed rape (Brassica napus L.). A population of 60 doubled-haploid (DH) lines and two generations of hybrids were evaluated in field trials to assess six yield-related traits: plant height, number of branches per plant, number of siliques per plant, silique length, number of seeds per silique, and thousand seed weight. Heterosis effects for each trait were estimated by a comparison of the particular hybrid with: (1) the trait mean over both parents—mid-parent heterosis and (2) to the value of better parent—best-parent heterosis. Traits with clear positive heterosis and traits with varied heterosis were observed in this study. For the first group, we include plant height, silique length, and the number of seeds per silique—a large number of hybrids expressed significant positive heterosis for these traits, independent from the year of observations and the type of hybrid. For the second group, with varied heterosis, we can include the number of branches and siliques per plant and thousand seed weight. For these traits, hybrids exhibited both positive and negative significant heterosis, without a clear pattern for the years and types of hybrids.

Rapeseed (Brassica napus L.) meal is an important source of protein, but the presence of anti-nutritional compounds, such as fibre and glucosinolates, still limits its use as a livestock feed. Understanding the genetic basis of seed fibre biosynthesis would help to manipulate its content in seeds of oilseed rape. Here, we applied high-resolution skim genotyping by sequencing (SkimGBS) and characterised 187,835 single-nucleotide polymorphism (SNP) markers across a mapping population subsequently used for a genetic mapping study (R/qtl). This approach allowed the identification of 11 stable QTL related to seed quality traits and led to the identification of potential functional genes underlying these traits. Among these, key genes with a known role in carbohydrate metabolic process, cell wall, lignin, and flavonoid biosynthesis, including cellulase GH5, TT10/LAC15, TT4, and SUC2, were found. This study furthers the understanding of the molecular mechanisms underlying seed fibre content and provides new markers for molecular breeding in B. napus.

The identification of markers responsible for regulating important agronomic traits in rapeseed supports breeding and increases the seed yield. Microsatellite (SSR) markers are mainly used as ‘neutral’ genetic markers but are also linked with many biological functions. The objective of this study was identification of microsatellite markers associated with important agronomic traits affecting the seed yield of winter oilseed rape and with the heterosis effect for these traits. The plant material consists of four parental lines, 60 doubled haploid (DH) lines, 60 single cross hybrids, and 60 three-way cross hybrids. The association between molecular markers and observed traits was estimated using regression analysis. Among 89 SSR markers, 43 were polymorphic, and 15 were selected for mapping because they demonstrated stability in both years of observation. These markers were physically mapped in the rapeseed reference genomes and their immediate vicinity was searched to identify candidate genes associated with the studied traits. Six markers (BrGMS3837, BnEMS1119, BrGMS2901, BnGMS0509, BrGMS3688, BrGMS4057), which showed a positive estimation effect in our association analysis, and thus increased the value of a given trait or heterosis effect, turned out to be linked with genes that could be responsible for the development and growth of plants.

The plants have developed several defense mechanisms to counteract pathogens. Among others, it includes activation of antioxidant enzymes likeβ-glucosidase and guaiacol peroxidase (GPX). These proteins participate in the oxidation of phenolic compounds, contributing to their increased fungitoxicity. The study aimed to analyze changes in the activity ofβ-glucosidase and GPX in four genotypes of winter oilseed rape (Mendel, Monolit, Polka, line L1425) inoculated with seven isolates:Alternaria brassicicola,Alternaria brassicae,Alternaria alternata(3 strains),Ulocladium chartarum(syn.A. chartarum), andCladosporium cladosporioides. We noted that the varieties of oilseed rape, tested fungal species, and time of the plant material collection had significant (P < 0.001) effect on the activity ofβ-glucosidase and GPX per protein and fresh matter content comparing to the control group.A. brassicicolacaused the highest mean increase inβ-glucosidase and GPX activity in all examined genotypes, while other pathogens had a lower impact. Significantly lowerβ-glucosidase activity inoculated by various pathogens was noted between the L 1425 line and other varieties. GPX activity was in the opposite, the lowest activity was recorded in the Mendel variety, and the highest in the L 1425 line.

Limited genetic variability is a major problem in rapeseed breeding, whose strict selection, limited geographical range and a short period of domestication has led to a reduction in genetic and phenotypic diversity. Assessing specific populations for the greatest genetic diversity for many traits simultaneously, requires the evaluation of multi-feature characteristics. The aim of this study was to estimate the variability of DH (doubled haploid) lines and two generations of winter oilseed rape hybrids. In addition, the relationship between the Mahalanobis distances of parental forms and the effect of heterosis in hybrids was investigated. The results of MANOVA showed that the genotypes and years as well as genotype × year interaction were significantly different (p < 0.001) for all eight observed traits. The first (V₁) and the second (V₂) canonical variate explained 38.57% and 27.55% of the total variation in 2015, and 50.19% and 31.84% in 2016, respectively Canonical variate analysis showed that the traits, flowering time and number of branches per plant had a very large influence on the differentiation of genotypes. Graphs demonstrated that the tested DH lines and hybrids are characterized by a similar, wide range of variability. It was observed, that when using a diverse population of DH lines for crossbreeding with only one CMS/Rfo line, there was no significant reduction of variation in hybrid generations and between these generations. The phenotypic distance values determined by the results of Mahalanobis analysis were similar in both years, but slightly wider in 2016. The observed minimum and maximum ranged from 1.324 to 22.356 in 2015, and from 1.105 to 27.792 in 2016, respectively. No significant correlation was observed between the hybrid heterosis effect and the Mahalanobis distance of the parental lines.

In this paper 60 doubled haploid lines of oilseed rape (Brassica napus L.) were studied. Genetic parameters as additive and epistasis effects were estimated for nine quantitative traits. The results indicate the importance of both additive and epistasis gene effects of number of branches per plant, number of siliques per plant, number of seeds per silique and silique length in this study.