Microsatellite or simple sequence repeat (SSR) markers are routinely used for tagging genes and assessing genetic diversity. In spite of their importance, there are limited numbers of SSR markers available for Brassica crops. A total of 627 new SSR markers (designated BnGMS) were developed based on publicly available genome survey sequences and used to survey polymorphisms among six B. napus cultivars that serve as parents for established populations. Among these SSR markers, 591 (94.3%) successfully amplified at least one fragment and 434 (73.4%) detected polymorphism among the six B. napus cultivars. No correlation was observed between SSR motifs, repeat number or repeat length with polymorphism levels. A linkage map was constructed using 163 newly developed BnGMS marker loci and anchored with 164 public SSRs in a doubled haploid population. These new markers are evenly distributed over all linkage groups (LGs). Given that the majority of these SSRs are derived from bacterial artificial chromosome (BAC) end sequences, they will be useful in the assignment of their cognate BACs to LGs and facilitate the integration of physical maps with genetic maps for genome sequencing in B. napus.
Seed oil content is a key seed quality trait determining the economic value of rapeseed (Brassica napus L.). However, it is a complex quantitative trait controlled by multiple genes. To this point, its genetic mechanism in rapeseed remains to be revealed. In the present study, we separately identified the quantitative trait loci (QTL) controlling seed oil content of B. napus using three generations of recombinant inbred line (RIL) populations (F 4:5 , F 5:6 , and F 6:7 ) derived from a cross of two contrasting parents (M201, a high-oil parent, and M202, a low-oil parent) in four trials. The results indicated that the additive effects may be the primary factors contributing to the variation in seed oil content in B. napus. A total of 15 QTL for seed oil content were mapped. Two of them, namely qOC-A9-3 and qOC-A10, were consistently detected across two and all four environments, respectively. Meanwhile, qOC-A10 showed a large effect on phenotypic variation in seed oil content. The stability and significance of qOC-A10 was also validated in the near isogenic lines (NILs-qOC-A10) developed from the RIL population (F 4:5 ) using marker-assisted selection. The qOC-A10 is of particular interest for further fine mapping and map-based cloning.Key words: Brassica napus L., quantitative trait loci, oil content, additive genetic effect, SSR marker.Résumé : La teneur en huile de la graine est un caractère crucial de la qualité qui détermine la valeur économique du colza (Brassica napus L.). Il s'agit néanmoins d'un caractère quantitatif complexe, car de multiples gènes le régulent. Jusqu'à présent, ce mécanisme génétique du colza nous échappait. Dans la présente étude, les auteurs ont identifié séparément les locus quantitatifs (QTL) qui commandent la concentration d'huile dans la graine de B. napus grâce à trois populations (F 4:5 , F 5:6 , et F 6:7 ) de lignées autogames recombinantes (RIL) issues d'un croisement entre deux parents contrastants (à savoir, M201, une variété riche en huile, et M202, une variété pauvre en huile), au terme de quatre essais. Les résultats indiquent que des effets additifs pourraient principalement être à l'origine de la teneur en huile variable des graines de B. napus. Ils ont cartographié 15 QTL régulant la concentration d'huile dans la graine. Deux, en l'occurrence qOC-A9-3 et qOC-A10, ont constamment été détectés respectivement dans deux et les quatre situations. Parallèlement, qOC-A10 a une profonde incidence sur la variation phénotypique de la teneur en huile. La stabilité et l'importance de qOC-A10 ont également été validées par les lignées quasi isogéniques (NILs-qOC-A10) obtenues de la population (F 4:5 ) des RIL après sélection avec des marqueurs. Le locus qOC-A10 revêt un intérêt particulier en vue d'une cartographie plus précise du génome et du clonage à partir de la carte génétique. [Traduit par la Rédaction] Mots-clés : Brassica napus L., locus quantitatif, teneur en huile, effet additif des gènes, marqueur SSR.
Plant grafting can provide resistance to nematodes. There is a distinct need to determine the role of Meloidogyne incognita-resistant rootstocks on the growth and quality of grafted cucumber plants. Cucumber (Cucumis sativus L.) cultivar Jinchun No.4 (J) was hole grafted onto the pumpkin (Cucurbita moschata) cultivars Xiuli (X), Banzhen No.3 (B) and its root to generate JX, JB, and JJ plants. The histopathology and M. incognita development associated with JX, JB, and JJ were analyzed under incubator and high plastic tunnel conditions. Under incubator conditions, M. incognita root galls and egg mass indices associated with the JX and JB resistant rootstocks were significantly (P < 0.05) lower than those associated with JJ susceptible rootstocks. In addition, the number of eggs were 73.3 ± 8.8% and 85.3 ± 7.7% less, respectively. The number of second-stage juveniles (J2s) in JX roots decreased by 57.1 ± 9.2% compared with that in JJ, and the giant cell and J2 development were poor in JX and JB roots. In pot experiments under a high plastic tunnel, plant height, stem diameter, leaf area, and yield of M. incognita-infected JX plants were not significantly different from those of non-inoculated control. There was no significant difference in fruit weight, length, firmness, soluble solids, and color among the three grafted plants. The yield per JB plant was increased compared with that of JJ, irrespective of nematode presence. In the M. incognita-infested soil experiment in a high plastic tunnel, the yield per JX and JB plant were significantly higher than JJ (P < 0.05). Thus, the pumpkin rootstock Xiuli and Banzhen No.3 are promising rootstocks for managing M. incognita without affecting cucumber fruit quality. Grafting provides a good basis for studying the defense mechanism of rootstocks against M. incognita.
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