Tissue Lignification, Cell Wall p-Coumaroylation and Degradability of Maize Stems Depend on Water Status.

Water supply and valorization are two urgent issues in the utilization of maize biomass in the context of climate change and replacement of fossil resources. Maximizing maize biomass valorization is of interest to make biofuel conversion competitive, and to increase forage energetic value for animal fodder. One way to estimate biomass valorization is to quantify cell wall degradability. In this study, we evaluated the impact of water supply on cell wall degradability, cell wall contents and structure, and distribution of lignified cell types in maize internodes using dedicated high-throughput tools to effectively phenotype maize internodes from 11 inbred lines under two contrasting irrigation scenarios in field trials over three years. Overall, our results clearly showed that water deficit induced significant changes in lignin content and distribution along with a reduction in lignin p-coumaroylation, thereby impacting cell wall degradability. Additionally, we also observed that responses to a water deficit varied between the lines examined, underscoring biochemical and histological target traits for plant breeding.

Combined mapping of DALP and AFLP markers in cultivated sunflower using F9 recombinant inbred lines.

A genetic map was constructed with specific PCRs, DALPs and AFLPs using F8-generation sunflower recombinant inbred lines. RI lines generated from a F2 population of one cross between the two cultivated inbred lines HA89 (maintainer for Pet1 CMS) and LR4 (restorer for Pet1 CMS) were used. A total of 305 markers were located using seven sPCR, 64 DALP and 301 AFLP loci. They were generated with one, seven and 14 primer pairs, respectively. The map construction consisted of a two-step strategy using 6 and 3.1 LOD scores revealed by a simulation file. Mapped markers were assembled into 18 linkage groups covering 2,168.6 cM with an average of 6.1 cM. The distribution of DALPs and AFLPs revealed that both markers tagged different regions to enable covering most of the sunflower genome. This leads to the longest map published so far for sunflower.

Specifying the introgressed regions from H. argophyllus in cultivated sunflower (Helianthus annuus L.) to mark Phomopsis resistance genes.

A method based upon targetting of introgressed markers in a Phomopsis-resistant line (R) of cultivated sunflower, issuing from a H. argophyllus cross was used to mark the Phomopsis resistance regions. Our study was based upon 203 F(3) families derived from a cross between an inbred line susceptible to Phomopsis (S1) and the introgressed resistant line (R). Families were checked for Phomopsis resistance level in a design with replicated plots and natural infection was re-inforced by pieces of contaminated stems. Thirty four primers were employed for RAPD analysis. Out of 102 polymorphic fragments between (S1) and H. argophyllus, seven were still present in (R) suggesting that they marked introgressions of H. argophyllus into (R). The F(2) plants were scored for the presence or absence of 19 fragments obtained from five primers, and the relationships between the presence/absence of fragments in F(2) plants and Phomopsis resistance/susceptiblity in the F(3) progenies was determined by using an analysis of variance. We found that at least two introgressed regions, as well as favourable factors from sunflower, contributed to the level of Phomopsis resistance in cultivated sunflower.

Mapping genetic factors controlling pollen viability in an interspecific cross in Helianthus sect. Helianthus.

Segregation of 48 genetic markers, including one CMS restorer gene, one morphological character gene, six isozymes and 40 RAPD loci, was scored in a backcross progeny of an interspecific hybrid H. argophyllusxH. annuus cv RHA274. A linkage map was generated taking into account segregation distortions for 11 of the 48 loci in the frame of two different models considering locus-pair segregation in the context of either independent selection pressures or non-equilibrated parental classes. The map consists of nine linkage groups and nine isolated markers covering 390 cM. Approximately half of the plants of the BC1 were male fertile as expected for the segregation of one dominant male-fertility restorer gene; however, these displayed a large range of variation for pollen viability. About 80% of this variation was explained by three genomic regions located on linkage groups 1, 2 and 3. The observation of meiotic chromosomes revealed a significant rate of mispairing (rod bivalents and tetravalents) in tight correlation with pollen viability, indicating that chromosome rearrangements (translocations) are the preponderant factors reducing pollen viability in this progeny. Cytogenetic and mapping data suggest that the three genomic regions involved in pollen-viability variation are located close to translocation points which differentiate the parental-species karyotypes. Segregation distortion was observed for loci correlated with pollen-viability variation. These were most likely the result of two possible suggested mechanisms.