Identification of single nucleotide polymorphisms (SNPs) for maize cell wall hydroxycinnamates using a multi-parent advanced generation intercross (MAGIC) population.

Higher hydroxycinnamate content makes maize tissues more recalcitrant to damage by insects, less digestible by ruminants, and less suitable for biofuel production. In a Genome Wide Association Analysis (GWAS) study carried out in a maize MAGIC population, we identified 24 SNPs associated with esterified cell wall-bound hydroxycinnamates, that represented 15 Quantitative Traic Loci (QTL). We identified new genomic regions associated to cell wall bound hydroxycinnamates in maize stover that could have an impact on their content across different genetic backgrounds. The high resolution QTL described in this study could be valuable for addressing positional mapping of genes involved in hydroxycinnamate biosynthesis and could uncover genes implicated in the esterification of hydroxycinnamic acids to the arabinoxylan chains that are poorly understood. However, we found that genetic correlation coefficients between hydroxycinnamate content and economical important traits such as saccharification efficiency, animal digestibility andi pest resistance were low to moderate, so modify specific hydroxycinnamates to indirectly improve cultivar performance will be unsuitable.

Free phenols in maize pith and their relationship with resistance to Sesamia nonagrioides (Lepidoptera: Noctuidae) attack.

The stem borer Sesamia nonagrioides (Lefèbvre) is the most important insect pest of maize, Zea mays L., in northwestern Spain. Among the metabolites present in maize, phenolic compounds could play an important role in resistance. The objective of this work was to determine whether a relationship between phenols and the amount of resistance exists. Amounts of free phenolic compounds in the pith of 13 inbred maize lines that differ in resistance were measured. The phenolic compounds identified were p-coumaric acid, cafeic acid, ferulic acid, vanillic acid, syringic acid, chorogenic acid, sinapic acid, p-hydroxybenzoic acid, and vanillin. The amount of free p-coumaric acid was correlated with the resistance level. Higher quantities of p-coumaric in the pith could contribute to general resistance to stem borer attack. Jointly with ferulic acid, p-coumaric could provide resistance mechanisms through cell wall fortification and lignification. The other compounds showed no or an unclear relationship with resistance. The vanillic acid showed a decreased tendency after silking, when maize is most attractive for S. nonagrioides, suggesting this acid could act as a chemoattractant for S. nonagrioides larvae or adults. Future studies that focus on these phenolic compounds could be useful in understanding S. nonagrioides resistance.

Relationship between maize stem structural characteristics and resistance to pink stem borer (Lepidoptera: Noctuidae) attack.

The pink stem borer, Sesamia nonagrioides (Lefebvre), is one of the most important insect pests of maize (Zea mays L.) in northwestern Spain. The objectives of this work were to evaluate, at different times during the growth of maize, structural traits related to the entry point and tissues on which larvae feed and to determine the relationship between these structural traits and the stem borer resistance. Six inbred lines with different levels of stem resistance to S. nonagrioides were evaluated in several trials. Potential structural resistance factors included rind and pith puncture resistance (RPR and PPR), rind thickness, length of the meristematic area (LMA), and pith parenchyma interlumen thickness (PPIT). Surprisingly, the inbred lines that showed the strongest stalks, EP42 and EP47, were not stem resistant to pink stem borer attack, while the stem resistant inbreds A509, CM151, and PB130 were among the least resistant to rind puncture. There were no significant differences among resistant and susceptible inbreds for the rind thickness. However, the susceptible inbred EP42 had the softest internode pith, and the resistant inbred PB130 showed the hardest, as was expected. Susceptible inbred lines in general showed higher values for the LMA, while the PPIT was important for individual inbreds. The results suggest that the usefulness of these characters as estimators of pink stem borer resistance is limited to some genotypes. Besides, even among those genotypes, other mechanisms of resistance that do not involve stalk strength could be present. Among the traits considered, the LMA was the most promising as an indicator of resistance to pink stem borer, although further experimentation is necessary.

Comparative analysis of allelopathic effects produced by four forestry species during decomposition process in their soils in Galicia (NW Spain).

The development of toxicity produced by vegetable litter of four forest species (Quercus robur L.,Pinus radiata D.Don.,Eucalyptus globulus Labill, andAcacia melanoxylon R.Br.) was studied during the decomposition process in each of the soils where the species were found. The toxicity of the extracts was measured by the effects produced on germination and growth ofLactuca saliva L. var. Great Lakes seeds. The phenolic composition of the leaves of the four species was also studied using high-performance liquid chromatographic analysis (HPLC). It was verified that toxicity was clearly reflected in the first stages of leaf decomposition inE. globulus andA. melanoxylon, due to phytotoxic compounds liberated by their litter. At the end of half a year of decomposition, inhibition due to the vegetable material was not observed, but the soils associated with these two species appeared to be responsible for the toxic effects. On the other hand, the phenolic profiles are quite different among the four species, and greater complexity in the two toxic species (E. globulus andA. melanoxylon) was observed.