Genetic and Management Effects on Barley Yield and Phenology in the Mediterranean Basin.

Heading time in barley is considered a key developmental stage controlling adaptation to the environment and it affects grain yield; with the combination of agronomy (planting dates) and genetics being some of the determinants of adaptation to environmental conditions in order to escape late frost, heat, and terminal drought stresses. The objectives of this study are (i) to apply a gene-based characterization of 118 barley doubled haploid recombinants for vernalization, photoperiod, and earliness per se; (ii) use such information to quantify the optimal combination of genotype/sowing date that escapes extreme weather events; and (iii) how water and nitrogen management impact on grain yield. The doubled haploid barley genotypes with different allelic combinations for vernalization, photoperiod, and earliness per se were grown in eight locations across the Mediterranean basin. This information was linked with the crop growth model parameters. The photoperiod and earliness per se alleles modify the length of the phenological cycle, and this is more evident in combination with the recessive allele of the vernalization gene VRN-H2. In hot environments such as Algeria, Syria, and Jordan, early sowing dates (October 30 and December15) would be chosen to minimize the risk of exposing barley to heat stress. To maintain higher yields in the Mediterranean basin, barley breeding activities should focus on allelic combinations that have recessive VRN-H2 and EPS2 genes, since the risk of cold stress is much lower than the one represented by heat stress.

Post-anthesis thermal stress induces differential accumulation of bioactive compounds in field-grown barley.

BACKGROUND: Barley (Hordeum vulgare L.) is a healthy grain because of its high content of dietary fibre and phenolic compounds. It faces periods of high temperature during grain filling, frequently reducing grain weight. Heat stress may also affect some of the bioactive compounds present in the grain. To produce quality grains that provide nutritional and health benefits, it is important to understand the effect of environmental stresses on the quantity and quality of bioactive compounds. RESULTS: We have studied the effect of post-anthesis thermal stress on barley bioactive compounds and antioxidant capacity under Mediterranean field conditions during two consecutive growing seasons in four barley genotypes. Thermal stress affected grain weight and size and changed the relative composition of bioactive compounds. The relationship between heat stress and grain ß-glucans and arabinoxylans content was indirect, as the resulting increases in concentrations were due to the lower grain weight under stress. Conversely, heat stress had a significant direct impact on some phenolic compounds, increasing their concentrations differentially across genotypes, which contributed to an improvement in antioxidant capacity of up to 30%. CONCLUSION: Post-anthesis thermal stress had a significant effect on ß-glucans, arabinoxylans, phenolic compound concentration and antioxidant capacity of barley grains. Final grain quality could, at least partially, be controlled in order to increase the bioactive concentrations in the barley grain, by cultivation in growing areas prone to heat stress. Late sowings or late flowering genotypes could also be considered, should a premium be implemented to compensate for lower yields. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Bioactive Compounds and Antioxidant Capacity in Pearling Fractions of Hulled, Partially Hull-Less and Hull-Less Food Barley Genotypes.

Three food barley genotypes differing in the presence or absence of husks were sequentially pearled and their fractions analyzed for ash, proteins, bioactive compounds and antioxidant capacity in order to identify potential functional food ingredients. Husks were high in ash, arabinoxylans, procyanidin B3, prodelphinidin B4 and p-coumaric, ferulic and diferulic bound acids, resulting in a high antioxidant capacity. The outermost layers provided a similar content of those bioactive compounds and antioxidant capacity that were high in husks, and also an elevated content of tocols, representing the most valuable source of bioactive compounds. Intermediate layers provided high protein content, ß-glucans, tocopherols and such phenolic compounds as catechins and bound hydroxybenzoic acid. The endosperm had very high ß-glucan content and relative high levels of catechins and hydroxybenzoic acid. Based on the spatial distribution of the bioactive compounds, the outermost 30% pearling fractions seem the best option to exploit the antioxidant capacity of barley to the full, whereas pearled grains supply ß-glucans enriched flours. Current regulations require elimination of inedible husks from human foods. However, due to their high content in bioactive compounds and antioxidant capacity, they should be considered as a valuable material, at least for animal feeds.

Impact of Rising Temperature in the Deposition Patterns of Bioactive Compounds in Field Grown Food Barley Grains.

High temperatures at the end of the season are frequent under Mediterranean conditions, affecting final grain quality. This study determined the deposition patterns throughout grain filling of dry matter, dietary fiber, phenolic compounds and antioxidant capacity for four barley genotypes under two contrasting temperatures. Deposition pattern for dietary fiber followed that of grain weight. Genotypic differences for duration were more significant than for rate. Anthocyanins followed a second-degree polynomial pattern, reaching a maximum before grain maturation. Free and bound phenols decreased as grain developed, suggesting that they are synthesized in early stages. Rate of bound phenols deposition was more sensitive to genotypic changes. Overall, antioxidant capacity decreased over time; the decay being less steep under stress for all genotypes. Heat stress negatively affected grain weight. It did not alter the profile of ß-glucans and arabinoxylans deposition but positively changed the accumulation of some phenolic compounds, increasing the antioxidant capacity differentially across genotypes. These results support the growing of food barley in high-temperature stress-prone areas, as some bioactive compound and antioxidant capacity will increase, regardless of the smaller grain size. Moreover, if a market develops for food-barley ingredients, early harvesting of non-mature grain to maximize antioxidant capacity should be considered.

CRISPR/Cas9 mutations in the rice Waxy/GBSSI gene induce allele-specific and zygosity-dependent feedback effects on endosperm starch biosynthesis.

KEY MESSAGE: Induced mutations in the waxy locus in rice endosperm did not abolish GBSS activity completely. Compensatory mechanisms in endosperm and leaves caused a major reprogramming of the starch biosynthetic machinery. The mutation of genes in the starch biosynthesis pathway has a profound effect on starch quality and quantity and is an important target for plant breeders. Mutations in endosperm starch biosynthetic genes may impact starch metabolism in vegetative tissues such as leaves in unexpected ways due to the complex feedback mechanisms regulating the pathway. Surprisingly this aspect of global starch metabolism has received little attention. We used CRISPR/Cas9 to introduce mutations affecting the Waxy (Wx) locus encoding granule-bound starch synthase I (GBSSI) in rice endosperm. Our specific objective was to develop a mechanistic understanding of how the endogenous starch biosynthetic machinery might be affected at the transcriptional level following the targeted knock out of GBSSI in the endosperm. We found that the mutations reduced but did not abolish GBSS activity in seeds due to partial compensation caused by the upregulation of GBSSII. The GBSS activity in the mutants was 61-71% of wild-type levels, similarly to two irradiation mutants, but the amylose content declined to 8-12% in heterozygous seeds and to as low as 5% in homozygous seeds, accompanied by abnormal cellular organization in the aleurone layer and amorphous starch grain structures. Expression of many other starch biosynthetic genes was modulated in seeds and leaves. This modulation of gene expression resulted in changes in AGPase and sucrose synthase activity that explained the corresponding levels of starch and soluble sugars.

ZmPBF and ZmGAMYB transcription factors independently transactivate the promoter of the maize (Zea mays) ß-carotene hydroxylase 2 gene.

The maize (Zea mays) enzyme ß-carotene hydroxylase 2 (ZmBCH2) controls key steps in the conversion of ß-carotene to zeaxanthin in the endosperm. The ZmBCH2 gene has an endosperm-preferred and developmentally regulated expression profile, but the detailed regulatory mechanism is unknown. To gain insight into the regulation of ZmBCH2, we isolated 2036 bp of the 5'-flanking region containing the 263 bp 5'-untranslated region (5'-UTR) including the first intron. We linked this to the ß-glucuronidase reporter gene gusA. We found that high-level expression of gusA in rice seeds requires the 5'-UTR for enhanced activation. Truncated variants of the ZmBCH2 promoter retained their seed-preferred expression profile as long as a prolamin box and AACA motif were present. We identified candidate genes encoding the corresponding transcription factors (ZmPBF and ZmGAMYB) and confirmed that their spatiotemporal expression profiles are similar to ZmBCH2. Both ZmPBF and ZmGAMYB can transactivate ZmBCH2 expression in maize endosperm. To eliminate potential confounding effects in maize, we characterized the regulation of the minimal promoter region of ZmBCH2 in transgenic rice. This revealed that ZmPBF and ZmGAMYB independently transactivate the ZmBCH2 promoter. The mechanism that underpins our data provides an exciting new strategy for the control of target gene expression in engineered plants.

Genome-wide association mapping of frost tolerance in barley (Hordeum vulgare L.).

BACKGROUND: Frost tolerance is a key trait with economic and agronomic importance in barley because it is a major component of winter hardiness, and therefore limits the geographical distribution of the crop and the effective transfer of quality traits between spring and winter crop types. Three main frost tolerance QTL (Fr-H1, Fr-H2 and Fr-H3) have been identified from bi-parental genetic mapping but it can be argued that those mapping populations only capture a portion of the genetic diversity of the species. A genetically broad dataset consisting of 184 genotypes, representative of the barley gene pool cultivated in the Mediterranean basin over an extended time period, was genotyped with 1536 SNP markers. Frost tolerance phenotype scores were collected from two trial sites, Foradada (Spain) and Fiorenzuola (Italy) and combined with the genotypic data in genome wide association analyses (GWAS) using Eigenstrat and kinship approaches to account for population structure. RESULTS: GWAS analyses identified twelve and seven positive SNP associations at Foradada and Fiorenzuola, respectively, using Eigenstrat and six and four, respectively, using kinship. Linkage disequilibrium analyses of the significant SNP associations showed they are genetically independent. In the kinship analysis, two of the significant SNP associations were tightly linked to the Fr-H2 and HvBmy loci on chromosomes 5H and 4HL, respectively. The other significant kinship associations were located in genomic regions that have not previously been associated with cold stress. CONCLUSIONS: Haplotype analysis revealed that most of the significant SNP loci are fixed in the winter or facultative types, while they are freely segregating within the un-adapted spring barley genepool. Although there is a major interest in detecting new variation to improve frost tolerance of available winter and facultative types, from a GWAS perspective, working within the un-adapted spring germplasm pool is an attractive alternative strategy which would minimize statistical issues, simplify the interpretation of the data and identify phenology independent genetic determinants of frost tolerance.

Genetic control of duration of pre-anthesis phases in wheat (Triticum aestivum L.) and relationships to leaf appearance, tillering, and dry matter accumulation.

The duration of pre-anthesis developmental phases is of interest in breeding for improved adaptation and yield potential in temperate cereals. Yet despite numerous studies on the genetic control of anthesis (flowering) time and floral initiation, little is known about the genetic control of other pre-anthesis phases. Furthermore, little is known about the effect that changes in the duration of pre-anthesis phases could have on traits related to leaf appearance and tillering, or dry matter accumulation before terminal spikelet initiation (TS). The genetic control of the leaf and spikelet initiation phase (LS; from sowing to TS), the stem elongation phase (SE; from TS to anthesis), and, within the latter, from TS to flag leaf appearance and from then to anthesis, was studied in two doubled-haploid, mapping bread wheat populations, Cranbrook × Halberd and CD87 × Katepwa, in two field experiments (ACT and NSW, Australia). The lengths of phases were estimated from measurements of both TS and the onset of stem elongation. Dry weight per plant before TS, rate of leaf appearance, tillering rate, maximum number of tillers and number of leaves, and dry weight per plant at TS were also estimated in the Cranbrook × Halberd population. More genomic regions were identified for the length of the different pre-anthesis phases than for total time to anthesis. Although overall genetic correlations between LS and SE were significant and positive, independent genetic variability between LS and SE, and several quantitative trait loci (QTLs) with different effects on both phases were found in the two populations. Several of these QTLs (which did not seem to coincide with reported major genes) could be of interest for breeding purposes since they were only significant for either LS or SE. There was no relationship between LS and the rate of leaf appearance. LS was strongly and positively correlated with dry weight at TS but only slightly negatively correlated with early vigour (dry weight before TS). Despite significant genetic correlations between LS and some tillering traits, shortening LS so as to lengthen SE without modifying total time to anthesis would not necessarily reduce tillering capacity, as QTLs for tillering traits did not coincide with those QTLs significant only for LS or SE. Therefore, the study of different pre-anthesis phases is relevant for a better understanding of genetic factors regulating developmental time and may offer new tools for fine-tuning it in breeding for both adaptability and yield potential.

A centromeric region on chromosome 6(6H) affects dormancy in an induced mutant in barley.

Genetic control of seed dormancy in barley (Hordeum vulgare L.) has mostly been described in terms of quantitative variation. Although some molecular markers for dormancy QTL have been identified, the corresponding genes involved in the regulation of the process have not been cloned. Induced barley mutants may constitute useful material to study the physiology and genetics of seed dormancy. The objective of this study was to identify the genetic control of this trait in a mutant (TL43) produced in the barley cv. Triumph. This mutant was selected for reduced dormancy and reduced sensitivity to abscisic acid (ABA). Two sets of F6 barley lines were selected for high and low levels of dormancy from a cross between the original dormant parent and the sodium azide-induced non-dormant TL43 mutant. Unexpectedly, given the near-isogenic nature of these two genotypes, polymorphism was detected for an SSR located in the centromeric region of chromosome 6(6H) out of a total of 92 molecular markers evenly distributed along the genome. Fortunately, upon three cycles of intensive divergent selection, every dormant and non-dormant F5 line consistently showed the genotype for this region identical to Triumph and TL43, respectively. Based on the mutagenic effect presumably attributed to sodium azide, mostly single point mutations, it cannot be clearly established if such extensive genomic variation on chromosome 6(6H) is due to the mutagenic treatment or may be an introgression from an unknown source. The means that could originate such heterogeneity are discussed; however, regardless of its origin, this genomic region shows a strong association with the expression of seed dormancy and provides an additional genetic locus for further studies of the mechanistic basis of this complex trait. In addition, since TL43 shows reduced sensitivity to ABA, the response to this hormone was determined on the F6 seed from the two sets of selected F5 lines. The results confirmed that the initial level of dormancy in the seed lot is the most important factor in determining ABA sensitivity.