Genetic Variability in Carotenoid Contents in a Panel of Genebank Accessions of Temperate Maize from Southeast Europe.

Carotenoids are an abundant group of lipid-soluble antioxidants in maize kernels. Maize is a key target crop for carotenoid biofortification focused on using conventional plant breeding in native germplasm of temperate areas traced back partially to traditional cultivars (landraces). In this study, the objectives were to determine the variability of lutein (LUT), zeaxanthin (ZEA), α-cryptoxanthin (αCX), ß-cryptoxanthin (ßCX), α-carotene (αC), and ß-carotene (ßC) contents in the grain of 88 accessions of temperate maize from the Croatian genebank, and to evaluate the relationships among the contents of different carotenoids as well as the relationships between kernel color and hardness and carotenoid content. Highly significant variability among the 88 accessions was detected for all carotenoids. On average, the most abundant carotenoid was LUT with 13.2 µg g-1 followed by ZEA with 6.8 µg g-1 dry matter. A Principal Component Analysis revealed a clear distinction between α- (LUT, αCX, and αC) and ß-branch (ZEA; ßCX, and ßC) carotenoids. ß-branch carotenoids were positively correlated with kernel color, and weakly positively associated with kernel hardness. Our results suggest that some genebank accessions with a certain percentage of native germplasm may be a good source of carotenoid biofortification in Southeast Europe. However, due to the lack of association between LUT and ZEA, the breeding process could be cumbersome.

Genetic diversity and selection signatures in a gene bank panel of maize inbred lines from Southeast Europe compared with two West European panels.

Southeast Europe (SEE) is a very important maize-growing region, comparable to the Corn belt region of the United States, with similar dent germplasm (dent by dent hybrids). Historically, this region has undergone several genetic material swaps, following the trends in the US, with one of the most significant swaps related to US aid programs after WWII. The imported accessions used to make double-cross hybrids were also mixed with previously adapted germplasm originating from several more distant OPVs, supporting the transition to single cross-breeding. Many of these materials were deposited at the Maize Gene Bank of the Maize Research Institute Zemun Polje (MRIZP) between the 1960s and 1980s. A part of this Gene Bank (572 inbreds) was genotyped with Affymetrix Axiom Maize Genotyping Array with 616,201 polymorphic variants. Data were merged with two other genotyping datasets with mostly European flint (TUM dataset) and dent (DROPS dataset) germplasm. The final pan-European dataset consisted of 974 inbreds and 460,243 markers. Admixture analysis showed seven ancestral populations representing European flint, B73/B14, Lancaster, B37, Wf9/Oh07, A374, and Iodent pools. Subpanel of inbreds with SEE origin showed a lack of Iodent germplasm, marking its historical context. Several signatures of selection were identified at chromosomes 1, 3, 6, 7, 8, 9, and 10. The regions under selection were mined for protein-coding genes and were used for gene ontology (GO) analysis, showing a highly significant overrepresentation of genes involved in response to stress. Our results suggest the accumulation of favorable allelic diversity, especially in the context of changing climate in the genetic resources of SEE.

Phenolic Acid Profiles and Antioxidant Activity of Major Cereal Crops.

Phenolic acids (PAs) are a dominant group of phenolic compounds in cereals, existing mostly bound to compounds of cell wall. In this study, a total of 25 cereal grain samples, including wheat, winter and spring barley, corn, and popcorn, were evaluated for bound PAs and antioxidant activity in a two-year field trial. The PA contents, determined by HPLC, were significantly affected by cereal type. The mean total PA content was highest in popcorn and corn (3298 and 2213 µg/gdm, respectively), followed by winter and spring barley (991 and 908 µg/gdm, respectively) and wheat (604 µg/gdm). Ferulic acid was the most abundant, accounting from 62% to 83% of total PAs (in popcorn and winter and spring barley, respectively). Across cereals, p-coumaric (35-259 µg/gdm) and p-hidroxybenzoic (45-79 µg/gdm) were also dominant, while in corn and popcorn o-coumaric (71 and 89 µg/gdm, respectively) also occurred in higher content. The mean total phenol content ranged from 853 µg GAE/gdm (wheat) to 1403 µg GAE/gdm (winter barley) with DPPH scavenging activity from 14% to 67%, respectively. A significant influence of crop years on the ferulic acid and total PA content was found, while the variability of other PAs was dependent on the cereal type. The results indicated a high health benefit potential of selected cereals.

Genetic Correlations Between Photosynthetic and Yield Performance in Maize Are Different Under Two Heat Scenarios During Flowering.

Chlorophyll fluorescence (ChlF) parameters are reliable early stress indicators in crops, but their relations with yield are still not clear. The aims of this study are to examine genetic correlations between photosynthetic performance of JIP-test during flowering and grain yield (GY) in maize grown under two heat scenarios in the field environments applying quantitative genetic analysis, and to compare efficiencies of indirect selection for GY through ChlF parameters and genomic selection for GY. The testcrosses of 221 intermated recombinant inbred lines (IRILs) of the IBM Syn4 population were evaluated in six environments at two geographically distinctive locations in 3 years. According to day/night temperatures and vapor pressure deficit (VPD), the two locations in Croatia and Turkey may be categorized to the mild heat and moderate heat scenarios, respectively. Mild heat scenario is characterized by daytime temperatures often exceeding 33°C and night temperatures lower than 20°C while in moderate heat scenario the daytime temperatures often exceeded 33°C and night temperatures were above 20°C. The most discernible differences among the scenarios were obtained for efficiency of electron transport beyond quinone A (QA) [ET/(TR-ET)], performance index on absorption basis (PIABS) and GY. Under the moderate heat scenario, there were tight positive genetic correlations between ET/(TR-ET) and GY (0.73), as well as between PIABS and GY (0.59). Associations between the traits were noticeably weaker under the mild heat scenario. Analysis of quantitative trait loci (QTL) revealed several common QTLs for photosynthetic and yield performance under the moderate heat scenario corroborating pleiotropy. Although the indirect selection with ChlF parameters is less efficient than direct selection, ET/(TR-ET) and PIABS could be efficient secondary breeding traits for selection under moderate heat stress since they seem to be genetically correlated with GY in the stressed environments and not associated with yield performance under non-stressed conditions predicting GY during flowering. Indirect selection through PIABS was also shown to be more efficient than genomic selection in moderate heat scenario.

Quantitative trait loci mapping of metal concentrations in leaves of the maize IBM population.

Characterizing concentrations of several beneficiary and toxic metals in maize leaves is of importance for ionomic studies and for silage production. The intermated B73 × Mo17 maize population (IBM) was evaluated for concentrations of eight metals (cadmium - Cd, copper - Cu, iron - Fe, potassium - K, magnesium - Mg, manganese - Mn, strontium - Sr and zinc - Zn) in ear-leaf to map quantitative trait loci (QTL) with 2161 molecular markers across the genome. QTL analysis revealed nine significant QTLs for concentrations of Cd, Cu, Fe, K, Mg and Sr combined over two environments. Median resolution for the QTL interval was less than 1 cM on a regular F2 map, which is a big improvement compared with the prior mapping (8 cM). The highest LOD scores of 15.52 and 15.31 were detected for K and Cd concentrations, respectively, explaining more than 20 percent of the phenotypic variance. No QTLs were found to be colocalized. QTL mapping in the IBM population did not confirm our earlier QTL results demonstrating considerable QTL ×genetic background interaction. The only exception is confirmation of the major QTL for Cd accumulation on chromosome 2. Our results could facilitate further genetic and physical mapping of genes for metal accumulation in maize.

Quantitative trait loci for biofortification traits in maize grain.

Detecting genes that influence biofortification traits in cereal grain could help increase the concentrations of bioavailable mineral elements in crops to solve the global mineral malnutrition problem. The aims of this study were to detect the quantitative trait loci (QTLs) for phosphorus (P), iron (Fe), zinc (Zn), and magnesium (Mg) concentrations in maize grain in a mapping population, as well as QTLs for bioavailable Fe, Zn, and Mg, by precalculating their respective ratios with P. Elemental analysis of grain samples was done by coupled plasma-optical emission spectrometry in 294 F(4) lines of a biparental population taken from field trials of over 3 years. The population was mapped using sets of 121 polymorphic markers. QTL analysis revealed 32 significant QTLs detected for 7 traits, of which some were colocalized. The Additive-dominant model revealed highly significant additive effects, suggesting that biofortification traits in maize are generally controlled by numerous small-effect QTLs. Three QTLs for Fe/P, Zn/P, and Mg/P were colocalized on chromosome 3, coinciding with simple sequence repeats marker bnlg1456, which resides in close proximity to previously identified phytase genes (ZM phys1 and phys2). Thus, we recommend the ratios as bioavailability traits in biofortification research.

Resistance Conferred by the Ht1 Gene in Sweet Corn Infected by Mixtures of Virulent and Avirulent Exserohilum turcicum.

The Ht1 gene conveys a chlorotic-lesion resistant reaction in corn infected by avirulent races of Exserohilum turcicum, the causal agent of northern corn leaf blight (NCLB). The widespread deployment of the Ht1 gene in field corn grown in North America since the 1960s resulted in an increased frequency of E. turcicum race 1, which is virulent against the Ht1 gene. The objective of this study was to assess the value of resistance conveyed by the Ht1 gene when initial inoculum consisted of different ratios of virulent and avirulent E. turcicum. Forty-two sweet corn hybrids with the Ht1 gene and 42 sweet corn hybrids without Ht1 were grown in five trials each in 2003 and 2004. In each trial, plants were inoculated with culture suspensions consisting of different percentages of E. turcicum race 0 and race 1, including: 100:0, 90:10, 75:25, 50:50, and 0:100. Severity of NCLB was rated visually from 0 to 100% leaf area infected when plants were about 3 to 4 weeks past the mid-silk growth stage. The Ht1 gene reduced severity of NCLB by as much as one-third when virulent isolates comprised 25% or less of the initial inoculum. Reduction in NCLB severity due to the Ht1 gene was more substantial on hybrids with susceptible backgrounds than on those with general resistance. When virulent isolates comprised 50% of the initial inoculum, NCLB severity was similar for hybrids with and without the Ht1 gene if hybrids had equivalent levels of general resistance (measured as NCLB severity from trials inoculated entirely with race 1). To accurately classify NCLB reactions of maize lines relative to their most probable performance in the United States, inoculum should consist of at least 50% E. turcicum race 1.