Strategic use of Iranian bread wheat landrace accessions for genetic improvement: Core set formulation and validation

Iranian wheat landrace accessions (IWAs) were collected from country‐wide farm fields and market places in 1935 by a professor at the University of Tehran and shared with University of California at Davis, California. IWAs were further submitted to the genebank of International Maize and Wheat Improvement Center (CIMMYT), Mexico. 2,403 IWAs from CIMMYT’s genebank were assayed by DArT‐seq technology to assess genetic diversity. No apparent ecogeographic patterns related to genetic diversity were detected, probably due to long‐term transport and frequent interchange of landraces among farmers. A multivariate clustering procedure combining genotypic and phenotypic information was used in selecting a core‐set, which represented 15% of the hexaploid wheat accessions included in this study. This subset captured an estimated 93% of rare (frequency <0.05) alleles. Multisite phenotypic data (India, Mexico) validated the ability of the core‐set in detecting useful variants. Potential donor accessions for multiple traits (disease resistance, zinc concentration) were identified from the core‐set for wheat‐breeding. This report illustrates a breeder friendly robust core‐set formulation strategy for harnessing the useful genetic variation stored in the genebanks.     

Introgression of useful genes from Thinopyrum intermedium to wheat for improvement of bread‐making quality

To study the influence of genes from Thinopyrum intermedium on traits affecting the bread‐making quality of wheat, two derivatives from a putative disomic addition line in cultivar ‘Vilmorin 27’ were used in cytological, biochemical and molecular characterization. Cytological analysis suggested that one of the derivatives (Line‐1) had a terminal deletion involving the long arm of chromosome 1D (2n = 42, Del‐1DL”), and the other (Line‐2) was a conventional addition line, but also carried the same deletion on chromosome 1D (2n = 44, Thi”+Del‐1DL”). Amplification and sequencing of high‐molecular‐weight glutenin subunit (HMW‐GS) genes coded by the Th. intermedium chromosome in Line‐2 indicated the presence of one x‐type with an extra cysteine and four (rather than one) unique y‐type genes. Rheological studies of Line‐1 showed significantly lower dough strength compared to ‘Vilmorin 27’, confirming the recognized role of Glu‐1D coded HMW‐GSs. Line‐2 showed significantly higher dough strength compared to the background cultivar, indicating a significant potential of Th. intermedium for improvement of bread‐making quality in wheat.     

Genetic and environmental effects on the occurrence of speltoids in winter wheat cultivars

The occurrence of speltoid off‐types during seed multiplication is one of the major causes for rejection of a wheat cultivar candidate due to phenotypic inhomogeneity. These aberrant plants express an atypical spear‐shaped spike with tenacious glumes. To analyse the frequency of speltoids under field conditions, field trials were conducted at three locations and two sowing times over 2 years based on speltoid off‐type spikes derived from 14 different wheat genotypes. One hundred single ear progeny were developed from the normal and speltoid progeny plants in 2007. A mean frequency of 21.1% and 36.6% speltoid off‐types in plots from normal and speltoid lines was observed, respectively. Plots sown late in the season displayed on average 5.3% less speltoid off‐types, in particular when both sowing times were far apart. Field trials from 2010 revealed 7.9% more aberrant plants compared with 2011. The percentage of speltoids within the field plots ranged from 0.2% to 83.7%, which indicates a large effect of the respective genotype. Finally, strategies to reduce the number of speltoid off‐types are discussed.     

The genetic architecture of zinc and iron content in maize grains as revealed by QTL mapping and meta-analysis

Micronutrient malnutrition, especially zinc (Zn) and iron (Fe) deficiency in diets, has aroused worldwide attention. Biofortification of food crops has been considered as a promising approach for alleviating this deficiency. Quantitative trait locus (QTL) analysis was performed to dissect the genetic mechanism of Zn and Fe content in maize grains using a total of 218 F_2:3 families derived from a cross between inbred lines 178 and P53. Meta-analysis was used to integrate genetic maps and detect Meta-QTL (MQTL) across several independent QTL researches for traits related to Zn or Fe content. Five significant QTLs and 10 MQTLs were detected. Two informative genomic regions, bins 2.07 and 2.08, showed a great importance for Zn and Fe content QTLs. The correlation between Zn and Fe level in maize grains was proposed by MQTLs as 8 of the 10 involved both traits. The results of this study suggest that QTL mapping and meta-analysis is an effective approach to understand the genetic basis of Zn and Fe accumulation in maize grains.     

Effects of the Gpc‐B1 locus on high grain protein content introgressed into Argentinean wheat germplasm

Wheat grain protein content (GPC) is important for human nutrition and has a strong influence on the quality of pasta and bread. The objective of this study was to analyse the introduction of the Gpc‐B1 allele into two Argentinean bread wheat cultivars. Near‐isogenic lines were developed in ‘ProINTA Oasis’ and ‘ProINTA Granar’ using marker‐assisted selection. Gpc‐B1 lines showed a significant (P = 0.01) increase in GPC and a significant (P = 0.001) decrease in grain weight in comparison with control lines without Gpc‐B1. Differences in yield were not significant (P = 0.49) between lines. Gpc‐B1 lines significantly reduced (P = 0.02) straw nitrogen concentration at maturity and significantly increased (P = 0.02) the nitrogen harvest index. When data were analysed by genotype and environment, differences in some analysed parameters were found, indicating that Gpc‐B1 expression may be affected by different genetic backgrounds and environmental conditions. These results suggest that the introgression of the Gpc‐B1 allele into Argentinean wheat germplasm could be a valuable resource for improving GPC with no detrimental effect on grain yield.     

Comparative study of the structure of chromosome 1R derived from Secale montanum and Secale cereale

We produced 15 dissection lines of common wheat carrying segments of chromosome 1R of wild rye (Secale montanum) (1R^m) by the gametocidal system. Using the 1R^m dissection lines and previously established 24 dissection lines of chromosome 1R from cultivated rye (Secale cereale cv. ‘Imperial’) (1Rⁱ), we conducted cytological mapping of 97 markers that were amplified in the 1Rⁱ addition line. Sixty‐eight of the 97 markers were amplified in the 1R^m addition line. To reveal what structural differentiation occurred in chromosome 1R during domestication, we compared the cytological map of chromosome 1Rⁱ with that of chromosome 1R^m, and also with the previously published cytological map of chromosome 1R from wheat cultivar ‘Burgas 2’ (1R^B). There was one discrepancy in marker order in the satellite region between chromosomes 1Rⁱ and 1R^B, while there were four discrepancies in marker order between chromosomes 1Rⁱ and 1R^m. These results suggested that during the domestication of rye, some intrachromosomal rearrangements had occurred in chromosome 1R, although this chromosome is regarded as the most stable chromosome in the rye genome.     

Marker‐assisted introgression of rare allele of β‐carotene hydroxylase (crtRB1) gene into elite quality protein maize inbred for combining high lysine,tryptophan and provitamin A in maize

Vitamin A deficiency in humans is a widespread health problem. Quality protein maize (QPM) is a popular food rich in lysine and tryptophan, but poor in provitamin A (proA). Here, we report the improvement of an elite QPM inbred, HKI1128Q for proA using marker‐assisted introgression of crtRB1‐favourable allele. HKI1128 was one of the parental lines of three popular hybrids in India and was converted to QPM in our earlier programme. Severe segregation distortion for crtRB1 was observed in BC₁F₁, BC₂F₁ and BC₂F₂. Background selection by 100 SSRs revealed mean recovery of 91.07% recurrent parent genome varying from 88.78% to 93.88%. Across years, introgressed progenies possessed higher mean β‐carotene (BC: 9.22 µg/g), β‐cryptoxanthin (BCX: 3.05 µg/g) and provitamin A (proA: 10.75 µg/g) compared to HKI1128Q (BC: 2.26 µg/g, BCX: 2.26 µg/g and proA: 3.38 µg/g). High concentration of essential amino acids, viz. lysine (mean: 0.303%) and tryptophan (0.080%) in endosperm, was also retained. Multi‐year evaluation showed that introgressed progenies possessed similar grain yield (1,759–1,879 kg/ha) with HKI1128Q (1,778 kg/ha). Introgressed progenies with higher lysine, tryptophan and proA hold immense potential as donors and parents in developing biofortified hybrids.