Morphological characterization and genetic analysis of tri-pistil trait, a precisely regulated pistil number mutation in bread wheat

Bread wheat (Triticum aestivum L.) is an important source of nutrients for humans. Therefore, improvement of its yields is essential to feed the increasing world population. The tri-pistil (TRP) trait in wheat has a high potential for increasing yields. We obtained a pure tri-pistil wheat line, 4045, and evaluated its morphological properties. The 4045 wheat line stably produced three independently inherited pistils, which led to 1-3 grains in each floret. Among the three pistils, two lately emerged pistils initiated at late anther primordia stage to early tetrads stage. Genetic analysis revealed that there were TRP penetrance variations among the 11 F1 populations of 4045. Fine mapping narrowed the single dominant TRP locus to a 97.3 kb region, containing two candidate genes, on the 2DL chromosome. However, further gene sequence, functional as well as comparative genomic analyses ruled out the only two candidate genes. Therefore, TRP is high-likely a unique gain-of-function mutation that does not exist in normal wheat genome. Transcriptome analysis of floral homeotic genes revealed that expressions of the C-class TaAG-2s, which are essential for carpel specification, significantly increased in 4045, implying that TaAG-2s have played important roles in TRP-regulated tri-pistil formation. This study highlights that TRP leads to a precisely regulated pistil number increase (PRPNI) mutations and proposed a regulatory model of PRPNI pistil architecture. PRPNI offers a novel abnormal pistil development resource for research of floral architectures and potential on crop yield improvement.

Oral Consumption of Bread from an RNAi Wheat Line with Strongly Silenced Gliadins Elicits No Immunogenic Response in a Pilot Study with Celiac Disease Patients

Celiac disease (CD) is a genetically predisposed, T cell-mediated and autoimmune-like disorder caused by dietary exposure to the storage proteins of wheat and related cereals. A gluten-free diet (GFD) is the only treatment available for CD. The celiac immune response mediated by CD4+ T-cells can be assessed with a short-term oral gluten challenge. This study aimed to determine whether the consumption of bread made using flour from a low-gluten RNAi wheat line (named E82) can activate the immune response in DQ2.5-positive patients with CD after a blind crossover challenge. The experimental protocol included assessing IFN-γ production by peripheral blood mononuclear cells (PBMCs), evaluating gastrointestinal symptoms, and measuring gluten immunogenic peptides (GIP) in stool samples. The response of PBMCs was not significant to gliadin and the 33-mer peptide after E82 bread consumption. In contrast, PBMCs reacted significantly to Standard bread. This lack of immune response is correlated with the fact that, after E82 bread consumption, stool samples from patients with CD showed very low levels of GIP, and the symptoms were comparable to those of the GFD. This pilot study provides evidence that bread from RNAi E82 flour does not elicit an immune response after a short-term oral challenge and could help manage GFD in patients with CD.

Chromosome morphology and cytomolecular characteristics of the perennial rye cultivar ‘Kriszta’

The perennial Secale cereanum cultivar ‘Kriszta’ is an artificial hybrid of S. cereale and S. strictum ssp. anatolicum. From the cross between the wheat line Mv9kr1 and ‘Kriszta’, which aimed the transfer of beneficial traits from rye to wheat, numerous translocation lines have been produced. For the identification of the translocated chromosomes, the unambiguous differentiation between chromosome arms of ‘Kriszta’ is essential. The identification of its short chromosome arms using conventional FISH probes is easy, but because of their similar hybridization patterns, its long arms cannot be distinguished. The present study aimed to create the detailed karyotype of ‘Kriszta’, especially that of long arms, by both chromosome measurements and FISH using highly repetitive, as well as subtelomeric tandem repeat, and synthetic microsatellite DNA sequences. Our results indicate that the chromosome complement of ‘Kriszta’ is not a simple combination of the chromosomes of the parental rye species but is composed of rearranged chromosomes. It is also showed that an adequate pair-wise combination of the DNA sequences pSc119.2, pSc200, pSc250, and (AAC)5 makes it possible to identify any of the long arms of S. cereanum cv. Kriszta chromosomes. The future usability of the identified wheat- ‘Kriszta’ translocated chromosomes is also discussed.

Mapping and Characterization of QTLs for Awn Morphology Using Crosses between “Double-Awn” Wheat 4045 and Awnless Wheat Zhiluowumai

Awns play important roles in seed dispersal, protection against predators, and photosynthesis. The characterization of genes related to the formation of awns helps understand the regulation mechanisms of awn development. In the present study, the “double-awn” wheat 4045, which features super-long lemma awns and long glume awns, and an awnless wheat line, Zhiluowumai, were used to investigate QTLs or genes involved in awn development. QTL analysis identified three loci—Qawn-1D, Qawn-5A, and Qawn-7B—using a population of 101 4045 × ZLWM F2 plants. Fine mapping with a total of 9018 progenies narrowed the mapping interval of Qawn-5A to an 809-kb region, which was consistent with the B1 locus, containing five genes on chromosome 5AL. Gene structure and expression analysis indicated that TraesCS5A02G542800 was the causal gene, which was subsequently verified by overexpression of TraesCS5A02G542800 in a “double-awn” wheat, Yangmai20. The retained “double-awn” phenotype of transgenic plants suggested that B1 represses the elongation but does not influence the emergence of the awns. Moreover, 4045 harbors a new allele of B1 with a 261-bp insertion in the promoter region and a lack of the EAR2 motif in the encoding region, which influences several important agronomic traits. In this study, we identify two novel QTLs and a novel allele of B1, providing new resources for exploration of awn development.

Characterization of Synthetic Wheat Line Largo for Resistance to Stem Rust

Resistance breeding is an effective approach against wheat stem rust caused by Puccinia graminis f. sp. tritici (Pgt). The synthetic hexaploid wheat line Largo (pedigree: durum wheat ‘Langdon’ × Aegilops tauschii PI 268210) was found to have resistance to a broad spectrum of Pgt races including the Ug99 race group. To identify the stem rust resistance (Sr) genes, we genotyped a population of 188 recombinant inbred lines developed from a cross between the susceptible wheat line ND495 and Largo using the wheat Infinium 90 K SNP iSelect array and evaluated the population for seedling resistance to the Pgt races TTKSK, TRTTF, and TTTTF in the greenhouse conditions. Based on genetic linkage analysis using the marker and rust data, we identified six quantitative trait loci (QTL) with effectiveness against different races. Three QTL on chromosome arms 6AL, 2BL, and 2BS corresponded to Sr genes Sr13c, Sr9e, and a likely new gene from Langdon, respectively. Two other QTL from PI 268210 on 2DS and 1DS were associated with a potentially new allele of Sr46 and a likely new Sr gene, respectively. Additionally, Sr7a was identified as the underlying gene for the 4AL QTL from ND495. Knowledge of the Sr genes in Largo will help to design breeding experiments aimed to develop new stem rust-resistant wheat varieties. Largo and its derived lines are particularly useful for introducing two Ug99-effective genes Sr13c and Sr46 into modern bread wheat varieties. The 90 K SNP-based high-density map will be useful for identifying the other important genes in Largo.

AMMI and GGE biplot analysis of yield of different elite Wheat line under terminal heat stress and irrigated environment

ABSTRACTWheat crop in Nepal faces terminal heat stress which accelerates the gain filling rate and shortens the filling period which leads to reduced grain weight, size, number, quality that is yield loss. For minimization of this loss, genotypic selection of high yielding lines should be performed understanding the gene-environment interaction. With the view to obtain a high yielding line with stable performance across the environments an experiment was conducted using 18 elite wheat line and 2 check varieties in alpha lattice design (2 replication and 5 blocks per replication) in different environments viz. irrigated and terminal heat stressed environment. The analysis of variance revealed that genotype, environment and their interaction had highly significant effect on the yield. Furthermore, which-won–where model indicated specific adaptation of elite lines NL-1179, NL-1420, BL-4407, NL-1368 to irrigated environment and BL-4919 and NL-1350 to terminal heat-stressed environment. Similarly, Mean-versus-stability study indicated that elite line BL-4407, NL-1368, BL-4919, NL-1350 and NL-1420 had above average yield and higher stability whereas elite lines Gautam, NL-1412, NL-1376, NL-1387, NL-1404 and N-1381 had below average yield and lower stability. Also, ranking elite lines biplot, PCA1 explaining 73.6% and PCA2 explaining 26.4% of the interaction effect, showed the rank of elite line, NL-1420 > NL-1368> NL-1350 > other lines, close to ideal line. From these findings, NL-1420 with high yield and stability can be recommended across both the environment while NL-1179 is adapted specifically for irrigated and NL-1350 adapted specifically for terminal heat-stressed environment.

Mapping and Validation of Stem Rust Resistance Loci in Spring Wheat Line CI 14275

Stem rust caused by Puccinia graminis f. sp. tritici (Pgt) remains a constraint to wheat production in East Africa. In this study, we characterized the genetics of stem rust resistance, identified QTLs, and described markers associated with stem rust resistance in the spring wheat line CI 14275. The 113 recombinant inbred lines, together with their parents, were evaluated at the seedling stage against Pgt races TTKSK, TRTTF, TPMKC, TTTTF, and RTQQC. Screening for resistance to Pgt races in the field was undertaken in Kenya, Ethiopia, and the United States in 2016, 2017, and 2018. One gene conferred seedling resistance to race TTTTF, likely Sr7a. Three QTL were identified that conferred field resistance. QTL QSr.cdl-2BS.2, that conferred resistance in Kenya and Ethiopia, was validated, and the marker Excalibur_c7963_1722 was shown to have potential to select for this QTL in marker-assisted selection. The QTL QSr.cdl-3B.2 is likely Sr12, and QSr.cdl-6A appears to be a new QTL. This is the first study to both detect and validate an adult plant stem rust resistance QTL on chromosome arm 2BS. The combination of field QTL QSr.cdl-2BS.2, QSr.cdl-3B.2, and QSr.cdl-6A has the potential to be used in wheat breeding to improve stem rust resistance of wheat varieties.