Genetic and molecular studies of loose smut resistance in Durum Wheat

The most economic and effective way to control loose smut disease of wheat is by the development of resistant cultivars. This study was conducted to screen tetraploid species of wheat resistant to Ustilago tritici races, to investigate the genetic similarities among different races of U. tritici, to determine the genetic control of resistance to race T33 in three crosses and to identify molecular markers linked to loose smut resistance. About 160 selected lines of tetraploid species of Triticum carthlicum, T. dicoccoides, T. dicoccum, T. polonicum, T. turanicum, and T. turgidum were screened for resistance to three races (T33, T32, and T26). The highest percentage of resistant lines was observed in three species, T. carthlicum, T. dicoccoides, and T. dicoccum to the three races of U. tritici. T. polonicum, T. turanicum, and T. turgidum had a lower percentage of resistant lines. Twenty races of U. tritici collected from durum and bread wheat were analysed to assess the degree of similarity based on molecular genetic data. Cluster analysis indicated that races collected from durum and bread wheat did not have any consistent grouping according to the wheat species they were collected from. Three crosses (Stewart 63 x Biodur, DT662 x D93213, and D93221 x DT658)were evaluated to determine the inheritance of resistance to race T33 of U. tritici. In Stewart 63 x Biodur, resistance appeared to be dominant and under the control of more than one gene, probably one major gene along with minor gene(s). Resistance in DT662 x D93213 was dominant and controlled by a single gene whereas in D93221 x DT658, resistance was recessive and conditioned by three genes. Although, allelic studies were not conclusive, the presence of smutted progenies from crosses among the resistant parents as well as the results of molecular studies indicate that the resistance genes studied may not be allelic. To identify molecular markers linked to loose smut resistance, bulked segregant analysis was used to screen two recombinant inbred populations from the crosses Stewart 63 x Biodur and DT662 x D93213. In the Stewart 63 x Biodur population, five Amplified Fragment Length Polymorphism (AFLP) markers were identified. Two markers were on one side of a smut resistance locus at a distance of 19.3 cM whereas three markers were on the other side at a distance of 15.5 cM. Marker E32/M55R accounted for up to 41% of the disease reaction variability. Since these markers were flanking the smut resistance locus, they can be effectively used for marker-assisted selection despite being loosely linked. In DT662 x D93213, five markers including two AFLP, two wheat microsatellites (WMS) and one Sequence Characterized Amplified Region (SCAR) were identified. The SCAR marker was on the one side of a smut resistance locus at a distance of 3.2 cM and accounted for up to 64% of the disease reaction variability whereas the other markers were on the other side of the smut resistance locus at distances ranging from 5.9 cM to 35.9 cM

AAC Whitehead hard white spring wheat

AAC Whitehead, an awned hard white spring wheat (Triticum aestivum L.) cultivar, combines high grain yield and good agronomic characteristics with excellent disease resistance. Based on 34 station years of registration trial data from 2017 to 2019, AAC Whitehead had grain yield significantly higher than all of the check cultivars. AAC Whitehead had maturity similar to the checks, low lodging scores, and significantly shorter plant height than Snowstar and Whitehawk. AAC Whitehead had significantly lower test weight and higher kernel mass than than all the check cultivars. AAC Whitehead expressed resistance to the prevalent races of leaf, stripe and stem rust, and common bunt; and moderate resistance to Fusarium head blight. It also expressed tolerance to the orange wheat blossom midge. AAC Whitehead expresses quality attributes within the range of the check cultivars and is eligible for grades of Canada Western Hard White Spring wheat.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Polymorphic homoeolog of key gene of RdDM pathway, ARGONAUTE4_9 class is associated with pre-harvest sprouting in wheat (Triticum aestivum L.).

Resistance to pre-harvest sprouting (PHS) is an important objective for the genetic improvement of many cereal crops, including wheat. Resistance, or susceptibility, to PHS is mainly influenced by seed dormancy, a complex trait. Reduced seed dormancy is the most important aspect of seed germination on a spike prior to harvesting, but it is influenced by various environmental factors including light, temperature and abiotic stresses. The basic genetic framework of seed dormancy depends on the antagonistic action of abscisic acid (ABA) and gibberellic acid (GA) to promote dormancy and germination. Recent studies have revealed a role for epigenetic changes, predominantly histone modifications, in controlling seed dormancy. To investigate the role of DNA methylation in seed dormancy, we explored the role of ARGONAUTE4_9 class genes in seed development and dormancy in wheat. Our results indicate that the two wheat AGO4_9 class genes i.e. AGO802 and AGO804 map to chromosomes 3L and 1L are preferentially expressed in the embryos of developing seeds [corrected]. Differential expressions of AGO802-B in the embryos of PHS resistant and susceptible varieties also relates with DNA polymorphism in various wheat varieties due to an insertion of a SINE-like element into this gene. DNA methylation patterns of the embryonic tissue from six PHS resistant and susceptible varieties demonstrate a correlation with this polymorphism. These results suggest a possible role for AGO802-B in seed dormancy and PHS resistance through the modulation of DNA methylation

List of primers used in mapping studies.

<p>List of primers used in mapping studies.</p

Retroposon insertion in the <i>AGO802B</i> gene, in 10 wheat accession with varying reaction to pre-harvest sprouting.

<p>Retroposon insertion in the <i>AGO802B</i> gene, in 10 wheat accession with varying reaction to pre-harvest sprouting.</p

Phylogenetic comparison of ARGONAUTE4_9.

<p>Comparison of ARGONAUTE4_9 class of genes using a Phylogenetic tree from wheat, barley, rice, maize, sorghum and Arabidopsis.</p

Analysis of a retro-transposon insertion in the <i>AGO802B</i> transcripts.

<p>Polymorphism as observed on agarose gel in different wheat varieties with varying reaction to pre-harvest sprouting, due to insertion of a retro-transposon insertion in the <i>AGO802B</i> transcripts.</p

Comparing wheat homoeologs.

<p>DNA sequence comparison of wheat homoeologs of <i>AGO802</i> and <i>AGO804</i>. The three wheat <i>AGO802</i> homoeologs are almost 100% identical for the sequence and <i>AGO804</i> has sequence homology of about 98% among its three homoeologs.</p

Methylation differences between wheat varieties.

<p>DNA extracted from the embryos of mature seeds was digested with <i>Msp</i> I restriction enzyme and probed with 5S rDNA. PHS resistant varieties RL4137, Snowbird, AC Domain, AC Karma show reduced methylation as compared to a PHS susceptible variety AC Andrew. DNA methylation in CDC Teal, a variety with medium PHS reaction was also less, compared to AC Andrew but more than the PHS resistant varieties.</p

Expression analysis of <i>AGO802</i> and <i>AGO804</i>.

<p>Expression of <i>AGO802</i> and <i>AGO804</i> homoeologs in embryos during seed development in Chinese Spring cultivar. QRT-expression analysis was performed at six different stages consisting of ovaries at 5 DAP stages and embryos at 10, 15, 20, 25 and 30 DAP, shown on X-axis of graph as 1–6 respectively.</p