ALBERT

Description: The transfer of alien genes to crop plants using chromosome engineering has been attempted infrequently in tetraploid durum wheat ( Triticum turgidum L. subsp. durum ). Here, we report a highly efficient approach for the transfer of two genes conferring resistance to stem rust race Pgt -TTKSK (Ug99) from goatgrass ( Aegilops speltoides ) to tetraploid wheat. The durum line DAS15, carrying the stem rust resistance gene Sr47 derived from Ae. speltoides , was crossed, and backcrossed, to durum 5D(5B) aneuploids to induce homeologous pairing. After a final cross to ‘Rusty’ durum, allosyndetic recombinants were recovered. The Ae. speltoides chromosomal segment carrying Sr47 was found to have two stem rust resistance genes. One gene conditioning an infection type (IT) 2 was located in the same chromosomal region of 2BS as Sr39 and was assigned the temporary gene symbol SrAes7t . Based on ITs observed on a diverse set of rust races, SrAes7t may be the same as Sr39 . The second gene conditioned an IT 0; and was located on chromosome arm 2BL. This gene retained the symbol Sr47 because it had a different IT and map location from other stem rust resistance genes derived from Ae. speltoides . Allosyndetic recombinant lines carrying each gene on minimal alien chromosomal segments were identified as were molecular markers distinguishing each alien segment. This study demonstrated that chromosome engineering of Ae. speltoides segments is feasible in tetraploid wheat. The Sr47 gene confers high-level and broad spectrum resistance to stem rust and should be very useful in efforts to control TTKSK.

Description: Pyrenophora teres f. maculata is the cause of the foliar disease spot form net blotch (SFNB) on barley. To evaluate pathogen genetics underlying the P. teres f. maculata –barley interaction, we developed a 105-progeny population by crossing two globally diverse isolates, one from North Dakota and the other from Western Australia. Progeny were phenotyped on a set of four barley genotypes showing a differential reaction to the parental isolates, then genotyped using a restriction site-associated-genotype-by-sequencing (RAD-GBS) approach. Genetic maps were developed for use in quantitative trait locus (QTL) analysis to identify virulence-associated QTL. Six QTL were identified on five different linkage groups and individually accounted for 20–37% of the disease variation, with the number of significant QTL ranging from two to four for the barley genotypes evaluated. The data presented demonstrate the complexity of virulence involved in the P. teres f. maculata –barley pathosystem and begins to lay the foundation for understanding this important interaction.

Description: Wheat stem rust, caused by Puccinia graminis f. sp. tritici Eriks. & E. Henn, can incur yield losses in susceptible cultivars of durum wheat, Triticum turgidum ssp. durum (Desf.) Husnot. Although several durum cultivars possess the stem rust resistance gene Sr13 , additional genes in durum wheat effective against emerging virulent races have not been described. Durum line 8155-B1 confers resistance against the P. graminis f. sp. tritici race TTKST, the variant race of the Ug99 race group with additional virulence to wheat stem rust resistance gene Sr24 . However, 8155-B1 does not confer resistance to the first-described race in the Ug99 race group: TTKSK. We mapped a single gene conferring resistance in 8155-B1 against race TTKST, Sr8155B1 , to chromosome arm 6AS by utilizing Rusty/8155-B1 and Rusty*2/8155-B1 populations and the 90K Infinium iSelect Custom bead chip supplemented by KASP assays. One marker, KASP_6AS_IWB10558 , cosegregated with Sr8155B1 in both populations and correctly predicted Sr8155B1 presence or absence in 11 durum cultivars tested. We confirmed the presence of Sr8155B1 in cultivar Mountrail by mapping in the population Choteau/Mountrail. The marker developed in this study could be used to predict the presence of resistance to race TTKST in uncharacterized durum breeding lines, and also to combine Sr8155B1 with resistance genes effective to Ug99 such as Sr13 . The map location of Sr8155B1 cannot rule out the possibility that this gene is an allele at the Sr8 locus. However, race specificity indicates that Sr8155B1 is different from the known alleles Sr8a and Sr8b .

Description: Parastagonospora nodorum , the causal agent of Septoria nodorum blotch in wheat, has emerged as a model necrotrophic fungal organism for the study of host–microbe interactions. To date, three necrotrophic effectors have been identified and characterized from this pathogen, including SnToxA, SnTox1, and SnTox3. Necrotrophic effector identification was greatly aided by the development of a draft genome of Australian isolate SN15 via Sanger sequencing, yet it remained largely fragmented. This research presents the development of nearly finished genomes of P. nodorum isolates Sn4, Sn2000, and Sn79-1087 using long-read sequencing technology. RNAseq analysis of isolate Sn4, consisting of eight time points covering various developmental and infection stages, mediated the annotation of 13,379 genes. Analysis of these genomes revealed large-scale polymorphism between the three isolates, including the complete absence of contig 23 from isolate Sn79-1087, and a region of genome expansion on contig 10 in isolates Sn4 and Sn2000. Additionally, these genomes exhibit the hallmark characteristics of a "two-speed" genome, being partitioned into two distinct GC-equilibrated and AT-rich compartments. Interestingly, isolate Sn79-1087 contains a lower proportion of AT-rich segments, indicating a potential lack of evolutionary hotspots. These newly sequenced genomes, consisting of telomere-to-telomere assemblies of nearly all 23 P. nodorum chromosomes, provide a robust foundation for the further examination of effector biology and genome evolution.

Description: Cadmium (Cd) is a heavy metal that has no known biological function and is toxic for many living organisms. The maximum level of Cd concentration allowed in the international market for wheat grain is 0.2 mg kg –1 . Because phenotyping for Cd uptake is expensive and time consuming, molecular markers associated with genes conferring low Cd uptake would expedite selection and lead to the development of durum cultivars with reduced Cd concentrations. Here, we identified single nucleotide polymorphisms (SNPs) associated with a novel low Cd uptake locus in the durum experimental line D041735, which has hexaploid common wheat in its pedigree. Genetic analysis revealed a single major QTL for Cd uptake on chromosome arm 5BL within a 0.3 cM interval flanked by SNP markers. Analysis of the intervening sequence revealed a gene with homology to an aluminum-induced protein as a candidate gene. Validation and allelism tests revealed that the low Cd uptake gene identified in this study is different from the closely linked Cdu1-B gene, which also resides on 5BL. This study therefore showed that the durum experimental line D041735 contains a novel low Cd uptake gene that was likely acquired from hexaploid wheat.

Description: Tan spot and Septoria nodorum blotch (SNB) are important diseases of wheat caused by the necrotrophic fungi Pyrenophora tritici-repentis and Parastagonospora nodorum , respectively. The P. tritici-repentis necrotrophic effector (NE) Ptr ToxB causes tan spot when recognized by the Tsc2 gene. The NE ToxA is produced by both pathogens and has been associated with the development of both tan spot and SNB when recognized by the wheat Tsn1 gene. Most work to study these interactions has been conducted in common wheat, but little has been done in durum wheat. Here, quantitative trait loci (QTL) analysis of a segregating biparental population indicated that the Tsc2 -Ptr ToxB interaction plays a prominent role in the development of tan spot in durum. However, analysis of two biparental populations indicated that the Tsn1 -ToxA interaction was not associated with the development of tan spot, but was strongly associated with the development of SNB. Pa. nodorum expressed ToxA at high levels in infected Tsn1 plants, whereas ToxA expression in P. tritici-repentis was barely detectable, suggesting that the differences in disease levels associated with the Tsn1 -ToxA interaction were due to differences in pathogen expression of ToxA . These and previous results together indicate that: (1) the effects of Tsn1 -ToxA on tan spot in common wheat can range from nonsignificant to highly significant depending on the host genetic background; (2) Tsn1 -ToxA is not a significant factor for tan spot development in durum wheat; and (3) Tsn1 -ToxA plays a major role in SNB development in both common and durum wheat. Durum and common wheat breeders alike should strive to remove both Tsc2 and Tsn1 from their materials to achieve disease resistance.