Characterization of Leaf Rust and Stripe Rust Resistance in Spring Wheat 'Chilero'.

Since 1984, the 'Chilero' spring wheat line developed by CIMMYT has proven to be highly resistant to leaf rust and stripe rust. Amid efforts to understand the basis of resistance of this line, a recombinant inbred line (RIL) population derived from a cross between Avocet and Chilero was studied. The parents and RILs were characterized in field trials for leaf rust and stripe rust in three locations in Mexico between 2012 and 2015 and genotyped with DArT-array, DArT-GBS, and SSR markers. A total of 6,168 polymorphic markers were used to construct genetic linkage maps. Inclusive composite interval mapping detected four colocated resistance loci to both rust diseases and two stripe rust resistant loci in the Avocet × Chilero population. Among these, the quantitative trait locus (QTL) on chromosome 1BL was identified as a pleotropic adult plant resistance gene Lr46/Yr29, whereas QLr.cim-5DS/QYr.cim-5DS was a newly discovered colocated resistance locus to both rust diseases in Chilero. Additionally, one new stripe rust resistance locus on chromosome 7BL was mapped in the current population. Avocet also contributed two minor colocated resistance QTLs situated on chromosomes 1DL and 4BS. The flanking SNP markers can be converted to breeder friendly Kompetitive Allele Specific PCR (KASP) markers for wheat breeding programs.

Identification and Mapping of Adult Plant Resistance Loci to Leaf Rust and Stripe Rust in Common Wheat Cultivar Kundan.

Leaf rust (LR) and stripe rust (YR) are important diseases of wheat worldwide. We used 148 recombinant inbred lines (RIL) from the cross of Avocet × Kundan for determining and mapping the genetic basis of adult plant resistance (APR) loci. The population was phenotyped LR and YR for three seasons in field trials conducted in Mexico and genotyped with the diversity arrays technology sequencing (DArT-Seq) and simple sequence repeat markers. The final genetic map was constructed using 2,937 polymorphic markers with an average distance of 1.29 centimorgans between markers. Inclusive composite interval mapping identified two co-located APR quantitative trait loci (QTL) for LR and YR, two LR QTL, and three YR QTL. The co-located resistance QTL on chromosome 1BL corresponded to the pleiotropic APR gene Lr46/Yr29. QLr.cim-2BL, QYr.cim-2AL, and QYr.cim-5AS could be identified as new resistance loci in this population. Lr46/Yr29 contributed 49.5 to 65.1 and 49.2 to 66.1% of LR and YR variations, respectively. The additive interaction between detected QTL showed that LR severities for RIL combining four QTL ranged between 5.3 and 25.8%, whereas the lowest YR severities were for RIL carrying QTL on chromosomes 1BL + 2AL + 6AL. The high-density DArT-Seq markers across chromosomes can be used in fine mapping of the targeted loci and development SNP markers.

Yr60, a Gene Conferring Moderate Resistance to Stripe Rust in Wheat.

Stripe rust, caused by Puccinia striiformis f. sp. tritici W., is a devastating disease of wheat worldwide. A new stripe rust resistance gene with moderate seedling and adult plant resistance was mapped using an F5 recombinant inbred line (RIL) population developed from the cross of the resistant parent 'Almop' with the susceptible parent 'Avocet'. The parents and RILs were phenotyped for seedling stripe rust response variation in a greenhouse and in field trials at Toluca, Mexico for 2 years. Almop showed moderate levels of resistance at both seedling and adult plant stages compared with the highly susceptible response of Avocet. The distribution of homozygous resistant, homozygous susceptible, and segregating RILs conformed to segregation at a single locus. Seedlings and adult plant responses were correlated, indicating that the same gene conferred resistance at both stages. A bulk segregant analysis approach with widely distributed simple sequence repeat (SSR) markers mapped the resistance gene to the distal region of the long arm of chromosome 4A. The SSR marker wmc776 cosegregated with this gene, whereas markers wmc219 and wmc313 were tightly linked and both located at 0.6 centimorgans. The resistance locus was designated Yr60.

Genetic Analysis of Resistance to Leaf Rust and Yellow Rust in Spring Wheat Cultivar Kenya Kongoni.

The Kenyan wheat (Triticum aestivum L.) 'Kenya Kongoni' exhibits high levels of adult plant resistance (APR) to leaf rust (LR) and yellow rust (YR). We determined the genomic regions associated with LR and YR resistance in a population of 148 recombinant inbred lines generated from a cross between 'Avocet-YrA' and Kenya Kongoni. Field experiments to characterize APR to LR and YR were conducted in four and two Mexican or Uruguayan environments, respectively. A linkage map was constructed with 438 diversity arrays technology and 16 simple-sequence repeat markers by JoinMap 4.1 software. Genetic analyses showed that resistance to both rusts was determined by four to five APR genes, including Lr46/Yr29 and Sr2/Lr27/Yr30. Quantitative trait loci (QTL) analysis indicated that pleiotropic APR loci QYLr.cim-1BL corresponding to Lr46/Yr29 and QYLr.cim-7BL that is a putative novel QTL accounted for 5 to 57% and 12 to 35% of the phenotypic variation for resistance to LR and YR, respectively. These loci, in combination with another three LR QTL and two YR QTL, respectively, conferred high levels of resistance to both LR and YR in wheat under Mexican and Uruguayan environments. Among other detected QTL, QLr.cim-1DS, QLr.cim-2BL, and QYLr.icm-7BL may be new loci for APR to both rusts in common wheat.

Genetic Analysis of Resistance to Leaf Rust and Stripe Rust in Wheat Cultivar Francolin#1.

Leaf rust and stripe rust are important diseases of wheat and can be controlled by growing resistant varieties. We investigated the genetic basis of resistance to both rusts in 198 F5 recombinant inbred lines derived from a cross between 'Avocet' and 'Francolin#1'. The population was phenotyped in greenhouse and field, and genotyped with known gene-associated molecular markers. Seedling resistance of Francolin#1 to leaf and stripe rusts was attributed to the loosely linked genes Lr16 and YrF, respectively, with a recombination frequency of 0.36. Field segregation indicated that adult plant resistance (APR) to leaf and stripe rusts was conferred by three and five additive genes, respectively. Among them, Lr46/Yr29 was associated with resistance to both rusts in Francolin#1, Lr16 reduced field leaf rust severity by 8 to 9%, and YrF contributed to 10 to 25% reductions in stripe rust severity. The Lr16 region was also associated with a 5 to 16% reduction in stripe rust severity, which is likely due to its linkage with YrF or another unidentified stripe rust APR gene. Significant additive effects on stripe rust were detected between YrF and Yr29. We conclude that APR in Francolin#1 to leaf and stripe rusts involves a combination of seedling and APR genes.

Lr72 Confers Resistance to Leaf Rust in Durum Wheat Cultivar Atil C2000.

Leaf rust, caused by Puccinia triticina (Pt), has become a globally important disease for durum wheat (Triticum turgidum subsp. durum) since the detection of race group BBG/BN, which renders ineffective a widely deployed seedling resistance gene present in several popular cultivars including Mexican cultivars Altar C84 and Atil C2000. The resistance gene continues to play a key role in protecting durum wheat against bread wheat-predominant races since virulence among this race group has not been found. We developed F3 and F5 mapping populations from a cross between Atil C2000 and the susceptible line Atred #1. Resistance was characterized by greenhouse seedling tests using three Pt races. Segregation tests indicated the presence of a single gene, which was mapped to the distal end of 7BS by bulk segregant analysis. The closest marker, wmc606, was located 5.5 cM proximal to the gene. No known leaf rust resistance genes are reported in this region; this gene was therefore designated as Lr72. The presence of Lr72 was further investigated in greenhouse tests in a collection of durum wheat using 13 Pt races. It was concluded that at least one additional gene protects durum wheat from bread wheat-predominant Pt races.

Quantitative trait loci of stripe rust resistance in wheat.

Over thirty publications during the last 10 years have identified more than 140 QTLs for stripe rust resistance in wheat. It is likely that many of these QTLs are identical genes that have been spread through plant breeding into diverse backgrounds through phenotypic selection under stripe rust epidemics. Allelism testing can be used to differentiate genes in similar locations but in different genetic backgrounds; however, this is problematic for QTL studies where multiple loci segregate from any one parent. This review utilizes consensus maps to illustrate important genomic regions that have had effects against stripe rust in wheat, and although this methodology cannot distinguish alleles from closely linked genes, it does highlight the extent of genetic diversity for this trait and identifies the most valuable loci and the parents possessing them for utilization in breeding programs. With the advent of cheaper, high throughput genotyping technologies, it is envisioned that there will be many more publications in the near future describing ever more QTLs. This review sets the scene for the coming influx of data and will quickly enable researchers to identify new loci in their given populations.

[In vivo sensitivity of Plasmodium falciparum to piperaquine phosphate assayed in Linshui and Baisha counties, Hainan Province].

Fifty-three cases of falciparum malaria in Linshui County, Baisha County and Sanya Municipality were treated with piperaquine phosphate at a total dose of 1.5g base over 3 days in July to December, 1986. The mean defervescence time was 36 +/- 20.7h; the mean asexual parasite clearance time was 69.7 +/- 20.9h. At 14-28d follow-up recrudescence was observed with asexual parasitemia in 7 of the 47 cases, showing RI resistance to piperaquine. Gametocytemia was positive in 35 cases (74.5%) during the follow-up period.