Identification and genetic mapping of the putative Thinopyrum intermedium-derived dominant powdery mildew resistance gene PmL962 on wheat chromosome arm 2BS.

KEY MESSAGE: Powdery resistance putatively derived from Thinopyrum intermedium in the wheat line L962 is controlled by a single dominant gene designated PmL962 and mapped to chromosome arm 2BS. Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive disease affecting the production of wheat (Triticum aestivum). Powdery mildew resistance was putatively transferred from Thinopyrum intermedium to the common wheat line L962, which conferred resistance to multiple Chinese Bgt isolates. Genetic analysis of the powdery mildew response was conducted by crossing the resistant line L962 with the susceptible line L983. Disease assessments of the F1, F2, and F2:3 populations from the cross L983/L962 indicated that resistance was controlled by a single dominant gene. A total of 373 F2:3 lines and 781 pairs of genomic simple sequence repeat (SSR) primers were employed to determine the chromosomal location of the resistance gene. The gene was linked to four publicly available and recently developed wheat genomic SSR markers and seven EST-STS markers. The resistance gene was mapped to chromosome arm 2BS based on the locations of the linked markers. Pedigree, molecular marker and resistance response data indicated that the powdery mildew resistance gene in L962 is novel. It was temporarily designated PmL962. It is flanked by Xwmc314 and BE443737at genetic distances of 2.09 and 3.74 cM, respectively, and located in a 20.77 cM interval that is co-linear with a 269.4 kb genomic region on chromosome 5 in Brachypodium distachyon and a 223.5 kb genomic region on rice (Oryza sativa) chromosome 4. The markers that are closely linked to this gene have potential applications in marker-assisted breeding.

Genetic mapping of a putative Thinopyrum intermedium-derived stripe rust resistance gene on wheat chromosome 1B.

KEY MESSAGE: Stripe rust resistance transferred from Thinopyrum intermedium into common wheat was controlled by a single dominant gene, which mapped to chromosome 1B near Yr26 and was designated YrL693. Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is a highly destructive disease of wheat (Triticum aestivum). Stripe rust resistance was transferred from Thinopyrum intermedium to common wheat, and the resulting introgression line (L693) exhibited all-stage resistance to the widely virulent and predominant Chinese pathotypes CYR32 and CYR33 and to the new virulent pathotype V26. There was no cytological evidence that L693 had alien chromosomal segments from Th. intermedium. Genetic analysis of stripe rust resistance was performed by crossing L693 with the susceptible line L661. F(1), F(2), and F(2:3) populations from reciprocal crosses showed that resistance was controlled by a single dominant gene. A total 479 F(2:3) lines and 781 pairs of genomic simple sequence repeat (SSR) primers were employed to determine the chromosomal location of the resistance gene. The gene was linked to six publicly available and three recently developed wheat genomic SSR markers. The linked markers were localized to wheat chromosome 1B using Chinese Spring nulli-tetrasomic lines, and the resistance gene was localized to chromosome 1B based on SSR and wheat genomic information. A high-density genetic map was also produced. The pedigree, molecular marker data, and resistance response indicated that the stripe rust resistance gene in L693 is a novel gene, which was temporarily designated YrL693. The SSR markers that co-segregate with this gene (Xbarc187-1B, Xbarc187-1B-1, Xgwm18-1B, and Xgwm11-1B) have potential application in marker-assisted breeding of wheat, and YrL693 will be useful for broadening the genetic basis of stripe rust resistance in wheat.

Chloroplast ultrastructure regeneration with protection of photosystem II is responsible for the functional 'stay-green' trait in wheat.

CN17 is a functional stay-green wheat variety that exhibits delayed leaf senescence and enhanced photosynthetic competence. To better understand these valuable traits, levels of chlorophyll a and b, soluble proteins, unsaturated fatty acids, and other components of CN17 were assayed. In addition, chloroplast ultrastructure, chloroplast number, and differences in gene expression between CN17 and a control variety, MY11, were examined. By 21 d post-anthesis (DPA), CN17 leaves exhibited a significantly higher maximal photochemical efficiency for photosystem II (PSII) (F(v) /F(m) ) and a significantly higher efficiency of excitation capture by open PSII reaction centres (F(v) '/F(m) '). In addition, chlorophyll degradation in CN17 was delayed by approximately 14 d, and was not blocked as observed in cosmetic stay-green phenotypes. The soluble protein content (Ps) of CN17 was higher than MY11 at all timepoints assayed, and the ratio of unsaturated to saturated fatty acids was significantly higher. CN17 also exhibited isolated granal lamellae associated with vesicles and diminished peroxidation, and between 35 and 42 DPA, a sharp decrease in chloroplast number was detected. Taken together, these results strongly support the hypothesis that chloroplast ultrastructure regeneration is responsible for the functional stay-green trait of CN17, and gene expression data provide insight into the mechanistic details.

A new long terminal repeat (LTR) sequence allows to identify J genome from J S and St genomes of Thinopyrum intermedium.

A repetitive sequence of 491 bp, named pMD232-500, was isolated from S. cereale cv. Kustro using wheat SSR marker Xgwm232. GenBank BLAST search revealed that the sequence of pMD232-500 was highly similar to a part of retrotransposon Nusif-1. Fluorescence in situ hybridization (FISH) analysis using pMD232-500 as probe indicated that only 14 Thinopyrum intermedium chromosomes and all the chromosomes of S. cereale cv. Kustro bear FISH signals, however, no FISH signals were observed on Dasypyrum villosum chromosomes. In addition, the FISH signals were distributed on whole arms except their terminal regions. Further genomic in situ hybridization (GISH) analysis using genomic DNA from Pseudoroegneria spicata indicated that the 14 Th. intermedium chromosomes bearing FISH signals should belong to J genome. Thereafter, the repetitive elements pMD232-500 showed the unambiguous features of genomic constitution of Th. intermedium. In addition, the results in the present study have indicated the similarity of genomes from Th. intermedium and S. cereale.

[Gossypol acetate users].

PIP: The blood lymph cell chromosomes of 30 offspring of previous users of gossypol acetate were examined and compared with those of a control group. The fathers of test group members had been previously given oral doses of 20 mg/day gossypol acetate until sperm counts of less than 4 million/ml were achieved (generally 60-90 days after 1st medication), after which dosage was shifted to 40 mg/week. Mean duration of gossypol treatment was 440 days; mean total dosage for this period was 3382.34 mg. Fathers were not fertile until 18 months (average) after termination of medication. Results indicated that when the test group was compared with the control group, no significant differences in chromosome breaks, gaps, and sister chromatid exchange were observed.^ieng