The identification of a new gene for leaf pubescence introgressed into bread wheat from Triticum timopheevii Zhuk. and its manifestation in a different genotypic background

Leaf pubescence is widespread among higher plants. In bread wheat, a relationship was found between this trait and the efficiency of photosynthetic processes and productivity. In this work, we established the chromosomal localization of the gene for leaf pubescence introgressed from Triticum timopheevii into a bread wheat line 821 and studied its expression in the genetic background of two wheat cultivars differing in genetic control and phenotypic expression of pubescence. To obtain quantitative characteristics of pubescence in cultivars and hybrid populations, the LHDetect2 program was used, which makes it possible to estimate the length and number of trichomes on a leaf fold. A genetic analysis showed the dominant inheritance of the gene. Monosomic analysis F2 was used to establish chromosome localization and investigate the expression of the gene in cultivars Saratovskaya S29 (S29) and Diamant 2 (Dm2). As a result, the gene Hltt, introgressed from T. timopheevii, was identified and localized in the distal region of the long arm of 5A chromosome for the first time. In both F2 populations, the gene reduced the density of trichomes and formed long trichomes, uncharacteristic for the two recipient cultivars S29 and Dm2. A larger number of long trichomes was formed in the genetic background of S29, which carry the bread wheat gene Hl1 and Hl3 for leaf pubescence, than in Dm2. Development of substitution and isogenic lines with the fragment of introgression carrying the gene Hltt will allow determining function and assessing the adaptive significance of the gene more precisely.

Genetic analysis of Aegilops tauschii-derived seedling resistance to leaf rust in synthetic hexaploid wheat

SummarySeedling resistance to leaf rust available in the synthetic hexaploid wheat line Syn137 was characterized by means of cytogenetic and linkage mapping. Monosomic analysis located a single dominant gene for leaf rust resistance on chromosome 5D. Molecular mapping not only confirmed this location but also positioned the gene to the distal part of the long arm of chromosome 5D. A test of allelism showed that the gene, tentatively named LrSyn137, is independent but closely linked to Lr1. It appears that Syn137 is occasionally heterogeneous for Lr1 since the analysis of the Lr1-specific marker RGA567-5 in the mapping population indicated the presence of Lr1. Syn137 represents another source of genetic variation that can be useful for the diversification of leaf rust resistance in wheat cultivars.

Inheritance and molecular mapping of genes for all-stage resistance to stripe rust in wheat cultivar N. Strampelli

N. Strampelli, an Italian wheat variety that has been grown in China since 1974, is still resistant to most prevalent Chinese races of Puccinia striiformis f. sp tritici in the seedling stage. To identify genes conferring all-stage resistance to stripe rust, F1, F2, F3 and BC1 seedling progenies derived from the cross N. Strampelli × Mingxian 169 were inoculated with Chinese races CYR29, CYR29-mut3 and CYR31 and those from cross N. Strampelli × Chinese Spring were tested with CYR29-mut3 and CYR33 in the greenhouse. N. Strampelli possessed different recessive genes for resistance to each race. The genes were located on chromosomes 1B and 5B by monosomic analysis. Linkage maps were constructed with three SSR markers, Xgwm499, Xwmc415 and Xwmc537, for the gene on chromosome 5B conferring resistance to CYR29-mut3 (temporarily designated as YrN.S-1) with genetic distance ranging from 5.4 to 10.7cM and four SSR markers, Xcfa2147, Xgwm124, Xwmc719 and Xwmc44, for the gene on chromosome 1B conferring resistance to CYR33 (temporarily designated as YrN.S-2) with genetic distance ranging from 3.2 to 10.3cM. The markers could be useful in pyramiding these resistance genes with others to develop wheat cultivars with high-level and durable resistance to stripe rust.Key words: Puccinia striiformis f. sp. tritici, monosomic analysis, molecular mapping

Identification of genes for resistance to a Digitaria isolate of Magnaporthe grisea in common wheat cultivars

Common wheat cultivars are resistant to Magnaporthe grisea , a crabgrass ( Digitaria sanguinalis )-specific species of the blast fungus. To dissect the genetic basis of this “nonhost” type of resistance, we need an exceptional cultivar that is susceptible to M. grisea. A screening under various conditions revealed that Triticum aestivum ‘Chinese Spring’ (CS) was susceptible to M. grisea isolate Dig41 when incubated at high temperature (26 °C) after inoculation. By contrast, T. aestivum ‘P168’, ‘Shin-chunaga’ (Sch), ‘Norin 4’ (N4), ‘Norin 26’ (N26), ‘Norin 29’ (N29), ‘Red Egyptian’ (RE), and ‘Salmon’ (Slm) and Triticum compactum ‘No. 44’ (Cmp) were highly resistant even at the high temperature. When F2 seedlings derived from crosses between the resistant cultivars and CS were inoculated with Dig41, they segregated in a 3:1 ratio of resistant to susceptible, suggesting that the resistance of each cultivar is controlled by one major gene. Crosses of N4 with P168, Sch, N26, N29, and Cmp yielded no susceptible F2 seedlings, suggesting that these six cultivars share the same gene. Similarly, a cross between RE and Slm yielded no susceptible F2 seedlings, suggesting that these two cultivars share the same gene. On the other hand, crosses between the N4 group and the RE group produced resistant and susceptible seedlings in a 15:1 ratio, indicating that these two groups carry different genes inherited independently. The gene in N4 was located on chromosome 4A by a monosomic analysis and designated Rmg4, while the gene in RE was located on chromosome 6D using a series of chromosome substitution lines and designated Rmg5. These results suggest that the resistance of common wheat to M. grisea, an inappropriate species of the blast fungus, is under a simple genetic control.