J. B. Sharma

Evaluation of 19,460 Wheat Accessions Conserved in the Indian National Genebank to Identify New Sources of Resistance to Rust and Spot Blotch Diseases

A comprehensive germplasm evaluation study of wheat accessions conserved in the Indian National Genebank was conducted to identify sources of rust and spot blotch resistance. Genebank accessions comprising three species of wheat–Triticum aestivum, T. durum and T. dicoccum were screened sequentially at multiple disease hotspots, during the 2011–14 crop seasons, carrying only resistant accessions to the next step of evaluation. Wheat accessions which were found to be resistant in the field were then assayed for seedling resistance and profiled using molecular markers. In the primary evaluation, 19,460 accessions were screened at Wellington (Tamil Nadu), a hotspot for wheat rusts. We identified 4925 accessions to be resistant and these were further evaluated at Gurdaspur (Punjab), a hotspot for stripe rust and at Cooch Behar (West Bengal), a hotspot for spot blotch. The second round evaluation identified 498 accessions potentially resistant to multiple rusts and 868 accessions potentially resistant to spot blotch. Evaluation of rust resistant accessions for seedling resistance against seven virulent pathotypes of three rusts under artificial epiphytotic conditions identified 137 accessions potentially resistant to multiple rusts. Molecular analysis to identify different combinations of genetic loci imparting resistance to leaf rust, stem rust, stripe rust and spot blotch using linked molecular markers, identified 45 wheat accessions containing known resistance genes against all three rusts as well as a QTL for spot blotch resistance. The resistant germplasm accessions, particularly against stripe rust, identified in this study can be excellent potential candidates to be employed for breeding resistance into the background of high yielding wheat cultivars through conventional or molecular breeding approaches, and are expected to contribute toward food security at national and global levels.

Genetics and mapping of a new leaf rust resistance gene in Triticum aestivum L. × Triticum timopheevii Zhuk. derivative ‘Selection G12’

A Triticum timopheevii-derived bread wheat line, Selection G12, was screened with 40 pathotypes of leaf rust pathogen, Puccinia triticina at seedling stage and with two most commonly prevalent pathotypes 77-5 and 104-2 at adult plant stage. Selection G12 showed resistance at both seedling and adult plant stages. Genetic analysis in F1, F2 and F2:3 families at the seedling stage revealed that leaf rust resistance in Selection G12 is conditioned by a single incompletely dominant gene. The leaf rust resistance gene was mapped to chromosome 3BL with SSR markers Xgwm114 and Xgwm547 flanking the gene at a distance of 28.3 cM and 6 cM, respectively. Based on the nature of resistance and chromosomal location, it is inferred that Selection G12 carries a new gene for leaf rust resistance, tentatively named as LrSelG12.

Genetics and molecular mapping of stem rust resistance in bread wheat line WR95

The bread wheat line WR95 showed seedling resistance to several Indian stem rust (Puccinia graminis Pers. f. sp. tritici) isolates. Genetic analysis of stem rust resistance in WR95 was undertaken in populations derived from crosses NI5439/WR95 and Agra Local/WR95. The F1, F2, and F3 generations derived from the cross NI5439/WR95 were tested against stem rust isolate 40A and genetic analysis showed a recessive gene for resistance. The results were confirmed in another F2 population derived from the cross Agra Local/WR95. Interestingly, genetic analysis in F2 population from the later cross i.e. Agra Local/WR95 identified a dominant gene against isolates 11 and 11A. The recessive gene against isolate 40A was mapped to the long arm of 5D chromosome. WR95 showed resistance to virulent isolates of Sr30 which is also located on 5DL chromosome. The dominant gene in WR95 that conferred the resistance to isolate 11 and 11A was mapped towards telomeric region of the long arm of 2B chromosome. The long arm of chromosome 2B also carries stem rust resistance genes Sr9, Sr16 and Sr28. WR95 showed resistance to virulent isolates to Sr9b (11, 11A, 21A-2 and 40A), Sr9e (15-1 and 40A) and Sr28 (11, 11A, 15-1, 21A-2 and 40A). The map position of dominant gene identified in WR95 is different from Sr9 and Sr28 while Sr16 is towards telomeric region and not mapped so far. Therefore, the dominant gene in WR95 may be either Sr16 or a new gene.

Strategic Research to Enhance the Yield Potential Through Redesigning of Wheat Plant Architecture

In India wheat is the second most important crop occupying 27.3 million hectare area with production and productivity of 72 million tons and 2.64 tons per hectare, respectively. To cope up the ever increasing demand which will be 109 million tons by the year 2020, the present level of productivity has to be increased to 4.4 tons per hectare. The only approach for achieving quantum jump in productivity is to restructure the wheat plant architecture which can yield up to 8 tons/hectare. The Indian Agricultural Research Institute, New Delhi, India has developed new plant type (NPT) wheat, utilizing a local germplasm SFW and released wheat and genetic stocks, which has high 1000 grain weight (45–50g), high number of grain per spike (90–100), higher biomass, thick, broad, semi erect and dark green leaves, thick stem, plant height 85–100 cm and good root system. Efforts are on to increase the productive tillers in these wheats along with diverse genes for resistance to diseases in order to break the yield barrier

Molecular characterization of Triticum militinae derived introgression lines carrying leaf rust resistance

Triticum militinae Zhuk. et Migusch. belongs to timopheevii [Triticum timopheevii (Zhuk.) Zhuk.] group of wheats with 2nxa0=xa04xxa0=xa028 chromosomes and genome formula AtAtGG. Triticum militinae Zhuk. et Migusch. is known to carry resistance to fungal diseases including rusts and powdery mildew. Genes from timopheevii wheat can be incorporated into cultivated wheat by either direct hybridization or through development of amphiploids. Three T. militinae derived introgression lines (ILs) Triticum Militinae Derivative (TMD) 6-4, TMD7-5 and TMD11-5 were selected for the current study based on cytological stability. All three ILs showed resistance against wide spectrum of Indian pathotypes of leaf rust. More than 1200 SSR markers were used for genotyping of ILs and parental lines. The ILs showed variable and multiple introgressions in different chromosomes of A, B and D genome of wheat. The introgression points were distributed mostly in the distal regions though significant introgressions were also observed in proximal regions of some chromosomes. The extent of introgression in ILs TMD6-4, TMD7-5 and TMD11-5 was 2.8, 8.3 and 8.6% respectively. The set of ‘informative markers’ in the Molecularly Tagged Chromosome Regions (MTCR) of T. militinae origin can also be used in future for tagging of genes associated with traits of economic importance apart from leaf rust resistance. The transferability of Triticum aestivum L. SSR markers to T. militinae was 96.4% for A genome, 95.8% for B genome and 84.3% for D genome. Transferability of wheat SSR markers to T. militinae can be used in preparing genetic maps in timopheevii group of wheats.

Marker-assisted pyramiding of Thinopyrum-derived leaf rust resistance genes Lr19 and Lr24 in bread wheat variety HD2733

This study was undertaken to pyramid two effective leaf rust resistance genes (Lr19 and Lr24) derived from Thinopyrum (syn. Agropyron), in the susceptible, but agronomically superior wheat cultivar HD2733 using marker-assisted selection. In the year 2001, HD2733 was released for irrigated timely sown conditions of the north eastern plains zone (NEPZ) of India became susceptible to leaf rust, a major disease of the region. Background selection helped in developing near-isogenic lines (NILs) of HD2733 with Lr19 and Lr24 with 97.27 and

Molecular marker assisted pyramiding of leaf rust resistance genes Lr19 and Lr28 in bread wheat (Triticum aestivum L.) variety HD2687

98.94%

A study of transcriptome in leaf rust infected bread wheat involving seedling resistance gene Lr28

98.94%, respectively, of genomic similarity with the parent cultivar, after two backcrossing and one generation of selfing. NILs were intercrossed to combine the genes Lr19 and Lr24. The combination of these two genes in the cultivar HD2733 is expected to provide durable leaf rust resistance in farmers’ fields.