Madhu Meeta

Wheat Stripe Rust Resistance Protein WKS1 Reduces the Ability of the Thylakoid-Associated Ascorbate Peroxidase to Detoxify Reactive Oxygen Species

The wheat WKS1 protein reduces the activity of a chloroplast enzyme that detoxifies reactive oxygen species and causes cell death in the infected regions, conferring partial resistance to stripe rust. Stripe rust is a devastating fungal disease of wheat caused by Puccinia striiformis f. sp tritici (Pst). The WHEAT KINASE START1 (WKS1) resistance gene has an unusual combination of serine/threonine kinase and START lipid binding domains and confers partial resistance to Pst. Here, we show that wheat (Triticum aestivum) plants transformed with the complete WKS1 (variant WKS1.1) are resistant to Pst, whereas those transformed with an alternative splice variant with a truncated START domain (WKS1.2) are susceptible. WKS1.1 and WKS1.2 preferentially bind to the same lipids (phosphatidic acid and phosphatidylinositol phosphates) but differ in their protein-protein interactions. WKS1.1 is targeted to the chloroplast where it phosphorylates the thylakoid-associated ascorbate peroxidase (tAPX) and reduces its ability to detoxify peroxides. Increased expression of WKS1.1 in transgenic wheat accelerates leaf senescence in the absence of Pst. Based on these results, we propose that the phosphorylation of tAPX by WKS1.1 reduces the ability of the cells to detoxify reactive oxygen species and contributes to cell death. This response takes several days longer than typical hypersensitive cell death responses, thus allowing the limited pathogen growth and restricted sporulation that is characteristic of the WKS1 partial resistance response to Pst.

Field performance of micropropagated plants and potential of seed cane for stalk yield and quality in sugarcane

Two field experiments were conducted to ascertain the potential of micropropagation technique for faster production of seed cane by using tissue culture plants raised through apical meristem culture in first generation (TC 0) followed by clonal propagation through cane setts in next generation (TC1). About 18, 520 plants, produced from a single shoot through micropropagation, were required at row to row and plant to plant spacing of 90 and 60 cm, respectively as compared to 88 quintal of cane seed in conventional methods for planting in an area of one hectare. Multiplication ratio was 100–150 times using tissue culture plants as compared to 11–12 using conventional cane setts, leading to drastic reduction in seed cane requirement. The TC 1 exhibited superiority over vegetatively propagated conventional crop for millable canes and stalk yield by 17 and 10.4 per cent, respectively. Though the single cane weight and cane diameter (non-significantly) were slightly lesser in TC1 as compared to conventional crop, this did not distress its potential as seed crop. The incidence of Ratoon Stunting Disease (RSD) and Leaf Scald Disease (LSD) was very low in TC 1 crop as compared to conventional crop. The findings established the potential of tissue culture technique for the production of quality seed free of pests and pathogens in the existing varieties and rapid multiplication of newly released varieties for quick adoption by the growers.

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.

Inheritance of spot blotch resistance in barley (Hordeum vulgare L.)

Singh, S., Singh, H., Sharma, A., Meeta, M., Singh, B., Joshi, N., Grover, P., Al-Yassin, A. and Kumar, S. 2014. Inheritance of spot blotch resistance in barley (Hordeum vulgare L.). Can. J. Plant Sci. 94: 1203-1209. Spot blotch, caused by Bipolaris sorokiniana, is a major disease of barley hampering its commercial production in many parts of the world. Growing resistant cultivars is the most effective, economical and eco-friendly approach to control the disease. To understand the inheritance of resistance, F1, F2 and F3 generations of two crosses, involving susceptible (PL426 and RD2503) and resistant (BL9 and BL10) parents were studied. The susceptibility of F1 plants and a ratio of 13 susceptible:3 resistant in F2 populations in both crosses indicated that the reaction to spot blotch is hypostatic and is governed by two genes with an epistatic/inhibitory effect of first on the second one. The resistant reaction appeared due to the presence of dominant allele of the second gene. The first gene in dominant homozygous or heterozygous condition had an inhibitory effect over the second gene. The inheritance pattern was confirmed from the segregation pattern of F3 progenies of both the crosses. One hundred-fifty F2:6 recombinant inbred lines (RIL) derived from PL426/BL10 cross gave a good fit to the ratio of 1 resistant:3 susceptible lines under artificial and natural epiphytotic conditions. Recovery of transgressive segregants in the RIL population indicated the presence of some modifiers or minor genes. Test of allelism involving susceptible (PL426)×susceptible (RD2503) and resistant (BL9)×resistant (BL10) parents revealed that both the susceptible parents as well as resistant parents were allelic to each other.