Manilal William

Genetic and physical mapping of photoperiod insensitive gene Ppd-B1 in common wheat

Photoperiod response is a major determinant of duration of growing stages in wheat. Conscious selection for these photoperiod response genes in plant breeding programs will yield genotypes with better adaptation to diverse environments. To provide a starting point for the development of molecular markers useful for the selection process, genetic maps around the photoperiod insensitive gene Ppd-B1 were built employing three segregating populations. Of 25 markers that were selected for the Ppd-B1 region, only two could be mapped across all three populations. In pairwise comparisons, the extent of transferable markers ranged from three to eight. Recombination frequencies of markers distal to Ppd-B1 were more homogeneous than those of proximal markers. This finding suggested a closer proximity of Ppd-B1 to the markers that were mapped distal to breakpoint 0.83 in the physical map of chromosome 2BS.

Transfer of rust resistance from Aegilops ovata into bread wheat (Triticum aestivum L.) and molecular characterisation of resistant derivatives

An interspecific cross was made to transfer leaf rust and stripe rust resistance from an accession of Aegilops ovata (UUMM) to susceptible Triticum aestivum (AABBDD) cv. WL711. The F1was backcrossed to the recurrent wheat parent, and after two to three backcrosses and selfing, rust resistant progenies were selected. The C-banding study in a uniformly leaf rust and stripe rust resistant derivative showed a substitution of the 5M chromosome of Ae. ovata for 5D of wheat. Analysis of rust resistant derivatives with mapped wheat microsatellite makers confirmed the substitution of 5M for 5D. Some of these derivatives also possessed one or more of the three alien translocations involving 1BL, 2AL and 5BS wheat chromosomes which could not be detected through C-banding. A translocation involving 5DSof wheat and the substituted chromosome 5M of Ae. ovata was also observed in one of the derivatives. Susceptibility of this derivative to leaf rust showed that the leaf rust resistance gene(s) is/are located on short arm of 5M chromosome of Ae. ovata. Though the Ae. ovatasegment translocated to 1BL and 2AL did not seem to possess any rust resistance gene, the alien segment translocated to 5BS may also possess gene(s) for rust resistance. The study demonstrated the usefulness of microsatellite markers in characterisation of interspecific derivatives.

The international breeding strategy for the incorporation of resistance in bread wheat against the soil borne pathogens (Dryland Root Rot and cyst and lesion Cereal Nematodes) using conventional and molecular tools.

Soil borne pathogens (SBPs) including the Dryland Root Rots and Cereal Nematodes are causing economic yield loss in many parts of the world where cereals dominate the cropping system and sub-optimal growing conditions or cultural practices are common. One of the most effective control measures of these SBPs is the use of host resistance, whereby the inoculum level of these pathogens can be reduced to below economically damaging thresholds. CIMMYT International in collaboration with The Turkish Ministry of Agriculture and Rural Affairs have established an International field and laboratory screening program for identifying spring and winter wheat accessions with resistance to SBPs. Several screening protocols for assessing resistance to both cereal root rots and nematodes have been modified and optimized. Known resistance sources to SBPs from other regions of the world have been tested against Turkish isolates of SBPs and several of these have been shown to be effective in the region. In addition new sources of resistance with genetic variability have been identified against the prevalent SBPs. These diverse genes for resistance are being pyramided into both spring and winter bread wheat backgrounds using both conventional and molecular tools where feasible

Genomics of Wheat, the Basis of Our Daily Bread

Wheat, being an important source of calories across the Americas, Europe, North Africa and Asia, is the most widely grown food crop in the world. Wheat yields have undergone a spectacular rise over the last half century, contributing to the Green Revolution in Asia. However, productivity increases appear to have reached a plateau in recent years and many consider that new advances in genomics will be essential to delivery the rates of productivity increases necessary to prevent hunger. New molecular tools will enhance on-going wheat breeding, offering the plant breeder considerable advantages in time, cost, and response to selection. Perhaps most importantly, it is believed that genomics tools will also facilitate much more efficient utilization of new sources of genetic variation for important agronomic traits from wild species. This chapter provides an overview of the botany and conventional breeding of wheat including a summary of past successes, the current primary breeding targets, and the major constraints to achieving those goals. We then focus on genomic advances in bread wheat and durum wheat during the past decade and the implications of these advances for increasing resilience, stability and productivity in tropical, sub-tropical and semi-arid production systems across the world. This includes the use of genomics to improve the search for, and the characterization of, new beneficial genetic variation and the identification of molecular markers to facilitate the efficient manipulation of that variation in breeding programs. Finally, we provide a list of the currently available trait markers and a perspective on likely future trends and challenges in wheat molecular breeding.

Genetics of Host-Pathogen Interaction and Breeding for Durable Resistance

Disease control to achieve stable food production has been one of the challenges to wheat pathologists, geneticists and breeders during the 20th century. An understanding of disease epidemiology, genetic basis of host-pathogen interaction, search for resistance genes, and development of cultivars with built-in disease resistance to a number of important diseases has reduced the occurrence of large-scale epidemics that were common in the first half of the 20th century. Improper use of the major, race-specific type of resistance to control rapidly evolving pathogens (e.g., the rusts of wheat) has led to boom-and-bust cycles that make it necessary to replace cultivars a short time after their release. Durable resistance is based on interaction of minor, additive genes. In case of leaf and yellow rusts of wheat, accumulation of 4–5 slow rusting genes results in a high level of resistance that approaches immunity. This is the type of resistance needed in the 21st century to ensure food security.