Germplasm enhancement through wide hybridization and molecular breeding

Wild relatives of wheat are a rich source of novel variability for disease resistance, quality and other traits of economic importance. Evaluation and cataloguing of 1,000 accessions of wild Triticum and Aegilops species identified a number of new sources of resistance to leaf rust, stripe rust, powdery mildew, loose smut, leaf spots and cereal cyst nematode. Study of high molecular weight (HMW) glutenin subunit composition by SDS-P AGE revealed large intra-specific diversity in the wild species and identified novel Ax and Ay subunits at the Glu Al locus. Interspecific crossing of resistant accessions of three wild Triticum species with susceptible Triticum durum (AABB) lines, followed by back-crossing to the cultivated species, resulted in the transfer of: leaf rust resistance from six diverse accessions of T araraticum(AAGG)stripe rust resistance from one accession of T. urartu (A u A U), two accessions of T araraticum and one accession of T dicoccoides(AABB)and powdery mildew resistance from two accessions of T. araraticum. Transfer of novel Ax and Ay subunits from T urartu, T boeoticum (A b A b), T. dicoccoides and T araraticum resulted in significant increase in gluten strength indicated by increases in SDS sedimentation value from 37-40 for T durum to 48-75 for the derivatives. Non-progenitor Aegilops species with C, U and M genomes have been found to be excellent sources of resistance to leaf rust and stripe rust. Rust resistant interspecific derivatives carrying alien chromosome substitution/addition or translations from Ae. ovata (UUMM) and Ae. triuncialis (UUCC) have been identified using C-banding and genomic in-situ hybridization techniques. Studies showed that the inhibitor of the Ph locus (Ph1 from Aegilops speltoides, now available in the background of T aestivum cv. Chinese Spring, is useful to induce homoeologous pairing of alien chromosomes with wheat chromosomes in interspecific crosses. Induced homologous pairing coupled with C-banding and genomic in-situ hybridization are useful to transfer small alien segments carrying desirable genes and thus reduce linkage drag. A molecular linkage map has been constructed for the diploid cultivated species T monococcum - a good source of resistance to diseases and pests and possessing resistance to herbicides. Molecular markers linked to protein content and seed size have also been identified. Also, in a pre-breeding program to improve two spring wheat cultivars, novel genes for disease resistance, high protein content, bread making quality and other agronomically important traits have been transferred from various genetic stocks. The improved durum and bread wheat materials, particularly those with rust resistance and processing quality , seem to have great potential for deployment in East Africa including Ethiopia.