Genetic diversity for wheat improvement as a conduit to food security

Authors: MUJEEB-KAZI, A - National Institute Of Biotechnology And Genetic Engineering (NIBGE); KAZI, A - National University Of Science And Techology (NUST); DUNDAS, I - University Of Adelaide; RASHEED, A - Quaid-I-university Islamabad; BUX, H - University Of Sindh; CHEN, P - Nanjing Agricultural University; Wang, Richard; Xu, Steven; MAHMOOD, T - Quaid-I-university Islamabad

Submitted to: Advances in Agronomy
Publication Type: Book / Chapter
Publication Acceptance Date: 6/12/2013
Publication Date: 9/21/2013
Citation: Mujeeb-Kazi, A., Kazi, A.G., Dundas, I., Rasheed, A., Bux, H., Chen, P., Wang, R., Xu, S.S., Mahmood, T. 2013. Genetic diversity for wheat improvement as a conduit to food security. Advances in Agronomy. 122:179-258.

Interpretive Summary: Genetic diversity is paramount for any crops genetic improvement and this resides in three gene pools of the Triticeae for wheat. Access to the diversity and its exploitation is based upon genetic distance of the species relatives from the wheat genomes. Apart from the conventional genetic base for wheat improvement, novel variation from distant resources has been an exciting research investigation area called wide crosses over the past several decades. Close relatives of the primary gene pool have been preferred as they permit homologous genetic exchanges to occur between related genomes exemplified by the A and D genome diploid progenitors. One strategy based upon first producing genetic stocks and then capturing the potential of these diploids is via bridge crossing where the D genome synthetic hexaploid wheats (2n=6x=42, AABBDD) are exploited. The enormous potential of the D genome has been in the forefront over the past two decades around its usage for combating various biotic / abiotic stresses and for providing assistance in the development of molecular tools for enhancing breeding efficiency. The synthetics are products of crosses between elite durum wheat cultivars and various Aegilops tauschii accessions; Triticum turgidum / Ae. tauschii. Around this base, diversity of the A and B genomes has also been assembled in unique synthetic combinations that are genomically represented as AABBAA (T. turgidum / A-genome diploids T. boeoticum, T. monococcum, T. urartu), AABBBB (or AABBSS), (T. turgidum / Ae. speltoides). Digressing from these stocks permits variations of usage of the diversity manifold by strategies of direct crosses between parental diploids and recipient wheat cultivars extended to give even swifter products by top- or backcrossing the F1 combinations with either durum or bread wheats. Not much exploited are genetic stocks developed from some perennial tertiary gene pool species that fall under the umbrella of "intergeneric hybridization". This gene pool is much removed from the wheat genetic structure and hence affecting transfers of value for applied gains has been labeled as being complex and time consuming. The potency of valued diversity, however, warrants exploiting this distant resource and has maintained its research charisma despite the multifaceted impacts that are rapidly spreading from intraspecific and interspecific approaches; more the latter. Presented here are major facets of intergeneric hybridization embracing a taxonomic consideration of genetic diversity within the Triticeae, its selective use, the exploitation protocols, pre-breeding strategies, applied outputs from distant hybridization with a major focus on wheat/alien chromosomal products classed as "translocations" that have a lot to offer for wheat improvement but are under-exploited despite their benefits as evidenced from global wheats that possess the T1BL.1RS and to a lesser degree the T1AL.1RS Robertsonian translocations. This paper also attempts to relate the exploitation of the Triticeae genetic diversity with wheat productivity as a means of addressing diverse stress constraints that if countered will provide yield enhancing outputs necessary for over-riding environmental limitations of climate change, global warming and catalyzing gains for food security with wheat.

Technical Abstract: Genetic diversity is paramount for any crops genetic improvement and this resides in three gene pools of the Triticeae for wheat. Access to the diversity and its exploitation is based upon genetic distance of the species relatives from the wheat genomes. Apart from the conventional genetic base for wheat improvement, novel variation from distant resources has been an exciting research investigation area called wide crosses over the past several decades. Close relatives of the primary gene pool have been preferred as they permit homologous genetic exchanges to occur between related genomes exemplified by the A and D genome diploid progenitors. One strategy based upon first producing genetic stocks and then capturing the potential of these diploids is via bridge crossing where the D genome synthetic hexaploid wheats (2n=6x=42, AABBDD) are exploited. The enormous potential of the D genome has been in the forefront over the past two decades around its usage for combating various biotic / abiotic stresses and for providing assistance in the development of molecular tools for enhancing breeding efficiency. The synthetics are products of crosses between elite durum wheat cultivars and various Aegilops tauschii accessions; Triticum turgidum / Ae. tauschii. Around this base, diversity of the A and B genomes has also been assembled in unique synthetic combinations that are genomically represented as AABBAA (T. turgidum / A-genome diploids T. boeoticum, T. monococcum, T. urartu), AABBBB (or AABBSS), (T. turgidum / Ae. speltoides). Digressing from these stocks permits variations of usage of the diversity manifold by strategies of direct crosses between parental diploids and recipient wheat cultivars extended to give even swifter products by top- or backcrossing the F1 combinations with either durum or bread wheats. Not much exploited are genetic stocks developed from some perennial tertiary gene pool species that fall under the umbrella of "intergeneric hybridization". This gene pool is much removed from the wheat genetic structure and hence affecting transfers of value for applied gains has been labeled as being complex and time consuming. The potency of valued diversity, however, warrants exploiting this distant resource and has maintained its research charisma despite the multifaceted impacts that are rapidly spreading from intraspecific and interspecific approaches; more the latter. Presented here are major facets of intergeneric hybridization embracing a taxonomic consideration of genetic diversity within the Triticeae, its selective use, the exploitation protocols, pre-breeding strategies, applied outputs from distant hybridization with a major focus on wheat/alien chromosomal products, classed as "translocations" that have a lot to offer for wheat improvement but are under-exploited despite their benefits as evidenced from global wheats that possess the T1BL.1RS and to a lesser degree the T1AL.1RS Robertsonian translocations. This paper also attempts to relate the exploitation of the Triticeae genetic diversity with wheat productivity as a means of addressing diverse stress constraints that if countered will provide yield enhancing outputs necessary for over-riding environmental limitations of climate change, global warming and catalyzing gains for food security with wheat.