Strategic crossing of biomass and harvest index—source and sink—achieves genetic gains in wheat
Authors: Reynolds Matthew P. , Pask Alistair J. D. , Hoppitt William J. E. , Sonder Kai , Sukumaran Sivakumar , Molero Gemma , Pierre Carolina Saint , Payne Thomas , Singh Ravi P. , Braun Hans J. , Gonzalez Fernanda G. , Terrile Ignacio I. , Barma Naresh C. D. , Hakim Abdul , He Zhonghu , Fan Zheru , Novoselovic Dario , Maghraby Maher , Gad Khaled I. M. , Galal ElHusseiny G. , Hagras Adel , Mohamed Mohamed M. , Morad Abdul Fatah A. , Kumar Uttam , Singh Gyanendra P. , Naik Rudra , Kalappanavar Ishwar K. , Biradar Suma , Sai Prasad Sakuru V. , Chatrath Ravish , Sharma Indu , Panchabhai Kishor , Sohu Virinder S. , Mavi Gurvinder S. , Mishra Vinod K. , Balasubramaniam Arun , Jalal-Kamali Mohammad R. , Khodarahmi Manoochehr , Dastfal Manoochehr , Tabib-Ghaffari Seyed M. , Jafarby Jabbar , Nikzad Ahmad R. , Moghaddam Hossein Akbari , Ghojogh Hassan , Mehraban Asghar , Solís-Moya Ernesto , Camacho-Casas Miguel A. , Figueroa-López Pedro , Ireta-Moreno Javier , Alvarado-Padilla Jorge I. , Borbón-Gracia Alberto , Torres Araceli , Quiche Yei Nayeli , Upadhyay Shesh R. , Pandey Deepak , Imtiaz Muhammad , Rehman Monsif U. , Hussain Manzoor , Hussain Makhdoom , Ud-Din Riaz , Qamar Maqsood , Sohail Muhammad , Mujahid Muhammad Y. , Ahmad Gulzar , Khan Abdul J. , Sial Mahboob A. , Mustatea Pompiliu , von Well Eben , Ncala Moses , de Groot Stephan , Hussein Abdelraheem H. A. , Tahir Izzat S. A. , Idris Amani A. M. , Elamein Hala M. M. , Manes Yann , Joshi Arun K. 
Published: October 2017

To accelerate genetic gains in breeding, physiological trait (PT) characterization of candidate parents can help make more strategic crosses, increasing the probability of accumulating favorable alleles compared to crossing relatively uncharacterized lines. In this study, crosses were designed to complement “source” with “sink” traits, where at least one parent was selected for favorable expression of biomass and/or radiation use efficiency—source—and the other for sink-related traits like harvest-index, kernel weight and grains per spike. Female parents were selected from among genetic resources—including landraces and products of wide-crossing (i.e. synthetic wheat)—that had been evaluated in Mexico at high yield potential or under heat stress, while elite lines were used as males. Progeny of crosses were advanced to the F4 generation within Mexico, and F4-derived F5 and F6 generations were yield tested to populate four international nurseries, targeted to high yield environments (2nd and 3rd WYCYT) for yield potential, and heat stressed environments (2nd and 4th SATYN) for climate resilience, respectively. Each nursery was grown as multi-location yield trials. Genetic gains were achieved in both temperate and hot environments, with most new PT-derived lines expressing superior yield and biomass compared to local checks at almost all international sites. Furthermore, the tendency across all four nurseries indicated either the superiority of the best new PT lines compared with the CIMMYT elite checks, or the superiority of all new PT lines as a group compared with all checks, and in some cases, both. Results support—in a realistic breeding context—the hypothesis that yield and radiation use efficiency can be increased by improving source:sink balance, and validate the feasibility of incorporating exotic germplasm into mainstream breeding efforts to accelerate genetic gains for yield potential and climate resilience.