Selection for high spike fertility index in early generations increases grain number per unit area (and yield) of advanced breeding lines in bread wheat.

Spike fertility index (a.k.a. fruiting efficiency) at maturity (FE m ) has been proposed as a promising selection criterion for improving grain yield (GY) in bread wheat. However, its usefulness as an early-generation selection criterion aiming at increasing GY in advanced generations remains to be established. On the other hand, there is no information about the feasibility of using spike harvest index (SHI) as an indirect selection criterion for increasing GY. In this study, a biparental population derived from a cross between 'Baguette 10' and 'Klein Chaja'', Argentinian spring bread wheat cultivars with contrasting FE m , was evaluated from early generations (F2 and F3) to recombinant inbred lines (RILs, tested in seven experiments). Associations of FE m and SHI measurements between early generations and RILs were established. Also, responses in grain number/m 2 (GN) and GY in the RILs after simulated selection for high FE m or high SHI in early generations under four selection strategies comprising combinations of different selection intensities (50%, 25% and 10%) were assessed. Significant and positive correlation was found between FE m measured in early generations and in the RILs (r=0.32, P<0.05) and SHI measured in the F 3 and in the RILs (r=0.26, P<0.05). After selection for high FE m in early generations, responses in GN were positive in all the experiments under all four simulated selection strategies: GN increased by 5.1 to 22.1% as compared with the population mean, depending on the selection strategy. Responses in GY were positive in three out of four selection strategies, averaging -1.3 to 2.1% depending on the selection strategy. Contrarily, responses to selection in GN and GY in the RILs using SHI as a selection criterion in early generations were negative or neutral. In this way, our results validate the use of FE m as a selection criterion in early generations for increasing GN and GY in advanced generations of bread wheat breeding programs.